voltage regulator tubes...tubes found ok, and upon examination and checking for voltage it also was...

TECHNICAL SECTION

Copyright 1943, Sylvania Electric Products Inc. (Formerly Hygrade Sylvania Corporation)

JAN.-FEB., 1943 EMPORIUM, PENNA. Vol. 10, No. 2

Voltage Regulator TubesSylvania Types 0B3/VR9O and oD3/VR150

Two well-known Sylvania voltage regulator tubes, TypeVR-90 and Type VR-150, have recently been assigned regularRMA numbers and are now designated as Type OB3/VR90and Type 0D3/VR150 respectively. The double brandingassists in recognizing the tube type, especially in view of thelong usage of the older designations.

It has been apparent in' many instances that some mis-understandings have existed regarding the operation of theseregulators, particularly the operation limits and regulationcharacteristics. The following descriptions and explanationmay help to clarify the general appliCationz of these regulators.

CHARACTERISTICS0113/VR9O OD3/VR150

No Heater Voltage RequiredStarting Supply Voltage 125 Volts Min. 180 Volts Min.Operating Voltage (Design Center) 90 Volts 150 VoltsOperating Current Range*. 10 Ma. Min. 5 Ma. Min.

30 Ma. Max. 40 Ma. Max.Regulation over Operating Current Ranget 6 Volts Max. 7.5 Volts Max.

*Adequate resistance required in series with tube to limit tube current to maximumvalues specified.

tRefer to tekt and curves.

Types 0B3/VR90 and 0D3/VR150 are gas filled, coldcathode regulator tubes. They are characterized by a prac-tically constant internal voltage drop across which a loadrequiring good voltage regulation may be connected.

Both types are mounted in ST -12 bulbs with the standardsmall 6 -pin octal base. The outside, cylindrical electrode isthe cathode and is connected to base pin No. 2. The innerelectrode is the anode and is connected to pin No. 5. Thejumper within the base serves as a switch to open the powersupply circuit when the regulator tube is removed from itssocket, providing the proper socket connections are employed.

As indicated in the accompanying diagram, a currentlimiting resistor should always be used in series with theregulator tube and the supply voltage. The amount of currentdrawn by the load will of course determine the size of thisresistor, but it should be such as never to allow an operatingcurrent of more than 30 nia. to flow through the 0B3/VR90,or more than 40 ma. to flow through the 0D3/VR150, in casethe load is disconnected.

TYPE

I I

OD3/VR15O

l

MAXIMUM STARTING VOLTAGE = 180 VOLTS

.165

CURRENT RANGEOPERATING

.160 -

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145

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CURRENT

20

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30

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TYPE OB3/VR9O

MAXIMUM STARTING VOLTAGE

II= 125 VOLTS

100

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80

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70

OPERATING

10

CURRENT

20

THROUGH 0B3/VR90

30

IN MA. D.C.

To start the tube operating some definite d -c voltage mustbe applied to ionize the gas in the tube. For Type 0B3/VR90this voltage is approximately 115 volts but should neverrequire more than 125 volts. Once started, the 0B3/VR90continues to operate at some voltage within the operatingrange of 80 to 100 volts. For the 0D3/VR150 the startingvoltage is approximately 165 volts but should never requiremore than 180 volts and once started the 0D3/VR150 con-tinues to operate at some voltage within its operating range of

(Continued on page 4, column 1)

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Plate and Screen Dissipation RatingsTheir Relation to Tube Performance and Life <

Editor's Note: Numerous requests have been re-ceived for information concerning dissipation ratings.It is hoped that this article will provide helpfulinformation on this subject and that it will encourageattention to and respect for published tube ratings.

Vacuum tube ratings provide anaccurate guide to assist the engineer orserviceman in securing efficient tubeperformance. The use of this informa-tion, coupled with careful attention tocircuit considerations and proper in-stallations will generally pay dividendsin acceptable operating efficiency.Among the important factors included intube data are the ratings of maximumplate and maximum screen dissipations.The discussion which follows deals pri-marily with dissipation considerations.

The interpretation of tube ratingspublished in the Sylvania TechnicalManual and other Sylvania technicalliterature are in accordance with RMAstandards and the conditions outlined inthe introductory section of the manualfor the plate and screen are:

A -C or D -C Power Line: The maxi-mum ratings of plate and screenvoltages and dissipations given on.thetube type data sheets are DesignMaximums. For equipment designedfor use in the United States on nomi-nal power -line services of 105 to 125volts, satisfactory performance andserviceability may be anticipated,provided the equipment is designed soas not to exceed these Design Maxi-mums at a line voltage of 117 volts.Storage Batteries: Automobile bat-tery operated equipment should bedesigned so that when the batteryvoltage is 6.6 volts, the plate voltage,the plate dissipation, the screen volt-age, the screen dissipation, and therectifier load current will not exceed90% of the respective recommendedDesign Maximum values given in thedata for each tube type."B" Batteries: Equipment operatedfrom "B" batteries should be designedso that under no condition of batteryvoltage will the plate voltage, theplate dissipation, the screen voltage,and the screen dissipation ever exceedthe recommended respective maximumvalues shown in the data for eachtype by more than 10%.

In general, electrode dissipation is thepower dissipated in the form of heat byan electrode as a result of electronand/or ion bombardment. Each tubetype must have maximum ratingsassigned, these being dependent uponthe tube design, its component parts andthe kind of service it is to perform. Ex-perience has shown that when maximumratings are exceeded, particularly for anappreciable time, the performance capa-bilities may be impaired and the tubelife shortened.

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The total power dissipated by the tubeconsists of plate and grid losses plus thepower used in heating the cathode. Allof this heat must be carried away fromthe tube, principally through the enve-lope of the tube. A major proportion ofthe energy which is dissipated in tubeshaving glass bulbs is produced at theplate of the tube. Consequently, theplate has to be capable of radiating allthe heat generated at its surface, andalso the heat radiated to the plate by thecathode and other elements, withoutdamage or adverse results. Any exces-sive heat, above that stipulated by themaximum dissipation ratings, can pro-duce very detrimental effects. Thesewill be covered in more detail later.

Triode Class A Power AmplifiersAs a first example, consider a triode

power amplifier such as a Type 6A3,operated resistance -coupled, under therated Class A conditions. The accom-panying plate characteristic indicatesthat with 250 volts applied to the plate,-45 volts grid bias and the recommendedload of 2500 ohms, the rated plate cur-rent is 60 ma. This requires a platesupply voltage of 400 volts for with 60ma. flowing through the load resistor of2500 ohms there will be a voltage dropacross RL of 0.06 ma. x 2500 ohms or 150volts, and hence an applied voltage of250 volts. The d -c power dissipated inthe load resistor will be I2 RL or (Eb -En)Iwatts. Using the latter expression thisgives 150 volts x 0.06 ampere or 9 watts,and this power is represented on thediagram by the rectangle at the right.The plate dissipation of the tube will beEpI or 250 volts x 0.06 ampere whichequals 15 watts. This is represented by

the rectangle at the left as designated.These values only apply when no inputsignal is applied to the grid.

When an alternating voltage is im-pressed on the grid, the voltage at theplate of the tube will also fluctuate sinceit will differ from the supply voltage bythe drop in the load impedance. Withthe signal on the positive half cycle, theplate current will increase, this causing alarger drop in RL so that the plate poten-tial will be less than its value at theoperating point. On the negative halfcycle the instantaneous grid voltage willbe more negative than -45 volts, theinstantaneous plate current will be lessthan the average value and the drop inRL will be reduced. Consequently theinstantaneous plate voltage is higherduring the negative half cycle.

With an impressed input signal whosepeak voltage equals the bias voltage, thea -c power developed in the load is ratedat 3.2 watts. This a -c power is dissi-pated in RL in addition to the d -c powerdissipation of 9 watts mentioned above.The plate dissipation is therefore re-duced by the amount of the power out-put. This decrease in plate dissipationunder dynamic operating conditions is acharacteristic of all class A amplifiers.Hence, Class A power amplifiers shouldbe so designed that the dissipation understatic conditions will not be exceeded.

The RMA ratings for Type 6A3specify a maximum plate voltage of 325volts and a maximum plate dissipationof 15 watts. Since a plate current of 60ma. is obtained when 250 volts areapplied to the plate with a grid bias of-45 volts, it is apparent that if a higherplate voltage is employed, the maximum


sWrAleuts.THE information presented in the Sylvania Service Exchange is contributed

by servicemen as the result of practical experience. It is very carefully con-sidered before being accepted, and we believe it to be correct and authentic.However, we assume no responsibility with respect to results. Please do notsend routine or generally known information.

Philco 53 and 59. Watch for shortedfilter condenser caused by pressure ofi -f trimmer condenser plate being pressedagainst terminal during adjustment,causing short to ground.-William An-derson, Bronx, New York.

* * *

Philco 112X. This receiver when play-ing would play fine for periods of 15 to30 minutes after which it would fade andthe customer would have to turn the dialto catch up with the station. Tubesfound OK, and upon examination andchecking for voltage it also was as pervoltage measurement by Philco. Butthe R-51 (value is 15,000 ohm 5 watt)unit, after disconnecting, was found tomeasure 2000 ohms and this is a bigchange in resistance. Replace with anew unit 15,000 ohms, but make sureyou replace with a wire -wound resistorinstead of carbon. Also replace C-42with any reliable condenser rated .02mfd. 600 volts. This set is playing fineand the customer is more than satisfied.-Stephen M. Skovran, N. S. Pittsburgh,Pa.

* * *

Arvin #518. Tubes all light up but noreception. Replace the C-8 couplingcondenser between 41 tube grid and 76plate. This condenser was open butmake sure that it is replaced with a 600volt unit instead of the 400 volts.-Stephen M. Skovran, N. S. Pittsburgh,Pa.

* * *

Buick Sonomatic. If you can tunethis set with the push buttons but notwith the manual control when the set ison, look for a broken spring on the righthand side of the condenser push buttonassembly. Look real close because thespring is small and is very easily missed.This spring is supposed to kick back therocker arm with the return of the pushbutton when it is used. This rocker armhas a switch on the right side of it, whichit opens and closes each time it swingsback and forth. The switch in turn con-trols a relay which releases the manualcontrol from the condenser when thepush buttons are used. If the spring isbroken the rocker arm does not returnback to the position in which it should beand the switch on the side stays closed.Therefore, the manual control is releasedfrom the condenser and you are unable totune with it. To remedy put a newspring in the set. In order to do this thecondenser and push button assemblymust be pull td out of the set.-MichaelYurkovich, llighland Park, Mich.

THANK YOUOur announcement in the last

issue of the NEWS that it is nolonger possible to give tubes asawards for material submitted forthis section has not slowed up theincoming mail one bit. We greatlyappreciate the patriotic endeavor ofall of you who are continuing toshare your valuable knowledgewith other servicemen.

Loss of Sensitivity. When the set willplay weakly and all voltages and tubescheck OK, take your signal generator,set it for the i -f frequency and send asignal thru the first detector. If youfind that there is not as much volumewith the generator connected to thedetector as there is with it connected tothe first i -f and loosening of the trans-former adjustments tends to bringthe signal up, examination of the i -fpadders will probably show that theyare either wet or have been wet. Re-place the mica between the plates, adjustthe i -f padders and you will find yourgain is OK. The mica kits Sylvania sellsso reasonably will furnish mica for jobsof this type for several years. Now thatwe are unable to get many types of partsit is our duty to conserve and repair allof those that we know can be repairedand will still give service.-J. W. Brewer,Jr., Sinton, Texas.

* * *

Delco R -113o. No control of volumeregardless of the setting. Upon checkingfound a leaky condenser C-29 (10 mfd.25 volts) in the a -v -c circuit. Replace

SALVAGE SUGGESTION

If you servicemen will go overyour accumulation of old trade-ins,which have been collecting dustand taking up room, you can helpthe good old U.S.A. two ways. Justjerk out the old tubes and sell thechassis and power packs for junk.With the money you obtain buyBonds and Stamps. By doing thisyou are supplying needed metalsand helping finance the cost to"Keep Em Rolling". You don'teven have to reach in your "jeans".It will only take a couple hours ofyour time. Come on boys! Wecan do it, can't we?-Oliver F.Klein, Milwaukee, Wisconsin.

with a new unit of 10 mfds. and thevoltage should be at least 35 or 50 volts.-Stephen M. Skoovan, N... Pittsburgh,Pa.

* * *

Emerson 462 Combination. On acomplaint of very low volume similar toan open voice coil, check the 2.2 megohm0.1 watt 6SJ7 a -f screen resistor for anopen. It is also advisable to check the0.05 mfd. 400 volt bypass condenser atthe screen terminal.

When replacing the 0.1 watt resistora slightly larger unit is recommended,such as a % watt resistor.-Joseph S.Napora, Uniontown, Pa.

* * *

Truetone Model D-715. IntermittentService -Cutting Off when tilting. Spaceand adjust throwout switch contactpoints back of push button tuning motorso that contact is made only while motoris in operation. Beudix button in motordoes not draw back into motor suffi-ciently to release contact points, butappears to do so.-Walter Reynolds, Jr.,Hattiesburg, Mississippi.

* * *

Wurlitzer Multi - Selector. Recordstops playing during normal runningoperation. Open back of cabinet andlocate large fiber gear and small wormgear combination. Examination maydisclose that some teeth are worn, thusallowing worm to be disengaged with theresult that record stops after one revolu-tion. To repair, note that worm gear ison a separate carriage. Four nuts holdcarriage to top of board. Loosen nutsand insert small thin shims of sufficientthickness to insure that gear teeth engageworm when nuts are again tightened.This repair job was done in half an hourand the set works as good as new. (Aprevious estimate by the company fornecessary repairs was $25.00). I hopethis may help some other serviceman.-W. J. Dingwell, Port Monmouth, NewJersey.

* * *

Silvertone Models. In Silvertonesand other similar receivers I find that theplate voltage exceeds. the manufacturer'stube ratings, especially on output tubes.Sometimes a new tube will .act the same.I find that lowering the plate voltage 10to 25 volts makes for better performance,thus saving critical material. The littledifference in volume can usually be madeup by a tune-up which will also eliminatefurther troubles when high line voltageoccurs.-James DiChiera, Westernport,Md.

syia#41AfewsPLATE AND SCREEN DISSIPATION RATINGSTHEIR RELATION TO TUBE PERFORMANCE AND LIFE

(Continued from page 2)

plate dissipation will be exceeded unlessmore bias is provided to reduce the platecurrent to a safe value. In general, theallowable plate dissipation will determinethe maximum operating plate currentfor a given plate voltage. For some tubetypes the allowable dissipation may behigh enough so that the operating pointand load resistance may be based uponconsiderations of distortion, flow of gridcurrent and desired power output.

Pentodes And Beam TubesWith pentodes and beam tubes addi-

tional factors must be taken into con-sideration. The total B -supply inputpower will be the power in the platecircuit plus the power dissipated in thescreen circuit. With an input signalwhose peak voltage equals the bias, thepower delivered to the plate circuit is theproduct of the maximum signal platecurrent and the corresponding platevoltage. The heat dissipated by theplate will be the power supplied to theplate circuit less the power delivered tothe load.

Screen dissipation increases quiterapidly with applied signal voltage andmay be several times greater at the maxi-mum signal condition than when thesignal is zero. The increase in d -c screencurrent with signal occurs because of theinfluencing effect of plate potential onscreen current and is particularly notice-

able when a high value of load resistanceis employed. This condition should beavoided, not only to maintain the screendissipation within limits but also to keepthe distortion at an acceptable. value.

Typical ExampleAs a second illustration of zero -output

and rated -output screen and plate con-ditions we will survey the ratings forType 7C5, or the octal -based equivalentType 6V6GT/G, when employed as asingle -ended Class A amplifier. Maxi-mum ratings are:Plate Voltage 315 VoltsScreen Voltage 250 VoltsPlate Dissipation 12 WattsScreen Dissipation 2 Watts

Recommended operatingare:

conditions

Heater Voltage 6.3 6.3 VoltsPlate Voltage 250 315 VoltsScreen Voltage 250 225 VoltsGrid Voltage -12.5 -13 VoltsPeak Input Signal 12.5 13 VoltsPlate Current (Zero Signal) 45 34 Ma.Plate Current (Max. Signal) 47 35 Ma.Screen Current (Zero Signal) . . 4.5 2.2 Ma.Screen Current (Max. Signal) 7.0 6.0 Ma.Load Resistance 5000 8000 OhmsPower Output 4.5 5.5 WattsTotal Distortion 8 12 Per Cent

For the 250 volt condition the dissi-pation values computed from the abovefigures show:Zero output plate dissipation is 250X0.045=11.25 WattsZero output screen dissipation is 250X0.0045 =1.125 WattsFull output plate dissipation is

(250X 0.047)-4.5 = 7.25 WattsFull output screen dissipation is 250X0.007=1.75 Watts

VOLTAGE REGULATOR TUBESSylvania Tubes oB3/VR90 and oD3/VRI50


145 to 160 volts. For either type oftube the operating voltage will be lessthan that required for breakdown.

Regulation CharacteristicThe operating voltages are also de-

pendent upon the current passingthrough theltube, generally being severalvolts higher at high current drains thanat low values of current. This differencein operating voltage on any particulartube is a measure of the regulation forthat tube. For Type 0B3/VR90 themaximum regulation is 6 volts over theoperating . range of 10 th 30 ma. ForType 0D3/VR150 the maximum regula-tion is 7.5 volts over the operating cur-rent range of 5 to 40 ma. On an idealtube the regulation would have a zeroslope and for such a case the operatingvoltage would be constant over theoperating current range. This conditionis rarely obtained in actual practice.The regulation tends to improve duringthe life of a tube.

Possible Tube -To -Tube DifferencesOne very important factor which

should be noted is that individual tubesmay not deliver identical voltages to the

load. For example, if a given 0B3/VR90tube is checked and found to deliver88 volts to the load and this tube isreplaced with another OB3/VR90 thistube might deliver 92 volts or some othervoltage to the load. Nevertheless, thevoltage should always be within thespecified limits for operating voltagewhich would be 80 to 100 volts for the0B3/VR90, and the regulation 6 voltsor less; while for the 0D3/VR150 thevoltage will be between 145 volts and160 volts and the regulation would be7.5 volts or less.

Series Operation

Two or more regulator tubes of thesame type may be connected in seriesto obtain higher voltages which aremultiples of the drop for a single tube.Voltage taps may be taken from thejunction points of the regulator tubes asindicated in the circuit diagram. AType 0B3/VR90 and an 0D3/VR150cannot be used in series principallybecause of the difference in breakdownvoltage required and because of thedifferences which exist in the operatingranges for the two regulator tubes.

We see, therefore, that as the outputgoes from zero to 4.5 watts the platedissipation drops froth 11.25 watts to7.25 watts while the screen dissipationincreases 0.625 watt.

Similar computations could be madefor the 315 volt condition. It is to benoted that the recommended operatingconditions have been designated so asnot to exceed the maximum dissipationratings. One should bear in mind thatpublished ratings represent averagetubes and that any particular tube whenmeasured may differ to some extent fromthese figures for plate and screen values,power output and distortion.

Special PrecautionsIt has been pointed out that because

of the reduction of minimum plate volt-age which occurs with increase in load,the average and maximum values ofscreen current increase with load resis-tance. Hence, permissible screen dissi-pation limits the maximum load that canbe employed. This justifies the pre-caution that the load should never beremoved from the output transformersecondary of a pentode or beam tubesince the effective load impedancewill increase and the resulting excessivescreen dissipation will damage the tube.

Removing the plate voltage, withoutalso removing the screen voltage, givesrise to abnormally high screen currentseven though rated screen voltage andrated bias .are normal. This means ex-cessive screen dissipation will be encoun-tered and the tube soon ruined if opera-tion continues.

Dissipations higher than the specifiedmaximum values generally result indetrimental effects such as secondaryemission, high gas currents, warpage oftube elements and actual tube destruc-tion.

A recent issue of Sylvania News (Vol.9 No. 10 June 194f2) carried an articleentitled "Tracking Down Grid Emis-sion" in which appeared the precautionthat excessive heat is the factor thatmust be avoided to prevent grid emis-sion troubles. It is suggested that youreview that article since it containsvaluable information which is closelyrelated to the present subject.

Old Tubes for NewA rule requiring owners of radio

sets to turn in their old tubes whenthey buy new ones is being workedout by the WPB and will probablygo into effect soon. The tube turn -in regulation is intended to controlthe number of tubes distributed.It also will permit the salvaging oftube bases which, in some cases,can be refabricated. Watch ournext issue for more information.

TECHNICAL SECTION


MARCH, 1943 EMPORIUM, PENNA. Vol. 10, No. 3

Converter Tube Design FeaturesService problems related to converter tubes may often be clarified through knowl-

edge of the tube design of the particular type in question. Numerous convertertube types have been employed in superheterodyne receivers. Five principal de-signs are in general use and these will be briefly described as to their constructionalfeatures and the functions associated with the various grid structures. Severaltypical performance curves are also discussed.

TRIODE-HEPTODE CONVERTERSTypes 7J7, 7S7 14.J7, 14S7, 6J8G

The superheterodyne receiver requires a converter tube whosefunction is to mix or beat (heterodyne) the incoming signal fre-quency with a locally generated frequency to obtain an inter-mediate frequency. If the output from a conventional triodeoscillator is suitably coupled to a tuned r -f voltage amplifier, thepentode plate circuit will contain four frequencies: the signalfrequency, the oscillator frequency, and the sum and the differ-ence frequencies of these two. The latter are obtained by beat-ing the first two frequencies mentioned. Since more gain issecured at lower frequencies in the i -f amplifier stages, the differ-ence frequency (called the i -f frequency) is the one desired. Thiscan be obtained when the tuned circuits in the pentode plateare designed to resonate at the i -f frequency, in which case theywill reject the other three frequencies.

T.IOD!nAT[ NOTOOt

PLAN

Such a circuit can be simplified considerably by combining thetriode oscillator with the mixer tube in one bulb. Furthermore,improved efficiency and stability can be secured by adding an in-jector grid in the mixer section which is connected directly to thegrid of the oscillator section, thereby permitting both the mixercontrol grid and the injector grid to control the electron stream.This provides true electron coupling. An illustration of such atube is the triode-heptode Type 7J7 shown above. The dia-gram indicates that the cathode is common to both units, theupper portion being associated with the triode oscillator and thelower section with the heptode mixer. A typical circuit dia-

gram is shown wherein plate -tuning of the oscillator is indicated.Grid -circuit tuning is also widely employed with triode-heptodetubes, in which case the oscillator circuit resembles that shownfor the pentagrid converter described below.

A.T. SIGNAL d PIINIUTI P-) O

d +100r +4 0r

THE PENTAGRID CONVERTERTypes ILA6, IA7GT/G, 7A8, 7B8, 6A8G, and others

Pentagrid Converter is the name applied to a tube having fivegrids in addition to the cathode and plate and intended forfrequency conversion in superheterodyne radio receivers. Suchtubes combine the functions of oscillator, mixer and amplifierwithin one structure. The No. 1 and No. 2 grids are used as theoscillator grid and oscillator plate respectively. Electronspassing through grids No. 1 and No. 2 are further controlled bythe signal input grid No. 4. This grid is shielded from theoscillator section by grid No. 3 and from interaction with theplate by grid No. 5. Screen grids No. 3 and No. 5 are connectedtogether internally. The circuit on the next page illustrates theuse of the pentagrid converter, such as Type 7B8. Voltages ofsignal and oscillator frequency reaching the plate are bypassedto ground, since the tuned circuit in the plate is resonant onlyto the beat or intermediate frequency (I.F.) which is to be fur-ther amplified.

