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It is getting hard in many communities to service home radiosets properly in order to "keep 'em listening."

The shortage of radio service engineers is acute-the militaryforces have priority on radio technical skill.

But, those of you who remain on the home front have the chanceof a lifetime to render important service to your community.Make a list of the names of all the "old timers" you can remem-ber. See and talk to each one. Chances are they're still radio"bugs" and will be willing and anxious to help if told of the needthat exists.

re

Organize a service club in your community . . see to it thatevery bit of existing knowledge is put to work. We will help you.Now is the time to pinch hit to "keep 'em listening." Will youdo your part?

P. R. MALLORY & CO., Inc., INDIANAPOLIS, INDIANA

P.

MALLORYR. MALLORY 8. CO.Inc.

Approved Precision Products

II

Vol. 4, No. 6 * June, 1943

MEMBER

UDIT

UREAUOf

RCULATI S

Editor & PublisherSANFORD R. COWAN

Advisory EditorM. L. MUHLEMAN

Contributing EditorsJOHN H. POTTS JOHN F. RIDER

"On Leave" MajorU. S. Sig. Corps

Circulation ManagerR. ALAN

Executive & Editorial Offices132 West 43rd St., New York

SERVICE -DEALERSOUNDMAN AND JOBBER.

Rep. U. S. Pat. Off.

_Ad indexAerovox CorporationPaper Tubular Condensers

Anchor Radio Distrib, Service Co.Radio Parts-Accessories

CentralabParts

Clarostat Mfg. Co., Inc.Controls & Resistors

General Electric Co.Consumer Acceptance

International Resistance Co.Potential New Markets

Ken-Rad Tube & Lamp Corp.Radio Tubes

30

30

25

31

3

27

Lafayette Radio Corp. 25Replacement Parts, Kits & Books

Mallory & Co., Inc., P. R., 2nd CoverService Club Plan

Meissner Mfg. Co. 12Radio Training Kits

Ohmite Mfg. Co. 28Resistors

Racon Electric Co. 4Horns, Trumpets & Speakers

Radio & Technical Pub. Co. 11

New Troubleshooters Handbook

Raytheon Production Corp. . .4th CoverIn Fever Machines

RCA Mfg. Co., Inc. 3rd CoverCathode Ray Tubes

Sprague Products Co. 7"Trading -Post" & Condensers

Standard Transformer Corp, 31Replacement Transformers

Sylvania Electric Products, Inc. . 26Technical Manual on Tubes

Triplett Elec. Co.Combat Line Instruments

Universal Microphone Co., Ltd. . . .

Plugs & Jacks

U. S. Treasury Dep't. 24This Year's Bonds

ContentoEditorial 2

To Be Or Not To Be-"Susfu"----"Victory" Lines OK'd

Trouble -Shooting Short -Cuts 5By John H. Potts

Superheterodyne Receivers, Part 2 8

By Oscar E. Carlson

Technical Service Portfolio-XXXI 13Electrolytic Condensers

Battery Production & "MR" Tubes 18By San D'Arcy

Signal Corps Training Kits 19By J. P. Hollister

Servicing Facilitated By L-265 Order 25By Charles Colenpa'ul

A Hint About Your Signal Tracer. . 25By Robert Boudreaux

Cover Picture(OFFICIAL U. S. SIGNAL CORPS

PHOTO)

At Signal Radio Repair Shops alltypes of radio and radar (meaning"radio detection and ranging") ap-paratus is serviced by especiallytrained men, many of whom wererecently civilian radio servicemen.Military restrictions prohibit describ-ing the circuits of radar and com-

munications equipment. Suffice to

say, such units are totally unlikecommercial radio sets or transmit-ters in design, type of component,

31 etc.

Any trained radioman seeking a30 commission in the Signal Service

should apply at his nearest induc-tion center or write to his SelectiveService Board for particulars.

Entire Contents Copyright 1943 by Cowan Publishing Corp.All rights reserved-no part of this magazine may be reproduced in any form, by anymeans, or translated into foreign languages without permission in writing from the publisher.

