he first and only national radio weekly new screen grid six! · 2019-07-17 · duo tone brown; it...

AUG. 181928

FIFTEEN

CENTS

REG. U.S.PAT. OFF

he First and Only National Radio Weekly334th Consecutive Issue-Seventh Year

New Curves RevealScreen Grid Mysteries

Two B EliminatorsAdvised for Each Set

Rating in HorsepowerProposed for Stations

NEW SCREEN GRID SIX!

DETECTOR

LOUD SPEAKER

ii 11 III

).....

31.12R.F: 2t1P. R.F: ISTR.F 2.t2A.F.AMP. 15.IA.EAMP ANTENNA,AMPLIFIER AMPLIFIER AMPLIFIER BROAD

ANTENNA,SELECTIVE

GROUND

Here is a receiver remarkable in its appeal to eye, ear and purse-the new S -M Shielded Grid Six, No. 720,designed by McMurdo Silver. See article on pages 3, 4 and 5.

STATIONS SYNCHRONIZE SUCCESSFULLY

ARE CHAIN PROGRAMS A NUISANCE?

RADIO WORLD August 18, 1928

IN four short years Silver -Marshall, Inc. has forged upfrom obscurity to the position of dominant leadershipin the radio parts and kit field-interesting, you say,

but just what does that mean to you?S -M leadership means just one thing-better radio for

less money. Ask any one of the thousands of listeners andexperimenters who have used and recommended S -M into supremacy.

They'll all tell you that S -M leadership means better radio at less cost.And S -M will lead again in 1928 and 1929 by giving you new develop.ments that enable made-to-order or home -built radio sets to equal inexternal finish the finest factory productions, parts that place theperformance of such sets utterly beyond competition, and, thru

knock -down kits, radio receivers that will consistently outperformall ready-made sets at anywhere near their amazingly low prices.

New S -M Offerings Now ReadyNever has there been a design which so perfectly fulfills the re-

quirements of the setbuilder as does the new Silver -Marshall 720Screen Grid Six-successor to the famous Shielded Grid Six of such un-paralleled popularity during early 1928. The 720 Screen Grid Six is asix -tube dual control screen grid receiver using three screen grid tubesin individually copper -shielded r. f. stages and two audio stages with themarvelous new S -M transformers-a set absolutely unequalled at the price.On a summer evening test in Chicago, 41 stations (two on West Coast)were logged, 5 of which (in N. Y., N. J., Fla., Ga., and La. respectively)were on adjacent channels (only 10 kc. apart) to locals then on the air.The 720 Kit, complete without cabinet, is priced at $72.50. Custom-builtcomplete in cabinet as illustrated, it costs $102.00.

And at $51.00 S -M offers the '740 "Coast to Coast" Screen Grid Four-a kit that is a revelation in four -tube results. Type 700 metal shieldingcabinet,as illustrated .is but $9.25 additional, for either set, finished induo tone brown; it marks a new standard of style and distinction.., The Sargent-Rayment Screen Grid Seven, type 710, is the wonder setof the season, and S -M offers, exclusively, the approved kit at $120.00.It is complete with aluminum shielding, cabinet and will bring in 100stations on any average evening.

tThe S -M "Round the World" Short Wave sets are the trimmest, mostefficient short wave sets yet, priced from $36.00 to $51.00 complete withshielding cabinet. New S -M condensers Are marvels of rigidity and flex-ibility in Universal single, and triple types. The 685 Public AddressUnipac-the first really high-powered amplifier yet offered-is pricedat only $160 wired, or $125 for the kit. It will turn out music or voice thatcan be heard by 1000 to 10,000 people. Other Unipacs and Power Suppliestake care of every power need.

Of course, the most startling audio development of the last two yearswould logically come from S -M laboratories, as it did two years ago. Thenew Clough audio transformers were deservedly the sensation of theJune radio trade show. In open comparative tests, S -M 255 and 256 ($6.00transformers) have excelled the performance of all competitive types tested,regardless of cost. The 225 and 226 transformers at $9.00each simply leave the most skeptical marveling.r R - - - - my lo - - - llom owi - mil °""°' 1 These and many other startling new S -M parts leave111 Silver -Marshall, Inc. I small wonder at S -M leadership. They prove that you canI 878 W. Jackson Blvd., Chicago, U. S. A. I get the best radio for the least cost from S -M.i Please send me, free of charge, thei complete S -M Catalog.fl:rg:enclosed in stamps, send me the

M. 0) Next 25 issues of THE RADIOBUILDER

SM SM LEADERSHIP

maTgehler adj0SM

No. Salt Tr.a.ft,nncrs1.4 1 011.1(1311 A mr!i Pcrf,tru.

111111111111111111.11111111111111111111

Are you receiv-ing "The Radiobuilder"

regularly? Published everymonth, this little magazineprovides you with the earliestinformation on forthcomingS -M developments and withoperating hints and kinks thatwill help you to get the mostout of radio.

You can't afford to be with-out "The Radiobuilder," forbesides general news of in-terest to every setbuilder itgives advance notice and pre-views c.f new products anddetailedconstructional andoperating data on new appa-ratus before the informationappears in the S -M DATASHEETS.

To S -M Authorized ServiceStations, "The Radiobuilder"is mailed each month, free ofcharge, together with all newData Sheets and Service Bul-letins as they come from press.To all others a nominal chargeis made; see coupon.

If you want to keep abreastof the very newest and mostpractical in radio building de-velopments, be sure to mailthe coupon today.

I ....75Tcd Next 12 issues of THE RADIOBUILDER

S -M DATA SHEETS as follows, at 2c,each:I ....No. 1. 670B, 670ABC Reservoir Power Units....No. 2. 685 Public Address Unipac....No. 3. 730. 731, 732 "Round -the -World" Short

Wave Sets....No. 4. 223, 225, 226, 255, 256, 251 Audio Trans-

formersI ....No. 5. 720 Screen Grid Six Receiver. No. 6. 740 "Coast -to -Coast" Screen Grid Four.. j\lo. 7. 675ABC Power Supply and 676 Dynamic Speaker Amplifier

Instruction. (500 Sargent-Rayment BookletName

AddressNO us

If you don't wish to build, yet want your radio to becustom-made, with all the advantages that this implies,a S -M will gladly refer your inquiry to an AuthorizedS Silver -Marshall Service Station near you. If, on the other

hand, you build sets professionally, and are inter-ested in learning whether there are valuable Service Sta-ll tion franchises yet open in your territory, please writeus.

SILVER -MARSHALL, Inc.878 W. Jackson Blvd., Chicago, U. S. A.

AUGUST 18, 1928Vol. XIII, No: 22 Whose No. 334

15c Per Copy[Entered as second-class matter, March1922, at the post office at New York,

N. Y., under Act of March, 1879.]

"UNINTERRUPTED READER INTERESEVERY WEEK `--1 EVERY YEAR

Technical Accuracy Second to None A Weekly Paper published by HennessyRadio Publications Corporation, fromPublication Office, 145 West 45th Street,

New York, N. Y.(Just East of Broadway)

Phone: BRYant 0558 and 0559

McMurdo Silver's LatestA REMARKABLE AND SENSITIVE DEVELOPMENT

The 720 Screen Grid SixBy McMurdo SilverHead of Silver -Marshall, Inc.

AI -C Af +45To ISO C -3SLACK- BLACK SLACK- BROWNGREEN PED

+135 C.A.PMAROON GOLD+

60010

TO CACKE CV)

FIG. ITHE SCHEMATIC DIAGRAM OF THE SM-720 SCREEN GRID SIX, McMURDO SILVER'S LATEST CIRCUIT, PUB-LISHED HEREWITH FOR THE FIRST TIME. THE PARTS ARE CODED AND THE SAME CODE REFERENCEOBTAINS IN THE LIST OF PARTS. NEXT WEEK THE PICTURE LAYOUT WILL BE PUBLISHED WITH THE

SAME CODE REFERENCES.

[Presented herewith for the first time is thenew S -M 720, a screen grid, shielded sixtube tuned radio frequency receiver, de-signed by McMurdo Silver, of Silver -Mar-shall, and constituting one of the most ex-ceptional designs to emanate from the bril-liant scientific mind. of this design -master.The circuit uses three TRF stages of screengrid amplification, a detector tube and twostages of Clough auto -transformer coupling,with options as to which power tube to useas output. Selectivity of from 10 to 15 kc.is provided, tuned stages are individuallycopper -shielded, two tuning dials (plus aselectivity booster in one optional form ofantenna coupling) and a potentiometer inthe first ouclio for volume control, areused. The complete kit is available in fac-tory -sealed cartons, list price $72.55. Type700 shielding cabinet, $9.25 list price extra.Total of both $81.80 list price.-EnrroR.]

PART IARECEIVER of such low cost, com-

pared with the results obtained, asto intrigue every one interested in theconstruction of a superb radio receiver isthe new Screen Grid Six. Why the re-ceiver is outstanding I shall relate, withspecial and detailed emphasis on the qual-

ity and degree of amplification, at bothradio frequency and audio frequencylevels.

So that first you will have a brief wordpicture of the receiver, the followingepitome is offered z

There are three high -gain radio fre-quency stages, using screen grid tubes, adetector tube stage and two steps ofClough transformer -coupled audio. Thereare four tuned circuits, the first, or input

FIG. 2The front view of the completed re-

ceiver, in a type 700 shielding cabinet.Antenna tuner knob is at left, RF tunerknob at right, selectivity booster for DXat lower left, volume control at lowerright.

circuit, being separately tuned, and theremaining three jointly tuned.

The results obtained are 10 to 15 kc.selectivity, a quite regular reception rangeof 2,000 miles, by proven demonstrations,a closer approach to realism than hithertoobtained, and the stability of operationdue largely to the individually copper -shielding of the tuned stages.

Fine Eye AppealAdd to these points a standardized as-

sembly cautiously designed to present themost attractive appearance, and you havethe situation in a nutshell.

But let us crack open the shell with theclenching curiosity with which all of usconcerned with radio as a life work, sideline or pastime are endowed.

From a mere examination of the circuitdiagram and photographs the Screen GridSix may not strike any one as unusual,although at this writing there is no knownready-made set incorporating the full ad-vantages of screen grid RF amplification.

If there is anything at all unusual aboutthe set, it is the fact that the three RFtubes have been made to average about250 times the amplification obtained fromthis same number of tubes in an ordi-

(Continued on next page)

4 RADIO WORLD August 18, 1928

41 StationsHeard LoudlyOn Hot Night

The S -M 720 Screen Grid, Six wasoperated one warm June evening in atypical residential section a few milesfrom Chicago's twenty -odd stations. A35 -foot antenna was all that was used.Distant stations gave practically local vol-utile. Here is a list of the 41 stationstuned in, with location, right-hand dialsetting (left one may vary a trifle) andfrequency in kilocycles :

RightStation Location Dial Kc.WNBA Forest Park III 1 1440KSTP St. Paul, Min. 4 1360WJKS Gary, Ind. 6 1290WGES Chicago 8 1240WOK Chicago 12 1190QJAZ Chicago 19 1140WTAS Elgin, Ill. 18.5 1090WENR Chicago 23 1040WTMJ Milwaukee 24 1020KMOX St. Louis, Mo. 26 1000WHT Chicago 28.5 980KDKA Pittsburgh 31.5 950KFAB Lincoln, Nebr. 32.5 940KOA Denver, Colo. 34.5 920KFQB Ft. Worth, Tex. 36 900WSM Nashville, Tenn. 37 890WLS Chicago 32 870WEBH Chicago 47 820WDAF Kansas City 47.5 810WOC Davenport 50 800WGY Schenectady 51 790WBBM Chicago 54 770KWKH Shreveport, La. 55 760WTAM Cleveland - 57 750WCCO Minneapolis 59.5 740WGN Chicago 62 720WOR Newark, N. J. 63.5 710WLW Cincinnati 65 700WJ Chicago 71 670WJQZ New York 73 650KRLD Dallas, Texas 75 650KFI Los Angeles 77 640WSB Atlanta, Ga. 79 630WCFL Chicago 82 620WEAF New York 84.5 610KTHS Hot Springs 86.5 600WOW Omaha, Nebr. 89 590WFLA Clear Water, Fla. 92 580KYW Chicago 95 570WHO Des Moines 98 560KSD St. Louis, Mo. 100 550

[Both dials tracked very closely, but theinput tuning circuit may be a little "off" insome instances, due to different fundamentalwavelengths of antennas used. Since thillog was compiled a much larger number ofstations was tuned in at the same location.]

ol

10

60

So

2,000 -Mileand 10 to 15 kc. S

Outstanding Features of Silver'sLatest Circuit

The predominating features of the new S -M 720, the extraordinary six -tubereceiver designed by McMurdo Silver, follow:

10 to 15 kilocycle selectivity.Regular receiving range, 2,000 miles.Realistic reproduction, due to the new Clough auto -transformers.Moderate cost of factory -sealed kit.Three stages of screen grid RF, each stage individually copper -shielded.

40 to 100 stations a night on a 30 -foot ntenna, a station for almost everydegree of the dial.

New low -resistance, almost ideal RF coils.Stability of operation.Versatility, of power tube choice.

(Continued from preceding page)nary set, while the audio gain has beenabout doubled.

How this is done is quite easily seen bytaking as a typical example a representa-tive ready-made six -tube set costing about$150.00. In this common type of set thefirst RF tube has its grid circuit connectedacross a small RF choke directly in theantenna circuit, across which is developedthe signal voltage.

Other Set Not Much GoodThis type of coupling gives no voltage

step-up between antenna and first RFtube, and does not contribute in any wayto selectivity.

The first tube, with the TRF trans-former that follows it, in such a factory -made set, shows an average amplificationof less than 10 times between 200 and550 meters. This figure is quite generous.Two additional RF tubes, with two moreTRF transformers, give a gain of 10 pereach stage. Thus, 10x 10 x 10=1,000,shows the amplification between antennaand detector grid circuit in the factory -made set.

Following the detector are the audiotubes, a UX201A and a UX112A, havingmus of about eight, operating with trans-

Nom.

A

AAA

I t -.. 4t I, ,t

FIG. 3 FIG. 4

V.

formers, which, while. deficient on baseamplification, show an average ratio of1 -to -3. Thus, the AF gain is 3x8x3x8-=576, though from a sensitivity angle onlythe RF gain need be considered.

Now, compare the results. For theScreen Grid Six a tuned antenna inputcircuit was designed having the very bestpossible characteristics which could beattained in practice. This circuit consistedin final form of a very low resistance coilhaving 39 turns of No. 20 enameled wireupon a threaded bakelite form 4 incheslong and 2g inches in diameter.

Coil Well DesignedThe values of 3.3 ohms RF resistance at

550 meters and 11.5 ohms at 200 meters,obtained upon this coil tuned by a .00035mfd. condenser, represent an unusuallygood circuit.

The coil itself has a "figure of merit"practically double that of the best com-mercial coils found on the open market.

This input coil, Ll, is tuned by a singlecondenser, Cl, activated by the left-handdrum, Dl. A representative antenna of400 mmfd. capacity, 25 ohms resistanceand 28 micro -henries inductance wascoupled to the input coil through an op-tional small primary coil of 20 turns, or a

1 t

FIG. 5Fig. 3-Curve A shows the voltage step-up of the tuned a ntenna input. Curve B shows an untuned antenna input. CurveC is the measured voltage amplification of one individual stage.Fig. 4-Curve D is the over-all voltage amplification of t he three tuned stages following (but not including) the antenna

stage. E, F and G are the selectivity curves of the three in dividual stages ending with the detector.Fig. 5-Curve H represents the actual performance of the radio frequency channel of the receiver.

the flattening effect of the volume control on the high frequ ency amplification use. The abrupt rise is a vice as it bringsinstability or kills signals entirely, so curve H represents a distinct practical 'gain over curve J.The dotted line shows

August 18, 1928 RADIO WORLD

)teady Range Follows CodeList of Parts

tectivity Attained of Identity

large primary of 60 turns in series with a75 mmfd. junior condenser, C5, which wasused to regulate selectivity.

What the Curves ShowCurve A of Fig. 3 shows that the volt-

age step-up provided by this tuned an-tenna input circuit varies from 64 at 200meters (1,500 kc.) to 28 at the middle ofthe broadcast 'band and rises to 100 timesat 550 meters. As 550 meters is wherethe greatest step-up is always needed, forthe amplification of any practical RF am-plifier always falls off at high waves, aswill be shown, this reversed characteristicflattens the general amplification curveby the gain method.

The shape of the first stage curve isnot wholly ideal, but there is certainlyno comparison between the voltage am-plification that can be had from this cir-cuit with its one additional tuning dial,as compared to curve B of Fig. 3. (CurveB, representing the voltage amplificationof good =tuned antenna coupling choke,is hardly distinguishable from the baseline of the curve of Fig. 3!)

The dip in the center of curve A shiftswith different size antennas and may fur-ther be shifted by adjustments of themidget antenna coupling condenser, C5,so that it is seldom necessary to operatethe receiver with as low a voltage step-upin the antenna coupler as is shown by thelower bend of curve A.

This dip is shown as it would be werecondenser, C5, left untouched in tuningthroughout the broadcast band, which is,obviously, not an obligatory condition.

Three Circuits IdenticalThe antenna input circuit is followed by

three identical tuned circuits, each housedin individual copper shielding cans SH1,SH2, SH3. These circuits employ smallplug-in inductances L2, L3, L4, the sec-ondaries of which consist of 981A turnsof No. 29 enameled wire wound upon athreaded moulded bakelite form 1% inchesin diameter and 1Y2 inches long. Two ofthese tuned circuits feed the two remain-ing screen grid amplifier tubes, S5 and S6,while the third circuit feeds the detectortube S9.