The pentagrid converter may be considered as operating verymuch like a conventional variable-mu tetrode first detector withan associated triode oscillator, except that the oscillator triodegrid is located next to the cathode which is common to both thefirst detector variable -mu tetrode and the oscillator triode.Electrons emitted from the cathode surface are influenced by thevarious grid and plate voltages and divide up so that grid No. 1receives about 3 to 6 per cent of the electrons, the oscillatoranode receives about 40 per cent of electrons, grids 3 and 5(screen grid) receive about 25 to 30 per cent of the electrons, andthe plate receives the remaining electrons emitted. Because ofthe oscillator grid's strategic 'position next to the cathode, .any

(Continued on following page)

OUTPUT

SrsiNewsConverter Tube Design

(Continued from previous page)

oscillator voltage on this grid will modulate the entire electronstream regardless of the ultimate destination of the electrons.Referring to the diagram, it is interesting to observe the actionthat takes place within the tube when it and the associatedcircuit components are operating normally. When the set isfirst turned on, the No. 1 grid is at zero potential because it istied to the cathode by the 50,000 ohm grid leak. As the cathodeheats up and starts to emit electrons, the feedback betweenoscillator anode and grid causes regeneration which immediatelystarts the triode circuit to oscillating. When the oscillatorcircuit is oscillating, the No. 1 grid is driven alternately positiveand negative. While the grid is positive, grid current flowsthrough the grid leak in such a direction as to make the No. 1grid negative with respect to the cathode. This grid swing may

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make the grid negative by as much as 30 to 40 volts, and thisbecomes the grid bias point about which the grid varies inamplitude alternately in a positive and then a negative directionunder the influence of plate circuit feedback. From this it canbe seen that the maximum instantaneous negative voltage onthe No. 1 grid may be 60 to 80 volts.

Electrons from the cathode are accelerated through the No. 1grid by the positive oscillator plate and the positive screen grid.The oscillator plate actually consists of a pair of side rods butno grid wires are strung on these rods. Many of the electronsapproaching the oscillator plate possess high velocities so thatthey shoot past the oscillator plate and for the most part throughthe screen grid No. 3 and approach grid No. 4. The No. 4 gridhas a negative potential which therefore retards the oncomingelectron stream. This cloud of retarded electrons between gridsNo. 3 and No. 4 constitute á virtual cathode for the tetrodesection of the tube. Electrons may be drawn away from thissource (virtual cathode) in a manner quite analogous to that bywhich they were originally accelerated away from the regularcathode.

If grid No. 1 is only slightly negative or even somewhatpositive, then the virtual cathode has an ample electron supplyfor the tetrode section of the tube. Whenever grid No. 1 swingsto more negative values, the number of electrons arriving at thetetrode plate is temporarily reduced or possibly cut off. Pulsesof current are therefore supplied to the tetrode section at oscilla-tor frequency and the electron stream to the tetrode plate ismodulated by the r -f signal voltage on the grid No. 4. Thus,the oscillator can modulate the signal in the tetrode section andproduce the i -f beat note in the plate circuit of the tetrodesection.

The current necessary to have sustained oscillations is con-trolled by the oscillator grid and not by the signal grid, thelatter being incapable of producing cutoff in the oscillatorsection. The gain of the tube can be controlled over a con-siderable range by a variable negative bias on grid No. 4 withoutsubstantially affecting the oscillator section.

THE PENTAGRID MIXERTypes 6L7 and 6L7G

Type 6L7G pentagrid mixer used with a separate oscillatortube. Type 6L7G has the No. 1 grid as the signal grid, gridsNo. 2 and No. 4 connected internally as screen grids, grid No. 3as the oscillator injector grid and the No. 5 grid as the suppressor(connected internally to cathode). Thus, the 6L7G is quitesimilar to the mixer section of Type 7J7.

Features

THE TRIODE-HEXODETypes 6K8, 6K8G and 6K8GT

Such converters have a rather unconventional structure. Theoscillator plate is so located that it is completely removed fromthe cathode to mixer plate electron stream. The oscillatorplate and mixer plate are on opposite sides of the cathode. GridNo. 1 completely surrounds the cathode so that the side towardsthe oscillator plate acts as the oscillator grid, while the other sideis associated with the mixer and modulates the cathode to mixerplate electron stream at oscillator frequency. With this con-struction a single grid suffices to screen the oscillator grid fromthe signal grid as well as to screen the signal grid from the mixerplate. The signal control grid is made in the form of a flatwound grid with one-half of the windings (those facing theoscillator plate) removed. Specially designed metal shieldssuitably connected to the cathode prevent stray electrons fromproducing undesirable couplings and also serve to isolate theoscillator and mixer sections. In addition, they cause a potentialminimum to exist between the screen and plate. Sufficientlyhigh plate resistance is obtained so that a suppressor grid is notrequired.

THE PENTAGRID 6SA7 TYPETypes 6SA7, 6SA7GT/G, 7Q7, I2SA7GT/G, 14Q7

This construction, as exemplified by Types 6SA7, 6SA7GT/Gand 7Q7, is somewhat like 6L7G except that the functions ofgrids No. 1 and No. 3 are interchanged. Grid No. 1 is the os-cillator grid and grid No. 3 is the signal grid, the latter having aremote cutoff characteristic. The side rods for grid No. 3 arelocated 90° from the plane of the other side rod supports and aretherefore directly in the center of the electron stream. Thenegative voltage on the signal grid repels some of the electronstraveling to the plate back towards the cathode. However,these electrons will not affect the space charge near the cathodesince most of the electrons turned back are intercepted bycollector plates fastened to the side rods of the No. 2 screen grid.Hence, the collector plates of the screen provide isolation of thecathode space charge and the signal grid so that changes insignal grid voltage produce little change in the cathode current.Any changes in plate current due to signal grid voltage changesare offset by opposite and nearly equivalent changes in screencurrent. Screen grids No. 2 and No. 4 are connected internally.Grid No. 5 is the suppressor and serves to increase the plateresistance of the converter.

DEFINITIONSConversion Conductance (gc) is defined as the ratio of the

intermediate frequency component of the plate or outputcurrent of the converter tube in a superheterodyne receiver tothe radio frequency component of the signal voltage applied tothe control grid. The value is expressed in micromhos. Withreference to the performance of a frequency converter, it isemployed in the same manner as mutual conductance is used insingle frequency amplifier computations.

(Continued on page 4)

CORRECTIONIn the last issue (Vol. 10, No. 2) there appeared an in-

complete statement regarding the use of voltage regulatortubes in series. The final sentence of that article (P. 4)indicated that a Type OB3/VR-90 and a Type OD3,/VR-150 could not be used in series. This was incorrect, as suchan arrangement can be employed if the operating con-ditions do not exceed the specified values for each type.The statement as it appeared should have been clarified toindicate that it is not practical to manufacture a combina-tion regulator consisting of these two structures in a singleenvelope.

:.:...i:iiiiiiiii:'iiiii::::::iii®: THE information presented in the Sylvania Service Exchange is contributedby servicemen as the result of practical experience. It is very carefully con-

sidered before being accepted, and we believe it to be correct and authentic.However, we assume no responsibility with respect to results. Please do notsend routine or generally known information.

Slipping Drive Cables. For dial drivesthat have a tendency to slip, we use amixture of Fuller's Earth and shellac,about 1% Fuller's Earth and % shellacand a small amount of resin. Thisbrushed lightly on the drive cable onlyand left to dry for an hour or so, willmake it taunt and ready to drive thecondenser. A small brush of the camel'shair type is just the thing. The solutionshould be well shaken and very sparinglyused.-Ben's Radio, Boston, Mass.

* * *

Repair Cement. I find that commonfingernail polish is fine for repairingplastic cabinets, speaker cones, to holddial cables, etc. Laurel color sticks bestin my brand. You may have better luckwith different shades in different brands.-Oscar's Radio Service, Merrill, Iowa.

* * *

Setting Push Buttons. In settingpush buttons on sets without tuningindicators, first adjust oscillator trimmerto proper station, then de -tune this con-denser a trifle. Adjust r -f trimmercondenser for maximum output fromspeaker. Readjust oscillator trimmerfor maximum output. Set other stationsthe same way. Due to a -v -c action it isimpossible to peak up the r -f trimmersatisfactorily when the oscillator trim-mer is in tune.-Neupauer Radio,Cleveland, Ohio.

* * *

AC -DC Sets. These sets have a habitof burning tubes out in different locationswhere the line voltage has a tendency togo up. The sets in mind have 6 tubes,four 12 -volt types and two 35 -volt types.This adds up to 118 volts. I have checkedline voltage as high as 123 volts. These setscome in often so I have asked the custo-mer if he has trouble with tubes rightalong. If he does I install in place of the35L6GT power tube a 50L6GT tube whichdoes the trick. This does not affect theset if you balance the set after installingthe 50L6GT tube. This will work on anyac -dc set using 35L6GT power tubes.-Oliver Nicholas, Olean, N. Y.

* * *

Majestic 300. Lack of plate voltageon Type 58 tubes is usually due toburned out coil which is choke in diallight circuit. This coil carries plate cur-rent for 58 type tubes. If replacementchoke is not available, this choke may bebridged across with a 500 ohm resistor.Be sure to replace a .25 mfd. condenserbypassing plate circuit, as this unit isusually shorted, and caused the originaltrouble.-W. H. Updegrove, Carterville,Missouri.

Clough-Brengle CRA Oscilloscope. Ifthe vertical control has no effect on theimage, or if the sensitivity of the verticalamplifier is low, it may be due to achange in resistance value of the 100,000ohm % watt plate load resistor of theType 57 vertical amplifier tube.

In a recent experience, the originalunit changed value from 100,000 to750,000 ohms.-Joseph S. Napora,Uniontown, Pa.

* * *

Philco Mystery Control ConsoleRadios. Mystery control does not work.Open mystery control box, and checkloop which acts as primary for 30 oscilla-tor tube. Usually open and best bet toreplace even if good to avoid repeat call.-Vito F. Daidone, Newark, New Jersey.

* * *

Temporary Tube Salvage. In repair-ing AC -DC sets using the 35Z5GT/Grectifier it is possible to connect a resistorfrom pins 2 to 3 and to restore service inthose cases where the tapped part of theheater has burned out. I have beenusing a 50 ohm resistor and leaving thedial light out of the socket. The setsseem to work as well as ever. Of coursethis will be changed back as soon as newtubes become available-Wm. G. Aust-gen, Dyer, Indiana.

* * *

Philco PT -25 Code #121. Heavy a -chum, sound indicated open filter con-denser or possible open grid. Test showedthat neither of these were the cause.Trouble was located in resistor #29 (seeRiders 12-4 under Philco). This dualresistor is in the filament circuit and hasa resistance of 53 and 175 ohms, and wasgrounded to the chassis, thereby feedingraw AC to the grids through several con-densers. The cure-replace it. Or Ihave found that the ground very seldomaffects the resistance in which case in-sulate it from the chassis.-R. R. Harris,Ojus, Florida.

* * *

Emerson AX -211, AX -212 ETC. Ifthe sensitivity of this model is low, andif the antenna trimmer on the condensergang will not resonate, also if the wave -trap will not tune to resonance, theprobable cause is a broken lead to theground lug of the antenna coil.

To repair, remove the coil and care-fully scrape away black pitch near theground lug, also clean the enamel insula-tion off the wire, then resolder. Installthe coil and realign in the conventionalmanner.-Joseph S. Napora, Union-town, Pa.

Aetna AC -DC Sets.. When thesesets are operative on 500 to 650 kc. only,look for open in coil in pentagrid cón-verter circuit, (6A7 or 6A8) especiallywhen the station which is heard on thisfrequency tunes very broad.-W. H.Updegrove, Carterville, Missouri.

* * *

Phono Pickups-Crystal or Magnetic.Pickup used either on radio phono com-bination or in a public address system.No phono operation, although you hearthe vibration of pickup needle in recordgrooves. To definitely ascertain whetherpickup head is defective, as it usually is,disconnect pickup. Place a pair of goodcrystal headphones to the pickup leads.If the pickup is OK, you will hear therecording in the headphones while play-ing, otherwise, pickup is defective.-VitoF. Daidone, Newark, New Jersey.

* * *

Amrad 81. This model has r -f chokein detector circuit. An open in thischoke causes set to be inoperative. Thistype of choke, if not available, can besatisfactorily replaced with resistor 1000to 2000 ohms.-W. H. Updegrove,Carterville, Missouri.

Grounding Clips. To make the foil -lined tube shield serviceable when sub-stituting GT tubes for metal or G typetubes, particularly in the growing num-ber of instances where bakelite is beingsubstituted for the metal base, we arefinding it convenient to slip a groundingclip over the shield prong and octal basecenter lug; then bend it up and slip thefoil -lined tube shield over it. In thosecases where a G type tube has formerlybeen used, and the tube shield base isattached to the chassis, we have found itnecessary to drill out the rivets and re-move the manufacturers tube shield baseso as to permit insertion of the slightlylarger diameter GT tube base. Thesocket may be refastened with nuts andbolts or riveted in place. In those caseswhere no provision has been made forgrounding the shield pin underneath thechassis and the shield pin clip has beenomitted from the tube socket, a secondgrounding clip fitted over the octal basepin and tube pin underneath the chassisforms a convenient lug to which to soldera wire, grounding the other end on somenearby ground contact point in the chas-sis. Philco Type 38-7 or 8 are cases inpoint. Grounding clips have been ad-vertised in several parts catalogs.-LeRoy Brown, Rhinebeck, New York.

4.5;_/-a#41 News

Converter Tube Design Features(Continued from page 2)

Conversion Gain is the ratio of the intermediate frequencyvoltage developed across the load to the radio frequency voltageapplied to the control grid. When tube and circuit constants areknown the conversion gain may be computed from the formula:

Conversion Gain = g` rp RLrp RL

Where ge is the conversion conductance, rp the plate resis-tance and RL the resonant impedance of the i -f transformermeasured across the primary terminals.

400

ó360 O

320

z280 ,,,

UZ4

240 ú0z

200 ó3

ZO

160 Ñw>

120

U

80

-

40

12

NEGATIVE

8

CONTROL

4

GRID VOLTS

0

I

Fig. A

Several curves may prove helpful in illustrating performancecharacteristics of converters. Fig. A shows how the conversionconductance for a typical triode-heptode converter varies withthe negative control grid (heptode) voltage. The recom-mended control grid voltage would be approximately -3 volts,under which conditions the tube has a conversion conductanceof about 300 micromhos. The curve also indicates the cutoffcharacteristic, since the conversion conductance is reduced toonly a few micromhos when the control grid voltage reaches-16 volts.

TECHNICAL MANUALA few typographical errors have been found in the

latest edition (1942) of the Sylvania Technical Manual.We regret that these were not discovered soon enough tochange the final copy before printing. It is our hope thatany which exist will not cause serious confusion. Shouldyou discover any errors, the Editor will appreciate havingthem called to his attention.

Please make the following notations in your copy:Page 148-Change heading from 707 to 7Q7. Page 219

-Change base view designation for Type 117L7/M-7GTfrom 8 -AD to 8-A0.

CONVERSION CONDUCTANCE VS. OSCILLATOR GRID CURRENT

O30c

O

az

700u

V

-

OZo,I4

Z0 OSCILLATOR GRID LEAK RESISTOR = 50.000 OHMSIX

O 0u 100

OSCILLATOR

200

GRID

300

CURRENT IN

400

MICROAMPERES

500 600

Fig. B

For optimum receiver performance too much emphasis can-not be placed on the curve of Fig. B. This gives the variationin conversion conductance for oscillator grid current thru aspecified grid leak resistance. It shows how important it is tokeep the minimum oscillator strength above the "knee" of thecurve. Attention is called to the fact that beyond the knee ofthe curve the uniformity is excellent over a wide range ofoscillator voltage. The developed oscillator voltage is given bythe product of the oscillator grid current and the grid leakresistance. For example, 200 microamperes through 50,000ohms gives a developed oscillator voltage of 10 volts.

CONVERSION

CALCULATED

GAIN VS.

PROM

PLATE LOAD

GAIN -

RESISTANCE

G. Ro R,

-170

ZQ 80OZO

á1

O40

V

R, }

pE

í0.`O

IR,f--Eºl

E

PEN AGRLO

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° 01

PLATE

01

LOAD RESISTANCE

3

IN MEGHOMS

0. 0.5

Fig. C

Since converter tubes of different constructions, such asthose already discussed, have different ratings and electricalcharacteristics it is natural that performance characteristicsalso differ from type to type. Although conversion gain is afunction of conversion conductance, the gain also depends uponthe load impedance (RL) of the converter section. Forexample, a pentagrid converter may have a higher rated con-version conductance than a triode-heptode converter, but ifdue consideration is given to the load impedance the conversiongain of the triode heptode will not be reduced in the ratio of therespective conversion conductances of the types involved.Considering that the rated oscillator voltage is obtained fromeach type, Fig. C shows gain curves calculated for both typesusing the gain formula specified. Verification of the perform-ance characteristics mentioned above is indicated by thesecurves.

TECHNICAL SECTION


APRIL, 1943 EMPORIUM, PENNA. Vol. 10, No. 4

SUBSTITUTION CHART FORBATTERY TUBE TYPES

The difficulty in obtaining replacement tube types has beenacute in most sections of the country. Recognizing that theuse of substitute types often requires set modifications, theeditors of Sylvania News have prepared the following chart toassist servicemen, dealers and distributors in ascertainingquickly the principal changes involved in order to utilize asubstitute type. For convenience, the changes are designatedby letters. These refer to the specific changes listed at the topof the chart.

The present list is confined to types employed in batteryoperated receivers. According to the WPB civilian radio tubeprogram, 18 battery types are to be manufactured. Sometypes occurring in Column 2 are marked with an asteriskindicating that they appear on the WPB list. Since every typeon the WPB list may not always be available in any givenlocality, the use of an alternate type may be necessary. Alimited number of battery types, particularly miniatures, havenot been included in Column 2 since space limitations generallyprohibit the substitution of a type having larger physicaldimensions.

COLUMN 1 COLUMN 2 CHANGES REQUIRED

Typeson

WPB I.ist

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A BCDE FGHK LM1A5GT/G

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1H5GT/G

1LA4

1LB4

1A5G1A5GT1F41F5G

`1LA4`1LB41A7G1A7GTA1B7G1B7GT1C7G1D7G1A61061LA6

'1LC61C5G1C5GT1G5G1G5GT1G5GT/G1H5G1H5GT1B5/25S1H6G

'1LH41A5GIA5GT

1A5GT/G1F41F5G

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n W k'li list.

TYPES ONWPB LIST

USE TOREPLACE

CHANGES REQUIREDABCDE FGHK LM

1LB4 (Continued) '1A5GT/G . . . . . . . E ... ... ... ... L ...1F4 B C ... E ... ... ... ... L M1F5G B C ... E ... ... ... ... L M

*1T5GT E ... ... ... ... L ...1LC6 1LA6 F ... ... ... ... M

1A7G1A7GT ... ... ... ... E F ... H ... ... M

'1A7GT/G ... ... ... ... E F ... H ... ... M1B7G1B7GT1C7G1D7G1A6106

1LD5 1F61F7G

1LE3 1E4G E F ... ... ... ... ...1G4G E F ... ... x ... ...1G4GT E F ... ... K ... ...1G4GT/G ... ... ... ... E F ... ... K ... ...1H4G

301LH4 1H5G E ... ... H ... ... ...

1H5GT E ... ... H ... ... ...1H5GT/G ... ... ... ... E ... ... H ... ... ...1B5/25S B C ... E ... ... ... ... ... M11I6G B C ... E ... ... ... ... ... M

1LN5 1LC5 ... ... ... ... ... F ... ... ... ... M1N5G ... ... ... ... E F ... H ... ... ...IN5GT . - . . . . . . ...

'1N5GT/G ... ... ... ... E F ... H ... ... ...1A4P1A4T1B4P1D5G1D5GP B C... E F... H... ... M1D5GT1E5G1E5GP s C... E F... H... ... M1E5GT

1N5GT/G 1N5G A ... ... ... ... F ... ... ... ... ...1N5GT A ... ... ... ... F ... ... ... ... ...1A4P s c ... E F ... ... ... ... M1A4T B C ... E F ... ... ... ... M1B4P B C ... E F ... ... ... ... M1D5G s C ... ... F ... ... ... ... M1D5GP $ C ... ... F ... ... ... ... M1D5GT B C ... ... F ... ... ... ... M1E5G B c ... ... F ... ... ... ... M1E5GP B C ... ... F ... ... ... ... M1E5GT ... B C ... ... F ... ... ... ... M

*1LN5 E F G ... ... ... ...1LC5 ... ... . E F G ... ... ... M1P5GT/G 1P5G A . . . . . . . . . . . . F . . , . . . . . . . . ,

1Q5GT/G 1Q5GT A ... ... ... ...F

... ... ... ... ... ...1Q5GTA3Q5G

... ... ... ... ... ... ... ... ... ...3Q5GTp'3Q5GT/G

...

.........

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...... ... .. D ... ... ... ... ... ... ...1T5GT 1A5G B C ... ... ... ... ... M1F4 .. ... ... . .`1LB4 ... ... ... E ... ... ... K3Q5GT/G 3Q5G3Q5GT

A . . . , , . . .. ... ... ... ...'

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...:

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Cross Index of Signal Corps and CommercialMany servicemen and dealers, as well as radio mechanics

now serving in the armed forces, are somewhat familiar withthe type designations for vacuum tubes as used by the army.Because commercial type numbers are usually better known,and since more published data have been made available ontubes as designated by their commercial type numbers, it hasbecome apparent that a cross index would be very useful inconjunction with tube testing and servicing work on govern-ment communications equipment.

Vacuum Tube Types With Cathode RatingsRadio tubes procured by the army, under Signal Corps

specifications have been marked with a VT designation. Inthe case of GT tubes, some commercial types are brandedGT/G rather than GT as shown in the commercial listing.The listing of tube types on this page is given according toconsecutive VT numbers. The tabulation on the next pageis based upon the commercial type number sequence and crossreference given for the Signal Corps designations.