RADIO SERVICE DEALER, published monthly at 34 N. Crystal Street, East Stroudsburg, Pa., by the Cowan Publishing Corp.,Executive and Editorial Offices at 132 W. 43rd Street, New York. N. Y. Subscription rates-United States and Possessions, $2.00for 1 year, $3.00 for 2 years; elsewhere $3.00 per year. Single copies 25c. Printed in U.S.A. Entered as Second Class MatterOctober 3, 1941, at the Post Office at East Stroudsburg, Pa., under the Act of March 3, 1879.

Radio Service -Dealer, June, 1943 1

editoria

FLASH-VICTORY LINES OK'D-

* We can't give you details as the presses are roll-ing. This much we do know-that WPB hasamended its order L-63 and now a line of "Victory"Transformers and Condensers should start in pro-duction. More next month.

TO BE OR NOT TO BE--Leading radio-electronic-radionic manufacturers

are working on war orders to capacity yet each isgiving much thought to the Postwar Era. Thewide divergence of opinion amongst top manufac-turers, regarding radio's future, warrants muchconsideration on the part of jobbers and service -dealers, for their destinies are positively controlledby the policies of manufacturers.

One faction in radio now feels that immediatelyfollowing cessation of hostilities manufacturerswill revert to pre-war merchandising policies. Un-der this setup, sets at first will resemble small 1941models in style, price and production volume. Thenwill come the deluge of F -M and Television re-ceivers, along with consoles and record-players.We'll be back in the old groove, feels this faction,and the life of service -dealers will be complacent,because at first they'll be dealers primarily engagedin selling sets to a set -starved market. Later, serv-ice -dealers will be busy keeping 'em perking.

Another faction believes that after the war sometop manufacturers will want to control their prod-.ucts and markets right down the line-having theirown exclusive Distributors, Dealers and Super -Service Stations. Under such a setup, believes thisparticular faction, the independent parts jobberand servicing organization will be frozen out ofexistence.

Still another faction believes that after the warthe radio industry will be split into two or threesemi -interlocking competitive groups whereby cer-tain top manufacturers will set their caps for theultra -swank radio, console-F-M--Television mar-ket, leaving the dregs of midgets and portables tothe small -fry set producers to whom large volumeand low price means everything. And at the sametime, this particular faction feels that the big -shotswill go after the industrial -control fields with ven-geance to skim the cream off the while lush profitsmay be had. On this basis, feels this group, we areheaded into an age of industrial-control-an era inwhich radio servicemen will be forced to sell andservice cheap sets only or else get on the payrollof a plant that uses many electronic devices, in thecapacity of electrical -electronic maintenancemen.

We believe that a happy combination of all fac-tional opinions will eventuate. We feel that indus-

trial -control by means of radio frequency apparatusis a certainty of the future-and such equipmentwill need maintenance staffs. We disagree with amanufacturer who believes that television has beenoversold and the public bilked. Progress cannotbe stopped. Television represents a form of prog-ress in the art of entertainment and communica-tions. It must come, and will come, unless some-thing better is born to take its place. We believethat the Super -Service Station and exclusive dis-tribution planning system must fail. It didn't workfor the automotive industry. Even Ford broadcastsdaily, "bring any make of car to our shops andwe'll help you keep 'em rolling." Besides, no onewill buy a set if he knows that he is entirely de-pendent upon one source of supply for its futurecontinuance in operation.

The jobber has his work cut out for him. He mustrefrain from competing with his customers. Ifforced to add to his income during the emergencyit is logical that he should service sets, on a whole-sale basis, for service -dealers who are swamped.In the Postwar. Era let the jobber look to allied -to -radio markets and go into selling public address orelectronic control systems. He's a natural for thecoming industrial markets. Lastly, we feel that adeluge of trained radipmen will come from thearmed services prepared to take their old place inthe scheme of things. Then there will be competi-tive scrambles in which ability above all will be thedecisive factor. The coming industrial era will seecountless radio-electronic-radionic installations re-quiring constant adjustments and repairs. As wesee it, there will be no period of depression or re -cessation for competent, technically trained serv-ice -dealers in our time.

SUSFU A very polite definition of this old radio term is"Situation Unchanged, Still Fouled Up." And Susfueloquently describes the present state of the radio-electronic maintenance field.

Our May issue editorial "Misleading StatementsBy WPB" brought many comments from retailers,servicemen and jobbers. Without exception it wasthe consensus that if WPB cannot find a way toget replacement tubes into civilian radios at leastWPB should not becloud the issue by releasingdual -meaning blurbs.