The actual measured voltage amplifica-tion of one individual stage is shown inCurve C, Fig. 3, and is seen to vary from14 per stage at 550 meters to 30 at 200meters.

While this amplification may seem verylow for a screen grid RF amplifier stage,it must be borne in mind that the highamplification that may be obtained fromthem in practice -the maximum voltagegain which can be had from these tubesin the broadcast band with practical cir-cuits -will vary between 30 and 65 perstage, and that in order to obtain suchamplification selectivity must be sacrificed.

In the Screen Grid Six, this sacrificepurposely has not been made. The effec-tive amplification of the three shielded RFamplifier stages has been purposely heldso that selectivity would be high.

Antenna CapitalizedThe over-all voltage amplification of

the three screen grid stages, neglectingthe antenna coupler, is shown by CurveD of Fig. 4, and will be seen to vary from2,500 times at 550 meters to to 15,500times at 200 meters (Curve D is simply

Wiring EasyBy Blueprint

The wiring of the S -M Shielded GridSix, the new receiver developed by Mc-Murdo Silver, head of Silver -Marshall,Inc., is made easy indeed by followingthe official blueprint, with its clear, ex-plicit exposition of every part, lead,wire and connection, and revealing thesimplest, most attractive method of doingthe wiring.

Besides the great help of the blueprint-which of itself is a fund of informationon the circuit -there is an official eight -page instruction booklet on the buildingof this most remarkable receiver. Inaddition to this there is a clear, largeschematic wiring diagram.

Therefore anybody who wants to buildthis set may do so by following theblueprint, and of course it is a goodplan to read the fascinating construc-tional details so carefully set forth in thebooklet, as well as consulting the bigschematic diagram to round out to ex-treme fullness one's knowledge of thetheory and construction of this circuit.

the cube of Curve C of Fig. 3). It would,of course, be ideal if Curve D could bemade flat, but, unfortunately, in a prac-tically stable RF amplifier, this cannotbe accomplished sufficiently effectively tojustify the complications the effort wouldintroduce.

The few means which have been de-vised for flattening out the curve havenot been wholly successful, to judge fromthe popular desuetude into which theyhave fallen.

In the Screen Grid Six advantage istaken of characteristics of the antennacircuit in a unique way to flatten out gain-fully the over-all amplification curve.

Note the relative selectivity of thethree -stage RF amplifier unaided by theantenna circuit (which contributes a veryhigh degree of selectivity in itself.)

Three measured selectivity curves forthe three tuned circuits shielded in thesmall copper cans is shown by Curves E,F and G of Fig. 4, and it will be seenthat they are in themselves ample to pro-vide 10 kc. selectivity.

The addition of the selectivity providedby the antenna input circuit tends tosharpen up the "skirts" of Curves E, Fand G, and result in a more rectangularcurve, which, in turn, results in a clean"chop -off" of unwanted signals more than10 to 15 kc. off resonance.

In Fig. 5, Curve H, is shown the cal-culated RF amplification from antenna todetector grid for the Screen Grid Six.

This amplification was calculated be-cause of the practically impossible task ofmeasuring the over-all gain of such a sen-sitive receiver.

The curve is based upon the actualmeasured amplification for individual am-plifier stages, and corresponds to Curve Dmultiplied by Curve A.

As regeneration is not seriously pres-(Continued on page 18)

The number of items is at left, the codenumbers as shown in the diagram come next,then the description, and finally the list price.

1-B1-E1-D1

1-D2

1-Cl

1 -C2 -C3 -C4

1-05

3-S H1 -S H-2SH3

1-LI

3 -L2 -L3 -L4

3 -S1 -S2 -S3

5 -S4 -S5 -S6 -S7 -S8

1-T1

1-T2

1-w

1-R1

1 -SW

2 -J1 -J2

3 -R2 -R3 -R4

1-R6

1-R5

1-C6

6 -C7 -C8 -C9 -C10 -C11 -C12

1-C13

1-C14

1-R7

1-R8

1-S9

3-BP1-BP2-BP3

_

-S-M 701 Universalpierced chassis $3.00

-S-M 809 dual con-trol escutcheon 2.75

-S-M 806L (left) ver-nier drum dial 2.50

-S-M 806R (right)vernier drum dial 2.50

-S-M 320R .00035 mfd.Universal condenser 4.00

-S-M 323 .00035 mfd3 -gang condenser 13.50

-S-M 342B .000075mfd. midget cond 1.75

-S-M 638 copperstage shields @ $1.50

---3-M 140 antennacoil

-3-M 132A plug-inRF transformers @$1.25

-S-M 512 5 -prongtube sockets @ $0.60

4.50

3.00

3.75

1.80

-S-M 511 tube sock-ets @ $0.50 2.50

-S-M 255 first stageAF transformers 6.00

-S-M 256 2nd stageAF transformer 6.00

-S-M. 708 10 -lead, 5 -ft. connection cable 1.75

-S-M 818 hook-upwire (25 ft. to car-ton) .50

-Yaxley 53000-P 3,000ohm junior poten-tiometer . 1.25

-Yaxley 500 switchattachment .40

-Yaxley 420 insulatedtipjacks @ $0.125 .25

-Carter RU10, 10ohm resistors @$0.25 ., .75

-Carter AP -6, 6 ohmsub -base rheostat.. .50

-Carter H11/2, 11/2ohm resistor .25

-Potter No. 4 type, 1mfd. bypass cond 1.00

-Sprague or Polymetmfd. midget con-

densers @ $0.75 4.50-Polymet .00015 mfd

grid condensers withclips .50

-Polymet .002 mfdbypass condenser .40

-Polymet 2 megohmgrid leak .50

-Durham .15 meg-ohm resistor withleads .50

-Naald 481XS cush-ioned tube socket. .65

-Moulded bindingposts consisting of8/32 screw, nut, andmoulded top @

$0.10 .30-Set hardware aslisted below: 1.00

* *$72.55

*

[The above list or parts is the officialone, specially veried and corrected, so thatall who purchase the kit will know exactlywhat they should receive.]

RADIO WORLD' August 18. 1928

New CurveHidden Secrets of

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FIG. 1GRID VOLTAGE, PLATE CURRENT CURVES OF ASCREEN GRID TUBE WITHOUT LOAD IMPEDANCE.

THESE ARE STATIC CURVES

STATIC curves of vacuum tubes areusually taken without any load on the

tube. Since a tube will never be operatedin this manner such curves are not so in-structive as dynamic curves but they dogive an indication of the capabilities ofthe tube, hence they are interesting.

The three curves shown in Fig. 1 weretaken on a screen grid tube operating with3.3 volts on the filament and with negli-gible resistances in the grid and plate cir-cuits. The resistance in the grid circuitwas only that of the 400 -ohm potentio-meter used to adjust the grid bias andthis for most of the readings was consid-erably less than 400 -ohms. '1 tie resistancein the plate circuit was only that of themillimeter and the dry cell batteries, atotal of less than 50 ohms. Hence thecurves are the characteristics of the tubeitself.

Curves Are RegularThe curves are taken only on the nega-

tive side of the grid voltage axis, for thetribe should never be operated with apositive bias.

The plate voltage for all the curves waskept at 130 volts. The lowest curve atthe right is that obtained when the screengrid voltage was kept at 22 volts, themiddle curve that obtained with a screengrid voltage of 45 and the highest curvethat obtained with a screen grid voltageof 67 volts.

All the curves are regular and in everyrespect similar to those obtained withthree -electrode tubes. The slope of thecurves, which indicates the amplification,is not as high as was expected. On themiddle curve at a bias of 11/2 volts theslope is 235 microamperes per volts. Theslope of the highest curve at a bias of4 volts, where it is greatest, is 253 micro-amperes per volts. These slopes arethe respective mutual conductances. Therated value is 300/850,030, or 353 micro-amperes per volt, or micromhos. The dif-ference might be due to a lower amplifica-tion constant of the tube used or to ahigher internal plate resistance.

It does not seem that the use of 22volts on the screen grid is conducive tomuch amplification. Suppose the gridbias is adjusted to 1/2 volt. The slope atthis point for a signal amplitude ofvolt is only 142 micromhos. Besides thereis considerable curvature, so that the tube

'would detect.With 45 volts on the screen grid good

amplification is indicated with any biasfrom zero to about 4 volts. If the biasis obtained by tapping a 20 -ohm ballast inthe center the bias is 1.35 volts, assumingthat the voltage of the filament batteryis 6 volts. At this point the mutual con-ductance is 235 micromhos. If the gridreturn is connected to minus A the biasis 2.7 volts. At this point the mutual con -

Under Given Conditions Negatiis Critical to .1 volt-Exploratio

Knees and Heels=H04

By J. .E.Technical

ductance is 210 micromhos. Thus as faras these curves show there is little differ-ence between the amplification ofthe two returns of the grid. The lowerbias favors the amplification and the high-er draws less plate current.

At 2.7 volts bias on the highest curvethe mutual conductance is 245 micromhos.This is not far from the maximum on thatcurve. Therefore when the screen gridvoltage is 67 volts the grid return shouldbe to the negative end of the filament bat-tery. This makes the simplest connection.The curve for 67 volts screen voltageshows good amplification from zero to7 volts bias.

These conclusions do not hold whenthere is considerable resistance in theplate for this would change theshape of the curves.

Dynamic Curves

In Fig. 2 is shown a set of four curvestaken on the same screen grid tube whena resistance of 1 megohm was connectedin plate circuit. These curves give therelation between the grid bias and thevoltage developed across the plate resistor.The filament and applied plate voltagesare the same as in the case of the gridvoltage, plate current curves in Fig. 1.The four curves are for four differentscreen grid voltages as indicated.

Although these curves were taken bystatic means they are also dynamic sincethe load was a pure resistance. For highradio frequencies the curves do not rep-resent the performance of the tube be-cause at these frequencies the load im-pedance could not be considered as a pureresistance. They apply for practically allaudible frequencies.The output voltages were measured

with a vacuum tube voltmeter as explainedin the August 11th issue of RADIO WORLD,using a -50 tube with 450 volts on theplate.The first curve which appears in thelower right corner of the graph is par-ticularly interesting. This curve was ob-tained when the screen grid was connected

to the positive side of the 6 volt filamentbattery. While this curve is labeled 6the voltage on the screen grid relative tothe negative end of the filament was only3.3 volts, the drop in the filament.

High Detecting Efficiency.

Throughout this curve shows consider-able curvature and therefore detecting ef-ficiency. The curvature is greatest atabout 1.35 volts bias. Thus the tube maybe operated as a grid bias detector byconnecting the grid return to the mid -tapof the 20 filament ballast. This is very

August 18, 1928 RADIO WORLD 7

UncoverScreen Grid Tubes

d Bias fo rAmplificationveals Ample Detection) mu resultsndersonitor

convenient as no special provision of agrid battery need be made, and no leadneed be run from the screen grid to theplate voltage supply. The G post on thesocket is simply connected to the F pluspost on the same socket. The curvatureon the curve is as great as that on anyof the others. The only limitation is thevoltage swing which is permissible. Thisis somewhat smaller for this curve thanfor the others.

If this arrangement is to be utilized foramplification it may be done without muchwaveform distortion by using a bias lessthan 1/2 volt. For example, if the bias ismade volt a signal amplitude of thismagnitude is permissible and the amplifi-cation will be nearly 20 times. When ra-dio frequency is involved a little waveform distortion is of no consequence butunfortunately then the amplification willnot be that indicated, for the impedanceis no longer one megOhm.

It is clear that if the screen grid voltageis raised a little the (6) curve will moveto the left. The points of best detectingand amplification efficiency will be shiftedto the left also. This shifting may be doneby putting part or all of the ballast inthe positive leg of the filament and con-necting the screen grid to plus A. If allof the ballast is put in the positive legthe screen grid voltage will be six voltsbut then there will be no grid bias, andmore will be needed both for amplificationand detection. Other curves will be takenwith the object of finding the best com-bination.

Other Screen Grid VoltagesThe upper portions of curves (22), (45)

and (67) were published last week (Aug-ust 11th issue) under nearly the same con-ditions. While the same batteries wereused in taking those curves as the curvesin Fig. 2, the voltages were slightly dif-ferent, due to temperature differences.The plate voltage is 130 volts for all thecurves in Fig. 2 and the screen grid vol-tages are those indicated.

There are several interesting regions ineach of these curves. One is at the lowerbends. Curve (22) shows high detectingefficiency at 5 volts negative bias. A largepermissible voltage swing is indicated, thusgiving large undistorted output voltages,provided that the input is high. The (45)curve shows high detecting efficiency atabout 10 volts bias, and the (67) curveat about 15 volts.

Each of these curves shows a doublebend region where high detecting efficien-cy is possible. But at these points the in-put is quite limited. Each curve also hasan upper bend where the detecting effic-iency is high. The point of adjustmenton any bend is where the curvature isgreatest.

/5 /4 /3 /2 // /0 9 B 7 6 S 4 I&Rh:" VOLT:94TE

FIG. 2GRID VOLTAGE, PLATE OUTPUT VOLTAGE OF ASCREEN GRID TUBE WORKING INTO A RESISTANCE

OF ONE MEGOHM

/10

720

1101

LIS

/00;3

f0

80 I{

70

6-01,

50k

90

30

20

/0

Each curve also has two regions inwhich amplification is possible. Thus onthe (22) curve with a bias of 3 volts thecurve is relatively straight and the slopeis great. The amplification is 482. At7/2 volts on the (45) curve the amplifica-tion is 42. At 121/2 on the (67) curve theamplification is 26.5.

Most Interesting Region

Perhaps the most interesting region ineach curve is the straight vertical portionof each curve just below the upper knee.The output voltage., drops abruptly as awaterfall. In fact on the (67) curve thedrop is practically vertical. On the othercurves there is an appreciable slope.

Enormous amplification is indicated atthese points. On the (22) curve at 1.15volts bias the amplification indicated is90 with a signal amplitude of only .05 volt.At 5.65 bias on the (45) curve the amplifi-cation is estimated at 240. On the (67)curve at 9.6 volts it is still greater. Butthese values cannot be taken too seriously,for the grid voltage readings were onlytaken .25 volts apart and the drop in thecurves take place inside .1 volt. A muchmore sensitive voltmeter than that em-ployed would have to be used in taking

_the curves and a much finer voltage ad -j ustor.

Maximum Obtainable

The maximum voltage amplificationobtainable with a screen grid tube is theproduct of the mutual conductance andthe load impedance. Thus if the mutualconductance of the tube is 350 micromhosand the plate load resistance is 1 megohm,the voltage amplification possible is 350.

It is doubtful whether the steep portionsof the curves can be utilized in a practicalreceiver because of the extremely criticalgrid voltage adjustments necessary. Themost practical adjustment would seem to

a

be that indicated by curve (22) withvolts bias.

The curves -in Fig. 2 hold only for thescreen grid tube when the applied platevoltage is 130 volts and the load resistanceis one megohm. If the applied plate vol-tage is higher the curves will move tothe left a little and they will go consider-ably higher before they flatten out. Inany case they flatten out just before thevoltage drop in the output resistor is equalto the applied voltage.

Lower Resistor

If the plate coupling resistance is lower,the amplification will not be so high atany point, and the detecting efficiency willnot be as great. But both the amplifica-tion and the detection will be more nearlyequal for all frequencies in the audiblescale.

Different Results

It must be remembered that all thecurves in Fig. 2 were taken with 1 meg-ohm in the plate circuit. The curves willnot have the same shape when lowervalues are used. That is they would notcoincide if two sets were plotted to thesame scale on the same graph. This isbecause the internal plate resistance ofthe tube would bear a different ratio tothe load resistance. The slopes wouldnot be so great, indicating lower ampli-fication, and the effective voltage on theplate would be higher.

More CurvesCurves will be taken by the same

method on the same tube with plateresistors of .5 and 25 megohm so thatthe curves may be compared. Suchcurves would be useful because manytimes it is desired to hook up a circuitwith these values. Special type or cir-cuits will also be developed in whichuse is made of these curves.


A Set with Practical FTwo Separate

B Units EndMotorboating

It is now fully understood that motor -boating and many other troubles in re-sistance coupled amplifiers are caused bythe common impedance in the plate cir-cuits, or by the impedance of the B bat-tery eliminator. Harsh -sounding outputis also often caused by the B batteryeliminator, especially when the eliminatorhas not been designed to operate withhigh current drain such as is requiredwhen a power tube of the -50 type isused.

There are many methods available re-ducing the value of the common imped-ance. One is to connect large condensersacross the voltage divider. But ordinarilythis method is not practical because it re-quires too large condensers. Anothermethod is to power the receiver with astorage battery. This is the best of allfrom the quality point of view, but mostpersons object to the use of such a bat-tery because it requires constant atten-tion.

The next best thing is to use fresh drycell batteries. But here the question ofreplacement deters many. Also, whenhigh voltage and a tube of the -50 typeare used, B batteries throughout are outof the question.

Separate Voltage SupplyThere is really only one way of elim-

inating the common impedance, and thatis to use a separate voltage supply foreach tube in the circuit. This may bedone with either batteries or with bat-tery substitutes.

But is is admitted that this is no morea practical solution than the use of verylarge by-pass condensers. Still it ismore effective and it deserves considera-tion. If it is not practical to use 'a separ-ate battery or a separate battery elimin-ator for each tube in the circuit it ispractical to use two eliminators and dis-tribute the load between them so that thecommon impedances which are left do notcause any trouble.