ArmyNumber

Commercial CathodeNumber Type Volts Amps

ArmyNumber


ArmyNumber


VT -1 WE -203-A.. Fil. 3.6 1.1 VT -94-C 6J5G Spec'1.Htr. 6.3 0.3 VT -177 1LH4 Fil. 1.4 0.05VT -2 205-B Fil. 7.0 1. 35 VT -94-D 6J5GT Htr. 6.3 0.3 VT -178 1LC6 Fil. 1.4 0.05VT -4-B 211 Fil. 10.0 3.25 VT -95 2A3 Fil. 2.5 2.5 VT -179 1LN5 Fil. 1.4 0.05VT -4-C 211 Special.. Fil. 10.0 3.25 VT -96 6N7 Htr. 6.3 0.8 VT -181 7Z4 Htr. 6.3 0.9VT -5 215-A Fil. 1.0 0.25 VT -96-B 6N7 Special . Htr. 6.3 0.8 VT -182 3B7/1291.. . . Fíl. 2.8 0.11VT -6 212-A (obsolete) VT -97 5W4 Fil. 5.0 1.5 VT -183 1R4/1294... . Htr. 1.4 0.15VT -7 WX-12 Fil. 1.1 0.25 VT -98 6U5/6G5... . Htr. 6.3 0.3 VT -184 VR-90/30. . . Cold CathodeVT -17 860 Fil. 10.0 3.25 VT -99 6F8G Htr. 6.3 0.6 VT -185 3D6/1299.. . . Fil. 2.8 0.11VT -19 861 Fil. 11.0 10.0 VT-100 807 Htr. 6.3 0.9 VT -187 575-A Fil. 5.0 10.0VT -22 204-A Fil. 11.0 3.85 VT -100-A 807 Modif'd.Htr. 6.3 0.9 VT -188 7E6 Htr. 6.3 0.3VT -24 864 Fil. 1.1 0.25 VT -101 837 Htr. 12.6 0.7 VT -189 7F7 Htr. 6.3 0.3VT -25 10 Fil. 7.5 1.25 VT -103 6SQ7 Htr. 6.3 0.3 VT -190 7H7 Htr. 6.3 0.3VT -25-A 10 Special.. . Fil. 7.0 1.18 VT -104 12SQ7 Htr. 12.6 0.15 VT -191 316-A Fil. 2.0 3.65VT -26 22 Fil. 3.3 0.132 VT -105 6SC7 Htr. 6.3 0.3 VT -192 7A4 Htr. 6.3 0.3VT -27 30 Fil. 2.0 0.06 VT -106 803 Fil. 10.0 5.0 VT -193 7C7 Htr. 6.3 0.15VT -28 24, 24A Htr. 2.5 1.75 VT -107 6V6. Htr. 6.3 0.45 VT -194 7J7 Htr. 6.3 0.3VT -29 27 Htr. 2.5 1.75 VT -107-A 6V6GT Htr. 6.3 0.45 VT -195 CK-1005. . . . Fil. 6.3 0.1VT -30 01, 01-A. . . . Fil. 5.0 0.25 VT -107-B 6V6G Htr. 6.3 0.45 VT -196 6W5G Htr. 6.3 0.9VT -31 31 Fil. 2.0 0.13 VT -108 450-TH Fil. 7.5 12.0 VT -197-A 5Y3GT/G . ..Fil. 5.0 2.0VT -33 33 Fil. 2.0 0.26 VT -109 2051 Htr. 6.3 0.6 VT -198-A 6G6G Htr. 6.3 0.15VT -34 207 Fil. 22.0 52.0 VT -111 5BP4 Htr. 6.3 0.6 VT -199 6SS7 Htr. 6.3 0.15VT -35 35/51 Htr. 2.5 1.75 VT -112 6AC7/1852. . Htr. 6.3 0.45 VT -200 VR-105/30. . Cold CathodeVT -36 36 Htr. 6.3 0.3 VT -114 5T4 Fil. 5.0 2.0 VT -201 25L6 Htr. 25.0 0.3VT -37 37 Htr. 6.3 0.3 VT -115 6L6 Htr. 6.3 0.9 VT -201-C 25L6GT Htr. 25.0 0.3VT -38 38 Htr. 6.3 0.3 VT -115-A 6L6G Htr. 6.3 0.9 VT -202 9002 Htr. 6.3 0.15VT -39-A 869-A Fil. 5.0 18.0 VT -116 6SJ7 Htr. 6.3 0.3 VT -203 9003 Htr. 6.3 0.15VT -40 40 Fil. 5.0 0.25 VT -116-A 6SJ7GT.....Htr. 6.3 0.3 VT -204 HK -24-G. . . Fil. 6.3 3.0VT -41 851 Fil. 11.0 15.5 VT -116-B 6SJ7Spec'I..Htr. 6.3 0.3 VT -205 6ST7 Htr. 6.3 0.15VT -42-A 872-A Fil. 5.0 6.75 VT -117 6SK7 Htr. 6.3 0.3 VT -206-A 5V4G Htr. 5.0 2.0VT -43 845 Fil. 10.0 3.25 VT -117-A 6SK7GT. . . . Htr. 6.3 0.3 VT -207 12AH7GT. . . Htr. 12.6 0.15VT -44VT -45

3245

Fil.Fil.

2.02.5

0.061.5 VT -118 832 Htr. {12.

6.63 1.60.8

VT -208VT -209

7B8 Htr. 6.3 0.312SG7 Htr. 12.6 0.15

VT -46-A 866A Fil. 2.5 5.0 VT -119 2X2/879. . . . Htr. 2.5 1.75 VT -210 1S4 Fil. 1.4 0.1VT -47 47 Fil. 2.5 1.75 954 6.3 VT -211 6SG7 Htr. 6.3 0.3VT -48 41 Htr. 6.3 0.4 VT -121 955 Htr. 6.3 0 .15 VT -212 958 Fil. 1.25 0.1VT -49 39/44 Htr. 6.3 0.3 VT -123 A-5586 (Superseded by VT -128) VT -213-A 6L5G Htr. 6.3 0.15VT -50 50 Fil. 7.5 1.25 VT -124 1A5GT Fil. 1.4 0.05 VT -214 12116 Htr. 12.6 0.15VT -51 841 Fil. 7.5 1.25 VT -125 1C5GT Fil. 1.4 0.1 VT -215 6E5 Htr. 6.3 0.3VT-52 45 Special.. . Fil. 7.0 1.18 VT -126 6X5 Htr. 6.3 0.6 VT -216 816 Fil. 2.5 2.0VT -53 Superseded by VT -42-A VT -126-A 6X5G Htr. 6.3 0.6 VT -217 811 Fil. 6.3 4.0VT -54 34 Fil. 2.0 0.06 VT -126-B 6X5GT Htr. 6.3 0.6 VT -218 100-TH Fil. 5.0 6.5VT -55 865 Fil. 7.5 2.0 VT -128 1630 Htr. 6.3 0.3 VT -220 250-TH Fil. 5.0 10.5VT -56VT -57

5657

Htr.Htr.

2.52.5

1.01.0 VT -129 304 -TL Htr.

l

5.010.0

26.013.0

VT -221VT -222

3Q5GT Fil. 2.8 0.05884 Htr. 6.3 0.6

VT -58 58 Htr. 2.5 1.0 VT -130 250 -TL Fil. 5.0 10.5 VT -223 1H5GT Fil. 1.4 0.05VT -60 850 Fil. 10.0 3.25 VT -131 12SK7 Htr. 12.6 0.15 VT -224 RK-34 Htr. 6.3 0.8VT -62 801, 801A. . . Fil. 7.5 1.25 VT -132 12K8 Spec'1. Htr. 12.6 0.15 VT -225 307-A Fil. 5.5 1.0VT -63 46 Fil. 2.5 1.75 VT -133 12SR7 Htr. 12.6 0.15 VT -226 3EP1/1806-P1. Htr. 6.3 0.6VT -64 800 Fil. 7.5 3.25 VT -134 12A6. Htr. 12.6 0.15 VT -227 7184 Fil. 6.3 0.45VT -65 6C5. Htr. 6.3 0.3 VT -135 12J5GT Htr. 12.6 0.15 VT -228 8012 Fil. 6.3 2.0VT -65-A 6C5G. Htr. 6.3 0.3 VT -135-A 12J5 Htr. 12.6 0.15 VT -229 6SL7GT . . . . Htr. 6.3 0.3VT -66 6F6 Htr. 6.3 0.7 VT -136 1625 Htr. 12.6 0.45 VT -230 350-A Htr. 6.3 1.6VT -66-A 6F6G Htr. 6.3 0.7 VT -137 1626 Htr. 12.6 0.25 VT -231 6SN7GT . . . . Htr. 6.3 0.6VT -67 30 Special.. . Fil. 2.0 0.13 VT -138 1629 Htr. 12.6 0.15 VT -232 HY-E-1148VT -68 6B7 Htr. 6.3 0.3 VT -139 VR-150/30..Cold Cathode VT -233 6SR7 Htr. 6.3 0.3VT -69 6D6 Htr. 6.3 0.3 VT -143 805 Fil. 10.0 3.25 VT -234 HY-114-B.. . Fil. 1.45 0.145VT -70VT -72VT -73VT -74VT -75VT -76VT -77VT -78VT -80VT -83VT -84VT -86VT -86-AVT -86-B

6F78428435Z475767778808384/6Z46K76K7G6K7GT

Htr.Fil.Htr.Htr.Htr.Htr.Htr.Htr.Fil.Fil.Htr.Htr.Htr.Htr.

6.37.52.55.06.36.36.36.35.05.06.36.36.36.3

0.31.252.52.00.30.30.30.32.03.00.50.30.30.3

VT -144VT -145VT -146VT -147VT -148VT -149VT -150VT -150-AVT -151VT -151-BVT -152VT -152-AVT -153VT -154

813 Fil. 10.05Z3 Fil. 5.01N5GT Fil. 1.41A7GT Fil. 1.41D8GT Fil. 1.43A8GT Fil. 2.86SA7 Htr. 6.36SA7GT Htr. 6.36A8G Htr. 6.36A8GT Htr. 6.36K6GT Htr. 6.36K6G Htr. 6.312C8 Spec'1 Htr. 12.6814 Fil. 10.0

5.02.00.050.050.10.050.30.30.30.30.40.40.153.25

VT -235VT -236VT -237VT -238VT -239VT -241VT -243VT -244VT -245VT -246VT -247VT -249VT -250VT -252

HY-615 Htr. 6.3 0.17836 Htr. 2.5 5.0957 Fil. 1.25 0.05956 Htr. 6.3 0.151LE3 Fil. 1.4 0.057E5/1201. .. . Htr. 6.3 0.157C4/1203A. . Htr. 6.3 0.155U4G Fil. 5.0 3.02050 Htr. 6.3 0.6918 (Photo Tube)6AG7 Htr. 6.3 0.65CK-1006 Fi1. 1.75 0.2EF-50 Htr. 6.3 0.3923 (Photo Tube)

VT -87VT -87-A

6L76L7G

Htr.Htr.

6.36.3

0.30.3

VT -161VT -162

12SA7 Htr. 12.612SJ7 Htr. 12.6

0.150.15 VT -254 304-TH Htr.

l

5.0 26.010.0 13.0

VT -88 6R7 Htr. 6.3 0.3 VT -163 6C8G Htr. 6.3 0.3 VT -255 705-A Fil. 5.0 5.0VT -88-AVT -88-BVT -89VT -90VT -90-AVT -91VT -91-AVT -92VT -92-A

6R7G6R7GT896H66H6GT6J76J7GT6Q76Q7G

Htr.Htr.Htr.Htr.Htr.Htr.Htr.Htr.Htr.

6.36.36.36.36.36.36.36.36.3

0.30.30.40.30.30.30.30.30.3

VT -164VT -165VT -166VT -167VT -167-AVT -168-AVT -169VT -170VT -171

1619 Fil. 2.51624 Fil. 2.5371-A Fil. 5.06K8 Htr. 6.36K8G Htr. 6.36Y6G Htr. 6.312C8 Htr. 12.61E5GP Fil. 2.01R5 Fil. 1.4

2.02.0

10.00.30.31.250.150.060.05

VT -259

VT -260VT -264VT -266VT -267VT -268VT -269

829 Htr. 112.6 1.125l 6.3 2.25

VR-75/30. . Cold Cathode3Q4 Fil. 2.8 0.051616 Fil. 2.5 5.0WL-57812SC7 Htr. 12.6 0.15717-A Htr. 6.3 0.15

VT -93VT -93-AVT -94VT -94-AVT -94-B

6B8 Htr.6B8G Htr.6J5 . . . Htr.6J5G Htr.6J5 Special Htr.

6.36.36.36.36.3

0.30.30.30.30.3

VT -172VT -173VT -174VT -175VT -176

1S5 Fil. 1.41T4 Fil. 1.43S4 Fil. 2.81613 Htr. 6.36AB7/1853. Htr. 6.3

0.050.050.050.70.45

VT -286

VT -287VT -288VT -289

832-A Htr. r 6.3 1.6112.6 0.8

815 Htr. 6.3 0.812S117Htr. 12.6 0.1512SL7GT. . . Htr. 12.6 0.14

Cross Index of Commercial and Signal CorpsIn supplying these tube tabulations it is not to be inferred

that Sylvania Electric Products Inc. will furnish completetube data on all types listed. Technical information, includingbasing diagrams, tube dimensions, ratings and typical operat-ing conditions has been made available on a large majority ofthe commercial types in Sylvania Technical Manuals, Charac-teristic Charts, Sylvania News Technical Sections and otherSylvania literature. These publications should be consultedfor required details.

Vacuum Tube Types-Also Some Navy Types

Tubes procured by the Navy under Navy specificationshave been marked USN or US Navy, followed by the manu-facturer's code letters and Navy type number, which (underthe new Navy type number system) is in most cases identicalto the commercial number. Because of the similarity in typenumbers, a complete cross reference listing is not required.However, the necessary information regarding Navy typeswill be found in the extreme right column on this page.

Commercial Army Commercial Army Commercial ArmyNumber Number Number Number Number Number

01, OIA. VT -30 6SN7GT VT -231 VR-150/30 VT -1391A5GT VT -124 6SQ7 VT -103 WE -203-A VT -11A7GT VT -147 6SR7 VT -233 204-A VT -221C5GT VT -125 6887 VT -199 205-B VT -21D8GT VT -148 6ST7 VT -205 207 VT -341E5GP VT -170 6U5/6G5 VT -98 211 VT -4-B1H5GT VT -223 6V6 VT -107 211 Special VT -4-C1LC6 VT -178 6V6G VT -107-B 212-A VT -61LE3 VT -239 6V6GT VT -107-A 215-A VT -5iLH4 VT -177 6W5G VT -196 250-TH VT -2201LN5 VT -179 6X5 VT -126 250 -TL VT -1301N5GT VT -146 6X5G VT -126-A 304-TH VT -2541R5 VT -171 6X5GT VT -126-B 304 -TL VT -1291S4 VT -210 6Y6G VT -168-A 307-A VT -2251S5 VT -172 6Z4 VT -84 316-A VT -1911T4 VT -173 7A4 VT -192 350-A VT -2302A3 VT -95 7B8 VT -208 371-A VT -1662X2/879 . VT -119 7C7 VT -193 450-TH VT -1083A8GT VT -149 7E6 VT -188 575-A VT -1873EP1/1806-P1 VT -226 7F7 VT -189 WL-578 VT -2673Q4 . VT -264 7117 VT -190 HY-615 VT -2353Q5GT VT -221 7J7 VT -194 705-A VT -2553S4 VT -174 7Z4 VT -181 717-A VT -2695BP4/1802-P4 VT -111 10 VT -25 800 VT -645T4 VT -114 10 Special VT -25-A 801, 801-A VT -625U4G VT -244 WX-12 VT -7 803 VT -1065V4G VT -206-A 12A6 VT -134 805 VT -1435W4 VT -97 12AH7GT VT -207 807 VT-1005Y3GT/5Y3G VT -197-A 12C8 VT -169 807 Modified VT -100-A5Z3 VT -145 12C8 Special VT -153 811 VT -2175Z4 VT -74 12116 VT -214 813 VT -1446A8G VT -151 12J5 VT -135-A 814 VT -1546A8GT VT -151-B 12J5GT VT -135 815 VT -2876AB7/1853 VT -176 12K8 Special VT -132 816 VT -2166AC7/1852 VT -112 12SA7 VT -161 829 VT -"h596AG7 VT -247 12SC7 VT -268 832 VT -1186B7 VT -68 12SG7 VT -209 832-A VT -2866B8 VT -93 12SH7 VT -288 836 VT -2366B8G VT -93-A 12SJ7 VT -162 837 VT -1016C5 VT -65 12SK7 VT -131 841 VT -516C5G VT -65-A 12SL7GT VT -289 842 VT -726C8G VT -163 12SQ7 VT -104 843 VT -736D6 VT -69 12SR7 VT -133 845 VT -436E5 VT -215 22 VT -26 850 VT -606F6 VT -66 24, 24A VT -28 851 VT -416F6G VT -66-A HK -24-G VT -204 860 VT -176F7 VT -70 25L6 VT -201 861 VT -196F8G VT -99 25L6GT VT -201-C 864 VT -246G6G VT -198-A 27 VT -29 865 VT -556116 VT -90 30 VT -27 866A VT -46-A6H6GT VT -90-A 30 Special VT -67 869-A VT -39-A6J5 VT -94 31 VT -31 872-A VT -42-A6J5G VT -94-A 32 VT -44 879 VT -1196J5 Special VT -94-B 33 VT -33 884 VT -2226J5G Special VT -94-C 34 VT -54 918 VT -2466J5GT VT -94-D RK-34 VT -224 923 VT -2526J7 VT -91 35/51 VT -35 954 VT -1206J7GT VT -91-A 36 VT -36 955 VT -1216K6G VT -152-A 37 VT -37 956 VT -2386K6GT VT -152 38 VT -38 957 VT -2376K7 VT -86 39/44 VT -49 958 VT -2126K7G VT -86-A 40 VT -40 CK1005 VT -1956K7GT VT -86-B 41 VT -48 CK1006 VT -2496K8 VT -167 44 VT -49 HY-E-1148 VT -2326K8G6L5G6L66L6G6L7

VT -167-AVT -213-AVT -115VT -115-AVT -87

4545 Special464750

VT -45VT-52VT -63VT -47VT -50

1201, 7E5/1201 VT -2411203A, 7C4/1203A...VT-2431291, 3B7/1291 VT -1821294, 1R4/1294 VT -183

6L7G VT -87-A EF-50 VT -250 1299, 3D6/1299 VT -1856N7 . VT -96 51 VT -35 1613 VT -1756N7 Special VT -96-B 56 VT -56 1616 VT -266607 VT -92 57 VT -57 1619 VT -1646Q7G VT -92-A 58 VT -58 1624 VT -1656R7 VT -88 75 VT -75 1625 VT -1366R7G6R7GT6SA76SA7GT6SC7

VT -88-AVT -88-BVT -150VT -150-AVT -105

VR-75/3076777880

VT -260VT -76VT -77VT -78VT -80

1626162916302050

VT -137VT -138VT -128VT -245

6SG7 VT -211 83 VT -83 2051 VT -1096SJ7 VT -116 84/6Z4 VT -84 A5586 *VT -1236SJ7GT VT -116-A 89 VT -89 7184 VT -2276SJ7 Special VT -116-B VR-90/30 VT -184 8012 VT -2286SK7 VT -117 100-TH VT -218 9002 VT -2026SK7GT/G VT -117-A VR-105/30 VT -200 9003 VT -2036SL7GT VT -229 HY-114B VT -234 *Superseded by VT -128

Cross Reference ListNavy Types

A complete listing of Navy vacuumtube types vs commercial type numbersis of little value because the Navy hasadopted the procedure of employing thecommercial designations instead of speci-fying an entirely different number. It isnot to be inferred that every existingcommercial type would occur in a com-plete listing of Navy types. In factthere are many commercial types notnow utilized. When additional Navytypes are required, such tubes will bedesignated according to commercial nom-enclature, thus eliminating the necessityfor any cross index.

There are a limited number of excep-tions occasioned by previous assignmentof a 38,000 series number to certaintypes which have been utilized by theNavy. Correlation of such types withcommercial numbers is given by thefollowing tabulation.Old NavyNumber

CommercialNumber

38015 Obsolete38111-A None38112 212-E38116 4B2638120 Obsolete38142 None38205 VR-105/3038217 (0517) Obsolete38220 12038222 3B2338233 2C2138250 VR-150/3038275 VR-75/3038278 Obsolete38282 282-B38290 VR-90/3038401 3B2138402 4B2238403 4B2338404 4B2438405 3B2238412 312-A38674 Obsolete38674-A 4B2538897 4B27

Eight of the twenty-five types shownabove have very recently been assignednew commercial numbers. To assist inidentifying these types, the list belowindicates the old commercial numbers bywhich these were formerly designated.New Commercial Old Commercial

Number Number3B22 EL -1C4B24 EL -3C3B21 EL -302.54B22 EL -5B2.54B23 EL -5B -HD4B25 EL -6C3B23 RK-222C21 RK-33

These tabulations of tube types havebeen compiled by

SYLVANIA ELECTRIC PRODUCTS Inc.from approved Government data.

April 24, 1943Extra copies available upon request.

5y /Ves-FIFIE information presented in the Sylvania Service Exchange is contributedI. by servicemen as the result of practical experience. It is very carefully con-


~Y-w."" "} `-\ ia+'

Lafayette C31. Had considerabletrouble locating an intermittent short.Every time the set stopped playing, andI put it on the bench for a test, it testedOK and would play for a considerableperiod. Finally located the trouble.The wires running from the volume con-trol to the back of set are single rubbercovered wire, enclosed in braided metalsheath. This metal sheath was solderedto the chassis in two places, and the heatfrom the soldering had deteriorated therubber so that it broke and allowed the*ire to short to ground. So I replacedthese with a heavier insulated wire. Alsoreplaced all grid leads which are sheathedand soldered to chassis. Since then Ihave had other Lafayettes and a coupleof other sets using same kind of wire,same ailment, but have been able tolocate the trouble and fix the set to theowner's satisfaction by replacing allsheathed single rubber covered wire.-Charles A. Johnson, Republic, Mich.

* * *

Stromberg Carlson FM -515. If speak-er field is hot and voltage is low (below225 V.) change all .05 plate filter (dual)condensers to standard single unitsseparately to get normal voltage of250 V.-Mesmer Radio Service, Ottum-wa, Iowa.

* *

Battery Portables. Since I've beenhere, I find about ninety percent of thepersonnel have portables ,using the 1.4volt tube series. Often the pentagridconverter (1A7GT/G) fails to oscillate.After "sweating" many cases, I foundsome manufacturers use a series resistorto the screen grid, ranging from 10,000to 50,000 ohms. Usually by replacing'with a 100,000 ohm unit, the originaltube works satisfactorily.-Pvt. ClaytonMiller, Army Air Forces NavigationSchool, Hondo, Texas.

* * *

G. E.-Eioi, Eio5, E1o6. In somecases these sets are distorted or in-operative on broadcast, but work per- ,

fectly on the short wave bands, due tothe fact that the 6L6 grid is coupledthrough an .05 and an .005 condenser inseries; the latter is shorted out by thebandswitch for better bass response inB. C. position. If the .05 condensershorts, distortion results on short wave,6L6 grid is isolated from 6F5 platevoltage by the .005 condenser, even if.05 condenser shorts.-Clifford Stout,Muskegon Radio Service, R#5 Muske-gon, Michigan.

THANK YOU, MR. HUTTON"During the tube shortage, there

have been calls for tubes that I couldnot get from my jobber, so I havestudied my Sylvania Technical Man-ual very closely and have found that Icould substitute many different typetubes. Some I had only to changethe tube base, others I changed thecircuit; but with the help of the tubemanual every set that I have changedhas worked 100%.

"I could not get along without mySylvania tube manual. If otherservicemen would read their manualand not just look at it they will findthat it will be a great help to them inthese war torn times."-J. B. Hutton,Hutton Radio and Electric Service,Dermott, Arkansas.

Gloritone Model gg. When this radiodoes not operate at the low frequencyend of the dial, look for a defective 3,000ohm resistor or a .01 of condenser in thecathode circuit of the first detector -oscillator circuit.-Marion L. Rhodes,Knightstown, Ind.

* * *

Philco Model 37-611 (Code 121). Toeliminate oscillation below 550 KCconnect a resistor 1000 ohms in serieswith the red lead of the 2nd i -f trans-former (#23) also connect a condenser.05 mfd. 400 v. from the red lead toground.-M. S. Planovsky, Cleveland,Ohio.

* * *

Philco Mo Par 800-1941. Complaintof jerky reception or no reception. Takelid off radio and examine push buttonassembly closely. Bottom lead of pushbuttons is so close to chassis that itinvariably grounds. Wedge a screwdriver in between and place a piece ofgood adhesive tape or equivalent be-tween push button assembly and re-ceiver.-Vito F. Daidone, Newark, NewJersey.

* * *

RCA Model R-28. The bleeder resis-tors R9 and R10 through volume con-trol to ground often change value. Thischange will affect the volume controlaction and will ruin the volume controlas the resistance lowers, thus drawingtoo much current. Always measure theresistor values as it will save time inlocating the trouble in these sets. Youwill find similar bleeder arrangement onRCA #80 and 82.-C. A. Vaughn, LosAngeles, Calif.

Airline 93WG-I000. Oscillation afterset warms up-Tighten coil shields,change 17,000 ohm (R2) decouplingresistor.-Henry D. Morse, Homer, N.Y.

* * *

Truetone D920. Loud hum-Filterscheck OK-change volume control. --Henry D. Morse, Homer, N. Y.

* * *

Truetone Model D -7o5. This radiowas terribly distorted when connected toan antenna, but when not loaded, recep-tion was quite clear. From all indica-tions this would mean overloading thesecond detector or possibly the audiostage, excessive a -v -c action, or incorrecttime constant or possibly poor filtering ofcarriers in demodulator. However, itwas nothing of this nature. After re-placing all tubes, aligning the set,checking each bias voltage, everythingwas found normal except for distortion.The trouble was found in the second i -ftransformer having high resistance leak-age between turns on the secondarywinding. A new transformer clearedthe trouble entirely. This should bechecked on similar sets.-T. LeslieLindsey, Richmond, Va.

* * *

Philco Model 39-25T. The lightbrown, live rubber covered high voltageleads from the power transformer oftenshort to the case, resulting in overloadingand eventual burnout of the 70 ohm 0.5watt carbon, and 280 ohm 1.0 wattwire -wound bias resistors, located in thenegative side of the rectifier circuit.

Replace both resistors, and installoversize spaghetti insulation over thehigh voltage leads, pushing same wellinto the case to prevent future shortingof the high voltage leads.-Joseph S.Napora, Uniontown, Penna.

* * *

Admiral Model B-125. Abnormal a -chum may be due to the output trans-former picking up hum from the powertransformer field. To remedy, removethe output transformer from the speakerand mount it under the chassis in frontof the 75 tube socket.-Mr. James H.Johnston, Lakewood, New Jersey.

* * *

RCA Victor Model K -6o. Intermittentcut-off at low frequency end of dial.This trouble was found to be causedby a defective 6000 µµf. condenser con-nected between stationary section ofoscillator tuning condenser and thewave -band switch. The trouble wascleared by a new 6000 µµf. fixed con-denser.-L. W. Steuerwald, Dover, N.H.

TECHNICAL SECTION

Copyright 1943. Sylvania Electric Products Inc. (Formerly Hygrade Sylvania Corporation)

MAY -JUNE, 1943 EMPORIUM, PENNA. Vol. 10, No. 5

A NEW SYMBOL GUIDEFOR YOUR CONVENIENCE

The new Sylvania Radio Symbol Guide, shown above, is one of thosehandy tools -of -the -trade that servicemen and experimenters are alwayslooking for. It is, we feel, an improvement on the type which we havebeen offering for some time. If you like to draw your own circuits anddiagrams-and what dyed-in-the-wool radio man doesn't? a glance atthe symbols around the edge will show you what you can do with theSymbol Guide and a drawing pen or pencil.

The new Guide is made of a transparent plastic so that you can seethe work beneath while using it. It comes to you in a heavy paperenvelope, convenient for pocket carrying. A complete set of workinginstructions is provided with each Guide.

They are available through your Sylvania Distributor, or if you prefer,they can be ordered direct by using the coupon to the right.

Price-only 25 cents.

Former Technical EditorNow An Army Captain

Ralph Merkle, former Technical Editorof Sylvania News, has recently been ap-pointed to a captaincy in the U. S. Army.Captain Merkle has been in the office ofthe Chief Signal Officer, Washington,D. C. with a first lieutenant's commissionfor the past several months. He receiveda leave of absence from Sylvania lastJune to enter the Armed Forces.

Ralph was a valuable member ofSylvania's Commercial Engineering De-partment, and devoted much time andeffort to the preparation of varioustechnical publications which have been sopopular with dealers and servicemen. Inhis present work he is applying hisknowledge to our government's remark-able war -time communications develop-ments. We all join in wishing him con-tinued success.

Cross Reference Charts of Army, Navy andCommercial tube types published in the lastissue of the News are still available on request.

Sylvania News Technical Dept.Sylvania Electric Products Inc.Emporium, PennsylvaniaEnclosed is $ Please send :... Sylvania Radio Symbol Guides.

(Price -25c each)Name

StreetCity.State

Note-If you do not wish to destroythe chart on the back of this (rage byclipping the coupon, simply send orderon your own letterhead.

sWaida New's

Substitution Charts for 150 Milliampere

AC -DC Receiver Tubes

The necessity for using substitute tube types has been mostpronounced in connection with servicing ac -dc receivers. Inpractically all cases receiver modifications are required. Thechanges involved are generally the important factors governingthe cost and time for the conversion so as to maintain receiveroperation. To quickly ascertain the principal changes to bemade data have been prepared in chart form, similar to theone for battery types published in the April issue of SylvaniaNews. In the present issue only types having 150 milliampereheater ratings are listed. The 300 milliampere types will becovered in the next issue.

Chart 1 gives the 150 milliampere types which are not onthe WPB list and indicates possible replacements. Among thefirst and second choices, those preceded by an asterisk (*)occur on the WPB list and will be found in Column 1 onChart 2. Reference to Chart 2 under the type or typesinvolved will furnish the changes required by the substitution.For convenience, the changes are designated by letters. Theserefer to the specific changes listed at the top of Chart 2.

According to the WPB Civilian Radio Tube Programtwenty 150 milliampere tube types are to be manufactured.In addition to these twenty types, two 117 -volt tubes are alsoshown in Column 1, Chart 2 since one or the other often occursin the receiver tube complement under consideration. Manytypes in Column Q carry reference symbols and numbers.Explanations are given in the footnotes at the end of the chart.

CHART 1

150 ma.Types notOn WPB

List6D8G

Possible Replacements

1st Choice 2nd Choice*7A8 *12A8G'1'/Gt

6G6G *35A5 *35L6GT/Gt6L5G *12J5GT/G 14A46S7t *7B7 *14A76SS7 *7B7 *12SK7GT/Gí6ST7 12SR712A8Gf *12A8GT/Gt *7A812C8 6SF712F5GT *12SQ7GT/Gí *12Q7GT/Gt12J7GTí *12SJ7GTt 6W7G12K7Gt *12K7GT/Gt. *12SK7GT/Gí12K8t *12A8GT/Gí 14J712Q7Gt *12Q7GT/Gt *12SQ7GT/Gt12SA7t *12SA7GT/Gt 14Q712SC7 12SL7GT12SF5t *12Q7GT/Gí. *12SQ7GT/Gí12SF7 12C812SJ7 *12SJ7TGt 14C712SK7t *12SK7GT/Gt *14A712SL7GT 12SC712SN7GT 14N712SQ7t *12SQ7GT/Gt 12Q7GT/Gí12SR7 14E614A4 *12J5GTt 14E614B6 *7C6 *12SQ7GT/Gt14B8 *7A8 *12A8GT/Gt14C7 *7C7 *12SJ7GTt14E6 12SR714F7 12SL7GTt14H7 *12SK7GT/Gt 14W714J7 *12A8GT/Gt 14B814N7 12SL7GT14Q7 *12SA7GT/G 14B814S7 *12A8GT/Gt *7A835L6Gt *35L6GT/G *50L:GT35Y4 *35Z3 *35Z5GT/G35Z4GT *35Z5GT/G *50Y6GT/G35Z5Gt *35Z5GT/G *50Y6GT/G40Z5/45Z5GT *35Z5GT/G *50Y6GT/G50A5 *35A5 *35L6GT/G5006G *50L6GT . *35L6GT/G50Y6G *50Y6GT/G *117Z6GT/G50Z7G *50Y6GT/G *117Z6GT/G70A7GT *70L7GT *117L7/M 7GT

CHART 2


150 ma.Types

onWPB List

Useto

Replace

Vtoq

rvOZ

Y

>.:w

c

Údcs,

3y771 c

cáa L'OUm

=°IIa<U

j óa=ou

Fáv a90

oL CoVfi ddl01 1

;:mé«LU<x

=El.

e -,C L.co

dd

Yémm m

:7m

A BCDE F G HK LM7A8... .. . . .

7117 ..

7c:6

7C714C7

12A8GT/G....

12J5(:T

12K7GT/G

*6A76A8í6J8G6K8í6D8G12A8Gí14.1714B814S77S7

*7J712K8í7A76SK7t6K7t6E76U7G

*786D6

*39/446S7f6SS712B714A7...12K7Gt12SK7t.7B614B66T7G6Q7í6SQ7t

*757B46K5Gí6F5í12Q7Gí12SQ7Gí12SF5

6J7í6SJ7t6C6

*77*3612J7Gí12SJ7t6W7G12A8Gí14.1714B8

*7A86D8G6A8í

*6A76J8G12K8Gt6K8t14S77S7

*7J76J5í6AF5G

*766P5G

*376C5í6L5G

*7A414A4XXL12K7Gt12SK7t12B7

*14A77A7

*7B76SS76K7í6SL7t6U7G

*78

.....

...

...

...

...

..

Aí

...

...

...B

...

...

...

...

...

A

. . .

......

...

...

BBBB

...

...

BBBB

...B

...

BBB

B

BB

...

...

IIBB

B

B

BBBBBBsB...B

...

BBBBBCDBB

C

C

............

...

...C

CG...C

C.

...........................M

...

...C...

CCCCcC...............

C

...

...

...

...

cCC

C

CC

cCCcCC...C...C...

C......C

CC

...

...

...

...

...

...

...

...

...

...

...

...

...

............

...

...

...

...

...

...

...

..

...

...

...

...

.....E

...

...

..E......D...........................D

. . .

...D.........

E

EEE

.........

...E

E

EE...EE

...

...EEEE...EEEEE

...

EE

EEE

...EEE

...

...

...E

E

...

...E...E

...

...EEE

...

...EEEE............

F.

F

FFFF...FF

...F

F

FF

...FF

...

...........H

...

...

...

...

...

......

...

...

...

FF

FFF

.

FFF

FFFFFFFF

.........

...........................FFFFFFFFFF

...

...

...............

...

...

...

...

...

...

...

.....................

...

...

.........

...

...

...

...

...

...

...

G,C'

C

...............GGG

...

...

...

...

...

...

...

...

......GGGCG...G...G......

H

HHH

...

...

...

...

...H

HH......H.........H

...H...HHH............

H...H

............

...

...

...

...

...

...

...

...

...

...

...

...

...

...

...

......................... . .

...

...

...

...

...

.....................

......

...

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...

.. .

........................

...

...

.....................

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......

..

...

...

...

...

...

.....

......KKKK...........................

. . .

...

...

...

...

...

...

L

L......

...

...L

LL

L

L...............L......LLLLLL

...

...

...L

...

...

...

.....

.

LLL...L...LL

LLMLLLML...L...L

...

...

...

...L......LLLL

...

...

...MMMM...

...

...

...

...

...

...

MM

...M............

...

...

...

MMM

M

...

MM...

...MAt

MMM...M...MM

M

MM

MMM...M

...

...

...

...MMMMMMM

NewsCHART 2-(con

150 ma.Types onWPB List

Useto

Replace

CHANGES REQUIRED

A IBICIDIEIFIGIHIKILIM12K7GT/G . . . 6D6 . . . B C . . . E F . . . . . . . . . L M

(continued) *39/44 B C ... E F ... ... ... L M6S7t .. B ... ... ... F ... ... ... ... M

1207GT/G.... 12Q7Gt A ... ... ..12SQ7t D ... ... G ... ... ... ...6Q7t ... B C ... ... ... ... ... ... L M6SQ7t ... B C D ... ... G LM6T7G... B ... ... ... ... ... ... ... ... M

*75 ... B C ... E ... ...... ... L M7B6 ... B C ... E ... G ... ... L M

*7C6 . B ... ... E ... G ... ... ... M7K7 ... B C ... E ... G ... ... L M14B6 E ... G ... ... ... ...6ST7 B ... D ... ... G ... ... ... MXXFM ... B C ... E ... G ... ... L M7B4 B C ... E ... G LM12F5Gt D ... ... ... ... ... ... ...12SF5t D ... ... G ... ... ... ...

12SA7GT/G... 12SA7t A ... ... ... ... .

6SA7f B C ... ... F ... ... ... L M7Q7 B C ... E F ...LM14Q7 E F ... ... ... ... ...

12SJ7GT 12SJ7t A ... ... ... ... ... ... ... ... ... ...12J7t ... .. D ... F ... H ... ... ..

6SJ7t ... ..6J7í ... BCD ... F ... H ... L M6C6 . B C ... E F ... H ... L M

*77 ... B C ... E F ... H ... L M

6D7 ... B C ... E F ... H ... L M6W7G ... B ... D ... F ... H ... ... M

*7C7 ... B ... ... E F ... ... ... ... M14C7 E F ... ... ... ... ...

12SK7GT/G... 12SK7t A ... ... ... ... ... ... ... ... ... ...12K7Gt D ... F ... I -I ... ... ...6K7t . B CD ... F ... H ... L M6SK7t ... B C ... ... ... ... ... ... L M6U7G . BCD ... F ... H ... L M

*78 ... B C ... E F ... H ... L M

6D6 ... B C ... E F ... H ... L M

*39/44 ... B C ... E F ... H ... LM6S7 ... B ... D ... F ... H ... ... M

12B7 E F ... ... ... ... ..*14A7 E F ... ... ... ......7A7 . B C ... E F ... ... ... L M

*7B7 B ... ... E F ... ... ... ... M

6SS7 . B ... ... F ... ... ... ... M

14117 E F ...... K ......12SQ7GT/G... I2SQ7t A ... ... ... ... ... ... ... ... ...

6SQ7t ... BC ... ... ... ... ... ... L M

12Q7Gt ... ... ... n ... ... ... H ... ... ...6Q7í ... B CD ... ... ... H ... L M

*75 ... B C ... E ...... H ... L M

7B6 B C ... E ... ... ... ... L M

6T7G B ... D ... ... ... H ... ... M

14136 E ... ... ... ... ... ...*7C6 B ... ... E ... ... ... ... ... M7K7 B C ... E ... ... ... ... L M

6ST7 B L ...XXFM ... B C ... E...........LM.7B4 B C ... E ... ... ... ... L M

12F5GTí D ... ... ... H ... ... ...12SF5í ... ... ... D ... ... ... ... ... ... ..

14A7/12137.... *14A7 A ... ... ... ... ... ... ... ... ... ...12B7A ... ... ... ... ... ... ... ... ... ..7A7 B C ... ... ... ... ... ... L M

*7B7 ... B ... ... ... ... ... ... ... ... M

6SK7t ... B C ... E F LM6K7t B C ... E F ... H ... L M

6E7 ... B C ... E F ... H ... L M

6U7G ... B C ... E F ... H ... L M*78 ... B C ... E F ... H ... L M

6D6 ... B C ... E F ... H ... L M

*39/44 B C ... E F ... H ... L M

6S7 ... B ... ... E F ..H ... ...M6ST7G B ... ... E F ... ... ... ... h1

12K7Gí E F ... H ... ... ..12SK7í E F ... ... ... ... ..6SS7 B ... ... E F ... ... ... ... M14H7 F ... ... K ... ..

35A5 *35L6GT/G ... ... ... ... ... E ... ... ... ... ... ..14A5 B ... ... ... ... ... ... ... ... M50A5 B ... ... ... ... ... ... ... ... M

5006G ... B ... ... E ... ... ... ... ...M*50L6GT ... B ... ... E ... ... ... ... ... M

6G6G B ... ... E ... ... ... K ... M

25A6t B C ... E ... ... ...K L M

25B6G ... B C ... E ... ... ... K L M

12A5 ... B C ... E ... ... ... K L M

25L6t B C ... E ... ... ... ... L M

35L6GT/G... *35A5 E ..14A5 B ... ... E ... ... ... ... ... N

50A5 B ... ... E ... ... ... ... ... N

150 ma.Types es onWPB List

Useto

Replace

CHANGES REQUIRED

A1 B I C I D I E I F I G I H I K L I M

35L6G'1'/G.... 5006G B ... ... K ... M

(continued) *50L6GT ... B ... ... ... ... ... ... ... ...M6G6G s ... ... ... ... ... ... K ... M25A6t B C... ... ... ... ... K L M25B6G ... s C ... ... .. . . .. ..K L M25C6G ... B C... ... ... ... ... K L M25L6t B C ... ... ... ... ... ... L M

35Z3 357.5Gí . . 1 . . . . . . . . . . . . . . . E . . . . . . . . . . . . . . . . . .

35Y4 .1 D ... ... ... ... ... ... ...25Z5..2 B C ... E ... ... ... ... L M25Z6t..2 ... B C ... E. . . ... ... ... L P1

.. 1 . . . .... . . 13B ... ... E ... ... ... ... ... M*50Y6GT . .2. . . ... B ... ... E ... ... ... ... ...M50Z7GT..1,2 ... B ... ... E ... ... ... ... ...M25Y5..2 ... B C ... "E ... ... . . . . .. L M40Z5..1 B ... ... E ... ... ... ... ... M12Z3 ... B C ... E ... ...... ... L M

35Z5GT/G.... *35Z3 ... ... ... ... E ... ... ... ... ... ...35Y4 E ... ... ... ... ....25Z5..2 ... B C ......... ... ...... L M25Z6t..2 ... B C ... ... ... ... ... ... L M45Z5GT ... B ... ... ... ... ... ... ... ...M

*50Y6GT..2 ... s ... ... ... ... .. M50Z7GT..2 ... B ... ... ... ... ... ... ... ... M25Y5. .2. . . . . . . . . B C . . . . . . . . . . . . . , . . L M40Z5 ... B . . ... ... ... ... ... ...M35Z4GT E ... ... ... ... ... ...12Z3 ... B C ... E ... ... ... ... L M

50L6GT *35A5 B . . . . . . E . . . . . . . . M50A5 E ... ... .. ... ... ...5006G K ... ...

*35L6GT/Gt ... B ... ... ... ... ... M6G6G B ... ... ... ... ... ... K ... M25A6t B C ... ... ... ... ... K L M25B6G B c ... ... ... ... ... K L M25C6G ... B C ... ... ... ... ...K L M25L6t B C ... ... ... ... ... ... L M

50Y6GT/G.... *35Z3 B ... ... E.. ... ... ... ...NI35Y4..1 ... B ... ... > ... ... . .. ... . ..M25Z5 B c ... E LM25Z6t B C D ... ... ... ... ... L M45Z5GT..1 ... B ... D ... ... ... ... ... ... M35Z5Gt..1 ... B ... D ... ... ... ...NI50Z7GT. ,1, . . . . . . . . . . . D25Y5 B C ... E L M40Z5 .1...... ... B ... D ... ..M35Z4GT B ... ... ... ... ... ... ... ... M

*117Z6GT/G ... B C ... .. ... ... ... ... L M70L7GT *35A5 . B ... ... M

12A5 ... B C ... E ... ... ... K L M50A5 B ... ... E ... ... ... ... ... Nt5006G B ... D ... ... ... ... K ... M

*35L6GT/G ... B ... D ... ...M50L6GT ... B ... n ... ... ... ... ... ... M25A6t ... B CD ... ... ... ... K L NI25B6G ... B CD ... ... .. . .. K L hi25C6G ... B C D ... ... ... . .. K L M25L6í ... B C n ... ... .. .. ... L M25A7Gt ... B C D ... ... ... ... K L M12A7 B C ... E ... ... ... ... L M

*117L7/M7GT.... B C D ... ... ... ... K L M117P7GT . . . . . . . . B C D . . . . . . . . . . . .K L M117N7GT ... B C D ... ... ... ... K L M70A7GT..1 ... ... .. D ... ... ... ... ... ... ...

117Z6GT/G... *35Z3 B C . .. E . . ... ... ... L M35Y4. 1 B C ... E ... ... ... ... L M25Z5 ... B C ... E ... ... .. L M25Z6t45Z5GT..1 ... B C D ... .. ... ... ... L M35Z5GT/Gt 1... B C D ... ... ... ... ...L NI50Z7GT..1 ... B C D ... ... ... ... ... L NI25Y5 B C ... E ... ... ... ... L M40Z5..1 ... B C D ... ... ... ... . ..L NI35Z4GT s C D ...............LM

*50Y6GTt..... ... B C ... ... ... ... ... ... L NI117L7/M7GT.. 117P7GT D ... ... ... ... ... ... .

117N7GT . . . . . . . . . . . . . D . . . . . . . .70L7GT ... B CD ... ... ... ... ... L M25A7GTt ... B C D ... ... ... ... K L h170A7GT ... B C D ... ... ... ... ... L NI5006G B C D ... ... ... . .. K L M50A5 B C ... E ... ... ... ... L M50L6G R C D ... ... ... ... ... L M

NOTES:* These types appear on latest WPB list. No WPB type.t Indicates that the corresponding metal, G, GT, or GT/G types maybe employed if space permits. Shielding may be required in some cases.

1 If pilot lamp is required other provision must be made.2 This substitution possible if tube is used as a half -wave rectifier and ifthe load current does not exceed the rating of the WPB tube.

4.5;1~» YeatsTHE information presented in the Sylvania Service Exchange is contributed

by servicemen as the result of practical experience. It is very carefully con-sidered before being accepted, and we believe it to be correct and authentic.However, we assume no responsibility with respect to results. Please do notsend routine or generally known information.

GE LB53o. If rectifier step downtransformer T3 gets -very hot when oncharging position, check copper oxiderectifier. One or both discs may bedefective and they can be replaced.Also, acid from battery may have spilledon transformer which will cause wind-ings to become shorted.-Henry Hudson.

* * *

Philco Models 37-10, 37 -II. To im-prove the operation of the discriminatorcircuit, the transformer #48 wiring to the6H6G is changed as follows (use 6H6Gsocket for reference). Interchange P1and K1, interchange P2 and K2. Alsointerchange the wires of resistors #65and #66 on the terminal panel which isattached to condenser #63. The 6A8Gtube is changed to self biasing as follows:a resistor of 100 ohms is connected inseries with the 6A8G cathode and acondenser .01 mfd. is used to bypass theresistor. To prevent audio interference,remove the green and white wife ofaudio switch #37 from the volume con-trol center contact and connect it to thehigh side of volume control, that is, thecontact which is connected to condenser#58. Correction: the a -v -c bias con-tacts of the r -f transformers shown asconnected to D4 should be D3. Lead #4of r -f transformer #33 is connected to thethree contacts at D11 instead of oneonly. The above hints apply to Run #1,2, 3- and 4 of the above models speci-fically.-M. Planovsky, Cleveland, Ohio.

* * *

GE LC758 & LC768. A very noisytone control may be due to a leaky tonecondenser (C32), a .005 mfd. 600 -voltunit.-Henry Hudson.

* * *

Zenith Receivers. When tuning in onedirection only, trouble is noticeable thatsounds like a shorted plate in the tuninggang. Actually the flywheel or drivingpulley on the tuning shaft, when rotatedin one direction, catches on one of thetuning eye leads, twists the lead partway around and binds enough to wearand cut the insulation, thus groundingto chassis the eye lead. When rotated inthe other direction this does not happen.It cannot be seen as the break rolls backunder and out of sight. Slip spaghettiover the injured lead. Pull all eye leadsup through the chassis grommet andslide the clip down to hold the leadssnugly thus eliminating further occur-ances of wear on the wires. --Earl L.Pittsley, Binghamton, N. Y.

......,.---^- --------

THANK YOU, CORP. WANDWe have received a number of

compliments on our Cross Refer-ence Lists of Army, Navy andCommercial Tube Types publishedin our last issue. The following letterfrom Corp. Stanley Wand of BocaRaton Field, Florida, is particularlygratifying:

"I want to thank you for your courtesyin sending me an interesting issue of"Sylvania News". I had tried for severalmonths to obtain a VT cross index withcommercial types through official channelswithout obtaining anything complete.I have been using a makeshift of about4o or 5o of the common types, which Icompiled myself.

As a former radio serviceman in civilianlife I read with interest some of the ma-terial pertaining to civilian radio. I recallbuying Sylvania tubes from Dale Radio,New Haven, Conn. as I worked for a largeWaterbury radio store at the time I wasdrafted into Army life. I fix a radio nowand then just to keep my hand in.

If it would not be asking too much ofyou, I would appreciate your sending me"Sylvania News" regularly to keep usinformed about civilian radio. When it isall over, and I hope that will be soon, Iintend to take up radio where I left off,and that means I will be back in Connec-ticut in radio again. With a multitude oftypes and applications, I know I candepend upon Sylvania to keep ahead withthe latest developments that are everydaywork to us here."

All Wurlitzer 1940-41 Models. Whenthese phonographs refuse to trip a recordafter inserting coin (5, 10 or 25) take outthe electric coin selector mechanism.Take the covers off and polish all therelay points by using carbona cleaner.Ordinary cleaning will not do. Do notuse too much lubricant as this seems tobe the original cause of the above trouble.-B. Waters, Oneida, Tenn.