It is common difficulty with nearly alleliminators that they cannot deliver the

1

G N00

power required. They are rated in termsof voltage, not power. The regulation ofthese devices is so poor that the instanta considerable load is thrown on themthe voltage drops badly. This simplymeans that the internal impedance, orresistance, is high. And itis just thatwhich causes motorboating.

Now there are thousands of B batteryeliminators on the market and in usewhich are rated at 135 to 180 volts whenmoderate currents are drawn from them.These small eliminators may be obtainedfor a small price.

Small Eliminators UsefulAlthough these small B, battery elimin-

ators cannot deliver enough power forall the tubes in the high quality sets inuse today, they can be utilized to goodadvantage in a resistance coupled ampli-fier to power some of the tubes. For ex-ample, one of them might power the de-tector and the first audio amplifier. Thesame eliminator may also be used to sup-ply one ortwo radio frequency tubes.Another B battery eliminator of greatercurrent capacity and higher voltage thenmay be used to power the power tube andone of the resistance coupled tubes.

The common impedance has no sig-nificance in the radio frequency part ofthe circuit, for the by-pass condenser usedacross the voltage divider is large enoughto render the impedance to radio fre-quency currents negligible. Then onlythe detector and one audio tube remainon the small B battery eliminator. Al-though the common impedance at lowaudio frequencies is considerable, thereis not enough feedback from the firstaudio tube to the detector to cause muchtrouble. And the feedback will be in re-verse phase so that the amplification isreduced by a small amount, but this nevercauses any appreciable distortion. Onlyat the extremely low frequencies, sub -audible, is it possible for the feedback tobe in phase to increase the amplificationby a small amount. If the time constantof the resistance coupler is high eventhis will not occur.

Power Supply for Power TubeWhen the detector and the first audio

tube have been powered by one B bat-tery eliminator there remain only twotubes to be taken care of by anotherpower supply. These two tubes will havea common impedance, but it won't be highfor it is assumed that the power B bat-tery eliminator will have good regulation.

Chi

FIG. 1

Ce C3

By GeraFull -Blooded

QUALITY of a high order may beobtained either with resistance or

with transformer coupling in the audioamplifier. But if the quality obtainedwith the transformer coupled circuit isto be comparable with that obtained withresistance coupling the transformers mustbe of the very highest grade.

Resistance coupling units take verylittle room and they are not expensive. Ifmetallized resistors and good mica coup-ling condensers are used, little trouble willbe experienced with the amplifier andthe results will be good provided thatsuitable resistance and capacity valuesare used in the circuit.

Motorboating Possible

It is true that motorboating is oftenencountered in resistance coupled ampli-fiers. It is also met in transformer coup-led circuits of the same quality and ofthe same overall amplification in the audiochannel It may not be an actual oscil-lation in the transformer circuit but itusually appears as a frequency distortion.In such events very high amplificationpeaks may result.

Another factor against the resistancecoupled circuit is that one more tube isrequired to get the same amplification.But this is not serious, for tubes are notexpensive either to buy or to operate.And if high mu tubes are used in the cir-

will be considerablyhigher. In fact the amplification per stagein properly designed resistance coupledcircuits is about 20, which is about thesame as in a transformer coupled stageusing a good transformer.

In favor of the resistance coupled cir-cuit is the fact that a much lower platecurrent is required. This not only length-ens the life of the amplifier tubes but alsothat of the rectifier tube or tubes.

How to Banish Trouble

An object of this article is to showhow trouble in a resistance coupled am-plifier may be banished, or how it maybe reduced to a negligible amount. Themethod to be described holds also fortransformer coupling but it will be ap-plied to a resistance coupled receiverwhich has been giving superb results forsix months without the slightest trouble,

C/0

THE CIRCUIT DIAGRAM OF A HIGH QUALITY, RESISTANCE COUPLED RECEIVEREMPLOYING ONE SCREEN GRID TUBE.

Chl

B+45048+1800 8+135o 8+45

0 C*C-42


istancezwk

Indian

oupled

AT TOP IS AN ELIMINATOR OF LOW OUTPUT VOLTAGE WHICHMAY BE USED FOR POWERING THE RADIO FREQUENCY, DETECTOR

AND FIRST AUDIO TUBES (FIG. 2).THE DIAGRAM (FIG. 3) OF A HIGH. VOLTAGE B BATTERY ELIMINATORWHICH MAY BE USED FOR POWERING THE LAST TWO TUBES IN THE

QUALITY RECEIVER OUTLINED IN FIG. 1.

that is, trouble from motorboating andfrequency distortion.

Fig 1 shows the circuit diagram of thereceiver proper. It contains one stage ofscreen grid RF amplification. Thisstage is shielded, as shown by the dottedlines surrounding the first tube, the asso-ciated coils and condensers.

The circuit operates on an indoor an-tenna for local and medium distance sta-tions. For distant stations it would bepreferable to use an outdoor antenna,although it need not be so long and highas some antennas in use for TRF sets. Itis important to run the antenna lead sothat there is a minimum coupling be-tween it and the three circuit tuner. Analternative is to shield the detector andits associated tuned circuit as well as thefirst stage.

The first tuning coil in the circuit L1L2may be any good commercial coil thesecondary of which is wound to coverthe broadcast band with a .0005 mfd. vari-able condenser Cl. R1 is a midtapped 20ohm resistor, the purpose of which is tolimit the filament current to .132 amperewhen the filament battery voltage is 6volts. The tap is used to provide a suit-able grid bias for the screen grid tube.

A rheostat Rhl is put in the positiveleg of the filament for the purpose ofvarying the volume. It controls the RFamplification in the first tube. Its valuemay be 20 ohms.

Controlling OscillationThe shielding is not always sufficient

to prevent radio frequency oscillation inthe circuit. Hence an 85 millihenry coilChl is put in series with the lead to thescreen grid and a condenser of .01 mfd.

or greater value is connected between thescreen grid post and ground. This com-bination acts as a radio frequency filterwhich keeps the voltage on the screen gridconstant.

A similar filter, Ch2 and C3, is con-nected in the plate lead. It acts to keepthe RF voltage on the low side of L3 con-stant. Another object of these two filtersis to prevent RF currents from gettinginto the voltage supply. This tends toreduce any possible hum when the re-generation is advanced, due to inter -modulation of RF currents with the resi-dual ripple in the plate voltage. Only oneof the chokes Chl and Ch2 should be inthe same shield.

The three circuit tuner L3L4L5 may beany good commercial coil provided thatthe primary L3 has been wound for thescreen grid tube. If it has not been, moreturns may be added. There is no fixednumber of turns which is best, for thenumber of turns depends on the size ofthe tubing and on the turns on the sec-ondary L4. The secondary turns shouldbe counted or estimated closely and thenthe primary should be made to containabout five -sixths as many turns. Cutone end of the primary, connect any kindof insulated wire in series with it andwind the extra turns in the same directionas those already on. Fine wire is betterthan heavy.

Turns may also have to be added to thetickler, but this depends on the tube usedfor detector. Only enough turns shouldbe used on the tickler to make the tubeoscillate at all settings of the tuning con-denser C4.(Constructional information next week.)

AudioSpeaker ReturnMade to Centerof the Filament

The feedback from the last audio tubeto the previous tube is such as to re-duce the amplification by a small amount,just as in the case of the detector andfirst audio tube. Hence there should beno oscillation at any frequency, and onlya negligible change in the frequency char-acteristic.

The use of a choke coil and condenserin the output circuit will reduce theamount of feedback from the power tubeto the preceding tube to a small fraction,provided that the speaker is returned tothe filament directly. Trouble may pos-sibly occur at very low frequencies, butany sub -audible oscillation will be feebleand may be stopped by small changes inthe couplers.-J. E. A.

These changes are based on the ideaof reducing the amplification at the sub -audible frequencies, without at the sametime reducing it on the low audio fre-quencies appreciably.

One of the simplest methods of doingthis is to reduce the grid leak ,of thepower tube input.

A better way, though not so easily ef-fected, is to reduce the stopping con-denser between the two last tubes.

LIST OF PARTSLIL2-One RF transformer wound for

.0005 mfd.L3L4L5-One three circuit tuner wound

for .0005 mfd.Chl, Ch2, Chi-Three 85 millihenry RF

choke coils.Ch4-One filter choke of 30 henrys or

more to carry 55 milliamperes.T-One 71/2 -volt winding of a power

transformer.CI, C4-Two .0005 mfd. tuning con-

densers.C2, C3, C8, C9, C10-Five, .01 mfd. mica

condensers.C5-One .00025 mfd. grid condenser with

grid leak clips.C6-One .0005 mfd.. fixed mica conden-

ser.C7-One .00025 mfd. fixed condenser.C11-One 4 mfd. or larger condenser,

1,000 volt test.RI-One 20 -ohm midtapped ballast re-

sistor, or two tens in series.R2-One 2 megohm metallized grid leak.R3, R4, R5-Three IA amperites.R6, R8, R10-Three .25 or .5 megohm

metalized plate resistors with mounts.R7, R9, RH-Three 2 megohm metal-

lized grid leaks with mountings.Rhl-One 20 ohm rheostat.Sw-One filament switch.Five standard UX sockets.Twelve binding posts.Two condenser dials.One tickler knob.


Early and Late Britain StartsRadio Annoys Eight Stations,

Sleepy Folk of 50 kw eachThe British Broadcasting Company has

just approved the installation of eight sta-tions of 50,000 watts each, said Louis G.Pacent, president of Pacent Electric Com-pany of New York, on his recent returnfrom a trip to England. The transmittersare to supplement the twenty-one stationsnow operated by the B.B.C. throughoutthe British Isles. The new plan also in-volVes generous use of short-wave trans-mitters operating simultaneously to carrythe British programs regularly to thecolonies and to foreign countries, he said.

"The new development is part ,of agrowing plan to improve the general toneand quality of English radio offerings,"he added. "About 75 percent of the pro-grams now consists of talks or speechesand most of the presentations are poor inquality. The radio manufacturers recog-nize the conditions and are doing every-thing possible to get the broadcasters tochange things for the better."

One reason, according to Mr. Pacent,for the poor quality of received programsis that the listeners are taxed accordingto the number of tubes in the sets. Henceeverybody strives to get the greatest"gain per tube' used. Therefore sets madein England are superior to American setseconomically but inferior in respect toquality. The tubes are seriously over-loaded.

With eight new high -power stationsin addition to those already in service amuch better geographical distribution ofentertainment can be effected so that thegreat majority of British listeners willbe within good reception range of astation. This 'will enable the listeners toreceive satisfactorily with small setswithout overworking the tubes.

WashingtonThe Summer or "open window" season

brought into the Federal Radio Commis-sion scores of complaints from individualswho condemn early morning "calisthenics"and late night musical broadcasting as in-terfering with their rest, because of theundesirability 9f shutting windows duringwarm weather, and the consequent 'an-noyance".

At the same time it was stated orallyat the Commission that the Commission,as a Federal body, has no authority to cur-tail such broadcasts. Commissioner 0.H. Caldwell, of the First Zone has statedin reply to letters he has received thatappeals should be made to local authori-ties for protection against such nuisance.

"The Commission has no control overa matter of this kind," he writes.

One of the letters reecived, from M.Fields, of Brooklyn, N. Y., asked for theCommission's action if within its juris-diction, to prevent musical programs after11 p. m., with the possible exception ofSaturday nights. "I ask you this out ofconsideration of those who would likepeace after that time so that they mayenjoy a restful sleep," he wrote. "Thismatter may seem humorous in a way, butit is detrimental to the general healthif radio stations are permitted to broad-cast jazz music until 12 or 1 a.m., as someof them do. It is comparable to a jazzband standing outside one's door and play-ing to that hour every night.

"Multiply this over hundreds of thou-sands of loudspeakers, each speaker with-in annoying distance of hundreds of peo-ple, and you get a better conception ofthis menace."

Synchronization EndsStations' Heterodyne

Washington.Experiments in wave synchronization, by

which two radio stations assigned to thesame wave -length would be enabledto operate simultaneously without interfer-ence, conducted by WAIU Columbus, Ohio,and KMOX, St. Louis, have proved suc-cessful to a marked degree, according to areport received by the Federal Radio Com-mission from H. V. Akerbergi chief engi-neer of WAII.P.

Mr: Akerbery requested permission toextend the experimental privileges accordedthe stations "so that we may continue de-velopment of the various theories not yetplaced in practical operation."

Commissioner 0. H. Caldwell stated oral-ly that he would recommend that the sta-tions be allowed to continue the tests. Heexplained that synchronization could onlybe effected now during periods when thesame programs were broadcast by the sta-tions parties to the experiments.

Text of ReportThe full text of the report, addressed to

Commissioner Caldwell, follows:"We have your kind telegram of July

14, authorizing the writer to continue theexperimental synchronization at WAIU,Columbus, and KMOX, St. Louis. Wehave accomplished the following results :

"On July 3, between 8 and 10 p. m., weconducted the first of these series of experi-ments, and since have repeated the tests oneach succeeding Tuesday.

"As far as we can determine, from care-

fully placed observation points covering theterritory between Columbus and St. Louis,the experiments have been successful to amarked degree.

"The method we have been using is asfollows : WAIU transmitter during theseexperiments is not crystal controlled, theusual crystal oscillator being replaced by amanually controlled master oscillator com-pletely shielded, and accurate in mainten-ance of frequency to within 15 cycles overa period of five hours.

Beat Tests Made"KMOX employs a .standard Western

Electric 4-A transmitter which has beenfound to be accurate within 25 cycles overa like period of time. We determine theirvariation of frequency by the usualmethod of beating their carrier with a con-stant frequency oscillator located in Col-umbus.

"During the actual synchronization weuse a calibrated local oscillator at the trans-mitter. This oscillator is absolutely accur-ate at 1,000 kilocycles. We beat our car-rier against this local 1,000 kilocycle oscil-lator instead of against KMOX at St.Louis.

"Our observers listening in give us thecorrection before the program starts. Thiscorrection, usually in the neighborhood from100 to 500 cycles, is easily made at thetransmitter-the local constant frequencyoscillator corrected accordingly and the pro-gram continued. At intervals during theprogram the observers give ns additional

corrections. These corrections are made atonce at the transmitter.

Heterodyning Absent"We find that there is an entire absence

of heterodyning and the only problem thatwe have not yet quite overcome is that ofcross -talking during announcements. Wthave worked out a plan whereby we aredividing the announcing time-each stationutilizing half of the 15 -second intervals al-lotted by the chain for our local announce-ments.

"We are very carefully studying the dis-tortion factor. As yet we have experiencedno serious distortion of audio frequenciesdue to time lag, or due to either one ofthe two transmitters being slightly out ofphase.

"We would very much like to carry onthese experimental tests employing thermo-statically controlled crystals. For your in-formation, we have been successful in beat-ing two thermostatically controlled crystaloscillators for a period of seven days withthe result of no more than a 5 -cycle devia-tion over this period of time.

Suspended Cages Used"It is my opinion, that this method could

be very successfully applied to the syn-chronization of two stations-another note-worthy factor in the ability to hold ourtransmitter to a given frequency contin-ually is an unusual type of antenna design.We are using at the present time, and havefound it by far the least susceptible to fre-quency changes due to variation of capac-ity, atmospheric changes, etc., a systemcomprising two 40 ft. 8 inch diameter, 6wire horizontal cages.

"These cages are suspended between tow-ers 200 feet high. They are tightly stretchedbetween the towers. This tension being main-tained by an automatic compensator, thedown lead after much experimentation iscomposed of a 50 ft. 4. inch 6 wire cage atthe upper end.

"At the bottom of this vertical cage the6 wires are bunched, continuing 130 feetstraight down to the coupling house. Thisso-called rat tail lead is composed of 6No. 10 enameled copper wires woven to-gether. This lead is also under tension.

"The fundamental of the antenna systemis in the neighborhood of 326 meters. Theseries condenser is used to work it at 1,000kilocycles and 1,000 kilocycles.

"We have found this type antenna in-dispensable in maintaining an exact fre-quency. The counterpoise system is useddue to very high ground resistance.

"I am working with KMOX at the pres-ent time to have them install a temperaturecontrolled crystal so that we may furtherdevelop that idea.

Surprising Deviations"I would appreciate very much if the.

Radio Commission would extend our ex-perimental privileges during the Summermonths so that we may continue develop-ment of the various theories not yet placedin practical operation. If you wish, I willforward within the next few weeks the de-tail reports of each transmission as soon as.we have compiled them. They are very in-teresting and very instructive and will showsurprising deviation of frequency of someof our major broadcasters in the country.These observations have been made aftera long period of time and have proven veryvaluable.

"Will you kindly take up the matter ofextension of oar privileges so that it maycover the Summer months? If you requireadditional information will very gladly for-ward it to you at once."

"Synchronization of two or more sta-tions transmitting the same program atthe present time seems to be the onlypossible solution of the problem of ethercongestion," said one expert. "If itproves practical most of the stations nowoperating could continue without time-sharing. But to he successful it wouldseem that the synchronization wouldhave to be automatic as well as exact


A RESISTANCEIT SHOULD BE

R

3

CAP

FIG. 706COUPLED AMPLIFIER DESIGNED TO AMPLIFY TELEVISION SIGNALS BEFORE TRANSMISSION.POWERED WITH BATTERIES AS INDICATED AND THE STOPPING CONDENSERS SHOULD BE

LARGER THAN .01 MFD. CIRCUIT REQUESTED BY FORE ST HOLLIS.