* * *

U. S. Radio & Television Corp. Model46 & 47. No control of volume and Iowvoltages on screens of 24 tubes due to avery leaky 0.5 mfd. 400 -volt condenserin screen grid circuit of 24 tubes.-Henry Hudson.

* * *

Philco Model 37-60o. 'I'o increasesensitivity at the low frequency end ofthe BC band, change resistor #7, from200 ohms to 300 ohms and remove thesuppressor wire of the 6J7G i -f tubefrom the cathode terminal of the tubeand connect it to the lug of the sensitivitycontrol to which the secondary lead ofthe i -f transformer is connected.-M. S.Planovsky, Cleveland, Ohio.

ra-........----

Zenith Models 7S363, 9S367. Thecomplaint was a rumbling and crackingnoise at the slightest jar when automatictuning was used, but set worked OK onmanual tuning. Make sure that thefront of the automatic unit is set in thegroove on the bottom and that the nuton top fastening to the front of thecabinet is tight. Tighten chassis boltsenough to keep the bottom of the auto-matic unit from touching the top of thechassis. If the noise continues afterdoing this, proceed as follows: Take apiece of corrugated cardboard about3"x8" and fold to triple thickness. Liftthe back of the automatic unit as muchas possible and slip the cardboardbetween the bottom of the unit and topof the chassis. Make a tight fit. Thiswill eliminate the noise completely.-Meyer and Johnson, Rochester, NewYork.

* * *

Tube Substitution. Substitute 12A8-GT/G 12SA7 12SA7GT. Takelead off #8 grid prong of 12SA7 socket.Run it to grid top cap of 12A8GT/G.Disconnect all leads from #6 prong of12SA7 socket and connect to #8 prong.Leave #6 prong blank. Realign thei.f. or use a tube shield or both. Thischange -over has worked 100% in everycase.-W. G. Aiiringer, San Diego, Calif.

"I suppose the war precludes the possi-bility of y getting a double electrodephnnatron gaseous discharge rectifiertube, having an ambient temperatureranee of between 15 and 501"

Radio Retailing Today

TECNNI CA L1SECTION


JULY, 1943 EMPORIUM, PENNA. Vol. 10, No. 6

AC -DC RECEIVER CIRCUIT MODIFICATIONSTUBE SUBSTITUTIONS REQUIRE CAREFUL

ANALYSIS OF HEATER CIRCUITSThe past two issues of Sylvania News have covered substitu-

tions which might be made when battery tubes and 150 ma.tubes had to be replaced in existing equipment where onlycertain types might be available on the jobbers' shelves. Thisissue takes up the substitution of tubes for 300 ma. filamentdrain.

The following article explains one of the ways in which a 150ma. tube may be used to replace a 300 ma. tube in a receiverand also indicates a method for the substitution of a 300 ma.type for a 150 ma. tube. The tube types shown have simplybeen chosen as examples and do not indicate any specific equip-ment. The principles involved, however, are essentially thesame regardless of tube types.

SUPPLY

607GT

6Q7GT

SUPPLYR2

APPROX 80

6A8GT

n

CncCT

6K7GT

FIG. 1

25L6CT/G 25Z6GT/C

GV7CT 5OL6GT 2r,zccT;C

FIG. 2

R1 = 333

Fig. 1 shows a typical 300 ma. filament string including aseries resistance of approximately 150 ohms exclusive of thetapped section. The resistor is shown as a tapped resistor sincein many cases ballast resistors with the tap were used. In thiscase the pilot lamp rating will be less than 300 ma. Manyreceivers were built in which a 300 ma. pilot lamp was employedand no resistance was shunted across it. For those cases theresistor shunting the pilot light in Fig. 1 may be considered tobe open.

Let us now suppose that the 25L6GT/G tube has burned outand that it is impossible to obtain another output tube of thistype. Assume that the only power output tube obtainable is the50L6GT. This tube requires only 150 ma. and, therefore, wemust shunt the filament with a resistance which will by-pass

- 150 ma. of the total heater current. This will require a resistanceof 333 ohms. A 300 ohm resistor will be perfectly satisfactory inthis application. Originally the total voltage drop across thetubes was 68.9. volts leaving 48.1 volts drop across the series

resistor. In the revised circuit the total voltage drop across thefilaments of the tubes for proper operation will now be 93.9 volts.This means, therefore, that the series resistor must be reducedin value to approximately 80 ohms in order that 300 ma. willflow through the filament string. This series resistor may be inthe form of a line cord or actually may be a resistor mounted inthe receiver itself. If it is in the line cord, a resistor of from 150to 175 ohms may be shunted across the cord provided room maybe found to locate this resistor. This resistor will, of course,become quite warm and must be placed in such a position thatthe added heat from the resistor will not cause wax in condensersto melt. If the resistor is mounted in the receiver to begin with,and if a 75 to 80 ohm resistor of the same physical size can beobtained, then it should be substituted for the one which wasoriginally in the receiver.

The same general procedure must be followed if we wish toreplace any one of the other tubes in the string with a 150 ma.tube. Fig. 2 illustrates in heavy lines the changes which mustbe made.

To summarize, there are three things which must be done inmaking a change of this kind:

1. The filament of the 150 ma. tube must be shunted.2. The series resistor must be reduced in value so that 300 ma.

is still available for the filament string.3. The series resistor must be located in such a place so that

the added heat will not cause trouble. (Actually the total wattagedissipated in the entire series resistor system will be only abouthalf what it was before.)

12S07GT/G 12SA7GT/G 12SK7GT/C

SUPPL

56LCCT JSZSCT; C

FIG. 3

1250707/G 12SA7CT/G I2SK7CT/G 25L6GT G .r c.

P

SUPPLY

R_ = 233

FIG. 4

Let us now consider the filament string shown in Fig. 3. Agreat many more receivers are on the market employing a'circuit similar to the one shown. This differs from the circuitshown in Fig. 1 in that no series resistor is employed and thatthe pilot light is lighted from a tap on the 35Z5GT/G filament.


SYLVANIA NEWS

Substitution Charts for 300 MilliampereAC -DC Receiver Tubes

As indicated in the May -June issue, charts covering sub-stitutions for 300 milliampere types have been prepared. Theforms are similar to those for the 150 milliampere tubes. Chart 1gives the 300 milliampere types which are not on the WPB listand possible replacements. Among the first and second choices,those preceded by an asterisk (*) occur on the WPB list and willbe found in Column 1 on Chart 2. By reference to Chart 2,under the type or types involved, one can readily ascertain theprincipal changes required by the substitution. For con-venience, changes are designated by letters which refer to thespecific modifications listed at the top of the chart.

The WPB Civilian Radio Tube Program calls for the manu-facture of 32 types having a 300 milliampere heater rating.Since all of these types may not be universally available one mayfind it necessary to use a similar type with a 150 milliampereheater. In this event note the added reference given under eachtype in Column 1, Chart 2 and refer to the type indicated in the150 milliampere Substitution Chart published last month.

Prepared primarily for ac -dc applications these charts provideuseful information in cases where substitutions are made intransformer operated sets. For such cases disregard changes B,L and M which are not applicable since heater voltages mustcorrespond with transfer voltages existing in the receiver.Adherence to a given heater current rating is not essential if thepower transformer has adequate current carrying capacity.

CHART 1300 ma.

Types notOn WPB

List

Possible Replacements

1st Choice 2nd Choice

1-V *35Z3 12Z36A4/LA *38 *12A56AE5GT *76 6P5GT t6AF5G *35L6GT/G*t *376A8t *6A8GTt 6J8G6B8 *6B8G *6137

6C5 *6C5GT/Gt *6J5GT/Gt6C6 *77 *6J7GTt6D6 *78 6U7G6D7 *77 6C66F5t *6F5GT/Gt *6Q7GTt6F7 6P7G6H6t *6H6GT/Gt *7A66J5t *6J5GT/Gt *6C5GT/Gt6J7t *6J7GTt *6SJ7GTt6J8G *6A8GTt *7J76K5Gt *6K5GTt *6F5GT/Gt6K7t *6K7GTt *6SK7GT/Gt6K8t *76 8GTt *6A8GTt

*6J5GT/Gt6P5Gt6P7G 6F7607 *6Q7GTt *75...6R7t *6R7GT/Gt 856SA7t *6SA7GT/Gt 7Q76SF5t *6F5GT/Gt *6K5GTt6SJ7t *6SJ7GTt *7C7

6SK7t *6SK7GT/Gt *7137

6SQ7 *6SQ7GT/Gt *7C6

6U7G *6K7GTt *6SK7GT/Gt6V7G *6R7GT/Gt 85

6ZY5G *25Z6GT/Gt 12Z3

7A7 *7B7 *6SK7GT/Gt7B6 *7C6 *6SQ7GT/Gt7B8 *7A8 *6A8GTt707 *6SA7GT/Gt *12SA7GT/GI12A5 *25L6GT/Gt 25A7G12A7 *70L7GT 25A7G12Z3 *35Z3 *25Z5

25A6t *25L6GT/Gt 25A7Gt .

25A7Gt*70L7GT 12A5

25AC5GT/Gt *35L6GT/G*t 25L6GT/G*t25135 *25L6GT/Gt 25B6G25B6G *25L6GT/Gt 25B5

*35L6GT/Gt25C6G *25L6GT/Gt25L6t *25L6GT/Gt *35L6GT/Gt25N6G *25L6GT/Gt 25B6G25Y5 *25Z5 *25Z6GT/Gt25Z6t *25Z6GT/Gt 25Z5

32L7GT *70L7GT *117L7M7GT85 *6R7GT/Gt 6V7GXXFM *7C6 7B6

XXL *6J5GT/Gt *7A4

CHART 2


300 ma.

onWPB List

Useto

Replace

a

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F ad ó°v8i

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.0U<aUa

h.ámcm"0119d

A

éaTypes

e.0

aloA

ABC D E FGHK LMI, \7

(7A8)°

618GT

(7A8)°

6B7(12SF7)°

6B8G

(12SF7)°

6C5GT/G

(12J5GT)°

6F5GT/G

(7C6)°

6H6GT/G

6J5GT/G

(12J5GT)°

6.I7GT

(7C7)°

6K5GT/G

(7C6)°

6K7GT

(7B7)°

6i:8G'I'

(7:'04)'

6Q7GT

(7C6)°

6R7GT/G

(12SR7)°

*6A8GTt7B86J8G

*7J7*6K8GTtj7S7

*6A77B86J8GA

*7J77S7

*6K8GTt

6B7S*6B8Gt

*6B76SF77E77R7

6C5t6AF5G.......6AE5GT

*6J5GT/Gt . .

6P5Gt*7A43776

6F5t6SF5t

*6K5GTt7B4

61I6t

6J5t*6C5GT/G . . .

6AF5G6AE5GT6P5Gt

*7A43776XXL

6J7t6C6

*776D7

*6SJ7GTt1223

6K5Gt6F5t6SF5t7B4

6K7t*6SK7GT/Gt

*786U7G

6D67A7

*39/446E7

6K8t*6A8GTt6J8GA*6A7*7J77S7

6Q7t*757B6

*6SQ7GT/Gt*6F5GT/G

6R7t6V7G856SR77E66C7

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SYLVANIA NEW S

CHART 2-(continued)


Useto

Replace

CHANGES REQUIRED

GIHIKILIMABCDEF6SA7GT/G....

(12SA7GT)°6SA7t7Q7

A...

............... ... ...E

FF

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..

6SJ7GT 6SJ7*6J7GTt

w

.........

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6C6 E F G ... ... ... ...(7C7)° *77 E F G ... ... ... ..

6D7 E F G ... ... ... ...1223 E F G ... ... ... ..

6SK7GT/G. . . 6SK7t*6K7GTt

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. ..

.........

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FF ... H ... ... ...

6U7G D ... F ... H ... ... ...(7B7)° *78. E F ... H ... ... ...

6D6 ... ... ... ... E F ...H ... ... ...7A7 E F ... ... ... ... ...

*39/44 E F ... H ... ... ...

6SQ7GT/G.... 6SQ7t7B6Ew ... ... ... ... ......

...

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...

.........

......

(7C6)° *6Q7GTt D ... ... ... H ... ... ...*75 E ... ... H ... ... ...

7A4 76 E ... ... ... ... ... ...37 ... ... . E ... ... ... ... ... ...

(12J5GT)° *6J5GT/Gt ... ... ... ... E ...... ... K ... ...6P5Gt E ... ... ... x ... ...

*6C5GT/Gt ...... ... ... E ... ... ... ... ... ...6AF5G E ... ... ... K ... ...6AE5GT E ... ... ... K ... ..

7F7 '6C8G E ... ... H K ... ...14N7 B ... ... ... ... ... ... K ... t

7J77B8 A ... ... ... ... F ... ... ... ... .

'6A7 E F G ... ... ... ..*6A8GTt ... ... ... ... E F G ... ... ... ..

(12A8GT)° 6J8G E F G ... ... ... ..7S7w ... ... ... ... F ... ... ... ... ..*6K8GTt E F G ... ... ... ..

25L6GT/G.... 25L6f n ... ... ... ... ...... ... ... ... ..25A6 K ... ..25B6G K ... ..

(35L6GT/G)° 12A5 B ... ... E ... ... ... K ... ..25AC5GT/G*t . . . . . . . . . D . . . . . . . . . . . . K . . . . .

25B5 E ... ... ... x ... ..25C6G K ... ..25N6G D ... ... ... ... K ... ..

25Z5 25Z6GT/Gt .

(35Z5GT/G)° 25Y5 n ... ... ... ... ... ... ... ... ... ..

257,6GT/G.... 6ZY5G B ... D ... ... ... ... ... ... M25Z6t w ... ... ... ... ... ...... ... ......12Z3 B ... ... E ... ... ... ... ... ..

(35Z5GT/G)° *25Z5 ... ... ... ... E ... ... ... ... ... ..25Y514Y4

... ...s

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EE

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Use CHANGES

DIEREQUIRED

FIGIHIKILIMto

Replace36 6C6 ..........

*77... ... ... ... E

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...

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......

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.........

(7C7)° *6J7GTt E ... ... ... ... ... ...*6SJ7GTt E ... ... ... ... ... ...

37 76 . . .

*6J5GT/Gt ... ... ... ... E ... ... ... x ... ...6AF5G E ... ... ... x ... ...

(12J5GT)° 6P5G*6C5GT/G ... E ... ... ... x ... ...*7A4

... ... ...E ... ... ... K ... ...

XXL E ... ... ... K ... ...38 12A5 B ... ... E ... G ... x ... M

(35A5)° 6A4/LA D ... ... G ... x ... ...39/44 6K7t E F ... ... ... ... ...

*6SK7GT/Gt ... ... ... ... E F G ... ... ... ...6U7G E F ... ... ... ... ...

(7B7)° *78 E F ... ... ... ... ..6D6 E F ... ... ... ... ...7A7 ... ... ... ... E F G ... ... :.. ...

75 *6Q7GTt ...... ... ... ... ... E ... ... .. .. ... ...*6SQ7GT/Gt .. ... ... ... ... E ... G ... .. ... ...

(7C6)° 7B6XXFM

... ... ... ...EE

... GG...... ......

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.........

76 *6C5GT/Gt . . . . . .

6AF5G E ... ... ... x ... ...(12J5GT)° 6AE5GT ... ... ... ... E ... ... ... x ... ...

*6J5GT/Gt . . . . . . . . . . . . . . . E ........K . . . . .

6P5Gt E ... ... ... ... ... ...*7A4 E ... ... ... x ... ...*37 K ... ...

77 1221 w ... ... ... ... .F. ... ... ... ... ...*6J7GTt E F ... ... ... ... ...

(7C7)° 6C6 A ... ... ... ... F ... ... ... ... ...6D7 E F ... ... ... ... ...

*6SJ7GTt ... ... ... ... E F G ... ... ... ...*36 E F ... ... ... ... ...

78 *6K7GTt E F ... ... ... ... ...*6SK7GT/Gt ... ... ... ... E F G ... ... ... ...7A7 E F G ... ... ... ...

(7B7)° 6E7 E F ... ... ... ... ...6U7G E F ... ... ... ... ...6D6A ... ... ... ... F ... ... ... ... ...

*39/44 . E F ... ... ... ... ...NOTES:

* These types appear on latest WPB list. No WPB type.t Indicates that the corresponding metal, G, GT, or GT/G types may

be employed if space permits. Shielding may he required in some cases.° Listed in 150 ma. chart; May -June Issue Sylvania News.* 35L6GT/G replaces both 25AC5G and 6AF5G.

CIRCUIT MODIFICATIONS(Continued from page 1)

No series resistor is necessary since the sum of the voltages re-quired across the entire filament string is 122.8 volts. A receiverwith such a circuit comes in to be repaired and 4the 50L6GThas an open filament. As you no doubt'(have learned, thisis probably the most difficult type of tube to obtain. You find,however, that the jobber does have some 25L6GT/G tubes andassume they are the only power output tubes he has availablefor series receivers. This tube requires 300 ma. filament current.However, it can be employed provided we rewire the circuitin such a manner that 300 ma. can be supplied to the filamentof the 25L6GT/G. This can be accomplished by shunting thethree 12 -volt tubes with a 250 ohm resistor as shown in Fig. 4and by shunting the 35Z5GT/G with a 233 ohm resistor (250ohms would be satisfactory). The sum of the voltages acrossall of the filaments now adds up to 97.8 volts, therefore, a seriesresistor must be added to the string so that the total will addup to approximately the line voltage. The value of this resistorshould be approximately 83 ohms. This resistor may be addedat any place in the string but it must be added in such a positionthat the total 300 ma. flows through that resistor. If the tubewhich has to be replaced is located at either end of the filamentstring such as the 35Z5GT/G or the 12SQ7GT/G in Fig. 3,

then'only one shunting resistor would be required. The biggestproblem may very well be to find a place for the three resistorswhich will be required in most instances. The power dissipatedin these resistors will be considerable and precautions must beobserved .to prevent the heat developed from causing damageto the receiver. The wattage dissipated by a receiver changedover in the manner indicated in Fig. 4 dissipates twice the watt-age that the receiver originally was designed for and all of thatheat must be gotten rid of so that permanent damage to conden-sers and other parts in the receiver will not result. As in Fig. 2,the final changes are indicated in Fig. 4 with heavy lines.

To summarize, when a 300 ma. tube is used to replace a 150ma. tube, there are three things which must be observed:

1. Shunt resistors must be added to the 150 ma. tubes in thereceiver so that the tube which is being used as a replacement canobtain its full 300 ma.

2. A series resistor which will carry 300 ma. must be added torestore the voltage distribution across the filament string to itsoriginal value.

3. The series and shunt resistors must be placed in such amanner that the additional heat now developed in the receiver willnot cause permanent damage.

Obviously there are many changes which may have to bemade in equipment other than those indicated but the examplesgiven were chosen as typical ones which you no doubt will haveto make in the future. It is hoped that these suggestions willsave you time in keeping your customers' receivers in condition.

SYLVANIA NEWS

HE information presented in the Sylvania Service Exchange is contributed1 by servicemen as the result of practical experience. It is very carefully con-


GE HJgo5A. On this model the maintrouble is continual burn -out of the19 -ohm section in ballast tube. Thissection takes the full load of the twostrings of filaments in this 9 tube set.The best remedy is to install a 20 -ohm25 -watt wire wound resistor across thissection at ballast tube terminals.-Henry Hudson.

* * *

Philco Model 6o. While working on aPhilco 60 table model and using theRider Book "Aligning Philco Receivers,"I found that there was a mistake in thebook or that the code number was notincluded. After trying to align this setfrom the data book, I traced the variouspadders. I found that this set does nothave an L. F.. police padder (5). Thisset has both sides of the i -f transformerstuned and the sequence is (1) second i -fsecondary, (2) second i -f primary, (3)first i -f secondary, (4) first i -f primary(5) 600 Kc padder.

Naturally, this change in position willthrow many servicemen off trying toalign one of these sets and I believe thisexperience of mine should prove interest-ing to other servicemen working onthese receivers. -Chas. Hackenyos,Philadelphia, Pa.

* * *

Packard Bell Model 5 Kompak.Motorboating at the low end of the dialis quite usual in these models. At highvolume settings it also cuts the signal.To cure examine the set carefully andreplace the grid leads to the grid caps ofthe 6J7 and 6K7 tubes with shieldedwire and ground the shields carefully.This will eliminate the motorboatingentirely. -M. Margossian, Oakland,California.

* * *

Zenith 1939 Models (Automatic Tun-ing). In Zenith models which use the1939 circuit in their switching fromautomatic to manual, you will find asmall mica condenser, usually 0.0005;this condenser intermittently shorts toground and causes the automatic buttonto fail to work.-Martin L. Pitts,Terrell, Texas.

* * *

Pontiac 194o Custom Built DelcoAuto Radio. Complaint of distortionand low volume. Removing one outputtube has no change in volume. Replaceopen 0.05 condenser between driver tubeand 6V6 output tubes used in inversefeedback fashion.-Vito F. Daidone,Newark, New Jersey.

J. S. REED WRITES:"I am enclosing a P.O. money

order for a copy of your bindercomplete with file of TechnicalSections of Sylvania News.

I wish to express my apprecia-tion of the fine service you havebeen rendering servicemen andexperimenters in furnishing up-to-date technical information on radiotubes. I especially like the tubedesign features you have beencarrying recently. The serviceexchange is especially valuable andhas helped me in more than onecase to solve a vexatious radiorepair problem. Keep up the goodwork! Yours very truly," J. S.Reed, Jr., Lincoln, Nebraska.

Coronado Model 777. Motorboating.Add 0.01 mfd. condenser from plate ofr -f tube to ground.-Clifton S. KrumlingBlue Earth, Minn.

* * *

Ford Zenith Model 6MF49o. Re-ceiver dead. High voltage on controlgrid of 7B8. Coupling condenser inwave trap assembly shorted. Replacemica or use. small 10.100 µµf. (original0.115 µµf.) mica condenser. Thiscondenser is a trimmer type but there isnot provision (no hole) for adjusting.-Clifton S. Krumling, Blue Earth, Minn.

* * *

G. E. Models LF-115, 116; L.F.C.-1118, 1128, 1228. Am a reader ofSylvania News and I would like to makea suggestion on some sets I have repaired.

On these models I found that in eachcase the set was dead on standardbroadcast and short wave bands but wasok on the f -m band.

By checking the sets I found thatresistor #9 (1200 ohms) and resistor #11(2200 ohms) were open.

In testing the condensers in this set Inoticed failure usually started withcondenser #31, which is a 0.02 mfd. 400v. dc. Now when condenser #31 wasreplaced and resistors #9 and #11 werereplaced, the set would work for awhileand then C-32, C-14 or C-40 would go.When trouble of this sort occurs, I re-place C-14, C-31, C-32, C-40 using a0.02 mfd. 600 v.d.c. and this usually doesthe trick.

It is better to replace all four con-densers and play safe, than to replaceone at a time and have the same troublehappen again.-S. J. Battory, NorthAdams, Mass.

Philco Model 38-12. The frequentcomplaint on this set is that when it istuned to a strong station and the volumecontrol is suddenly advanced the setgoes dead for a few seconds beforecoming up to the desired volume. Thereis a 4 megohm resistor which is connectedfrom one of the volume control terminalsto the large terminal strip at the centerof the chassis. This resistor probablyhas increased in resistance or openedcompletely. It may be replaced by a 3or even 2 megohm resistor without anynoticeable change in performance.-J. Moller, Cincinnati, Ohio.

* * *

Wurlitzer Model 24. Very often thesemachines have to be serviced for thecomplaint of fading. The quick relaywill deliver the normal 9.75 volts duringthe warm-up period, but as soon as itclicks it drops to zero, which it shouldnot do. This is caused by no contactbetween the relay armature and the 6.3volt winding, causing the heater voltageto see -saw between 9.75 volts and zero,each time the relay clicks causing fading.To remedy, carefully re -adjust and cleanthe relay points and replace if necessary.-M. L. Rhodes, Knightstown, Ind.