CAP., C4

0

0 57'135g+45

01***0-0 A+ 6O 43- C+

O C- 7 XZC- 772MORE OR LESS

FIG. 707THE CIRCUIT DIAGRAM. OF A RADIO FREQUENCY AMPLIFIER, REGENE-RATIVE DETECTOR AND RESISTANCE COUPLED AMPLIFIER SUITABLE.FOR INPUTTING A PUSH-PULL AMPLIFIER. CIRCUIT REQUESTED BY

FOREST HOLLIS.

Radio UniversityWhen writing for information give your Radio

A FREE Question and An-swer Department con-

ducted by RADIO WORLDfor its yearly subscribersonly by its staff of Experts.Address Radio University,RADIO WORLD, 145 West45th St., New York City.

University subscription number.

PLEASE PUBLISH a circuit suitablefor the amplification of transmitted sig-nals in television. I wish to experimentwith transmission as well as with recep-tion.

(2)-Also please publish a circuit of aradio frequency amplifier, detector andone stage of audio suitable for inputtinga push-pull power amplifier which I nowhave.

FOREST HOLLIS,Troy, New York.

(1)-See Fig. 706 for such an amplifier.It shows the connection of the photo-electric cell as well as the position of thescanning disc relative to the cell.

(2)-Fig. 707 shows such a circuit inwhich screen grid tubes are used bothfor radio frequency amplifier and detector.The audio tube should be of the -12Aor the -01A type since the push-pull'stage will be coupled to it by means ofa transformer.

* * *

WHAT is the ratio between a killowattand a horsepower?

(2)-Could not the power of a broadcaststation be listed in horsepower and if itcould, would not this be a more easilyunderstood designation?

(3)-How is a watt defined? How ahorsepower?

WILLIS K. BRADFORD,Racine, Wisc.

(1)-A horsepower is very nearly equalto .746 killowatt. For approximate work

a horsepower may be regarded as three-quarters of a killowatt.

(2)-Yes, it could be, and no doubtmany people would understand the desig-nation better than the electrical unit. A

50 -kilowatt station would then be ratedat 66 horsepower.

(3)-A watt is the power of one volt-ampere. That is, if a current of one am-pere flows through a resistance and thevoltage across that resistance is one volt,the power dissipated in the resistance isone watt. A kilowatt is one thousandwatts. A hors power is defined as thepower required to raise the weight of onepound 550 feet in one second, or 33,000feet in one minute.

* * *

I HAVE OBSERVED a peculiar effectin my resistance coupled amplifier. WhenI first turn it on it works perfectly forabout fifteen minutes. The quality gradu-ally gets worse until after the fifteen min-utes it is terribly bad. I have checkedand rechecked the circuit and can findnothing wrong. What is my trouble?

PATRICK MOORE,Boston, Mass.

(1)-This is an effect often caused bystray leakage from the plates or platecoupling resistors to the grid of an am-plifier tube, usually the power tube. Thegrid gradually goes positive because theleakage from the positively charged partsis greater than the leakage from the gridbattery. The condition is often coincidentwith hot or moist weather. Dust on theinsulator surfaces is also a contributorycause. The quickest remedy is to use alower value of grid leak. A test whetherpositive leakage is the trouble is to pus.a milliammeter in the plate circuit ofthe suspected tube and observe the platecurrent. It will creep up gradually. Ina -50 tube it may creep up from 50 to100 milliamperes.

Join RADIO WORLD' University ClubAnd Get Free Question and Answer Service for One or Two years.

This Service Only for Those Who Subscribe by Filling outThis Coupon and Sending Remittance.

Subscribe for RADIO WORLD for one year (52 numbers, one each week) at $6, ortwo years at $10 (104 numbers) by filling out this coupon and enclosing remittance.You will then become a member of RADIO WORLD'S University Club and receivea secret number.Put this number on the outside of the forwarding envelope (not the enclosed returnenvelope) and also put at the head of your letter. If already a subscriber, send $6or $10 for renewal from close of present subscription and your name will be enteredin Radio University. No other premium given with this offer.RADIO WORLD, 145 West 45th Street, New York City.Enclosed find $6.00 for RADIO WORLD for one year (52 nos.); or $10.00 two years(104 nos.) and also enter my name on the list of members of RADIO WORLD'S Uni-versity Club, which gives me free information in your Radio University Departmentfor the period of this subscription, and send me my secret number indicating

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Advertising by RadioHas Its Own Technique

By Thomas F. LoganPresident, Lord & Thomas and Logan

Advertising AgentsBroadcast advertising has an entirely

new technique. Things that are orthodoxin printed advertising are taboo in radio,and you may do things in radio that areimpossible on the printed page.

For radio advertising we have had todevelop a new method of copywriting.We have had to train program builders,continuity writers and other specialists.We have had to devise new methods ofchecking reader, or, I should say listenerinterest and response. We have had tostudy the stage and the screen to deter-mine program appeal.

In fact, we have had to develop an en-tirely new art of advertising.

We are beginning to assemble forbroadcast advertising minute statistical in-formation.

We know, for example, that radio pro-grams are listened to from 7 in the morn-ing until midnight, with varying degrees ofcirculation volume. The biggest audience,of course, is in the evening, from 6 to 11,with the peak between 8 and 10. Theevening peak is later in the cities than inthe rural districts.

There is another midday peak, between12 and 1, which is greater in the rural dis-tricts, than in the cities.

Cities Gay, Farmer SleepsIt is interesting to note, by the way,

that while the farm audience fades rap-idly after 10 p. m.;the city and town audi-ence is still very large between 10 p. m.and 11 p. m.-larger, in fact, than at anyother time of the day except the threeprevious evening hours.

So far as we 'have been able to deter-mine from preliminary surveys, radio setsare in use an average of 850 hours a year.More than two-thirds of the radio setsof the country are in use from two to sixhours a day.

Winter audiences, like winter circula-tions of magazines, are larger than sum-mer, but investigation shows that fullyone-half of the radio audience makes asmuch use of radio in the summer as inthe winter, while another large section ofthe audience uses radio all summer, in-cluding vacation trips, but for shorterdaily periods.

Public Tastes KnownProgram building is not a difficult art.

There is not much guesswork about it.The likes and dislikes of the radio publicare very definitely known. There is nowabundant experience of scores of nationaladvertisers, as well as six years of studioexperience with all kinds of programs, toguide the new radio advertiser in programplanning.

The radio audience, as we have found,is very critical-far more so than the audi-ence in a theatre. It is now so accus-tomed to hear programs of the highestcharacter by artists Of the first rank thatanything mediocre falls with a thud.

When the radio audience doesn't likethe program, it either turns the dial tosome other station or else turns off theswitch.

An audience will stay through a poorshow in the theatre, trying its best to getits moneys worth, but it don't stickaround listening to an inferior programon the air, for which it has paid nothing.

10,000,006 to 15,000,000 HearFirst -night audiences of popular musical

programs by national advertisers run fromten to fifteen million listeners. The mostpopular feature on the air is classical mu-sic by the world's great composers, andthe most unpopular is jazz.

Compared with the growth of broad-casting, our amazing American progressin the use of the telephone, the electricBelt, automobiles and other American in-ventions has been slow, indeed. The radioaudience has grown rapidly in the pastsix years. The appeal of radio is uni-versal.

Any means of advertising pays if itoffers the seller of goods an economicalmeans of making his goods favorablyknown to the people that can use them.That is axiomatic.

Why Radio Is IncludedIf the potential market is nation-wide-

a market of millions of people-then themanufacturer naturally turns to thosemeans of advertising that most quickly,surely and economically reach this broadmarket. That is why the trend of adver-tising expenditures is more and moretoward newspapers and magazines of thelargest circulation and coverage.

And that is why experienced nationaladvertisers-many of the most successfuladvertisers-are now including radio, withits enormous audience and tested listeners'interest, as an integral part of their adver-tising expenditures.

Radio offers them a new means ofreaching the national market, of enteringthe homes of the people-quickly, surelyand economically.

Now Only An AuxiliaryLet me say right here that, despite the

great reliance we place on broadcastingas a new sales force in American business,we would not recommend to any adver-tiser that he place all or any very largeproportion of his advertising expenditurein this new medium.

The time may come when some adver-tisers can profitably use radio exclusivelybut we have no data today that wouldjustify such a policy. Broadcasting forthe present at least, must be an adjunctto printed salesmanship-and it is amighty powerful adjunct.

Newspapers, magazines and billboardshave been tried and proved to be effective.Each h'as established its definite place andits definite value.

Fourth Greatest HelpBroadcasting has become the fourth

great auxiliary force in the tremendoustask of national distribution. If usedproperly, it will play its useful part in theeconomics of distribution.-I am quite willing to risk my reputation

as a prophet in saying, while it is here tostay, it will not and can not replace theprinted page. The printed page is thefirm 'foundation of all profitable advertis-ing. It is the bedrock upon which ourmodern merchandising structure has beenso successfully built.

I have heard it said that there are somepoor souls who allege that they tune outthe advertisers' programs. By the sametoken, I suppose, they carefully tear outthe advertising pages of the popular maga-zines as soon as they leave the newsstand,and walk in the middle of the avenue so asnot to see the goods displayed in the shopwindows.

A MAN AND HIS WIFE PATCHEDESPITE THEIR DIFFERENT PO'FIFTY-FIFTY LISTENING IN 1SPEECHES, AND BY SYMBOLI2BOUDOIR INDIAN ELEPHANT A

THEIR TABLE MOD]

Perfect ReproJohn. P. Rider, for the Hiler Audio Co

poration, released the following:So many loudspeakers have been he

aided as being the ultimate, the only ofoffering fidelity of tonal reproduction, thit is time to doubt. Excessive enthusiasinvariably breeds suspicion. But whatit? Do we need a perfect loudspeakerIs perfection possible?'

According to E. A. Hiler, an Americ,engineer and inventor of the tuned doubimpedance system of audio amplificatiothe perfect loudspeaker is far removifrom the horizon.

"Why is there so much talk about pefect loudspeakers, when one of the greaest telephone engineering organizatioiin the world calls 50% operating efficienta success ? asks this engineer. "The re!roduction of sound is their forte, yet thewho really know do not herald perfereproducers,

"After all, do we need a perfect speak.-perfect insofar as its frequency charateristic and operating efficiency are colcerned?"

"The prime subject for discussion in tiradio press has been the frequency chaacteristic. Concerted clamor for improv.ments resulted in successful changes -without a doubt loudspeaker operatichas been improved. How much farthimust we go?

"We 'must not overlook the fact ththe loudspeaker is an inherent part of tiradio installation.; that its performancegoverned by the performance of its ass(crated equipment.

"Suppose that a perfect speaker is pr(duced. What changes will be necessatin radio receiver design? In the first placa square -topped resonance curve for tlradio frequency system will be imperativDistortion in the detector tube must teliminated. The operating characteristof the audio amplifier must be flat.

"The next problem is the possibilitythese developments consistent with conmercial radio practice.

"All of the above are possible-btwhen-and who will pay for them? Whwill happen to the millions of radio n

RADIO WORLD 1,IAugust 18, 1928

it" A PEACE IN THEIR HOUSEHOLD,A L FAITHS, BY AGREEING TO A

kEPUBLICAN AND DEMOCRATICC THIS FAIR DIVISION WITH A

HAPPY -WARRIOR TIGER ATOP4DIO INSTALLATION

'ucer Needed?`eivers already in use? Produce a per-.ect loudspeaker and you must change the'radio frequency system, the detector andhe audio frequency systems in these re-!eivers.

"Is it not simpler to forget the talkbout perfect loudspeakers and to adjusthe audio amplifier to compensate for theeficiency of the radio frequency system,he detector and the loud speaker? Labor-tory experiments prove this contention.aboratory experiments covering thether arrangements are yet impossible be -

pause there are no perfect loudspeakers."After all, the perfect loudspeaker and

he perfect receiver will combine to per-orm the function now being performedith the audio amplifier tuned or designed

qualify the operation of radio fre-tuency amplifier, the detector and the,ipudspeaker. It is much simpler to adjust, ne circuit, according to the deficiencies)f three, than to adjust three, to equal,the perfection of one.

"That audio amplifiers can be matchedmeet the requirements of the public

hen used with good speakers is beingaily displayed by the organizations thatroduce and sell loudspeakers with theirceivers. They recommend their loud-Baker with their receiver. The reason ismple. They know the characteristics ofeir loudspeaker and they can designeir audio amplifying system to compen-te for the loudspeaker deficiency."If the speaker is deficient on low fre-

uencies, they tune their audio amplifiercompensate for this deficiency. If the

me speaker is also deficient on some ofe frequencies of the upper audio regis-r, they adjust the same audio amplifier

accentuate the required frequencyand, the required amount. Why worry'bout perfect loudspeakers? The perfectudspeaker is unnecessary."The low frequency deficiency found ineakers of today is not lack of response

ue to inability to function at the low fre-uency, but rather to variations in powerecessary to actuate the parts. Accen-tation of these low frequencies within,he audio amplifier acts correctively."

Pair's Political Oddson Radio Evened Up

By Jim JoyceA politico -radio situation developed in Ed

,Harris's household.Ed has been a Democrat since ten years

before the party was born, to hear him tellit, while his wife once made a speech inbehalf of a Republican candidate for Alder-man and has been for the protective tariffever, since. So Ed is for Al Smith forPresident and his wife is for Herbert Hoo-ver, and between them, and their radio, toofor that matter, there is the polite dickensto pay.

Ever since the couple have been married,some six years, they have gotten along well,and there's no chance of politics disruptingthe equanimity of the home. But it doescreate a situation, for in politics life isnothing unless a situation develops.

To be frank, neither of them is politicallywise, and the wife in particular, whose nameis Winifred, is somewhat cloudy on politicalways and manners. It is recalled by dis-creet friends who listened to the broadcastof the Democratic National Convention inEd's home, with his wife serving all thelemonade and most of the conversation, thatshe lamented the fact that the Democratswere making a clean sweep.

Not One Republican"It looks like a clean sweep for the Demo-

crats," she remarked as not one Republicanwas even remotely suggested for either ofthe two high offices. "But wait! Our turnwill come !"

Her husband reminded her that the Re-publicans a few weeks previously had foughtshy of nominating any Democrat, and hecoyly remarked that it was only to be ex-pected that any political group would favoronly its own kind.

There was no problem during the conven-tions, since no conflicting hours of politicalbroadcasting were experienced, but withcampaign speeches it is different, since oneman will spout for one party and anotherfor the other party, at the same time, fromdifferent stations-and there's the "situa-tion."

Insists on Even BreakMrs. Harris insists that the Republicans

must be given an even break on the tuningin, and her husband, always chivalrous, ad-mits that's no more than fair, but his wifedoes not openly assure him that the speak-ers for the party of her choice will not begiven preference when he's not at home.

"Why should I sit for hours listening toorators of your party," she asks, "when I'malone in the house with the non-partisancanary? We'll go fifty-fifty on the hoursof reception for political speeches of thetwo parties when you're home, and that mayinduce you not to take so many nights off.But when I'm alone I insist on doing as Iplease, because you're not here to listen."

This seemed fair enough to Ed, as he isconcerned mostly about what visitors willthink, or neighbors say, if his wife com-pletely rules the roost when he's home. Hisidea is that neighbors, as such, never think,-but that visitors sometimes may do so, al-though this, too, is doubtful. He knowsneighbors don't think, 'because one of themwrote to the Federal Radio Commissioncomplaining that he has his set going untilafter midnight six days a week, at a fright-ful cost of sleep to said complainant, but Edfeels the neighbor was selfish not to men-tion Ed's own loss of sleep in a good cause.

Symbolic of the truce that's been patchedup, whereby the rule of fifty-fifty politics

prevails when they're both home, and all -one -way politics when either is home alone,the couple have ornamented their radio in-stallation with a fitting display.

This consists of a boudoir elephant, rep-resenting the Republican Party, and China"tiger", which Ed thinks is the DemocraticParty's informal emblem. He was born andbred in New York City, as was Smith, andwhen anything savoring of the DemocraticParty is broached, he always thinks of thetiger that is representative of TammanyHall, the New York branch of the Party.

It so happens that his wife says shebought the ornament for the drawing -roomtable and was told it was a puma, what-ever that is, but Ed assured her a pumais a tiger, and anyway, it's the principle ofthe thing that counts, seeing as he hasn'tbeen to the zoo these many years.

The Hindu elephant was depleted of thetrinkets it had cohtained when it had gracedMrs. Harris's bOudoir table, but it lookedjust as sullen when it was burdened withthose riches as it does now that Ed secretlyuses the interior as an ash receiver.

Their Expressions AnalyzedThe elephant seems to have something of

a scowl, Ed thought, and said so, but hiswife said an elephant's an elephant, andthat the fellow who fashioned this one fromclay didn't have in mind the unique pur-pose to which his work of art would beput.

"Well, the elephant is on the warpath, andits stern determination to be vic-

torious," said Mrs. Harris."I'll say for the tiger," piped Ed, "that

it seems to be sniffing the air with joy-more or less indifferent to the elephant'sscowl, and for all the world enjoying theconfident pose of the happy warrior!'

Recently the couple at breakfast timeheard Republican setting -up exercises andat bedtime listened to Democratic slumbermusic.

"The exercises were better for the stateof the union," said Mrs. Harris, who wasborn in West Branch, Iowa.

Convention BroadcastsBy N. B. C. Cost $181,000Spending $115 a second to broadcast the

Democratic National Convention, the Na-tional Broadcasting Company and asso-ciated stations are believed to have set anew high record in radio public service,said M. H. Aylesworth, president.