* * *

Ford Philco 1937. If this set is noisyor intermittent in operation, look for ashort circuit from BI- to ground insideof the speaker cable plug. One prong ofthis plug is a dummy. The correspond-ing socket terminal is connected to B+to provide a vibrator test terminal whenthe plug is removed. The cable shieldwhich is soldered to the inside of theplug cap touches the end of the dummyprong, thus shorting the "B" supply.-L. T. Anstine, Woodlawn, Maryland.

_ 7

You'll have to fix it on the run, I haven'ttime to stop. Radio Retailing Today.

TECHNICAL SECTION

Screen VoltageGrid VoltageCathode Bias ResistorZero Signal Plate CurrentZero Signal Screen CurrentMaximum Signal Plate CurrentMaximum Signal Screen CurrentPeak A -F Signal Voltage (Grid to Grid)Control Grid Resistor per Section.Load Resistance (Plate to Plate)Total Harmonic DistortionPower Output

Copyright 1943, Sylvania Electric Products Inc.

August -September, 1943 EMPORIUM, PENNA. Vol. 10, No. 7

Operating Conditions and Characteristics

RESISTANCE COUPLED AMPLIFIER CLASS A2(Per Section except heater)

Self Bias Fixed BiasHeater Voltage 48.0 28.0 VoltsHeater Current 0.400 0.400 AmperePlate Voltage 28.0 28.0 VoltsScreen Voltage 28.0 28.0 VoltsGrid Voltage -3.5 VoltsCathode Bias Resistor 390 OhmsZero Signal Plate Current 9.0 12.5 Ma.Zero Signal Screen Current 0.7 1.0 Ma.Maximum Signal Plate Current 6.5 8.1 Ma.Maximum Signal Screen Current 1.6 1.9 Ma.Plate Resistance 4200 OhmsTransconductance 3400 pmhosPeak A -F Signal Voltage 4.9 4.9 VoltsControl Grid Resistor per Section 0.5 0.2 MegohmLoad Resistance 4000 4000 OhmsPower Output 80 100 Mw.Total Harmonic Distortion 10 10 Percent

PUSH-PULL OPERATION -RESISTANCE COUPLED CLASS A2(Values are for both sections)

Heater Voltage 28.0Plate Voltage 28.0

28.0

28.0 Volts28.0 Volts28.0 Volts-3.5 Volts

180 Ohms18.5 25.0 Ma.

1.2 2.0 Ma.14.5 19.0 Ma.2.5 3.0 Ma.9.8 9.8 Volts0.5 0.2 Megohm

6000 6000 Ohms2.5 2.0 Percent175 225 Mw.

PARALLEL OPERATION -RESISTANCE COUPLED CLASS A2(Values are for both sections)

Heater Voltage 28.0Plate Voltage 28.0Screen Voltage 28.0Grid VoltageCathode Bias Resistor 180Zero Signal Plate Current 18.5Zero Signal Screen Current 1.3Maximum Signal Plate Current 13.1Maximum Signal Screen Current 2.8Peak A -F Signal Voltage 4.9Control Grid Resistor (both sections) 0.2Load Resistance 2000Total Harmonic Distortion 9.5Power Output 160

28.0 Volts28.0 Volts28.0 Volts-3.5 Volts

Ohms25.0 Ma.2.0 Ma.

16.0 Ma.3.5 Ma.4.9 Volts0.1 Megohm

2000 Ohms8.0 Percent200 Mw.

PUSH-PULL OPERATION TRANSFORMER COUPLED CLASS A2(Values are for both sections)

Heater VoltagePlate VoltageScreen VoltageGrid VoltageCathode Bias ResistorZero Signal Plate CurrentZero Signal Screen CurrentMaximum Signal Plate CurrentMaximum Signal Screen CurrentFeak A -F Signal Voltage (Grid to Grid)Load Resistance (Plate to Plate)Total Harmonic DistortionPower Output

f

28.0 Volts28.0 Volts28.0 Volts

0 Volts0 Ohms

64.0 Ma.4.0 Ma.

58.0 Ma.17.0 Ma.12.6 Volts1500 Ohms11.0 Percent600 Mw.

NOTE: -The above characteristics may be realized provided the d -c platecircuit resistance does not exceed 50 ohms per section.

SYLVANIA TYPE 28D7Double Beam Power Amplifier

For 28 -Volt OperationNo formal announcement has heretofore been made in Sylvania

News regarding Type 28D7. This tube was designed and developedby Sylvania some months ago to fulfill a need for an output tubewhich would deliver sufficient power at low operating voltages andthereby eliminate the need for auxiliary high voltage power supplies.Of primary importance in aircraft applications, the principal usageat present is confined to military requirements. Subsequent use incommercial equipment and perhaps in farm radios is anticipated.

It was found that certain other existing commercial tube typescan be employed in 28 volt operated devices. A suitable output tubewas not available prior to the release of Type 28D7. In order thatyou may become familiar with the characteristics of this new tube,pertinent data and circuit information have been prepared for thisissue.

Sylvania Type 28D7 is a Lock -In output tube designedespecially for operation directly from a 28 -volt battery withoutrequiring any auxiliary high voltage power supply. It consistsof two beam power amplifier units in the same bulb. Thecontrol grid and plate of each section are brought out to separatepins; a common connection is used for the cathodes and likewisethere is a common terminal for the screen grids. The heatersare connected in series internally, and the cathodes are not tiedto either heater terminal.

The two sections of the tube may be operated separately,they may be connected in parallel, or they may be employed in apush-pull circuit. Two different recommended loads per sectionare specified, the choice depending on whether both sections areto function as single -ended amplifiers or whether the twosections are to operate in push-pull. Where each section is usedas a single -ended amplifier, the load per section should be 4000ohms, to insure reasonably low second and third' harmonics. Ifthe two sections operate in parallel, the load would be approxi-mately half this value.


RATINGS

Heater Voltage 28.0 VoltsHeater Current 0.400 AmpereMaximum Plate Voltage (Per Section) 100 VoltsMaximum Screen Voltage (Per Section) 67.5 VoltsMaximum Plate Dissipation (Per Section) 3.0 WattsMaximum Screen Dissipation (Per Section) 0.5 Watt

PHYSICAL SPECIFICATIONSStyle Lock -InBase Lock -In 8 -PinBulb T-9Diameter 1-8e' Max.Overall Length 3-54" Max.Seated Height 2-%" Max.

BASE PIN CONNECTIONSSection

Pin 1 -HeaterPin 2 -Control GridPin 3 -Screen GridPin 4 -PlatePin 5 -PlatePin 6 -Cathode & BCPPin 7 -Control GridPin 8 -HeaterRMA Basing No. 8BS-L-O

e1&2

e1

SYLVANIA NEWS

SYLVANIAFor push-pull operation the load persection should be 3000 ohms since withthis value the third harmonic is low andthe second harmonic, although high, willcancel due to the push-pull circuit. Aplate -to -plate load of 6000 ohms shouldtherefore be employed.

In general, self bias will probably beemployed and under such conditionspower outputs exceeding 150 milliwattscan readily be obtained from a single tubeoperating in push-pull from a resistancecoupled driver. If a separate bias voltagesupply can be provided, fixed bias opera-tion will furnish additional power outputsince it permits utilization of the totalsupply voltage. An increase in effectiveB voltage of about 3.5 volts is an im-portant factor at low voltage operation.In some applications bias voltage may beobtained from an oscillator, thus makingit unnecessary to provide a separatebattery for grid bias and also permittingthe use of the total plate supply voltage.The d -c resistance of the output trans-former plate winding should be as low aspossible to minimize the voltage drop tothe plates.

Type 28D7 is designed to furnishcomparatively large amounts of power at

EsIG

TYPE 28D7 -(Continued from page 1)

low plate voltages. The cathode power isproportionately higher than usually usedin power output tubes. The precautionscustomarily recommended for satisfactoryperformance of output stages are particu-larly important with Type 28D7 tubes.In resistance coupled applications thegrid resistor should not exceed 0.5 meg-ohm per grid under self -bias conditionsand 0.2 megohm per grid for fixed -biasconditions to minimize the effects of gridcurrent. A low mu driver tube having anamplification factor of 20 or less is moresatisfactory for driving the Type 28D7tube to maximum output at low distor-tion.

SUITABLE DRIVER TUBESSeveral methods of driving the Type

28D7 tube are very satisfactory forapplications where a 28 -volt power supplyis the only source of operating voltage.Data are given to show the performancecharacteristics of a number of resistancecoupled circuits and a transformer coupledcircuit.

A number of low mu triode tubes usingresistance coupling, such as Types 14N7,14E6 and 14A4, are available to drive theType 28D7 to rated power output underlow voltage conditions. Pentodes having

characteristics similar to Type 14R7 arealso adaptable for this application. Theload shunting the plate resistor of thedriver tube consists of the following gridresistor and the grid -cathode resistanceof the Type 28D7 tube in parallel. Thelatter is an important consideration of thecircuit as the Type 28D7 tube is drivento grid current at the higher signal levels.

Considerably higher power outputs arepossible with push-pull transformer drivewhen another Type 28D7 is employed as adriver with both sections connected inparallel. At 500 milliwatts output thedriving power is less than 45 milliwattsand the grid -to -grid signal on the outputtube is approximately 10.5 r -m -s volts.At 600 milliwatts output these figures are80 milliwatts and 12.8 volts respectively.

The performance characteristics ofthese various circuits are given in thefollowing tables and the circuit constantsemployed are shown on the schematicdiagrams.

The power output of a Type 28D7 isvery flat over a wide range of heatervoltage. There is a drop in power outputof approximately 3% with a heatervoltage change from 32 volts to 17.5 volts.

LOW MU TRIODE DRIVERS FOR TYPE 28D7

TYPE 14E6 ORTYPE I4A4 ORTYPE I4N7 I SECTION

28 VOLTS

-+3.5V.

TYPE 28D7rr EFFECTIVE LOAD

2000 OHMS

2.8 VOLTS

TYPE 14E6 DRIVING A TYPE 28D7 (RESISTANCE COUPLED)

Esig to Power TotalDriver Output % 2nd % 3rd Distortion

0.10 Volt 26.6 Mw. 4.8% 2.4% 5.4%0,20 117.0 0.4 2.0 2.0

0.30 192.0 5.0 ' 4.0 6.4

0.35 216.0 6.7 5.9 9.0

0.40 240.0 8.2 8.3 11.6

TYPE 14N7 (SINGLE SECTION) OR TYPE 14A4 DRIVING TYPE28D7 (RESISTANCE COUPLED)

Esig to Power TotalDriver Output % 2nd % 3rd Distortion

0.10 Volt 50.0 Mw. 1.9% 3.8% 4.3%0.15 112.0 1.9 3.1 3.60.20 169.0 3.8 2.7 4.60.25 217.0 6.7 6.4 9.30.30 248.0 8.9 9.0 12.6

For Circuit Above For Circuit Above

TYPE 14R7 DRIVING TYPE 28D7 (RESISTANCE COUPLED) TYPE 28D7 DRIVING A TYPE 28D7 (TRANSFORMER COUPLED)Volts 22.3 Mw. 3.8% 2.9% 4.8%

Esig toDriver

PowerOutput % 2nd % 3rd

TotalDistortion

0.250.500.75

93.6196.0

4, 53.7

1.01.5

4.64.0

0.02 Volt 14.0 Mw. 3.3% 1.0% 3.4% 1.00 300.0 1.7 1.9 2.6

0.04 45.0 3.0 2.1 3.7 1.25 421.0 1.7 4.0 4.4

0.06 96.0 2.7 2.4 3.6 1.50 520.0 1.4 7.0 7.1

0.08 148.0 5.6 2.4 6.1 1.75 600.0 1.0 10.5 10.6

0.10 188.0 9.7 5.2 11.0 2.00 652.0 0.8 13.5 13.5

0.12 224.0 12.3 7.3 14.3 2.15 682.0 0.8 15.7 15.7

For Circuit on Next Pate For Circuit an Nexge

SYLVANIA NEWS

E SIG

oEsIG

0.1 MFD

w

PENTODE DRIVER - RESISTANCE COUPLED

TYPE I4R7 TYPE 28D7

EFFECTIVE LOAD2000 OHMS

}3.5 V.

28 VOLTS

TRANSFORMER COUPLED DRIVERTYPE 28D7

TYPE

28D7

o

on

IMP. RATIO5.75:1

PRIM. TOI/2 SEC.

28 VOLTS

o

28 VOLTS

PLATE TO PLATELOAD

1500 OHMS

V28 VOLTS

TYPE 28D7 PERFORMANCE WITH AIRCRAFT VOLTAGE SUPPLIESThe use of radio tubes operated with

the plate and screen voltages obtainedfrom the 28 -volt storage battery in a planeis becoming rather commonplace foraircraft equipment. Inasmuch as theplate, screen and filament supply of theequipment will be subjected to whatevervoltage variations occur in the supplyvoltage, it is important to know how theperformance will be affected by suchchanges. The operating supply voltageduring flight will vary from 27.5 to 28.5volts. When the plane is grounded, thesupply voltage may drop to as low as 22volts. In some instances a gasoline drivengenerator may be connected to the supplysource while the plane is grounded whichmay raise the voltage to 32 volts.

Power output and distortion data onType 28D7 are given in the followingtable with the heater, plate and screenvoltages varied from 22 volts to 30 voltsunder fixed and self -bias conditions.Values shown are for resistance coupledoperation with both sections connectedin parallel,

Iii. 2000 ohms, Esig=3.5 V. r.m.s.Fixed Bias

Rg=100,000 ohms, Ec1=-3.5 voltsEh =Eb =Ec2 P. O. % Distortion

22 volts 112 mw. 1524 135 1226 170 1028 200 830 235 8

Self -BiasRg=400,000 ohms, Rk=180 ohms, Re=10 µfEh=Eb=Ec2 P. 0. % Distortion

42 volts24262830

90 mw.109130160175

16141210

9

In applications where the tube isrequired to operate for any extendedperiod at heater voltages in excess of 28volts, a resistor should be inserted inseries with the heater supply voltageand the heater. The following data givethe performance characteristics of a Type

28D7 under conditions simulating voltagesupply variations from 22 volts to 32volts with a 10 ohm resistor in serieswith the heater voltage supply and theheater.

RL = 2000 ohms, Esig = 3.5 V. r.m.s.Fixed Bias

Rg=100,000 ohms, Ec1=-3.5 voltsEh Eb=Ec2 P. 0. % Distortion

18.8 volts 22 vol s 107 mw. 1620.7 24 135 1322.5 26 170 1024.3 28 200 826.1 30 235 828.0 32 260 8

Self BiasRg=200,000 ohms, Rk=180 ohms, Re= 10 pfEh Eb=Ec2 P. 0. % Distortion

18.8 volts20.742.524.326.128.0

22 volts2446283032

87 mw.107130160175195

171513121010

The operating temperature of Type28D7 is quite high. This fact should betaken into account when selecting socketsand also in locating parts with respectto the tube.

SYLVANIA NEWS

rr HE information presented in the Sylvania Service Exchange is contributedby servicemen as the result of practical experience. It is very carefully con-

sidered before being accepted, and we believe it to be correct and authentic.However, we assume no responsibility for results. Please do not send routineor generally known information.

Improving Tone Quality. Have hadmany auto sets, as well as 6 -volt batterysets, where the owners complained ofmushy, almost unintelligible tone. Byreplacing the 0.05 mfd. 150 -volt con-densers in the 6 -volt circuit in vibratorcompartment with the same size 200 -voltcondensers, the trouble was cleared up.Sometimes the leak in these condenserswon't show without a very high ohm-meter setting, (such as 20 megohms).Also, have cleared up the tone on batterysets, (same complaint) by installing anew "A" battery.-Charles A. Johnson,Republic, Mich.

Philco Model 651. Annoying oscilla-tion was traced to the i -f unit of thismodel. To eliminate same the i -ftransformer leads should be separatedfrom each other as far as possible, thatincludes separation of 1st i -f leads asmuch as possible. To cure any cause ofmotorboating at about 540. KC. the Bminus lead from the suppressor plateterminal of the 78 tube (RF) to thewiring panel mounted on condenser #72should be run close to the chassis andaway from the wave trap coil.-M. S.Planovsky, Cleveland, Ohio.

* * *RCA II -123 Chassis RC -421. Signal

cut-off, on short wave band only,caused by intermittent 5600 if tubularcondenser, (C-9), No. 13895. If exactduplicate is unavailable, use a standardtubular condenser of 0.005 µf capacity.-Joseph S. Napora, Uniontown, Pa.

MORE SERVICE HINTS, PLEASE

We appreciate the cooperation ofthose of you who have been submittingService Hints for, these columns; andfeel that the information they carryis especially helpful under today'sconditions of war -time servicing.Many of you who haven't beencontributing regularly undoubtedlyknow some "tricks -of -the -trade" thatwould be of value to other' servicemen.We ask that you please send them tous, so that we may continue to publishall suitable material.

Farnsworth AC55. The following is anunusual service problem which I en-countered that might be of interest toothers.

Recently a Farnsworth AC55 wasbrought in with the complaint of a loudhum. The filters with the exception ofNo. 30, on the diagram checked O.K.Replacing this condenser did not helpany. On checking further I found thatsome of the electrolyte from the condenserNo. 30 had seeped through the coiledwire shield and impregnated a spot onthe wire connecting the center tap of thevolume control and condenser No. 18.This wire picked up the hum from theshield and fed it to the grid of the 6SQ7tube. To repair simply replace wire anddress condenser away from the shield.-Henry D. Morse, Homer, N. Y.

RCA 26X4 and Similar ModelsSYMPTONS. Weak, and hiss at times

on stations and may even require anexternal aerial to get suitable reception,yet everything checks OK.

CURE. Dress filter leads away fromi -f leads and terminal strip under centerof chassis. Insulate carefully and realign.

EXPLANATION. Filter leads are cottoncovered-sometimes are saturated withelectrolyte and then dry out. Closeproximity of even the merest threads ofcotton affect the i -f gain without ap-parently affecting the i -f peaking. Resultsare well worth the effort.-Harry Isaac-son, Rochester, N. Y.* * *

WAR TIME EMERGENCY HINTSBattery Treatment. During the present

battery shortage I have been using aVeterinarian's hypodermic needle andinjecting hot water into each cell of theA and B batteries with surprisingly goodresults. Of course this is for batteries onwhich the zinc is still intact. Takes alittle time and trouble, but the radio isbrought back to life for a few weeks.-M. J. Edwards, Shreveport, La.

* * *Túbe Substitution. Type 6116 tubes

are hard to get here so we decided to useas a substitute a Type 6X5GT rectifiertube. Both cathode prongs on the 6H6socket should be tied together. The setsin which this has been done work fine.-Wentworth's Radio Service, So. Berwick,Maine.

RADIO TUBE SUBSTITUTION CHARTS FOR WAR -TIME SERVICING

War -Time Servicing

-dwal, - .,,- iáM

SYLVANIA ELECTRIC PRODUCTS IOC., EMPORIUM, PERIL

Because of popular demand,the Radio Tube SubstitutionCharts appearing in the pastthree issues of Sylvania Newshave now been combined in aconvenient folder. These chartscontain vital information forevery radio man, and should beput to use immediately. Theirpreparation is added proof ofSylvania's sincere desire to cons-tantly help servicemen face theproblems of these hectic times.

Your Sylvania Distributor willsupply you with reasonablequantities without charge on re-quest. If it is more convenient,write directly to us.

"Send a radio repairman to fix Corporal`wanson's radio, and maybe you'd better senda doctor with him!"

Radio Retailing Today

TECHNICAL SECTION

Copyright 1943, Sylvania Electric Products Inc.

October, 1943 EMPORIUM, PENNA. Vol. 10, No. 8

TUBE SUBSTITUTIONS ANDThe Sylvania Tube Substitution

Charts* have been of real assistance toservicemen and dealers in selecting work-able substitutes for many of the unobtain-able tube types. For each case thetabulated changes were based on theassumption that the appropriate socketwould be provided for the substitute type.However, we realize that occasions arisewhen objections are made to proposedreceiver alterations. The customer mayprefer to have the original wiring remainessentially intact or the serviceman mayconclude that the super -compactness ofthe receiver precludes satisfactory re-modeling. These situations suggest thepossible use of adaptors.

There is no hard and fast rule foradaptor usage. No set instructions formaking adaptors can be given althoughnumerous suggestions and precautionsare worthy of careful consideration.

Analyze Space LimitationsPerhaps the first condi-

tion to be analyzed is spacelimitation. The adaptoritself definitely adds to the

a."4effective overall length.Whenever space is at apremium the comparatively

short overall length of Lock -In types maypermit, their use whereas G or GT con-structions could not be utilized. This isespecially true where Lock -In types aresubstituted for regular or GT designsinvolving top cap connections since theLock -In versions are all of single endedconstruction and therefore shorter inlength. In general, tube diameters arenot as critical a dimension as the overalllength. Exceptions would be encounteredon substitutes for miniature types.

Extra CapacitancesLet us assume that a socket change is

not made and that space does permitusing an adaptor. What difficulties aremost likely to be experienced that couldbe attributed to the adaptor itself? Firstis the extra capacitances introduced,particularly the grid -to -plate value. Ther -f, i -f and converter tubes will be mostcritical in this respect and careful realign-ment will be necessary even though thesubstitute tube has the same capacitance*These are still available on request.

SOCKET ADAPTORSratings as the original type. A secondsource of trouble may be hum pick-upintroduced by the extra length of gridlead required on oscillators and amplifiers.In making an adaptor to use one of thesingle -ended tubes having the controlgrid brought out at a tube base pin, inplace of a top -cap style, a suggestedmethod is to fasten an old top cap to theside of the adaptor. Generally this willnot introduce too much additional capa-city. Should the reverse situation exist,that is, the use of a tube with top -cap con-nection in place of a single -ended style,it would be best to run the grid lead inshielded wire outside the socket and makeno connections to it in the adaptor be-cause special shielding of the grid lead isincorporated within the tube base. Thereis no easy way of continuing this shieldingthrough an adaptor.

Another precaution, easily overlooked,is that of employing suitable insulationfor any crossed leads present within theadaptor. The use of a good grade ofspaghetti is emphasized because some ofthe new synthetic types are not toosatisfactory.

Using Salvaged Bases

Perhaps the easiestway to make up adaptorsis to use the base from aburned out or otherwisedefective tube. First as-certain that the base isequipped with the required number ofpins and also that all pins present are inthe proper positions. Bear in mind thatevery tube base does not necessarily con-tain eight pins. Many octal bases, whetheron metal, G or GT tube types may haveonly 5, 6 or 7 pins as the normal numberinstead of eight. The metal shell baseemployed on numerous GT tube typesmay be somewhat simpler to handle thanthe bakelite style although the latter willsuffice if adequate care is used in drillingany additional holes that are foundnecessary. In case the adaptor must bemade sufficiently small in diameter so thata tube shield will fit over the tube andadaptor, the mounting projections of thesocket can be cut off. An alternative is touse a style of socket which normallywould be fastened to the chassis by a

locking ring. Wires about three incheslong are soldered to the socket terminalsand then arranged in the proper order topermit threading into the pins of theold base. Determine which leads, if any,will require insulation. Next, see thatthe old tube base is properly cleaned outand the pins entirely open to admit thewire connectors.

No specific instructions are being sug-gested for fastening the base and sockettogether since the procedure is largelygoverned by the style of base and socketcombination. The socket should providesome bearing surface on the top of, thebase to withstand the pressure exertedwhen a tube is inserted in the adaptor.With reasonable care in inserting andremoving the adaptor no mechanical con-nection other than the wires themselveswould have to be provided if fairly heavywires are used as connectors. Nowthread the wires into the base pins, pullup tight and bend each wire over the endof the pin. At this point a few extramoments spent in checking connectionswith a continuity meter to make certaineach wire is correctly terminated willoften save time and material. Recheckagainst base and socket diagrams. Thisdone, the wires can be soldered and theexcess wire clipped off close to the pin.Solder carefully and avoid applying solderto the sides of the pins. If chunks ofsolder remain on the pin walls tube in-sertion will be more difficult and thesocket contacts in the receiver propermay be permanently sprung and resultin faulty performance.