The Democratic convention was on theair for a total of 25 hours. The totalcost of the Democratic broadcast over thecoast -to -coast network of 43 radio sta-tions was $104,000, or $27,000 more thanthe Republican convention broadcast.

"While it is true that a few shorter pro-grams have cost more per second than theDemocratic convention report, thesebroadcasts have been commercially spon-sored," Mr. Aylesworth said. "The con-vention broadcasts, on the other hand,were paid for by the N. B. C. and asso-ciated radio stations and were not revenueproducing.

"We believe that the broadcasts of theRepublican and Democratic conventionsare outstanding examples of the serviceradio can render the nation as a whole."

The total cost of broadcasting both con-ventions, shared by the N. B. C. and asso-ciated stations, was $181,000.


Board Investigates`Domination' by Chains

Washington.It is becoming "increasingly evident"

that the 90 broadcasting wavelengthsavailable to the United States can carryonly 150 full-time stations of 500 watts andover, if the principles of good radio re-ception are to be preserved, and thereforedivision of broadcasting time by stationsapparently must be imposed to a largeextent said Commissioner 0. H. Caldwell,of the Federal Radio Commission.

The statement was made in connection,with a questionnaire sent to all of th,i ap-proximately 650 broadcasters in the coun-try, by the Committee on Reallocation,comprising Commissioners Caldwell andSam Pickard.

Commissioner Caldwell explained thatthe Reallocation Committee desires to getthe latest data as to the hours actuallyused by broadcasting stations so thatproper time-sharing may be scheduled inthe forthcoming allocation plan withoutundue hardship to any broadcaster.

The allocation plan is made mandatoryby the Davis amendment to the RadioAct, requiring equal distribution of radiobroadcasting time and facilities among thefive radio zones.

Queried on Chains

The questionnaires must be sworn toby station owners and must specify, inaddition to hours of operation, the numberof hours of "chain" programs and the typeof apparatus used to insure that the sta-tion keeps within its assigned frequencyand does not disturb stations broadcastingon neighboring channels.

The full text of the statement follows :"Reallocation Committee desires to get

latest status of the hours actually usedby broadcasting stations, in order thatproper time-sharing can be scheduled in

the new allocation plan, without unduehardship to any broadcaster.

"Stations being required to state underoath hours used each night (7 tr, mid-night, which are valuable commercialhours), also total such hours used duringpast six months, and proportion of suchnight hours of chain programs. Infur-mation to be ready when Commission re-sumes reallocation discussion.

"As reallocation work progresses it be-come, increasingly evident that our 90hroa 13tin2 v a. elengths can carry only150 full-time stations of 500 watts andover, if the principles of good radio re-ception are to be preserved. With some300 licensed transmitters to be accom-modated, it is evident that time -divisionmust be imposed to a large extent, andthe questionnaire will provide basis.

"The seriousness of the present duplica-tion of chain programs on 10 to 20 chan-nels with each chain now in operation isanother factor which the reallocation com-mittee is carefully studying, in the light ofthousands of protests received during theyear by the commission and by membersof Congress.

"The committee desires to get the latestfacts of actual 'chain' time used by eachstation.

"Proposal has been made that only onestation of 5,000 watts and over in eachzone be permitted to broadcast commercialchain programs. Another recommenda-tion urged is that chain programs be per-mitted only on stations of 500 watts orless, using shared channels.

"Regulations permitting repetition ofchain prograMs on high -power only witha. distance interval of 1,000 miles or so,have also been suggested.. The actualfacts concerning 'chain domination' of thebroadcasting hours will be obtainable fromreplies to questionnaire."

Kickers Keep ChainsOn Pins and Needles

By Walter C. Stoneof the Publicity Department, National

Broadcasting CompanyEvery broadcast program on the air

today is there because thousands of listen-ers throughout the country desire its con-tinuance. In the last analysis it is theradio .audience that determines what pro-grams shall be presented. The wholebroadcasting business, with its millions ofdollars invested in equipment and run-ning expenses, depends on the likes anddislikes of the listeners for its existence.

If an unwary broadcaster should put onthe air a program which did not please alarge group of listeners, that single errorof judgment would result in a flood ofprotests from every part of the country.Continuance of the one offending programwould mean the loss of a very considerablegroup of listeners.

Like everyone else whose success de-pends on the good -will of the public,broadcasters keep one ear constantlytuned to catch murmurs of disapproval.These, if there is something to evokethem, are manifested in several ways.

First of all come the general letters fromlisteners. The National BroadcastingCompany receives half a million or so ofthese a year. Many come direct, andothers, in which there is reference to net-

work programs, are forwarded by asso-ciated stations through which these pro-grams have been heard. Each of theseletters is read and those which offer criti-cisms and suggestion are noted.

Alert on Published KicksNewspaper comments from all parts of

the country are another fruitful sourcefor the broadcaster looking for public re-action to programs. At least a dozen of-ficers and members of the staff of theNational Broadcasting Company readeach newspaper review with a view to cor-recting the bad impression any one pro-gram may have made on more than one ortwo reviewers and to find constructivesuggestions for the future.

In addition, there are the wishes of thestations associated with the networks tobe considered. Before each program goeson the air, it must be analyzed to dis-cover how well it is adapted to the needsand desires of stations in widely separatedparts of the country. Network broadcast-ing, to be successful, must please not onlylisteners to stations in metropolitan areas,but also must be liked by farmers, ranch-ers, miners, merchants in small towns-

in fact, by a cross-section of America'spopulation.

A program unacceptable to the listenersof any group of stations would cause thosestations to drop from the system for theperiod it was on the air. No station iscompelled to take any program it does notcare to take, nor, as a matter of fact, couldthe National broadcasting Company forceit to do so. There are only three stationsin the country over which the companyhas any control. These are WEAF, inNew York, which it owns, and WJZ, NewYork, and WRC, Washington, which itmanages for the Radio Corporation ofAmerica.

No CompulsionOperating these three stations, however,

is only incidental to the real business ofthe company, which is the production anddistribution of programs of national in-tcrest. Its sustaining programs are de-signed with the idea of making them soattractive to network stations that theywill be willing to pay for the privilege ofreceiving them over network wires andbroadcasting them. If a sustaining pro-gram should be poor, it would not sell tothe network stations, and the producingcompany would receive no financial re-turn from it.

Nor is any network compelled to broad-cast any particular program sponsored bya commercial enterprise. When such aprogram is contemplated and the sponsorwishes to have his program heard in cer-tain areas the National Broadcasting Com-pany telegraphs each station, describingthe program and asking the station if itwill accept it. If it does, the station re-ceives a fee, but if the manager of thestation believes the program unsuitablefor its own audience he refuses the pro-gram and that is the end of this matter.

Each of the stations associated with thesystem as well as non -associated stationsreceives frequent opportunities to join in

public events of outstandingnational importance. In most instancesthese programs are offered to the stationswithout cost and the National Broadcast-ing Company bears the expense of pro-viding the facilities.

Kickers Not Bashful, Alas!The continuance of network broadcast-

ing, in truth, rests upon whether or notthe National Broadcasting Company, orany other company engaged in producingand distributing broadcast entertainmenton a national scale, can retain the good-will, not only of individual stations, butalso of large bodies of listeners. If thelisteners did not like the network pro-grams they would soon let the stationshear about it, and very soon these woulddrop off the networks.

Chicago Opera on AirWeekly this Season

Selections from the performances ofthe Chicago Civic Opera Company will beheard over radio once every week duringthe 1928-1929 operatic season, the NationalBroadcasting Company announced. Anetwork of stations of the broadcastingcompany will be connected with a bankof microphones placed on the stage of theChicago Auditorium to pick up the music.

The broadcast will begin on October 31,axe will continue until January 23, 1929,with one performance every Wednesdaybetween 9 and 10 p. m., Central StandardTime. The programs will be sponsoredby the Fansteel Products Company, radioset manufacturers.

KOBER IS APPOINTEDPaul A. Kober, formerly engaged on

television experimental work for GeneralElectric Co., and former assistant toE. F. W. Alexanderson, has been ap-pointed television engineer of 'the DavenRadio Co., Newark, N. J.


Are Chains a BlessingOr Infernal Nuisance?WELL SATISFIED

T N youir issue of Aug. 4, you publish a1 letter by Mr. A. S. McBryde, of De-troit, in which he complains of the presentbroadcasting situation. He blames theRadio Commission for his failure to enjoyradio as he did at one time. He alsocomplains of the quality of the receptionon relayed chain programs, and of thenature of the programs themselves.

As this is only one of many similarletters I have seen in print (with regret),I am venturing to state that I believe99.99% of the radio listeners are entirelysatisfied.

With regard to the chain programs,either direct or relayed through the threeprincipal Detroit stations, I have foundthem, at most times, exceedingly clear asregards reception, and far superior tothe locals as regards program.

Although complaint is made of theselection of chain programs,1 cannot seehow they can well be improved, so longas it is necessary to cater to listeners ofso great a diversity of tastes. PersonallyI would prefer a little more weight in theprograms, and less "jazz," but I appre-ciate that L'am in the minority.

Regarding Mr. McBryde's ,alleged in-ability to get certain stations (KDKA,WTAM and WLS) when the Detroitlocals are on, I am at loss to understand,as I have no such difficulty. Last nightI received without difficulty all of thestations named in his letter, first makingsure that WWS, WJR and WGHP wereall working. This was on an old Radiola25. Then I picked up each of the stationsspecifically named, on a Browning -Drake,operated on an light -socket antenna, (byno means a selective arrangement), whichI have on account of the exceptionalquality it gives with a push-pull amplifieron the locals.

Then a T. R. F. receiver with threeunneutralized R. F. stages was tried, andthe three stations named were easilybrought in without any interference.Then the Radiola 25 was used again, thistime with an extra stage of push-pullaudio added. The stations complained of(WLS, WTAM, KDKA and WLW), werebrought in with tremendous volume in aneffort to pick up side band interference.There was none detectable. Then theBrowning -Drake was tried again onWTAM, which is between WWS andWJR. Using a ground antenna, WTAMcame in very loud and in such goodquality that I kept it on the rest of theevening.

As I am just as near to WWJ as Mr.McBryde, and nearer by some miles toWGHP (which is not in Detroit, but inMt. Clemens), I feel that he should lookfor his troubles nearer home, and notblame the Radio Commission, which ismaking as good a job as anyone couldout of the mess Congress has handed it.

Incidentally, the heterodyne whistle onWGHP I was unable to detect, when ac-curately tuned, and suspect that the diffi-culty arises from some oscillating receiverin Mr. McBryde's neighborhood. A localstation, WBMH, which has a tendency towander a bit, interferes, now and again,with its harmonics. It is a very poorstation which I am glad to say the Com-mission has slated for discard.

If Mr. McBryde's receiver will not tunesharply enough to pick up the stationsnamed when WGHP, WWS and WJRare working, he must have about the mostbroadly tuning set in Michigan. It wouldscarcely be possible to place the stationsin the broadcasting band where theywould be less likely to interfere. In factthis is so evidently the case that I sus-

pect Mr. McBryde of attempting tostrengthen a case whose weakness he sus-pects, by adding a little testimony notunimpeachable. This is borne out by hislater statement that he tuned in "fivedifferent DX stations and heard the sameprogram from each of them."

I should be glad to see a list of fivestations, on the same chain, which wouldbe farther from Detroit stations thanWTAM.

PHILIP M. C. ARMSTRONG,Detroit Club, Detroit, Mich.

* * *

BLAMES POOR SETSEditor RADIO WORLD:

IHAVE just finished reading your lastissue and do not quite agree with two

of your readers' views of radio condi-tions. Kansas City has two chain stations,WDAF and KMBC. Chain programsreach here clear and undistorted and aresuperior to any local program, both incharacter and tone. I hear these with twogood receivers.

Many radio fans rap programs and sta-tions when they are using poor sets, cheapspeakers and sets in poor condition.

I have a log of more than 300 stations,have no trouble tuning out locals and amrarely bothered with a heterodyne whis-tle, which gets the blame of all receptiontroubles.

KWKH has 3,500 watts, so we get itsmusic louder.

A receiver several years old cannot beexpected to have the selectivity, powerand tone of a new AC set.

L. H. RAINES,Apartment 209, 425 W. 46th St. Terrace,

Kansas City, Missouri.* * ti

"LOCAL" TROUBLEEDITOR RADIO WORLD :T T seems as if there was somethingI decidedly "local" causing the poor qual-ity reception which your correspondentA. S. McBryde mentions in his letterpublished in RADIO WORLD. It is quiteapparent that he dislikes chain programsand that is probably the reason he getspoor reception.

There was a time when a program fromthe Pacific Coast or even from Chicago(sent to New York and rebroadcast) hada "canned" sound-but not lately.

Anything more natural or less "canned"sounding than the two conventions (oneither chain) it would be hard to imagine.

Either the engineers at the Detroit sta-tions don't understand amplificatibn(which is doubtful) or the writer of the.letter has one of those dollar ninety-ninespeakers which sound like Fourth of Julytooters.

A rabid chain Program fan,H. I. SMITH, Hanover, Mass.

Western Chain OpensOffice in N. Y. City

Believing that de luxe chain programsare most popular, the American Broad-casting Co., operating a network of Pa-cific Coast stations which may be ex-tended further Eastward soon, hasopened offices at 119 West 57th Street,New York City, which will b'e maintainedin addition to the main headquarters inthe Lloyd Building, Seattle, Wash.

It is understood that a Salt Lake Citystation will be added shortly to the net-work, which comprises KJR, Seattle,Wash.; KEX, Portland, Ore.; KGA,Spokane. Wash.; KYA, Sart Francisco,and KMTR, Los Angeles, linked up by

Postal wires.

North Americans

Meet to CodifyShort Wave Use

Washington.Radio officials of the Canadian, Mex-

ican and Cuban governments met inWashington to discuss policies in respectto the control and allocation of continentalshort waves.

The purpose of the conference was pri-marily to coordinate the general policieswith respect to the control and wave allo-cations on the North American continentso as to minimize interference that wouldresult through haphazard allocation ofshort wave or high frequency channelswithout consideration of other countrieson the continent.

The Radio Commission recently tooksteps to set aside certain specialty se-lected high frequencies for specific classesof usage, for types of services in whichseveral stations may share channels toadvantage. Information as to such as-signments was requested by the Commit-tee on Shorty, Waves, comprising Commis-sioners E. 0 Sykes and 0. H. Caldwell,prior to the allocation of radio high fre-quency channels for continental use.

The North -American conference wasexpected to further a plan for such shortwave allocation. A legal discussion as tothe public service of short wave alloca-tions for specialized uses has been prog-ressing within the Commission, it waspointed out.

Among these speial classes that wouldbe granted licenses are communication be-tween airplane; and ground stationscommunication between ships and ship toship and coastal stations by radio tele-phone; for police department; marinecalling frequencies for tentative use untilinternational agreement is secured; ex-perimental frequencies; geophysical work ;railway communication between engineand caboose of long freight trains; scien-tific expeditions ; portable stations andpower line control, has been the subjectof some discussion, it was stated. It in-volves short wave radio service for powerlines for emergency use.

WEAF Stuttering Dueto Moths in Condensers

Something was wrong at the W EAFtransmitter of the National BroadcastingCompany. Engineers at the- Belmore,Long Island, radio broadcasting plantcouldn't figure out why the transmitterwasn't functioning as it should.

O. B. Hanson, manager of plant opera-tion and enginering, ordered an investiga-tion. The trouble was located in an in-termediate amplifier. Hundreds of tinymoths had crawled between the condenserplates and had been electrocuted. Throughthe moths were dead, their execution hadresulted in a short circuit in the amplifier.

Now the condenser, previously il-luminated by a bright light which at-tracted the moths, is in darkness. Andas an additional precaution, the entire ap-paratus is surrounded by fine -mesh mos-quito netting.

"INSIDE" INTERFERENCEMuch heterodyne interference com-

plained of originates right in the re-ceiver either because it oscillates uncon-trollably or because it is an improperlydesigned Super -Heterodyne. Some re-ceivers of this type squeal and growl assoon as there are two or more stationson the air. The squealing is due to thefact that in every Super -Heterodyne anystation comes in at two dial settings, theso-called "one -spot" not excepted.

16 RADIO WORLD August 18, 1928A THOUGHT FOR THE WEEKMEBODY gravely announces that dur-ing the coming Fall and Winter one

million owners will exchange their presentsets for something newer and better-or, atleast for something different. What's to be-come of the old sets? Perhaps the radiotrade will resort to something like the meth-od adopted by the music trade a good manyyears ago when the old square piano was anuisance. Piano manufacturers and dealerscalled convention, which was held in Atlan-tic City, where square pianos from all overthe country were destroyed in a bonfire. Re-sult: the price of a square fell 100 per centbelow par the day following the bonfire.

Why not try the scheme for radio?

The First and Only National Radio Weekly

Radio World's Slogan: "A radio set for every hems."

TELHPHONES: BRYAN'r 0558, 0559PUBLISHED EVERY WEDNIEISDAY

(Dated Saturday of same week)FROM PUBLICATION OFFICE

HENNESSY RADIO PUBLICATIONS CORPORATION145 WEST 45TH STREET, NEW YORK. N. Y.

(Just East of Broadway)ROLAND BURKE HENNESSY, President

M. B. HENNESSY, Vice -PresidentHERMAN BERNARD, Secretary

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EDITOR, Roland Burke HennessyMANAGING EDITOR, Herman BernardTECHNICAL EDITOR, J. E. Anderson

ART EDITOR, Anthony Sedan)CONTRIBUTING EDITORS:

James H. Carroll and Capt. Peter V. O'Rourke

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order. Business Opportunities, 10 cents per word. $1.00minimum.

Entered an second-class matter March 23, 1922, atthe Post Mice at New York. N. Y., tinder the Act ofMarch 3. 1879.

Karas Brothers WinThe sailing yacht "Siren," owned and

sailed by the Karas brothers, L. L andA. E., recently won the Mackinac race,the Lake Michigan classic, for the sec-ond consecutive year. Both sailors arevice-presidents of Karas Electric Co.,prominent radio parts manufacturers,4040 N. Rockwell Street, Chicago.

Rating in HorsepowerFavored for Stations

WashingtonRequests made by Commissioner 0. H.

Caldwell of the Federal Radio Commis-sion, for an improved method of express-ing the power of broadcasting stations,because of recent public discussions of the"tremendous power" of such stations hasbrought from the Commission the sug-gestion that all radio stations be rated inthe "old familiar term of 'horsepower.' "

In a letter, Commissioner Caldwellpointed out a "20 -horsepower station," likeWBZ, of East Springfield, Mass., WGN,of Chicago, and KOA, of Denver, "seemsnot nearly so formidable as one called bythe uglier term of '15 kilowatts.' " Onehorsepower equals 746 watts.

"A sixty -horsepower station, like WE -AF of New York or KDKA of Pitts-burgh," he said, "is not such a terrifyingthing when compared to any seven -pas-senger automobile, which radiates almostexactly the same amount of power," hesaid.

Text of LetterThe full text of the letter, made public

without the name of the addressee, fol-lows :

"In answer to your several requests foran improved method of expressing thepower of broadcasting stations, it mightbe well, in view of recent public discus-sions of the 'tremendous power' of suchstations, to rate all radio stations in theold familiar by -gone terms of 'horse-power.'

"Speaking of a station in terms of its'horsepower' would probably give a clear-er conception of the actual power quan-tities involved, to the minds of the Radio

Commissioners, the general public, and theRadio leaders of Congress.

"One horsepower equals 746 watts.Knowing this ratio, one can readily trans-late bothersome electrical terms into fa-miliar farmer and shop language.

"Thus, a '20 -horsepower station' (likeWBZ, KGN or KOA) seems not nearlyso formidable as one called by the uglierterms of '15 kilowatts.'

One -Horse Stations"And, a 60 -horsepower station,' like

WEAF or KDKA, is not such a terrify-ing thing when compared to any seven -passenger automobile, which radiates al-most exactly the same amount of power.

"If a familiar comparison for the 20 -horsepower station is called for, it canbe found in the domestic electric rangeand water heater installed in hundredsof thousands of American homes, andwhich similarly consumes about 15 kilo-watts, or 20 horsepower.

"The only drawback to this nomencla-ture lies in the possibility of some wagreferring to broadcasters like WGR (Buf-falo), WBT, (Charlotte, N. C.), WHA,(Madison, Wis.), etc., as being 'One horsestations,' which, of course, they are-theiroutput of 750 watts being almost exactlyone electrical horsepower.

"Expressed in such homely language ashorsepower, familiar to every farmer andmechanic, the mystery of kilowatts andsuch gibberish is gone; the lay listenerwill no longer be mystified and impressedby ranters against high power ; and thecause and opportunity for much politicaloratory this winter will be automaticallyremoved."

Board Puts Check onExperimental Waves

Washington.The Federal Radio Commission will not

grant applications for experimental broad-casting licenses unless it is determinedthat the research is designed to accom-plish a definite purpose and to furtherthe art of broadcasting, CommissionerOrestes H. Caldwell announced.

Many requests for experimental licenseshave been received, said Mr. Caldwell,and there is not room to grant all appli-cations. Therefore, he said, the decisionhad been reached only to grant suchlicense when it is known and when anapplicant can prove beyond doubt thathe is setting out to discover facts oracquire information not already availableto the art.

Text of LetterThe full text of the body of a letter

sent by Commissioner Caldwell to an ap-plicant for an experimental license, set-ting forth in general the Commission'sviews follows :

"The Commission has asked me to re-port to it upon recommendation in thecase of your application for an experi-mental license.

"As you are aware, the Commission isbeing overwhelmed with requests for ex-perimental licenses by all groups of people,many of them wholly unequipped to carryon experimental work, or without definitepurpose as to what such work shall ac-complish.

"I have read over carefully the state-

ments filed with your application but Icannot find any definite reference to thework which you intend to accomplish, ifgranted this license.

"I believe the Commission is forced tolimit such liCenses to cases where theapplicant shows beyond doubt that he issetting out to discover facts or informa-tion not already available to the art.

Board Is Careful"The Commission keeps a careful cross

reference of the various classes of re-search work being done and often it ispossible to refer applicants to other workwhich has been accomplished by earlierexperimenter without issuing a specialexperimental license.

"Of course, you will understand that Ithoroughly encourage experimental workof all kinds. The development of radiohas come from experimentation and anycheck upon the freest use of such experi-ments would be fatal to the furtherprogress of the art.Novel Research Encouraged

"On the other hand, with the limitednumber of wavelengths available, and withthe great congestion in all parts of theland, it is necessary to observe the great-est possible scrutiny of every applicationto make sure that the work contemplatedis along wholly new and novel lines anddoes not merely duplicate investigations,the result of which are already well knownto the art."


I

The Radio Trade

Manufacturer StopsResale Price Fixing

WashingtonResale price maintenance on radio re-

ceivers and parts will be discontinued by amanufacturer of such apparatus accordingto terms of a stipulation agreement be-tween the company and the Federal TradeCommission, it has been announced. Thestatement regarding the stipulation, No.236, follows in full text :

"This company sought the cooperationof dealers in maintaining resale prices andenforcing them.

"In several instances it traced price cut-ters by means of serial numbers andsecret symbols placed on its productswhen shipped out. In other instances themanufacturer entered into contracts,agreements or understandings with cus-tomers, who had been cut off from theirsupplies, for maintenance by such cus-tomers of resale prices as a condition tothe' reopening of accounts.

Practices Described"The radio apparatus manufacturer

agreed to discontinue the following prac-tices :

"(a) Entering into contracts, agree-ments or understandings with dealers tothe effect that such dealers, in resellingthe products purchased by them from therespondent, will adhere to any system ofresale prices fixed or established by saidrespondent

"(b) From securing or attempting tosecure assurances or promises from deal-ers that they will observe the prices es-tablished by the respondent for resale ofproducts purchased from respondent bydealers; and

"(c) From securing or attempting tosecure the cooperation of dealers in main-taining or enforcing any system of resaleprices whatsoever, and

"(d) From acting upon information re-ceived from its cooperating dealers by

threatening to refuse, or refusing to sellits products to any dealer because of suchdealer's failure to adhere to any suchsystem of resale prices; and

Cooperation With Dealers"(e) From soliciting the cooperation of

dealers in reporting dealers cutting pricesor alleged to be cutting prices of respon-dent's products, and acting upon informa-tion thus obtained by cutting off or threat-ening to cut off such offenders ; and

"(f) From soliciting promises or assur-ances from such offenders that they wouldthereafter maintain the suggested resaleprices as a condition to further supplyingthem with products ; and

"(g) From directly or indirectly carry-ing into effect, by cooperative methods,any system for the maintenance of resaleprices eliminating or having a tendencyor capacity to eliminate price competitionon its products."

Armor Tubes in New HomeThe Armstrong Electric & Manufac-

turing Co., Inc., has removed to its newplant at 187 Sylvan Avenue, Newark, N.J., from 351 Halsey street, the same city.The Sylvan Avenue factory is of the mostmodern. type and is located in NorthNewark, near the Erie Railroad. The out-put of Armor tubes is more than quad-rupled, due to the larger space and extramachinery installed.

The plant has been working full time allsummer. G. A. Armstrong of the com-pany, predicts a splendid radio season.This concern makes a full line of radiotubes for all uses, including AC, rectifierand power tubes. New information onthe use of tubes may be had for the ask-ing from the above concern. MentionRADIO WORM-J. H. C.

Penn's New SpeakerGoes in for Colors

Since the inception of the first sound re-producing apparatus, George R. Penn hasbeen a leader in this field, inventing, ex-perimenting, perfecting and making unitsand loudspeakers of all types. He, there-fore, knows all the contributing factors thatmake for perfect reproduction and hasbrought out several remarkable speakers.

In line with his production of better re-producers, 'he has brought out two newspeakers for the coming season. One isthe Fabricone Wall Speaker, that gives won-derful tone reproduction on any type re-ceiver, electric or direct current. Thisspeaker is made of a special fabric treatedwith liquitone, both creations of Mr. Penn.

The speaker is fifteen inches in diameter,comes in beautiful colors, is bound in silkcordings with 'hangings and lovely decora-tive tassels. It is highly ornamental.

The driving 'motor of this speaker is' thefamous G. R. P. Cone Unit with sturdy,dependable horseshoe magnet with four pole

e

pieces and double adjustment, rendering itadjustable to all outputs. It matches filterand tube impedances so well that, coupledto any of them, it will please the most fas-tidious ear.

Mr. Penn also has ready the latest per-fected development of his 30 -inch doublecone speaker. This comes in kit form, butwith the advantage that the work is alreadydone, all that is necessary being to openthe cone, which comes all ready cut andpasted, insert the unit and brackets whichare tightened almost instantly, and the coneis ready to play. The cone is beautifullydecorated and the same finefunit is furnishedwith the kit.

Both these speakers are rigidly guaran-teed. Fans are therefore fully protected ontheir orders. This company has a goodproposition for dealers and jobbers who areinvited to correspond with George R. Penn,231 Mercer Street, New York City. Men-tion RADIO WORLD.-J. H. C.

LiteratureWanted

THE names and addresses of readers WIRADIO WORLD who desire *erasure

on parts and sets from radio nianigooser-ere, jobber., dealers and mail order hawsesare published in RADIO WORLD as re-quest of the reader. The blank hedow maybe used, or a post card or letter will doinstead.

RADIO WORLD,145 Wsst 45th St., N. Y. City.

I desire to receive radio literature

Name

Address

City or town

State

R. E. Hawk. 2440 Askew, Kansas City, Missouri.H. I. Viets, 808 W. Monroe St.i, Belleville, Illinois.John J. Fischett, 208 Willough y Ave., Brooklyn,

New York.Carl Hann, 3073 W. 114 St., Cleveland, Ohio.

Dullerin Ave., Wallaceburg, On-tario, Canada.

C.NEuygene Taylzr, 16 Maple Place. Port Chester,

Paul A. Hagen, 1530 Jeniter, Madison, Wisconsin.A. W. Hiz, 335 E. 209 St. (Apt. 20), New YorkP. J. Selzle, 4142 South 12th St., Omaha, Ne-

braska.Franck Myers, P. 0. Box 194, Berkeley, Cali-

fornia.Randall Sharwell, 5 Van Eyk Ct., Lyndhurst, New

ersey.B. Allen, 9006 Quincy Ave., Cleveland, Ohio.

WW. T. Hale, 5.39 Moss Ave., Roston, Massachu-

setts.Frank

Id. Taylor, 58 Corey St., Everett, Massa-chusetts.

Eugene Payor, 325 Bush Street, San Francisco,Calif.

J. G. Brohl, P. 0. Box 309, Hayward, Calif.New Smyrna Auto Electric Co., 202 N. Orange

St., New Smyrna, Fla.F. L. Hutchins, Tumbledown Mt. Forestry,Skinner. Maine.Gordon Battery Cp., 126 W. Albany St. Herkimer,

N. Y.S. Jupp, 3367 Wellington St., Verdun, Quebec,

Canada.Meyer D. Walters, 202 Aisguith St., Baltimore,

Md.John J. Bunnell, Box 967 Pampa, Texas.Robert S. Burgess, 1118 E. Douglas Ave., Nash -vale, Tennessee.Chas. E. Hilts, 241 Main Street, Reading, Mass.Eric Strahl, 726 E. 227 Street, Bronx, N. Y.Al Bloom, 67 E. 105 St., N. Y. City.E. A. Oardson, Stewards Dept., S.S. Leviathan,Pier 86, N. Y. C.Jacob Averbach, In E. 111 St., New York City.Lewis Brunett, Enumclau, Washington.Geo. T. Euard, Bradford, Illinois.M. Rubenstein, Dield & Co., DeKalb, Illinois.Herberts McClure, 2909 A Kossuth, City of St.Louis, Mo.J. J. Glade, 94 W. 52nd St., Bayonne, New Jersey.Carl A. Berger, 503 Delaware Ave., Albany, N. Y.G. M. Williams, 1700 Golden Ave., New YorkCity.Brown's Radio, 1139 St. Clair W., Toronto, Can-ada.Albert E. Taylor, 803 So. 2nd Street, Maquoketa,Iowa.R. B. Coffman, U.S.S. Relied, c/o Postmaster.San Pedro, Calif.Ted. V. Tazeau, 2855 G. G. Avenue, San Fran-cisco, Calif.Del E. Atcheson, 14882 Kentucky Ave., Detroit,

iganu.chner, 69 Moffatt Street, Brooklyn,MiFchB

j.Nij.Farrar, Yakima, Washington.Morris S. Cohen, 469 Pennsylvania Ave., Brook-lyn.C. E. NBialuirse.n, Oil City, Penna.L. P. Matte. Ban of Montreal, Quebec. Canada.J. Verlin Hunt, 628 So. 11th St.,Richmond,Indiana.

C. C. Lingo, 1052 Camp St., New Orleans,Louisiana.Doyle L. West, 3)02 W. 7th Ave., Corsicana,Texas.Louis Ruziecke, Jr., 848 West 42nd Pl., LosAngeles, Calif.Peter J. Schmitt, 847 Glenwood Ave., Buffalo,New York.V. J. Patterson, The Commodore, Seattle Wash-ing ton.

peEnna. J. Walker, 124 Washington St., Carbondale,C. L. Stooksberry, 1301 East 31st St.. Savannah,Georgia.Robert A. Brooks, Route 2, Box 50, Martin,Tennessee.Cameron Mill, Carrollton, Kentucky.Ray Lee Defries, Memphis, Tennessee.


ELIMINATEBATTERIES!

NO Change in Set WiringNO Change in Tubes

4ir Eliminator, Using Raytheon Tube,Replaces "B" Batteries and GivesGreat Satisfaction.

No. B16 -"B" Eliminator for 50 to60 cycle, 105 to 125 -volt AC housecurrent. Max. voltage, 180, with onevariable detector and one variable in-termediate voltage. Weight 16 lbs.Size, 6 x 61,45 x 11%". Quiet, eco-nomical. Requires no attention. Soldonly with Raytheon tube. Price, including RaytheonBH125 mil. tube and built in connector cord andplug.

Famous Raytheon TubeWith Each "B" Eliminator

'16

A`Pi I Eliminator, Using Dry Plate Recti-fication, Current Well Filtered;Replaces "A" Battery.

No. A22 -"A" Eliminator. Suppliesup to 2 z amperes at 6 volts. Vari-able resistance permits- adjustment tonumber of tubes in set. Supplies Acurrent and voltage to sets using from4 to 10 quarter ampere tubes, orequivalent current drawn by any othercombinations. Tip jacks for voltmeter readings. Re-ceptacle for "B" eliminator nlug. Pendant switchcontrols everything. Set switch needn't be touched.Device requires no attention. Uses no tube. glee:10%" high, fiY3" wide, 111/u" long. Shippingweight, 27 lbs.

'22

CUSTOM SET BUILDERS SUPPLY CO.,168 Washington Street, New York, N. Y.

Please ship at once -0 One 180 -volt maximum "It" eliminator, with

variable detector and variable intermediate volt-age (three different voltages in all); equippedwith one Raytheon BR tube, 125 milliampererating. I will pay $16, plus a little extra forfreight, on receipt of goods, which are to be onapproval for ten days (money back, if desiredafter 10 -day trial).

0 One "A" eliminator. 2 -ampere maximum at6 volts, using dry plate rectification, large chokeand large capacity condenser, AC switch, recep-tacle for any "B" eliminator plug, variable re-sistor, all built in for which I will pay $22,plus a little extra for freight.

El Both the "B" eliminator and the "A" elimina-tor, at total of $36, on same approval basis.

Note: If fast express shipment is preferred, ratherthan slower freight, put a cross here 0.

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City State

ALL SHIPMENTS MADE ONAPPROVAL FOR TEN DAYS

All prices quoted are NMI

Flat AmplificationWas Designer's Goal

(Continued from page 5)ent on the higher wavelengths there isevery reason to believe that the curve rep-resents the actual performance of thereceiver above 300 meters.

The rapid rise in amplification of the

NEW CORPORATIONSSalt City Radio Service, Syracuse.-Attys.,

Moot, Sprague, Brownell & Marcy, Buffalo, N. Y.Espey Mfg. Co.-Attys., Hays, Podell & Shul-

man, 39 Broadway, New York City.Simplex Radio Supply Co., Chicago, II -Colonial

Charter Co., Wilmington, Del.Baird Television Corp., Wilmington, Del. -

Corp. Trust Co. of America, Wilmington, Del.Baird Parent, Inc., Wilmington, Del., patents,

Corp. Trust Co. of America, Wilmington, Del.Martwel Sales Co., radio apparatus--Attys.

Bijur & Herts, 19 West 42nd St., New York,N. Y.

calculated curve below 300 meters is off-set by the fact that on these lower wavesthere is a tendency for the receiver tooscillate, which is in turn offset by reduc-ing the potential on the screen grids ofthe RF amplifier tubes by adjusting po-tentiometer, RI.