Tracing HumIn case it is necessary to use an adaptor

in a first audio stage or in a, P. A. systemhum may be traceable to an unshieldedgrid lead running parallel to the heaterwires in the adaptor. The obvious cureis to shield the lead and ground theshield. This might require an extra leaddirect to ground.

These notes are intended to "hit thehigh spots" relating to tube adaptors,recognizing that their use in servicingreceivers is principally a war -time expedi-ency and not a practice that is to berecommended if repairs can readily bedone in the orthodox manner.

SYLVANIA NEWS - -

SYLVANIA POWER MEASUREMENT LAMPS

A MEANS OF MEASURING HIGH FREQUENCY POWER OUTPUT OF RADIO EQUIPMENT

Many items now being made by Syl-vania cannot be discussed in these pagesbut the recently developed SylvaniaPower Measurement Lamps are notrestricted and many experimenters shouldfind them quite useful.

The accurate measurement of radiofrequency power has always been some-what of a problem. Even the use of goodthermocouple milliammeters in serieswith an incandescent lamp is .not toosatisfactory because neither the lampresistance nor the voltage are generallyknown. Vacuum tube voltmeters, ifavailable, offer some help but, in manycases the extra capacity, resistance and

inductance introduced into the circuitbeing measured change the conditions somuch that the results are not too reliable.

The Sylvania Power MeasurementLamps provide a simple and accuratemeans for measuring r -f power. Thereare six "lamps" in the series at present,with resistances from 40 to 310 ohmsover the useful ranges of the curves.Power measurements from 0.05 watt to25 watts can be measured directly andaccurately with a PM Lamp and metersreadily available to most radio experi-menters.

These lamps consist of two identicalfilaments ín the same bulb. Their small

BASE CHART

ANDCONNECTIONS

Pin 1 Fl Pin 5 F2Pin 2 * Pin 6. *Pin 3 * Pin 7..... *Pin 4 F2 Pin 8. Fl

"`External connections should not bemade to these pins.

50 2-1, 111111011101

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p.--.... 11111111111 .111=-- . %,11111 11111111 1--....- 1111..I1111111O011llOu.u.u.111111-M-.., . 1111111111 ---.. 111111I111.11111IIIIIII11.1.1.11111111111

1.1 1111111111111111111 111111111111111.111~.1.-.I111111111111."Iu1111111 11111111 MI. 1111111111111111111IIIII1111111..11111111

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SYLVANIA

_?? -_-. _ -"lllll ;eE POWER MEASUREMENT LAMPSlllllllllllll

--_ -- ._ ..i CALIBRATING VOLTAGE VS. POWER1 -1 a I AVERAGE CHARACTERISTICS

1- -___ I111 111 11O.. 1 11111--_ --_ . 111 ..11111 1 1111uu nuuuunu u11uu 11

11ununill unuuw-_. : l u 1 nuu 11---.... 11111111111 11111111.11111p~--nunuuu 11111111111

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4.0.4 1.0POWER IN WATTS (AF or RF)

10 40

SYLVANIA NEWS

50

2

1

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SYLVAN IA

POWER MEASUREMENT LAMPSCALIBRATING VOLTAGE VS. POWER

AVERAGE CHARACTERISTICS

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.04 .1 .4POWER IN WATTS (AF or RF)

1.0 4.0

size and direct connections enable onefilament to be placed in one of the leadsof the high frequency circuit being in-vestigated. The other filament is con-nected to a variable a -c or d -c powersource of which the voltage is measuredwith an ordinary meter and this isvaried until the brightness of the twofilaments are equal. The accuracy ofmeasurement is 5 per cent withoutspecial calibration of both filaments, butthis can be bettered by averaging tworeadings using the filaments reversed. Ifmore accurate results are desired thelamps can be calibrated by either im-pressing a voltage or measuring thecurrent in the calibration side, applyinga voltage to the load side and measuringthe load input when the two sides matchfor brightness. The power in the loadside is then known in terms of voltage orcurrent in the calibration side, and theaccuracy will be independent of anydifference between the two filaments.

Extending Useful RangeThe range may be extended into the

higher power region by using a darkglass filter for visual comparison offilament brightness. If a suitable photo-cell detector is available the useful rangecan be still further extended. It wouldnot be advisable to operate above themaximum power or voltage listed sincea permanent sag may be put in the fila-ment if these values are exceeded.

Because of the high heat conductivityand small diameter of the filament ma-terial, the temperature and color will be

constant for a given quantity of energydissipated, regardless of whether the heatis liberated uniformly throughout thecross section as with D. C. or non -uni-formly due to skin effect at ultra highfrequencies. Power can be measured atany frequency at which it is possible tocouple the energy into the lamp filament.(Series tuning capacitance or resonantlines may be required).

The high frequency resistance of thepower lamps does not differ appreciably

from the d -c resistance up to the fre-quencies given in the characteristics, fordue to the small wire size the depth ofpenetration is greater, or at least equal,to the wire radius. When the lamps areused at a higher frequency where skineffect becomes a factor, the resistive com-ponent increases; but the power will becorrectly indicated as the r -f current willbe less than the d -c current, resulting inequal r -f and d -c I2R products (powervalues) and equal filament brightness.

RATINGS AND CHARACTERISTICSTYPES

PM3 PM4 PM5 PM6 PM7*Maximum Frequency for

Z = R 15 15 25 25 30Maximum Frequency for

Rac = Rdc 100 100 150 200 400Inductive Reactance

at 55 Mc 125 100 225 140 120Inductive Reactance at

110 Mc 300 275 450 250 200Normal Power (Min.) 1.35 0.8 0.7 0.33 0.12Normal Power (Max.). 10.00 5.5 3.8 1.75 0.95Resistance at Normal

Power (Min.) 40 90 190 110 130Resistance at Normal

Power (Max.) 70Power Dissipation (Max.) 25.0Applied D -C Volts (Max.) 48

150 310 175 22012.0 7.5 3.5 2.0

48 55 28 24*Lamps may be used for voltage calibration or standardization upquencies.

**Reactance is negligible compared to the resistance.

PM8

55 Mc.

900 Mc.

** Ohms

90 Ohms0.05 Watts0.41 Watts

110 Ohms

195 Ohms1.0 Watts

16 Voltsto these fre-

SYLVANIA NEWS

THE information presented in the Sylvania Service Exchange is contributedby servicemen as the result of practical experience. It is very carefully con-


--.,,.,` . .........

Emerson Model 108 LW. Set playsnormally and then suddenly drops involume. Trouble may be caused by theoscillator coil which is located beneaththe chassis. The connections make andbreak contact at the lugs when the setwarms up. To make the set show upthis trouble quickly, place the chassis intoan empty shoe box where the accumula-tion of heat will hasten the breakdown.-Harold D Millen, Boston, Mass.

4 4RCA Model 46X11. Distortion and a

marked decrease in volume were tracedto the output beam power tube whichchecked OK on the tester. When thevoltages were checked it was found thatthe screen voltage was below normalalthough all parts checked perfect. Re-placing the output tube with anothertube cured the trouble.-Harold D.Millen, Boston, Mass.

4Crosley Model 170. When this set is

brought in for repairs with the complaintthat there is no reception over the entiredial, although the -set still seems to havea live sound coming from the speaker,the trouble nine times out of ten will becaused by the breakdown of one sectionof the dual unit condenser which is listedas part #W27204. The section whichconnects to the 10,000 ohm resistor is theone that always breaks down. For apermanent cure, replace with a 0.02-600volt unit. Another frequent complaint inthis model receiver is the breakdown ofthe dual resistor unit #W28471. Quiteoften either one or both of these resistorsopen and are generally replaced withregular single units mounted on thedefective resistor lugs. When this is thecase, the replacement units generallydevelop quite a bit of heat which in-variably causes the before -mentionedoscillator plate coil condenser to breakdown. It is a good policy after replacingthe defective resistors to slip a small pieceof asbestos paper under them and there-by protect any condensers which aremounted close to the resistors.-D. Cun-icky, Belle Vernon, Pa.

# 4 4Philco Model 38-7. Intermittent weak

signals. Replace the filter condenser onthe set side of the choke. This condenseralso acts as an audio by-pass.-DanielsBrothers, Everett, Penna.

Motorola Custom Deluxe (For Dodge1940). This set came in with the follow-ing symptoms: Very poor selectivity,low volume on other than local stationsand poor sensitivity. This would appearat all times except on a rainy day. Afterchecking all grounds plus routine checkson tubes and circuit alignment, I finallyfound the trouble. This set came throughwith a small antenna matching unitlocated in the base of the antenna. Anohmmeter reading showed several meg-ohms resistance from the tip of antennato end of lead-in at the set. Upon takingapart the base of antenna (which must bedone with extreme care to avoid breakingthe bakelite base), I found the matchingcoil full of corrosion. The supposedlywater and weather proof connectionswere not so. The weather had beengetting in, and in time the corrosion hadcreated a high resistance joint. Uponwetting the coil, I found the resistancehad dropped to about eight thousandohms, instead of the megohm readingwhen dry. Remedy: Take out coil,unwind the wire from the form and soldera jumper across the two ends of form andreplace. Realign the antenna circuit andset is perfect.-Frank Sikonski, CentralFalls, R. I.

4 4Detrola Battery Radios. On several of

these models and other such sets using avibrator power supply, the filter chokehas a bad habit of "going open". Thisunit can be repaired without disassemb-ling the entire power unit, by shunting a850 ohm, 5 or 10 watt resistor across theopen choke. The filter action is, seeming-ly, just as good. This is a quick, cheapand serviceable repair.-D. J. Shinn,Elgin, Kansas.

# 4 4General Electric G-50. Fading and

distortion with indications of a poor con-nection in the speaker cable. This iscaused by changes in capacity betweenthe wires of the speaker cable as they aremoved.

To remedy, connect a 0.05 µf con-denser from the screen of the 41 outputtube to chassis, right at the socket. Thefactory depended upon the capacitybetween the wires of the speaker cable,which become separated.-Albert VanNest, Orlando, Fla.

--

RCA Model M-101. Time and againthis set would play when pulled from acar and placed on the bench, but wouldnot play in car more than a few miles;and then it would be the same thing allover again. Trouble was in the blackwire where it enters into the specialaerial transmission matching box. Thisset has a special aerial lead-in setup toreduce noise which consists of a blackwire and a red wire covered by shielding.-T. Henshaw, Marysville, Kans.

* * *Philco Model 39-85 (Battery). No

signals, or intermittent. Replace thesmall control grid condenser in the oscilla-tor section of the 1A7G. This condenseris mounted on the wave band switch, theonly number on it is Type 0. We foundthat in several of these sets, this con-denser developed a high resistance leak,sometimes enough to put a positive biason the oscillator control grid.-DanielsBrothers, Everett, Penna.

# 4 4Reducing Microphonic Hum. On sets

using the 1.4 volt tubes and where thespeakers are mounted directly on chassis,there often exists microphonic hum.This can be cured by inserting rubberspacing washers between points touchingchassis and also where speakers aremounted on cabinet, install rubber spacersbetween baffle and speaker.-J. LeoRobey, Waldorf, Md.

Auto Radio Installation. Those "T"and "J" bolts used to hold auto radiosto bulkheads can waste a lot of yourtime. Try this method. Loosen the nutsto within a quarter of an inch of the boltends-remove and repair the radio-andhook it to the bolts you left hanging inthe bulkhead. Now, from the motorside, grasp one bolt end with a pair ofpliers. Hold it firmly to prevent it fromtwisting out of the slot in the radio andpull one end of the radio up snugly to thebulkhead. Now you can spin the nutclear up to the hilt with the fingers of yourother hand. Do the same with the otherbolt then a few tightening turns withyour wrench will finish the job quickerthan I can tell it. Saves a lot of wearand tear on your helper, as well.-DonBlair, Franklin, Pa.

TECHNICAL SECTION

Copyright 1943, Sylvania Electipc Products Inc.

November, 1943 EMPORIUM, PENNA. Vol. 10, No. 9

28 -Volt OperationThe August -September issue of Sylvania

News contained an article on Type 28D7.Because of the growing interest in low voltageoperation further information is now presentedon other tube types. Only a limited numberof existing types happen to have design charac-teristics such that they may also be operatedfrom a 28 -volt supply and still provide accept-able performance. Ratings on several recom-mended types appear in the present issue.

There is considerable interest at presentin the application of radio tubes inequipment designed for operation from28 volt d -c supply sources. The informa-tion given here was obtained to show theperformance to be expected when usingstandard tube types at this voltage. Theoperating characteristics of a completecomplement of tubes, except for theoutput tube, are described. The per-formance of equipment employing sucha complement should be very acceptableover a frequency range extending fromthe broadcast band to frequencies above100 mc. The Type 28D7 power outputtube designed for use with a 28 -volt supplywas discussed in Sylvania News Volume10, Number 7.

Grid current considerations are im-portant when operating at these voltages.Unless the tubes are operated in circuitsdesigned with this in mind the inputresistance will be very low.

of Standard Radio Receiving Tubes

SYLVANIA TYPE 14J7CONVERSION CONDUCTANCE VS. CONTROL GRID VOLTS

SUPPLY VOLTS = 28

50.000Rt--'100.0001

3 2

NEGATIVE CONTROL GRID VOLTS

r250=

CC

200

0O

CONVERTER

Type 14J7 was selected as the besttype of converter for use under 28 voltconditions. The frequency stability ofthe triode heptode is well known and isespecially useful where oscillator ampli-tude and frequency shifts with othertypes would cause trouble.

SYLVANIA TYPE 14J7CONVERSION CONDUCTANCE VS. OSCILLATOR GRID CURRENT

SUPPLY VOLTS = 28

20 40 60 80 100 120 140

OSCILLATOR GRID CURRENT IN MICROAMPERES

Type 14H7, which has a mutualconductance of 3800 micromhos under250 volt operating conditions shows amutual conductance of 2000 with 28 voltplate supply. This performance is morefavorable than that obtained with mostother pentodes having either higher orlower mutual under rated conditions.

Type 14R7 which has a mutual con-ductance of 3200 micromhos under 250volt operating conditions, shows a mutualconductance of 1500 with 28 volt platesupply. This performance is better thanthat obtainable with any other diodepentode tube which is regularly available.

TRIODE DRIVERSWhen triodes are used to drive the grid

of the Type 28D7 for 28 volt operationlow mu rather than high mu types aremore useful since the grid of the Type27D8 may be driven to grid current andrequires some power. The Type 14E6 isrecommended when a diode triode isneeded, while Type 14N7 is most usefulwhen a double triode is necessary.

The tabulated ratings on pages 2 and 3,together with the curves, indicate thatexcellent operating characteristics may beobtained under 28 volt operating con-ditions. The Type 28D7 ratings andperformance data appeared in a previousissue.

SYLVANIA NEWS

28 VOLT SUPPLY OPERATINGCONDITIONS ANDCHARACTERISTICS


SYLVANIA TYPE 14J7Heater Voltage 14.0 14.0 VoltsHeater Current....... .. 0.16 0.16 AmpereHeptode Plate Voltage 28.0 28.0 VoltsHeptode Screen Voltage 28.0 28.0 VoltsHeptode Control Grid

Voltage -0.75 -0.75 VoltHeptode Plate Current 0.41 0.40 Ma.Heptode Screen Current 0.56 0.55 Ma.Heptode Plate Resistance 0.25 0.25 MegohmHeptode Mutual

Conductance 370 370 MicromhosConversion Conductance 215 205 MicromhosTriode Plate Voltage 28.0 28.0 VoltsTriode Grid Resistor 50,000 100,000 OhmsTriode Grid Current 80 40 MlcroampsTriode Plate Current 0.46 0.50 Ma.Conversion Conductance at

Heptode Grid Bias of-5 Volts. 3 3 Micromhos

SYLVANIA TYPE 14H7Heater Voltage 14.0 VoltsHeater Current. 0.16 AmperePlate Voltage. 28.0 VoltsScreen Voltage 28.0 VoltaGrid Voltage - 0.75 VoltSuppressor and Pin #5 0 VoltPlate Current 1.20 Ma.Screen Current 0.45 Ma.Plate Resistance 0.4 MegohmMutual Conductance 2050 MtcromhosGrid Voltage for Mutual Conduct-

ance of 35 Nmhos -4.0 Volts

SYLVANIA TYPE 14R7Pentode Section as I -F Amplifier

Heater Voltage 14.0 VoltsHeater Current. 0.16 AmperePlate Voltage 28.0 VoltsScreen Voltage 28.0 VoltsGrid Voltage -0.75 VoltPlate Current 0.85 Ma.Screen Current 0.30 Ma.Plate Resistance 0.40 Megohm

O

SYLVANIA TYPE 14H7

PLATE CHARACTERISTICSEci = +0 .5

Ec: = 28+0.25

O 20 40 60PLATE VOLTS

0.0

-0.25

-0.5 -

-0.75-1.0-1.25-

80

TYPE 14R7 -(Continued)Mutual Conductance 1500 MicromhosGrid Voltage for Mutual Conduct-

ance of 35 Nmhos - 3.0 Volts

Typical Operation as a ResistanceCoupled Audio Amplifier

Plate Supply VoltageScreen Supply VoltageGrid Voltage*Plate CurrentScreen CurrentPlate Load ResistorGrid Resistor of Following StageScreen ResistorVoltage GainMaximum Output Voltage (R.M.S )

At 5% Distortion*Grid Resistor=10 Megohms

28.0 Volts28.0 Volts

0 Volt0.15 Ma.0.05 Ma.0.10 Megohm0.22 Megohm0.27 Megohm

30

2.4 Volts

SYLVANIA TYPE 14E6Transformer or Choke Coupled

A -F AmplifierHeater Voltage......, 14.0 14.0 VoltsHeater Current... 0.16 0.16 AmperePlate Voltage. ... 28.0 28.0 VoltsGrid Voltage 0* - 1.0 VoltPlate Current 2.0 0.9 Ma.Plate Resistance.... 12,200 16.000 OhmsAmplification Factor.. 15.0 17.7

Resistance Coupled A -FPlate Supply Voltage 28.0Grid Voltage* 0

Plate Current 0.08Plate Load Resistor 0.22Grid Resistor of Following

Stage

Amplifier28.0 Volts

0 Volt0.14 Ma.0.10 Megohm

1.0 0.22 Megohm

SYLVANIA TYPE 14H7MUTUAL CHARACTERISTIC

SUPPLY VOLTS

3

2

1

013 2 1 0

NEGATIVE GRID VOLTS

CO)

J0O0 OOOZ

C

0 0

U U= WCI t:.2Z ZoU y

1000_12000yQ W_ CCI -

HZ. 1-J0 o

CL.

SYLVANIA TYPE 14R7MUTUAL CHARACTERISTICS

RP

SUPPLY VOLT 28

-Ic2

2

VW

3 2 1

00 O

NEGATIVE GRID VOLTS a.

SYLVANIA NEWS

TYPE 14E6-(Continued)

Voltage Gain 9.8 9.3Maximum Output Voltage

(R.M.S.) At 5% Distor-tion

*Grid Resistor=l0 Megohms

SYLVANIA TYPE 14N7 (SINGLE SECTION)OR TYPE 14A4

Transformer or Choke CoupledA -F Amplifier

4.0 3.7 Volts

Heater Voltage 14.0Heater Currentt 0.16Plate Voltage 28.0Grid Voltage 0*Plate Current 2.9Plate Resistance 9,000Amplification Factor 16

Resistance Coupled A -FPlate Supply Voltage 28.0Grid Voltage* 0

Plate Current 0.07Plate Load Resistor 0.22Grid Resistor of Following

StageVoltage GainMaximum Output Voltage

(R.M.S.) At 5% Distor-tion 4.0

tFor Type 14N7 value is 0.32 ampere.*Grid Resistor=l0 Megohms.

1.013.4

14.0 Volts0.16 Ampere28.0 Volts

-1.0 Volt1.0 Ma.

13,000 Ohms20

Amplifier28.0 Volts

0 Volt0.12 Ma.0.10 Megohm

0.22 Megohm12.0

3.6 Volts

BUILD PRESTIGE SAVE TIME

Use Sylvania's New

WARNING CARDWith so many circuit changes and other unorthodox

methods being used in radio repairing today many receiversnow differ considerably from their original design. And,too, most of these emergency repairs are made with no recordor indication of what has been done to the set. This meansthat on the next service job on that particular radio it will benecessary for you or some other serviceman to analyze pre-vious changes before proceeding.

The Sylvania WARNING CARD willcorrect that situation if you faithfullyattach one to each job, noting on it anyunusual changes you have made andfiling the stub for future reference.Aside from giving a record of the workdone, the card with its word WARNINGin big red letters will have the psychologi-cal effect of making the owners feel youare the one to whom their set should besent when additional repairs becomeneeded. They will think of you as an"up-to-the-minute" radio technician andbusinessman when you use this means ofprotecting their set.

Furthermore, many of your customerswill want their radio restored to normalwhen the war is over-what better wayto bring those sets back to you than yourbig imprint on a card, attached to theset, which tells at a glance the war -timechanges you had to make? Or, beingmore aggressive, you could use the cardstubs as the basis of an excellent list towhich to send post-war reminders thatyou are then able to restore radios tooriginal designs.

The WARNING CARDis attractively finished inred and black ink on aheavy cardboard stockmeasuring 5"x7%".The punch -hole is slottedfor ease in attaching.The back is ruled tocarry your notations, anda perforation through thecenter facilitates quickhandling. The custo-mer's section containsyour imprint, the warn-ing notice, and list ofchanges; your section hasthe customer's name, setdata, and list of changes.

The cards, completewith imprint, carrySylvania's usual lowprices:

100.. $1.00250 1.75500.. 3.00

1000 5.00

CREATE REPEAT BUSINESS

Changes an SubstitutionsDate

vWARNINGv

CIRCUIT CHANGESDESCRIBEDON THE OTHER

SIDE OF THISCARD HAVE BEEN MADE INTHIS EQUIPMENTAS A WARTIME EXPEDIENCY.

by

YOURIMPRINT' HERE

We Recommend SYLVANIARadio Tubes

Job RecordChange: made in circuit of equipmentowned by-

Make

Model

Serial No.

Cord

itutions

Radio Tubes

Use ordercoupon on pagethree of theGeneral Section.

SYLVANIA NEWS



Philco Model 1908 (Mopar 801). Whendistortion develops in this receiver it maybe due to the opening of the % watt,220,000 ohm cathode resistor of the 7A4.Replace with a % watt resistor of thesame resistance. I have found this defecta rather common occurrence in thismodel.-D. B. Hanel, Martinsville, Va.

Motorola Model 50 Auto Radio.Recently I received one of these sets forrepair and found that the volume controlcable was completely twisted off andunraveled. Since I was unable to procurea replacement I made repairs in thefollowing manner: Unsoldered the oldwires going to the control, took out thevolume control and mounted it in thecontrol head of the radio. This waseasily done since all that was necessarywas to take out the cable housing andshaft, inserting the volume control andfastening same with the set screw thatformerly held the cable housing. Leadwires about 2 feet in length were thenconnected between the volume controland the original terminals in the receiverand the set works as good as ever.-Richard Wolf, Wishek, N. Dak.

General Electric Models E-81 andE-86. When noisy operation, fading andfrequent burnout on Type 6L6 areexperienced, check the 0.01, 1000 voltplate bypass condenser C-45. Some-times this condenser is actually missingin the receiver. I had this trouble twiceand now I make sure that the condenseris present when checking complaints onthis particular model. The condenser isconnected from the plate of the 6L6 tubeto the ground. Replace the faulty con-denser with one having a 1500 voltrating. - Henry Bollmann, BerkeleyHeights, N. J.