The effect of this reduction is to in-crease the plate impedance of the RFtubes, which, in turn, decreases the effec-tive amplification and increases the effec-tive selectivity. The net result is a flat-tening off of the over-all amplificationcurve much as shown by the dotted linesof Curve H, Fig. 5.

Curve H represents the actual perform-ance of the receiver. It is seen to bequite flat although the individual curvescomposing it were anything but flat tostart with.

At this point it is interesting to go backand compare the RF amplification of the

(Continued oni next page)

IN

No. 720Screen GridSIX KITS

OFFICIAL FACTORY- SEALED CARTONS

PRICELIST

X72.55Custom Set Builders!

Cash in on this Fine Op-portunity to Build an Out -

Performing Set!No. 700 Shielding Cabinet,

$9.25 extra, list price.

The beautiful chassis of the newest kit -setsensation, the S -M Shield Grid Six.

The set as it looks in a No. 700 shieldingcabinet This cabinet alone lists at $9.25.

UNUSUAL OFFER!(Applies to this kit enly I)

E extend not only the regular busi-ness courtesy to custom set builders,

but also make the unusual offer of FREEtechnical information and advice on theSM-720 Screen Grid Six. Any questionconcerning this circuit will be promptlyanswered. Write, telegraph, or visit us.

When you buy from us you have expertconsulting engineers at your command!

SPECIAL!Full-sized pictorialblueprint of the wiring,large schematic dia-gram and 8 -page de-tailed building instruc-tion booklet.

THE OFFICIAL PARTSOnly the official kit of tested parts, in factory -sealedcartons, is sold by us, all parts exactly as specified byMcMurdo Silver.These parts consist of:Designa- List

twn Nature of Parts PriceBEDID2CI

C2 -C3 -C4C5

SH I -SH2SH3LI

L2 -L3 -L4SI -S2-S3S4-85-8657-S8TI

WT2

RI

SW11-12R2 -R3 -R4R6R5C6C7 -C8 -C9CIO -C11 -C12

OneOneOneOneOne

OneOne

S -M 701 Universal Pierced chass1s $ 3.00S -M 809 dual control escutcheon 2.75S -M 806L (left) vernier drum dial... 2.50S -M 806R (right) vernier drum dial 2.50S -M 320R .00035 mfd. Universal con-denser 4.00S -M 323 .00035 mfd. 3 -gang condenser 13.50S -M 342B .000075 mfd. midget con-denser 1.75

Three S -M 638 copper stage shields @ $1.50One S -M 140 antenna coilThree S-01 132A plug-in RF transformers @

$1.25S -M 512 5 -prong tube sockets @ $0.60S -M 511 tube sockets @ $0.50Three

Five

OneOneOneOneOne

OneTwoThreeOneOneOne

Six

C13 One

CI4Ft7R8S9PPI-BP2BP3

OneOneOneOneThree

S -M 255 first stage A. F. transformer.S -M 256 second stage A. F. transformerS -M 708 10 -lead. 5 -foot connection cableS -M 818 hook-up wire (25 ft. to carton)Yaxley 53000, 3,000 ohm midget so-

tent,ometerYaxley 500 switch attachmentYaxley 420 insulated tiplacks @ $0.125Carter RU 10, 10 ohm resistors @ $0.25Carter A6. 6 ohm sub -base rheostatCarter HIV2, 11/4 ohm resistorPotter 104, I mfd. bypass condenser

Sprague 1/4 mfd. midget condensers @$0.75

Polymet .00015 mfd. grid condenserwith slips

Polymet .002 mfd. bypass condenserPolymet 2 megobm grid leakDurham .15 megohm resistor with leadsNaald 481XS cushioned tube socket

Moulded binding posts consisting of8/32 screw, nut, and moulded top @$0.10

One Set hardware as listed below

4.503.00

3.751,802.50

6.006.001.75.50

1.25.40.25.75.50.25

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HARDWARE SET CONSISTS OF:$72.55

One 34"x1/4" hollow condenser studs; eight 1%"x1/4" hollow coilstuds; eight 17/v"x6/32 R. H. machine screws; six I"x6/32 R. H.machine screws; twenty-nine %"x6/32 R. H. machine screws;thirty-seven 6/32 nuts; forty-six Shakeproof lock washers; four11/2"xNo. 10 R. H. wood screws; three lengths of spaghetti; fourlengths bus -bar; two sets binding post insulating washers; threesets instrument insulating washers; two tiplack insulating washers;one metal washer; eighteen long soldering lugs; three grad CUPS.

8 -page detailed Building Instruction Booklet, full-sizedpicture blueprint and schematic diagram FREE witheach kit order'.

GUARANTY RADIO GOODS OMPANY145 WEST 45TH STREET NEW YORK CITY

[A Few Doors East of Broadway]


(Continued from preceding page)Screen Grid Six, ranging as it does from250,000 times up, with the gain of the rep-.resentative set measured and describedpreviously.

The reason for the remarkable perform-ance of the Screen Grid is easily appre-ciated -when its voltage amplification of250,000 times is compared with the 1,000 -fold gain of the ready-made TRF sets.

Before passing on from the RF ampli-fier, it is well to mention that every pre-caution has been taken to render the per-formance of this portion of the receiveras stable and dependable as possible. Thiscan be easily realized from an examina-tion of the design, which reveals indi-viduial copper stage shielding for thetuned RF amplifier circuits, individual by-passing of all B supply leads by condens-ers directly in the stage shields, and theisolation of all RF currents from any com-mon paths which might cause couplingand instability.

No Stray Pick-upsThe antenna input circuit is thoroughly

shieldeid from the three remaining RFcircuits, and when the receiver cabinet isin place, it is thoroughly shielded fromextraneous interference. It is then prac-tically impossible to receive the strongestlocal signal if the antenna lead-in wire beremoved from the set.

Yet with a one -foot wire for an antennaadded, many stations come in with ampleloudspeaker volume, so great is the pick-up of the set.

To compensate for varying antennacharacteristics, the option of two methodsof antenna coupling is provided and oneis equipped with a variable selectivity con-trol in the form of a 75 mmfd. antennaseries condenser, CS. The single tuningcondenser Cl, tunes the antenna circuit,and the triple gang condenser, C2, C3, C4,tunes the three remaining RF circuitshoused in shields SH1, SH2, SH3.

The construction of this condenser issuch that its accuracy is permanently as-sured through the use of a heavy die-castframe which adequately protects and per-manently aligns all plate assemblies, whichare double-spaced. The condenser accu-racy is guaranteed by the manufacturersto within 1% over the upper half of thedial and to within 1 mmfd. over the lowerhalf of the dial, which accuracy is morethan ample to provide 10 kc. selectivity(1% pluis and 1% minus is usual tolerancefor the finer ready-made sets).

Compensators' Function

Three compensators are provided uponsections C2, C3 and C4, which allow com-pensation, once the set is assembled, forvariations in tube and circuit capacities.

Oscillation over the lower portion of thebroadcast band, and volume over the en-tire band, is controlled by the poten-tiometer, R1, which varies the potentialon the screen grids of the RF amplifiertubes, S4, S5, S6.

The detector, S9, presents no unusualfeatures, being the conventional grid-con-denser (C13) and leak (R7) type, withnegative filament return, since this wasfound to give better results in the ScreenGrid Six.

Other Illustration on Front Cover* *

[This concludes Part I of McMurdo Sil-ver's two-part article on the new ScreenGrid Six. Part II will be published nextweek, issue of August 25th. In subsequentissues others will present facts they havegleaned from personal operation of the re-ceiver over a period of two months.-Editor.]

Recent Issues of RADIO WORLD, 15 cents each.Any number published in 1928 available for ashort while. Six issues 75 cents, 10 issues $1.00.Send stamps, coin or money order NOW, beforethe issues are sold. RADIO WORLD, 145 West45th Street, New York City.

Selectivity Is PreferredTo Higher Gain Per StagePractical considerations of selectivity

have been invoked in the S -M 720 so thatinter -station interference will be absent,heterodyne interference reduced to a prac-tical minimum, since this is largely inde-pendent of receiver characteristics, andmaximum gain per stage is somewhat sac-rificed to attain 10 to 15 kc. selectivity.

The choice was dictated by experience,since a receiver is to be judged on itsactual performance rather than on theo-retical calculus. For instance, a gain of14 per stage at 550 meters and of 30 perstage at 200 meters, was an expert anddeliberate choice, since the 30 to 65 gainper stage easily attainable would destroythe selectivity.

The gain at the tuned input (antennacoil) is somewhat greater.

The Aerovox Research Worker is a freemonthly folder that will keep you abreast

of the latest developments in Radio.A postcard will put your name on

the mailing list. Write to-day. Aerovox Wireless

Corp., 72 Wash-ington Street,

Brooklyn,N. Y.

THE SHOW NUMBERof Radio World will be publishedunder date of

September 15thThis issue goes to'press Wednesday,

September 5th.It will contain extra features, is as-

sured of extra circulation, and com-memorates the Fifth Annual RadioWorld's Fair, Madison Square Garden,September 17th to 22nd.

Advertising rates in the Show Num-ber will not be advanced over usualrates. See editorial page of this issuefor rates.

RADIO WORLD145 West 45th Street, New York, N. Y.

THE DIAMONDOF THE AIR

Using General Purpose Tubes

4 TubesSet uses three type Atubes and one 112 type;has TRF stage, regen-

erative detector and two stages of trans-former coupled audio. (This is not ShieldedGrid Diamond.)

5 Tubes Same RF and detectoras the other, but hasone transformer and

two resistance coupled audio. Especiallysuitable for B battery operation. (NotShielded Grid Diamond.)411 awl.. A.m. Aim=

Guaranty Radio Goods Co,145 West 45th Street, New York City.Please send me one newly printed official blue-

print of the -0 5 -tube Diamond of the Air0 4 -tube Diamond of the Air

(Cheek off one you want.)and the textual data giving full directions for eon-etruction.

Enclosed please ilrd 25 cents to defray all ex-pense.

NAME

ADDRESS

CITY STATSI(These are not Shielded Grist Diamonds.)

A NewFabricone Wall Speaker

Designed byPenn

Made of specialfabric treatedwith liquitonewhich revolu-tionizes repro-duction. Fifteeninches in diam-eter, in beauti-ful colors, boundin silk cordings.and highly orna-mental. Drivenby the famousG.R.P. ConeUnit with stur-dy horse shoemagnet, f ourpole pieces anddouble adjust-ment whichrenders itadaptable to alloutputs.

Shipped in KitForm. $11.50

Easily and Quicklordersene

fc,crheck immeodriatemondees.

livery.Assembled.

GEORGE R. PENN CO.Dept. A

231 MERCER STREET NEW YORKCatalogue of Wall Sneakers and

accessories on request.

VICTOREENSuper Coils

Geo. W. Walker Co.2825 Chaster Avenue

Dept. B Cleveland, 0.

Socket WrenchFREE!

Push out the control lever withknob (as at left) and put wrenchon nut. Push down on handleonly (at right), then turn nutleft or right.

One of the handiest tools for a custom setbuilder, service man or home constructor is aBERNARD socket wrench. It consists of a61/2" long metal tubing in which is a plunger,controlled by a knob. The plunger has a grip-ping terminal (called a socket, hence the name"socket wrench") that may be expanded orcontracted to fit 6/32, 8/32 and 10/32 nuts, themost popular sized nuts in radio. Use theknob to push out the plunger, press down onthe handle to grip the nut, then turn the nutto left for removal or to right for fasteningdown. Total length, distended, includingstained wooden handle, 10". Gets nicely intotight places. Send $1 for 8 weeks' mail sub-scription for RADIO WORLD and get thiswrench FREE. No other premium with thisoffer. Act NOW!

RADIO WORLD- 145 WEST 45TH ST., N. Y. CITY

A few doors east of Broadway

20 RADIO IATORLD August 18, 1928

Industries BanquetTo Be Held Sept. 18

The Fifth Annual Radio IndustriesBanquet, sponsored by the three greatgroups composing the radio industry, willbe held Tuesday, Sept. 18, at the HotelAstor, New York City. The groups arethe National Association of Broadcasters,the Radio Manufacturers Association andthe Federated Radio Trade Association.

Linked together, from 10 to 12 o'clock,

DOUBLE SHIELDPORTABLE BLUEPRINTActual size, clear wiring in pic-

ture form, after H. G. Cisin's pat-tern, exactly as described in thisissue. Indorsed by him.

PRICE $1.00Send Check or M. 0. for Immediate Delivery

or Come in Person

Guaranty Radio Goods Co.145 WEST 45TH STREET

NEW YORK, N. Y.(Few Doors East of Broadway)

eastern daylight saving time, on this oc-casion, will be all of the station of theRed, Blue and Pacific Coast networksof the National Broadcasting Company,the chain of the Columbia BroadcastingSystem, and, in addition, a large numberof other stations not included in eitherchain, but members of the National Asso-cation of Broadcasters.

The Banquet is an annual affair heldin conjunction with the Annual RadioWorld's Fair at Madison Square Garden.The Fifth annual Fair will take place thisyear Sept. 17 to 22.

McCULLOUGH TUBES NOWPLENTIFUL

For some time, the McCullough ACtubes were reported as scarce. The A. C.Neon Corp., at 122 Greenwich Street, NewYork City, announces that it can supplyall demands. Those desiring detailed in-formation should address the above con-cern. Mention RADIO WORLD-J. H. C.

Recent Issues of RADIO WORLD, 15 cents each.Any number published in 1928 available for ashort while. Six issues 75 cents, 10 issues $1.00.Send stamps, coin or money order NOW beforethe issues are sold. RADIO WORLD, 145 West45th Street, New York City.

Bakelite Front and Aluminum Subpanelfor the

4 -Tube Screen GridDIAMOND OF THE AIR -

Five -Day Mons. -Bach GuaraidgView of the Completed Receiver, using Drilled Front Panel and Aluminum Subpanel

Finest eye appeal results from construction of the 4 -tube Screen Grid Diamondof the Air when you use the official panels. The front panel is bakelite, alreadydrilled. The subpanel is aluminum, with sockets built-in, and is self -bracketing.Likewise it has holes drilled in it to introduce the wiring, so nearly all of it isconcealed underneath set. Make your set look like a factory job.

Front panel alone, bakelite, drilled $2.35Aluminum subpanel alone, drilled, with sockets built-in 3.00Screws, nuts and insulating washers supplied with each subpeneL

GUARANTY RADIO GOODS CO.145 WEST 45TH STREET NEW YORK, N. Y.[A few doors east of Broadway)

$5.00

Take Your Choice of 5Other PublicationsFor NEW RADIO WORLD Subscribers Ordering NOWRadio World has made arrangements-To offer a year's subscription for any one of the following publications with one year'ssubscription for RADIO WORLD-RADIO NEWS or SCIENCE and INVENTION or BOYS' LIFE or RADIO DEALER orRADIO (San Francisco).

This is the way to get two publications-for the price of one:-Send $6.00 today for RADIO WORLD-for one year (regular price-for 52 numbers)-and select any one of the other-six publications for twelve months.

-Add $1.00 a year extra for-Canadian or Foreign Postage-Present RADIO WORLD subscribers-can take advantage of this offer by-extending subscriptions one year-if they send renewals NOWT

Radio World's Special Two -for -Price -of -One Subscription BlankRADIO WORLD, 145 West 45th Street, New York City.Enclosed find $6.00 for which send me RADIO WORLD for twelve months (52 numbers),beginning and also without additional cost,Radio News, or Science and Invention, or Radio Dealer, or Radio (San Francisco), orBoys' Life (or $10.00 for a two-year subscription to one address), thereby getting RADIOWORLD and the other selected magazine, BOTH for two years. No other premium withthis offer.

Indicate if renewal.

Offer Good UntilSeptember 15, 1928 City and State

NO OTHER PREMIUM OF ANY KIND WITH THIS OFFER

Name

Street Address

Kiley's Best SellerUnder the direction of Pat Kiley, known

from coast to coast, sales of the B. B. L.unit in the red box with the yellow label,are steadily increasing. The volume ofsales has been kept high even during thehottest weeks. The unit is manufacturedby the Best Manufacturing Company, ofIrvington, New Jersey, represented inNew York City by the Sanford RadioCorporation, 122 Greenwich street.

Mr. Kiley is the chief district salesmanager, with offices at 30 Church Street,New York City. He has a novel salesplan for dealers that he explains master-fully. Fans that want to know what thisunit can do for them in the line of tonequality also may address Mr. Kiley. Men-tion RADIO WORLD-J. H. C .

New Sonatron TubeThe Sonatron Tube Company, 108 W.

Lake St., Chicago, Ill., makers of radioreceiving tubes, announced the X171AC,especially designed for output tube in re-ceivers operated on alternating current, asa replacement tube for the -71 type. Itis claimed that the new tube offers alonger life, improves tone and increasesvolume. Those who are interested in thenew and specially designed AC tubeshould write Sonatron Tube Co., 108 W.Lake St., Chicago, Ill. Mention RADIOWORLD.

BIG OFFER!Radio World for5nFour Weeks .

Blueprint FREE!of 4 -Tube Screen Grid Diamond of the Air

At 15c per copy RADIO WORLD costsyou 60c for four weeks. But if you send50c NOW you get the first and only na-tional radio weekly for four consecutiveweeks and a blueprint FREE!This blueprint is life-sized and shows ineasy picture diagram form how to mountparts and wire this super -sensitive re-ceiver. One screen grid tube is used asradio frequency amplifier. The rest oftubes are two -01A and one 112A.This circuit gives you distance, tone qual-ity, ease of performance. No shielding, noneutralizing required!

ACT NOW!This offer holds good only until August30th and coupon below MUST be used asorder blank.

Radio World, 145 West 45th Street, New York CityEnclosed please find 50 cents (stamps, coin,check or money -order) for which please enter myname on your mail subscription list for the nextfour issues of RADIO WORLD, and send meFREE at once a blueprint of the Four -TubeScreen Grid Diamond of the Air (front panel andsubpanel wiring, schematic diagram and partslist.

Name

Address

City0 RenewalIf you are a mail subscriber for RADIO WORLDYou may extend your subscription four weeks.Put a cross in the square in front of the word"renewal," to show you are a subscriber already.

State

EVERY FRIDAY at 5.40 P. M. (Eastern Day-light Time) Herman Bernard, managing editor oflady World, broadcasts from WGBS, the GimbelBros. station in New York, dismissing radio topiea,mostly television.


Real MUSICAL Instruments Are Made of Wood!THE SWEET MELLOWNESSOF WOOD GIVES REAL MUSIC!

THE finest reproduction is made possible by the longtone chamber horn loudspeaker, for then you hearthe true sounds, without over -emphasis or uncter-

emphasis in other words, without distortion. Violins,pianos,flutes, 'cellos and the like are not made out ofpaper or cloth, but out of wood. Nature chose wood asthe unsurpassed vehicle of sound. Man utilized the longtone chamber to make the sound supremacy of woodavailable for radio reproducers.

With fine quality smoulded wood formed into a longtone chamber you hear the orchestral instruments standout individually,-sounds from the boom of the bassdrum, the zoom of the 'cello, to the sweet, high notes ofpiccdlo and clarinet. And the human voice is natural,real. The hissing sounds of speech-high audio frequen-cies-come through as realistically as the guttural.

Use a long tone chamberhorn, like the No. 595 illus-trated at right, with aspecially sensitive and faith-ful motor, (Cat. No. 112),shown at left and enjoy thebest. Cat. No. 595, horn loud-speaker, tone travel 8 feet;over-all dimensions,, 21%'f

high, 18'" wide, 13" or 15"deep. Nozzle takes standardsize unit. Price $10.80.

Felt -padded Baffle BoardFREE with each order for aNo. 595. The baffle is used asthe inside shipping box. Noneed to remove the horn fromthe box. Use the outfit asyou receive it, inside a ca -Horn Motor, Cat. No. binet, or in any other place

112. Price $4.20. you desire.

Smaller Model MeetsSpace Economy Needs

WHERE space requirements limityou to a smaller size horn, useCat. No. 570, illustrated below.

The tone quality of this medium-sizedmodel far surpasses that of the usualcones, but does not quite come up tothat of the No. 595 on the extremelylow register (40 cycles and less). How-ever, it is a very satisfactory horn, asgood as can be made for the smallerspace.

Your mounting i problems are solved com-pletely with this model, as with the other,due to the inclusion of a FRED baffle boardwith each order.

No one need hesitate ordering the smallermodel if space limitations compel such choice,for the result will be charming beyond ex-pectations.

Cat No. 570 horn loudspeaker. tone travel6 feet; over-all dimensions t15" high. 12"wide. 12" deep. Nozzle takes standard sizeunit. Price $7.80.

Felt padded baffle board FREE with eachorder for a No. 570. Baffle Board FREE with each horn

order!

Long tonechamber horn(tone travel, 8feet) Cat. No.

595. Price

FREE Baffle Boardwith Each Order

THE long tone chamber mouldedwood horns are sold with an offerof a FREE baffle board that is

felt -padded so that the horn is felt -suspended and doubly protected againstpossibility of rattles. This is the finalpoint of protection and perfection.

What DeForest Says:"I do not consider any of the cones now on

the market come anywhere near the perfectloudspeaker. Cones invariably favor somefrequencies at the expense of others and mostof the cones, while over -emphasizing the bass,put a mask of paper rustle over the higherfrequencies. There are certain types of non-metallic horns now on the market which, withProper loudspeaker units, give far better re-production than any 18 -inch cone. I stronglyadvocate a radio set built into a large consolecabinet with sufficient room to take in one ofthe larger exponential horns."

-Dr. Lee DeForest in "Radio News" forApril, 1928.

Why saddle a goodTravel 8 feet and get somewhere!

set to a poor speaker?Travel 6 feet and outstrip the others,

anyway!

SEND NO MONEY!ACOUSTICAL ENGINEERING 'ASSOCIATES, 143 West 45th Street, N. Y. City

Please ship me at once the following (check off) :

0 One No. 595 at $10.80 plus a little extra to defray shipping coots; also send FREE baffleboard. 15" width will be sent unless 13" is specified by a cross in this square 0

D Ond.e

No. 570 at $7.80 plus a little extra to defray shipping costs; also send FREE baffleboar

El One No. 112 horn motor (universal nozzle) at $4.20 plus a little extra for shipping.

Name

Address

City Mate

Medium sized tone chamber horn (tonetravel, 6 feet) Cat. No. 570. Price $7.80.

5 -Day Guarantee of Money Right Back if Not Delighted-No Stalling-No Questions!


ARE YOUINTERESTED IN

DX?It's by no means a lost art.Greater distances than ever beforecan be covered today-if you knowhow. Try some of the ingeniousstunts described in "The Gatewayrto Better Radio"-that big unselfish, understand-

able manual of 20.000 words and 88 illustrations,which is yours for 25 cents a copy. Get yours to-day from your dealer or direct fromCLAROSTAT MANUFACTURING CO., Inc.285 North Sixth St. : : Brooklyn, N. Y.

CLAR.05TAT -)RxG. U. S. PAT. O

United Fruit CompanyAsks Suit Dismissal

Washington.The United Fruit Company, one of the

eight respondents named by the FederalTrade Commission in its complaint ofmonopoly and unfair methods of competi-tion in the radio equipment and accessoryfield (Docket No. 1115), filed with theFederal Trade Commission a brief in sup-port of its motion to dismiss the complaint.

The brief, submitted by William K.Jackson, J. Harry Covington, and John L.Warren, charged that "erroneous" infer-ences and conclusions regarding manufac-ture of radio apparatus and radio com-munication as they affect the United FruitCompany had been made. The brief wasin reply to that filed by Edward L. Smith,

A Strong, Rugged Loud UnitThat

(&1111111111111114;

Drives Any Cone Speaker and ReproducesFine Tone at Great Volume!

This unit has a full floating armature,which means that armature is mounted sothat it acts like a plunger between two setsof magnets or pole pieces. As the magnet-ization of the armature changes under theinfluence of the signal it plunges first towardone pair of pole pieces and ther,i toward theother.

The large field magnet used insures astrong and permanent polarizing flux, whichprotects against loss of sensitivity from self-demagnetization to which some loudspeakerunits are subject.

The cone driving pin is directly coupledto the full floating armature at that pointon the armature where the force is greatest.This insures against loss of power throughcomplicated levers.

The sturdy construction and heavy weightof the assembled unit prevent motion of theunit itself and insure that all the power istransformed into sound.

The armature is adjustable from an exposed knobin the back.

Apex, chuck and thumbscrew supplied with each unit!This unit stands 150 volts unfiltered.

With filtered output the unit has stood upto 550 plate volts continuously withoutdamage.

Each unit is supplied with an apex, con-sisting of two metal plates, so that any typeof airplane cloth or cone speaker may bebuilt; also with each apex are supplied athreaded chuck and thumbnut for engagingthe pin. The screw firmly grips the pin.Besides, a 60 -inch cord with tips, is alsosupplied with each unit.The Powertune Giant Unit, complete withapex, chuck, screw and 60" cord; totalweight, 3 lbs. (Cat. No. 1098) $3.75

SEND NO MONEY!

GUARANTY RADIO GOODS CO.,145 West 45th St., New York City.

Please send me one cone speaker unit (Cat.1098), as advertised, with apex. I will paypostman $3.75, plus few cents extra for post-age. Your 5 -day money -back guaranty isaccepted.

Name

Address

City State5 -DAY MONEY -BACK GUARANTEE!

counsel for the Commission, and supple-mented the oral .argument of counsel forthe Company made June 19th.

Other respondents in the case are theRadio Corporation of America, the Gen-eral Electric Company, the American Tele-phone & Telegraph Company the WesternElectric Company, Inc., WestinghouseElectric & Manufacturing Company, theInternational Radio Telegraph Company,United Fruit Company and the WirelessSpecialty Apparatus Company.

NEXT WEEK'S ISSUEAmong the articles in next week's

issue of RADIO WORLD will be one on theconstruction of an AC or DC short-wave adapter. The value of Series Fila-ments will be discussed in another arti-cle. The S -M Screen Grid Six will befeatured again in the second instalment.Pointers on modulation will be printed.

N. Y. AND CHICAGO SHOW DATESThe Fifth Annual Radio World's Fair

will be held in Madison Square Garden,New York City, September 17th 22d. TheSeventh Annual Chicago Radio Showwill be held at the Coliseum, October 8thto 14th. These shows are for the public.

SUBSCRIBERS!Look at the Expiration

Date on YourWrapper

Please look at the subscriptiondate stamped on your last wrapper,and if that date indicates that yoursubscription is about to expire,please send remittance to coveryour renewal.

In this way you will get yourcopies without interruption andkeep your file complete.

Subscription Dept., RADIOW 0 R L D, 145 West 45th Street,New York City.

Recent Issues of RADIO WORLD, 15 cents each.Any number published in 1928 available for ashort while. Six issues 75 cents, 10 issues $1.00.Send stamps, coin or money order NOW, beforethe issues are sold. RADIO WORLD, 145 West45th Street, New York City.

Quick Action Classified AdsRadio World's Speedy Medium for Enterprise and Sales

10 cents a word - 10 words minimum - Cash with OrderFOR SALE: Sentinel Dry A -B -C power unitwith tubes $44.50. 8 foot orthophonic horn size24Y2x18x15 inches, with Temple unit $8.00. Frittssuper cabinet, panel size 7"x24" $12.00. Multi -valve receiver $5.00. Aerial kit $.98. SM 222output trans. $3.00. Utah upright type pianospeaker $4.00. Everything guaranted new.Charles Frick, 311 N. Cherry St., Van Wert,Ohio.

RECENT ISSUES of Radio World, 15ceach. Radio World, 145 W. 45 St.,N. Y. City.

ARTISTS and Art Students are printing 250signs or pictures an hour without machinery.Sample and particulars 10c. Staco, 1014 Mul-berry, Springfield, Ohio.

SCREEN GRID TUBES, famous standardmanufacturers, no bootleg, $4.50 each, Specialthree circuit tuner, high primary impedance forscreen grid tuned plate, $2.50. Antenna coilfor screen grid circuits, adjustable primary,$2.00. Aluminum shield caps fit over entirescreen grid tube, $1 each, C.O.D. only.-PhilipCohen, 236 Varet Street, Brooklyn, N. Y.

BLUEPRINTS of National Screen Grid Five,4 -tube Screen Grid Diamond and Karas 3 -tubeShort Wave Set-three blueprints-one donor.Guaranty Radio Goods Co., 145 W. 45th St.,N. Y. C.

Recent Issues of RADIO WORLD, 15 cents each.Any number published in 1928 available for ashort while. Six issues 75 cents, 10 issues $1.00.Send stamps, coin or money order NOW, beforethe issues are sold. RADIO WORLD, 145 West45th Street. NIw York City.


12 VITAL TESTSIn Only 41/2 Minutes !

The Handsome Outfit, Shown One -Half ScaleWith this Scientific Trouble Shooting AC and DC Tester (at left) and the high resistancevoltmeter (at right) twelve vital tests were made of tubes and receivers, in 472 minutes, because the com-

bination can be used quickly for the following purposes:

(1)(2)

(3)

(4)

(5)(6)

to measure the filament voltage, up to 10volts, of AC and DC tubes.to measure the plate current of any one tube,including any power tube, from less than 1milliampere up to 100 milliamperes;to measure the total plate current of a re-ceiver or amplifier, up to 100 milliamperes.(Hardly any set draws more). Open com-mon A and B of set and connect to P oftester socket and to P prong under adapterplug;to measure the B voltage applied to theplate of tube ; the voltage across B batteriesor B eliminators, up to 300 volts.To determine the condition of a tube, byuse of the grid bias switch.To measure any tube's electronic emission(tester cuts in at no load, hence plate currentequals filament emission).

GUARANTY RADIO GOODS CO.,145 West 9Sth Street, New York City.

Please send me at once, on a five-day money -back guaranty,one complete Two -in -One (AC and DC) scientific trouble -shootingtest set, consisting of one No. 215 and one No 346, for which Iwill pay the postman $13.50, plus a few cents extra for postage. If 0-500 v. high resistance voltmeter No. 347 is preferred, putcross in square and pay $14.50, plus postage, instead of $13.50,plus postage.0 One No. 215 alone, $10.00.0 One No. 346 alone, -$4.50.0 One No. 347 alone, $5.50. Two adapters for UV -199 tubes, $1.00.

NAME

ADDRESS

CITY STATE

To regulate AC line, with the aid of a powerrheostat, using a 27 tube as guide, turningrheostat until filament voltage is 2.5 or 2.25volts.To test continuity of resistors, windings ofchokes, transformers and circuits generally.To find shorts in bypass and other con-densers, as well as in inductances, resistorsand circuits generally.To read grid bias voltages, including thoseobtained through drops in resistors (bias readby noting plate current and voltage and con-sulting chart).to determine the presence of distortion andoverloading, by noting if milliammeter needlefluctuates.to determine starting and stopping of oscilla-tion, as milliammeter needle reads highercurrent for oscillation and lower for nooscillation.

Service Men, Custom Set Builders, Home Constructors,Experimenters, Teachers, Students, Laboratories

Order one of these combination 215 AC -DC testers and 346 meter 0-300 volts.Send 110 money. Just fill out coupon. If after live -day test you're not delighted,return and purchase price will be promptly refunded!. Here's what you get foronly $13.50.(I)

mnet ernerwysd ebsoighn.e d

STcawloe- Iens-pOenceally legiblevoltmeter

tof or7 1/4A Cv oansd.DC. SamsThis meterreads the AC and DC filament voltages.

(2) One DOUBLE reading DC milliammeter. 0 to 20 and 0 to 100 milliamperes,with changeover switch. This reads plate current, which Is always DC Inall sets.

(3) One 0-300 volts high resistance voltmeter, No. 346, with tipped 80" seed tomeasure B voltages.(4) One 5 -prong plug with 30 -Inch cord for AC detector tubes, etc., and one4 -prong adapter for other tubes.(5) One grid switch to change bias.

(8) Two binding posts.(7) One 4 -prong socket. $ 1 3s5°(6) One 5 -prong socket.

One handsome noire metal ease.00) One instruction sheet. SEND NO MONEY[if

510-.50.1500 voltmeter No. 347 Is desired Instead of No. 346, Prise of combinationis 4

No. 215 Universal AC -DC Tester AloneNo. 346 high resistance 0-300 voltmeter aloneNo. 347 high resistance 0-500 voltmeter alone

Sh°411.1


BY STORM!CHROME STEEL

TWIN MAC N ET'S(BOTH /77ATCHED)

DOUBLE SENSITIVITY

ROCKER GIVESOPT/ON OFA R/77 ATUR.EADJUSTMENT

MOULDEDALUMINum

FRAII7E

MOUNT/N& HOLE.(THIRD HOLE INSIDE

NOT VISIBLE)

DRIVING P/N,RE-DUCT/ON LEVER

AND COUPLING ROD,ONE P/ECE,CAN'T BREAK!

FULL-FLOATINGARMATURE

MOUNTING HOLE.(THIRD HOLE INSIDE

NOT VISIBLE)

smALL RIRGAPS FORGREAT .SENSITIVITY

TWO COILS IN PARALLEL,DOUBLE CURRENT CAPACITY ANDDOUBLE THE FLUX (PERMIT 2.5M.A.NO FILTER NEEDED AT /80 VOLTS)

The Polo Unit is shown 3/4 actual size. It weighs three full pounds.

SO obviously superior are its advantages t hat the New Polo Duo -Magnetic Unit hastaken the country by storm. Such enthusiastic success ..itas immediately greetedfew radio devices as attended the recent introduction of the Polo Unit.

Everybody who has the slightest knowle dge of what a unit should be could see at aglance that expert desigh at last realized what others vainly sought for years.

If you want a unit to improve your present speaker, or to make the speaker you areabout to build do more than you could reasonably expect, a unit giving you the utmostin volume, the finest in tone, capable of handling even the output of two -5 0 tubes inpush-pull, and, of course, any smaller out put, then use the Polo Duo -Magnetic Unit.

POLO ENGINEERING LABORATORIES,57 Dey St. (Suite 6), corner Greenwich St.,New York, N. Y.

Enclosed please find ten dollars for whichsend me one Polo Duo -Magnetic Unit,with five-foot cord, moulded metal bracket,apex, chuck and nut. YOU ARE TOPAY SHIPPING CHARGES. If after a10 -day trial I return the unit YOU WILLQUICKLY REFUND THE TEN DOL-LARS.NAME

ADDRESS

CITY STATE[Nate: Shipments Begin on August 25,Orders Filled in Sequence of Their Receipt]

Scientific minds combined their ingenuity and skillto produce the finest-and the popular verdict proves.the boundless measure of their success.

POLO ENGINEERING LABORATORIES57 Dey Street (Suite 6), Corner Greenwich Street

Tel. CORtlandt 5112New York, N. Y.

he first and only national radio weekly new screen grid six! · 2019-07-17 · duo tone brown; it...

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