Tube Substitution. I had been holdingfour receivers waiting for 6116 tubes. Theowners got worried, so I tried substituting6ZY5G by tying the cathodes togetherat the socket. The sets have worked OKever since.-John Stine, Jersey Shore, Pa.

4 4 4.

Emerson EA -357. This set would notplay on a power line supply due to thefact that the filter choke was open.Either replace choke or repair breakwhich usually occurs at connections.-Fred J. Ferrero, Kensington, Ky.

Transformer Insulation -1940 Models.(Philco). If the set is dead or weak,check the leads from the output trans-former. Sometimes these stick to thechassis, the insulation melts and ground-ing results. I have found both primaryleads in this condition on one set and onanother set, the secondary lead hadgrounded. In making repairs, additionalinsulation should be provided.-Fred J.Ferrero, Kensington, Ky.

* *

Philco 38-16. Intermittent signal wouldcome and go as dial knob was moved. Ifound that the wire soldered to thebottom of the gang oscillator section wasloose. A careful job of resolderingcorrected the trouble.-Fred J. Ferrero,Kensington, Ky.

Zenith Model 8S-154. I have had afew of these sets come into my shop withthe complaint of sharp whistle on thenear -by stations while the rest of thestations seemed to come in OK. Thetrouble was traced to the 2 and 81.Lf elec-trolytic condensers which were open.These two condensers were in one unit,Zenith part No. 22-491-F. Replace withnew condensers of same capacity and cor-rect the trouble.-A. C. Hulsizer, Plains,Pa. # 41

Line Isolation Transformer. An ef-ficient A -C line isolation transformer canbe made by following the schematic ofFig. 1. This unit is particularly usefulfor alignment of "AC -DC" receivers.

The two transformers should be alike,(from the electrical characteristic point.of view). If the transformers selected

TI 12

It, 11.

CT CT

CENTER TAPNOT USED

FKa.I

1I5VA.C.OUTPUT

have tapped primaries, a switchingarrangement could be provided to varythe output voltage.-Joseph S. Napora,Dayton, Ohio.

Insulation Repair. We are all troubledwith the insulation on battery plugs andbuilt-in antennae pushing back from theplug and the wires shorting together.Push the insulation close to the plug, wraptightly with a strong thread, then applysome cement. They never slip again.-C. A. Vaughn, Los Angeles, Calif.

Voice Coils. A quick check for con-tinuity without unsoldering. Use a lowrange ohm -meter (1 to 100 ohms) scale.Put the prods on the voice -coil terminalsand move the cone with your finger.Provided it is a PM speaker or a dynamicwith the proper field current flowing, aplainly evident reaction will be noted onthe meter scale following each movementof the cone. Ditto, if the coil is open-no deflection will be seen as the cone ismoved. The meter will, of course,indicate a close to zero ohms readingthrough the output transformer second-ary. Also, if a speaker has a signalpresent, the needle will attempt to followit. All these reactions will be plainlyrecognizable after a few moments experi-menting and altogether give you a quick,easy and accurate check on the wholespeaker circuit. You might say that thisproves that an electric current is generat-ed by moving a coil through a magneticfield. This current aids or opposes thecurrent flowing in the ohm -meter, thusmoving the needle as the cone assemblyis moved. It naturally follows that thissame idea has many other uses for testing.Magnetic pick-ups, dynamic microphones,headphones, even crystal pick-ups (if youuse a high range ohms scale) may betested without disconnecting. And, witha bit of experience, you will be able tojudge the sensitivity of such apparatusby the amount of meter deflection youget from a bit of pressure in the properplace. But don't use too much pressureon crystals-they break easily.-DonBlair, Franklin, Pa.

Freshman 533 (Belmont BRC-533).Some of the early models used live -rubberinsulation on the pilot light leads, andwhen servicing this model for HUM(similar to open filters), check for short tochassis, of the pilot leads. For a perma-nent repair, it is advisable to place alength of spaghetti over each lead, or toreplace the leads with hook-up wire.-Joseph S. Napora, Dayton, Ohio.

TECHNICAL SECTION

Copyright 1943. Sylvania Electric Products Inc.

December, I943 EMPORIUM, PENNA. Vol. 10, No. 10

CONSTRUCTIONAL FEATURES OF VACUUM TUBES

There is an old expression, "Alike astwo peas in a pod," which is often used toexpress a high degree of similarity, atleast as to physical appearances. Thetube manufacturer endeavors to make alltubes of any given type as nearly identicalas possible since industry requirementsnecessitate standardization of physicaland electrical characteristics. Tube short-ages incurred by the heavy demands forwar services have greatly amplified theuse of substitute tube types in order tohelp maintain operation of civilian radios.Consequently, considerable interest existsin the various versions of essentiallyequivalent types. Electrical similaritydoes not necessarily imply physical like-

ness. Perhaps many readers have care-fully inspected a worn-out tube byremoving the glass envelope and thenexamined the structure so as to becomemore familiar with the actual componentparts and construction. But how manyof you have made a comparative study ofequivalent types? Some points of interestare discussed in this article.

FOUR STYLES IN CROSS-SECTION

In order to provide concrete examples,special cross-sectional views of four tubeswere prepared. These are shown in thephotograph below and include the G, GT,metal and lock -in versions of the 6.3 -voltsharp cut-off r -f amplifier pentode. Eachtube is shown full size to permit direct

comparison. The cut through each tubewas made in essentially the same plane,that is, somewhat off center so that thecontrol grid and screen grid structureswould be preserved (front half of screengrid is hot present in the G constructionview). The front portion of the suppres-sor grid, plate and shield were cut away toshow the internal construction and therelative spacings of the various elements.The G type employs a cylindrical platewhereas the other three styles have"open" plate structures. A portion ofthe plate is visible behind the grids whilethe side ribs appear adjacent to thesuppressor grid support rod.


-.-.-., ,

TYpf 6J73 TYPE 6SJ7GT TYPE 6SJ7 TYPE 7C7

SYLVANIA NEWS

CONSTRUCTIONAL FEATURESOF VACUUM TUBES


FACTORS INFLUENCING SIZEThere are two major factors that

contribute to the larger size of the G typeof tube. These are the style of theenvelope and the length of the press. Thesmaller size of the G'I' tube is the result ofchanging both of these. The T bulb orstraight sided envelope is used and thepress has been shortened. The bulb isalso seated lower in the base. The stillsmaller size of the metal and lock -in tubesis a result of changing from a flat press to aheader type of construction. Instead ofthe lead wires being sealed into the glassin a single plane, they are sealed in theglass header in a circular pattern. Thiseliminates the necessity of the large typeof flare required in both the G and GTtubes below the press in order to seal themount to the glass envelope. In a metaltube the glass header is sealed to a metalring which in turn is welded to the metalshell or envelope. The metal shell iscrimped on the tube base in the samemanner as the base shell of the GT tube.The lead wires can be arranged in theheader in practically any desired order sothat cross-overs between the header andbase are eliminated. This also contribu-ted to a reduction in the required heightof the tube. The construction of thelock -in header likewise lends itself to anarrangement of the leads in such amanner as to require no extra spacing.In this construction the sealed -in leadsare also the contact pins for the tube andthe space required between the metalbase of the tube and the header arereduced to a minimum.

SPECIAL SHIELDINGThe exhaust tube, which can easily be

seen in the cut -away of the G tube, iscentered in the hole in the molded locatingpins of the GT and metal tube base. Inthe lock -in construction the exhaust tubeextends down into the base lock -in lug.A metal shield can be seen around theexhaust tube in the pictures of the GTand metal tubes. This shield whichextends down into the locating lug isgrounded to the number one pin of thebase on those tubes in which it is used asan expedient in maintaining the capaci-tances of the pins and leads at a minimum.The metal tube shown has, in addition, asmall conical shaped shield which fitsinto the top of the exhaust tube abovethe header which is also grounded to theNo. 1 pin of the base. The metal base ofthe lock -in tube serves the same purposeas these various shields required in theother types of bases.

LEAD LENGTHS OFTEN IMPORTANTThe overall length of the leads from

the socket contact points on the pins tothe element within the tube to which it isconnected has been materially reduced

in all of the newer types of tubes, especial-ly the lock -in construction. Before theintroduction of multiple -band receiversthis lead length was probably not of toogreat importance. As higher and higherfrequencies were utilized it was essentialto reduce the capacity between leads toas small a value as possible. This wasaccomplished by two methods; reducingthe length of each lead to a minimum andseparating the leads as far as possible.The GT type of structure has consider-ably shorter leads than the G type.However, the leads through the pressstill have approximately the same physi-cal relation to each other. The chancesfor leakage across the top of the press dueto getter deposit are about the same forboth of these constructions. In the metaltube the length of the leads is considerablyshorter than for the GT tube. Anotheradvantage that has been gained is thearrangement of the pins through theheader. The leads are sealed in theheader at points which are more advan-

nector is required from the pin to theelement within the tube. The spacingbetween the pin seals is considerablygreater than is possible in the otherconstructions shown as the seals are madenear the outside of the header.

INSULATION PROBLEMSThe spaghetti which can be seen cover-

ing certain lead wires on the G and GTtubes is not required on all the leads andin some tubes none is required. This isonly used to prevent short circuits be-tween leads that must cross other leadsin the space between the seal and the baseor where a lead may come close to agrounded element such as the centershield in the GT tube. Spaghetti that isused on such leads must have low dielec-tric loss, especially under high humidityconditions. If poor grades of spaghettiare used the impedance of the input oroutput circuits or the conductance of thetube may be appreciably lowered depend-ing on which leads have spaghetti and

Cathode

Control Grid

Screen Grid

Suppressor Grid

Plate

Shield

Bulb

Base

Scale-App. 2:1

Enlarged Top View of Lock -In R -F Amplifier Pentode

tageous from the standpoint of the basingof that tube. Crossing over of the leadsin the base of the tube is not required.The lock -in tube structure has theshortest length of lead from socket con-tact point to tube element of the fourtubes shown in the picture. The lengthof lead for the other three types must beconsidered from the contact point on thepin which varies with the type of socketused to the end of the pin where the lead-in wire proper is soldered to the pin andfrom there back up through the headerto the tube element. The length of leadfor the lock -in structure extends from thesocket contact point on the pin which isapproximately half way up that part ofthe pin outside of the seal, directly to thetube elements. In some cases no con -

with what element they are in contact.Tubes that can be made without employ-ing any spaghetti have this advantagein common.

SOLDERED AND WELDED CONNECTIONS

Several of the base pins in the abovepicture are cut to show how the lead-inwire is soldered at the end of the pin.When the sealed -off tube is assembled tothe base the lead wires are threadedthrough the body of the pins and extendout through small holes in the ends of thepins. These wires are then cut off evenwith the end of the pin and soldered. Asmall amount of solder enters inside theend of the pin to form the contact betweenthe lead ánd the pin. Every effort is made

(Continued on next page)

SYLVANIA NEWS

FOUR SYLVANIA TWIN -TRIODE AMPLIFIERS CHARACTERISTICSAND USES

Sylvania Types 6SL7GT, 12SL7GT,6SN7GT and 12SN7GT are voltageamplifier tubes consisting of two triodesections in one bulb.

Type 6SL7GT and 12SL7GT are thesame except for heater rating and thecharacteristics are identical to SylvaniaLock -In Types 7F7 and 14F7 tubesexcept for interelectrode capacitances. Thecircuit applications for both of these types

Physical Characteristics

8 -BD

Style GTBase Intermediate Shell,

Octal 8 -PinBulb T-9Diameter 1,4"Overall Length 3,4"Seated Height 2k"Mounting Position AnyRMA Basing 811D-0-0

Base Pin ConnectionsPln 1 Grid Triode 2Pin 2 Plate Triode 2Pin 3 Cathode Triode 2I'in 4 Grid Triode 1Pin 5 Plate Triode 1Pin 6 Cathode Triode IPin 7 HeaterPin 8 Heater

are the same as those given for Type 7F7in the Sylvania tube manual.

Types 6SN7GT and 12SN7GT are thesame except for heater rating and thecharacteristics are identical to SylvaniaLock -In Types 7N7 and 14N7 tubes. Thecircuit applications for these two types arethe same as for Type 6F8G as given inthe Sylvania tube manual.

SYLVANIA TYPES 6SL7GT AND 12SL7GTTwin Triode Amplifiers

RATINGS6SL7GT 12SL7GT

Heater Voltage (AC or DC) 6.3 12.6 VoltsHeater Current 0.3 0.6 AmpereMaximum Plate Volts 250 250 VoltsMaximum Plate Dissipation

(Per Plate) 1 1 WattMinimum Grid Volts 0 0 VoltsInterelectrode Capacitances:*

Triode 1 Triode 2Grid to Plate 2.8 2.8 µµf.Grid to Cathode 3.0 3.4 µµf.Plate to Cathode 3.8 3.2 µµf.Plate to Plate 0.4 0.4 µµf.Grid to Grid 0.65 0.65 µµf.Grid T2 to Plate TI 0.13 0.13 µµf.*With close htting shield connected to cathode.

Operating Conditions & CharacteristicsAmplifier (Class Al) Each Triode

Plate Voltage 250 VoltsGrid Voltage -2.0 VoltsAmplification Factor 70Plate Resistance 44,000 OhmsMutual Conductance 1600 pmhosPla teCurrent 2.3 Ma.

SYLVANIA TYPES 6SN7GT AND 12SN7GTTwin Triode Amplifiers

RATINGS6SN7GT 12SN7GT

Heater Voltage (AC or DC) 6.3 12.6 VoltsHeater Current 0.6 0.3 AmpereMaximum Plate Voltage 300 300 VoltsMaximum Plate Dissipation 2.5 2.5 WattsMinimum Grid Voltage 0 0 VoltsInterelectrode Capacitances:*

Triode 1 Triode 2Grid to Plate 4.0 4.0 µµf.

Grid to Cathode 3.2 3.8 µµt.Plate to Cathode 3.4 2.6 µµf.Plate to Plate 0.5 0.5 µµf.Grid to Grid 0.034 0.034 µµt.Grid T2 to Plate TI 0.12 0.12 µµf.*With close fitting shield connected to cathode.

Operating Conditions & CharacteristicsAmplifier (Class Al) Each Triode

Plate VoltageGrid VoltageAmplification FactorPlate ResistanceMutual ConductancePlate CurrentMaximum Grid Circuit

Resistance

900

2069003000

10

250 Volts-8.0 Volts

207700 Ohms2600 µmhos

9 Ma.

1 Megohm

Resistance Coupled Amplifier -Each TriodePlate Supply Voltage 90 180 300 VoltsPlate Resistor 0.1 0.1 0.1 MegohmGrid Resistor (For

Following Stage) 0.25 0.25 0.25 MegohmCathode Resistor 3940 2830 2400 OhmsVoltage Output* 17 34 56 Peak VoltsVoltage Gain** 13 14 14*Maximum voltage for start of grid current for following

stage.**For r -m -s output of 5 volts.

VACUUM TUBE FEATURES(Continued)

to have a minimum of solder on theoutside of the pin above the rounded end,as the presence of this soft metal on thestraight side of the polished nickel pinsmay greatly increase the amount ofpressure required to insert a tube in asocket. The majority of sockets havecontacts which cut into any such softmetal extending beyond the normaldiameter of the pin and scrape this metaloff when the tube is inserted in the socket.

There are no soldered connections tothe base pins used in the lock -in tubé.The contacts of the lock -in socket beardirectly upon the pins of this tube whichare also the leads that are sealed into theheader. These pins may be weldeddirectly to the tube element inside of thetube or short jumpers are welded at thepin and tube element to provide the re-quired connection.

Basing cement is employed to securethe evacuated envelope to the tube baseof the structures shown in all stylesexcept the metal tube. This cementrequires baking before it makes a goodadhesive bond to the base and glassenvelope. The lower part of the GTenvelope and the lock -in envelope areshaped in such a manner as to make abetter bond than the G type of envelopesince the bulbs fit the bases much tighterand less cement is required between theenvelope and base. These bulbs are alsoseated much lower in the bases so the

leverage between the glass envelope andbase is reduced and the chance of thecement becoming loose when tubes areinserted or removed from sockets islikewise reduced.

SINGLE ENDED CONSTRUCTION

The shortening of the leads in the baseof the tubes, as described earlier, con-tributed largely to the possibility ofmaking single ended tubes. With thecoupling between plate and grid leadsreduced to a minimum it was feasible toremove the top cap and connect the gridto a base pin. By eliminating the top caprequirement special sealing, cementingand soldering processes were done awaywith in the manufacture of such tubes.

External shielding is seldom requiredon any of the later types of tubes madewith the shorter mount structures. Themetal tube requires no shielding. The GTtube requires external shielding on someoccasions and for a very few applicationsthe lock -in tube may require shielding.All of the tube types of GT or lock -instructure which are intended for use incritical circuits where external shieldingwould normally be required have internalshields within the tube surrounding theplate. The only other parts of the tubethat might need shielding are the leadsbetween the base pins and the tubeelements. The metal shell of the basefor GT tubes which might be used for r -f,i -f and converter applications is usuallysufficient to shield these leads. Wherebakelite bases have been employed anexternal shield may sometimes be required

and if so a grounding clamp must be used.If shields are required with metal shellbases the shields are grounded throughthe base shell which is connected to thenumber one pin of the base. The lock -intubes designed for these critical applica-tions also employ a metal internal shieldwhich is brought out to a separate pin ormay be connected internally to anotherelement which is effectively at groundpotential under normal conditions. Inaddition, the metal base with its guidepin serves as an effective shield. Numer-ous types are especially suitable for usein UHF applications because of low leadinductances, low inter -electrode capaci-tances, and low dielectric losses.

As a further aid in visualizing thephysical relation of tube parts a differentview of the lock -in structure is shownon page 2. The glass dome has been cutoff and the top mica removed to exposethe various elements given in the tabula-tion. Comparison with the previousphotograph will enable óne to study theindividual details of element arrangement.

Many of the factors mentioned in thisdiscussion must be carefully consideredby the tube designer and manufacturer inorder to produce tubes that, at leastelectrically, will be interchangeable withsimilar types having different physicalspecifications. As an aid to servicemen,dealers, and users of tubes, Sylvania hasprovided numerous technical bulletinsand articles relating to tube characteris-tics and suggestions regarding the use ofsubstitute types.

SYLVANIA NEWS



Philco Model 37-675. To completelyeliminate 120 cycle hum in these sets,replace the 8 mfd. filter, diagram 125,with a 16 mfd. suitable condenser 450volts. In these same models to suppressa bad case of oscillation, replace bypasscondenser #79 (0.05) with a 0.5 µf tubularcondenser.-Fred Wolfenberger, Monroe,Michigan. - * #

War -Time Volume Control Repair.Remove switch which is on the back ofalmost all controls. It is not alwaysnecessary to unsolder leads. Now go overthe resistance strip with a common leadpencil from one end to the other full widthusing judgment as to the amount of mark-ing you do as a high resistance controlwill require less than a low resistance one.Now put about a drop of oil on a toothpick and shake off excess and wipe overthe marking you did, with tooth pick.Now work the control several times 'andit is ready to reassemble. This hassmoothed up all the controls the writerhas tried it on except wire wound ones. Ihave worked hundreds this way and theyseem as good as could be asked for.-Ralph O. 11'lillican, Lewisville, Texas.

General Electric Model H-500. I havehad the complaint of hum on several ofthese sets and have found that by solder-ing the metal can of filter condensersdirectly to the chassis that all humdisappears.-Emery Hazzard, Fort Ed-ward, N. Y. #

A Substitute for Adaptors. Here is ahint of a short cut in changing sub-stitution tubes. In changing to a Lock -intype for an octal type, my suggestion isthis: Cut the contact pins off of the oldtube. Crimp each pin at the top, andslip onto the pins of the Lock -in tube.You will find that the tube will fit intothe octal socket. Pins must be cut fromold tube with hack saw. Then changeyour circuit to fit substitution tube used.Servicemen will find that this procedurewill save fifty percent of time and alsohard to get sockets. Try it.-J. D.Walker, Jr., Comanche, Texas.

Editor's Note: An appropriate mark onLock -In tube base and socket should be madelo insure correct insertion of ¡Ube sincelocating lug will not engage keyway.Customer should be advised not to removetube without proper instruction.

Lock -In Adaptor Aids Substitution.Not being able to obtain any 12SK7tubes I took the base of one and wired alock -in socket on the top to use a14A7/12B7. A little realignment was allthat was needed to make the set operateperfectly, this being due to the increasedcapacity from the leads inside theadapter. I understand that 14A7 tubesare not on the WPB list, but myjobbers seem to have a fair stock yet, anddoubtless others over the country alsohave some.

The above mentioned tube substitutioncould be made by changing sockets in thechassis, but I believe the adapter solvesthe problem with less work. I havefound that usually changing a socket is a"major operation," mainly on account ofsockets being buried under so many otherparts.-John L. Cooper, Purvis, Miss.

* * *Tube Substitution. Type 1N6G will

replace the hard to find 1A5G. Thecharacteristics are the same with theexception of a diode plate on the #6 pinof the 1N6G. This is a blank pin on the1A5G. You can clip the #6 pin off the1N6G and you have a 1A5G, no changesor adjustments to make.-Lyle C. Mot-ley, Danville, Va.

* *

Substitute Dial Belt. I have used thefollowing idea for dial belts that werehard to get. Get some adhesive tape inthe %" size, cut to the desired length,then lap it over in the middle so that thesticky sides are on the inside. Sew thetwo ends together and there you have adouble -ply dial belt. Trim with a pair ofscissors to suit the pulley width. I haveused this a number of times with success.-George Motto, Wilkinsburg, Pa.

* * *

Crosley Model 52TE-U, Chassis #U-77.Complaint was hum which could not be

traced to filter trouble. I found the dialplate, (upon which - was mounted thepilot lamp), touching drive pulley ontuning condenser. The tuning condenseris above ground on this model, thus thedial plate which is at ground potentialcaused hum from pilot lamp when ittouched the tuning condenser.-A. S.

Wright, Tampa, Fla.

a.......--¡--

General Instrument 201, 202, 203.Rubber drive -wheel 65-70715 sometimesfails to run main -cam and gear 43-70517far enough to complete the cycle. Whenput into playing position and the turn-table rotated by hand, it was seen thatthe trip -lever pin (27) was actuated bythe automatic trip -cam (12) withoutresulting in disengagement of the rubberdrive -wheel train from the turntable.The rubber wheel was thus rotatedagainst the teeth of the now stationaryintermediate -drive gear, chewing off therubber. The trouble was traced to thecarrier -lever assembly (55-70722) bear-ings. The bearing hole is not round, butpurposely machined oval, apparently inorder to permit the drive -train pulley tomaintain full contact with the inner sur-face of turntable even though the latterdeparts from true vertical plane. Somechangers seem to have an over -generousamount of such ovalling, and the tripaction is absorbed by the play at thisbearing, leaving the pulley in contact withthe turntable. 'There are no adjustmentsto correct this, so the bearing hub wasremoved and a new one turned up in thelathe. The bearing hole was made by a#18 drill while the hub was still in lathe.The new hub, when mounted in thecarrier -lever, had enough play to assurefull pulley contact, but gave positive andprompt disengagement from the turn-table.

On this same changer, the record feed -spring 33-70754 seemed to have con-siderably more tension than required.This put a load on the small rubber drive -wheel. To overcome this, the,.end loopsof the spring were partially opened up,giving a fish-hook shape to them andresulting in an overall increase in springlength of %" or so. (Don't ever reducespring tensions by stretching the springout.) The turntable was then loaded tocapacity with twelve -inch records to makesure, the feed -spring could still push outthe bottom record. ---1V. S. Arns, Ken-more, N. Y.

*

Material Conservation. To conservesolvent in removing speaker cones applyto cone, inside, and outside if possible,then place entire speaker in box or tin,with cover. This permits deeper penetra-tion with less evaporation.-Frank Gause,Eustis, Florida.

voltage regulator tubes...tubes found ok, and upon examination and checking for voltage it also was...

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