Addressing the R.M.A. Service Managers Com-mittee on June 10th in Chicago, Mr. Frank H. Mc-Intosh of WPB explained that Order L-265 hadbeen amended and that after July 1st all tubesmade from materials allocated to civilian produc-tion will be stamped "MR"-meaning Maintenanceand Repair, not Military Reject. Such "MR" tubes.delivered to jobbers are restricted and can only besold to civilians, radio service -dealers or otherswho do not possess a military or high priority rat-ing. WPB deserves commendation for taking thisstep on behalf of "ordinary guys" like servicemenand set owners. - But, don't get too optimistic, forthere is a dark side to the picture. There is noassurance that tube manufacturers will ever pro-duce any "MR" tubes. The story is covered else-where in this issue under the caption, "BatteryProduction & MR Tubes." By all means read it.

2 Radio Service -Dealer, June, 1943

G -E Mazda Lamp G -E Electronic Tube

ON EACH THE G -E SYMBOL MEANS CONSUMER ACCEPTANCE

An "old friend" in practically everyelectrified home in the land is the G -EMazda Lamp. People rely on it as theydo on their telephones, and for muchthe same reason. It is dependable andefficient.

General Electric's aim is to make G -EElectronic Tubes for home receivers -FM, AM, television - just as widelyrelied upon by America as the lampbulbs that bear the famous G -E symbol.

To bring this about and to pre -sellthe vast replacement market that willbe waiting for your tube service afterthe war, G.E. is conducting a powerfulfour-color advertising campaign in thenation's big -circulation magazines.

A current advertisement of this cam-paign is illustrated at the right. Like all

J

of the series, it draws special attentionto G -E Electronic Tubes. General Elec-tric leadership in electronics, built upthrough years of experiments with andimprovements upon electronic products,is your assurance of the engineering ex-cellence of these tubes, outstanding prod-ucts of the famous G -E ElectronicResearch Laboratory.

When peace is restored, G -E Elec-tronic Tubes will be your fast-movingstock, thanks to constant forceful adver-tising and pfomotion aids that are pre -

selling your peacetime customers rightnow! . . . Electronics Department, This advertisement appears in:General Electric, Schenectady, N. Y.

;!..1

Collier'sThe Saturday Evening Post .

May 22,. May 29,

1943

-1943Fortune June, 1943 On Sunday night listen to the General Electric Country Gentleman June, 1943

Mazda Lamp program over N. B. C. See localnewspapers for time and station.

LookLife

June 1,June 14,

1943

1943

GENERAL ELECTRIC17643

Official Photo by U. S. Signal Corps;courtesy of Douglas Aircraft Co.

*A RACON Marine Horn Speaker is used in the cabinof the world's largest bomber, the B-19. Approved bythe Bureau of Marine Inspection and Navigation, De-partment of Commerce, these units are also to be foundaboard U. S. Navy and Army Vessels. Weatherproof andStormproof RACON Acoustic Material, plus superiorengineering design, are reasons why many types ofRACON Horns are used by all branches of the MilitaryServices. Shipyards, war factories, air bases and trainingcamps that use public-address systems can select justthe type of speaker needed from the complete linemade by RACON.

The quality, efficiency and dependability of RACONshave long been recognized. There's nothing finer. RA-CONs deliver more energy per watt input. Because ofRACON's exclusive Stormproof, Weatherproof, Acous-tic Material the elements cannot affect RACON's effi-cient operation. Use RACONs when planning your nextinstallation. Inquiries are invited-perhaps we can helpyou in some phase of the war effort. Ask for our freecatalog, too.

RACON ELECTRIC CO., 52 East 19th St., New York, N. Y.

BACON

RACON Speakers Used

By The U. S. Military

P -MHORNUNIT

MARINE HORNSPEAKER

RE-ENTRANTTRUMPETS

Here are but two of the many RACON Speakers and one of the manyP -M Horn Units. The Marine Horn Speaker is of the re-entrant type.for marine and general p -a applications. Available in several sizes, from5 to 50 watts, they may be used as loudspeaker or as microphone. (AP -proved by the Bur. of Marine Inspection, Don't of Commerce.) RACONRe-entrant Trumpets occupy small space but afford a long horn thatcarries highly concentrated sound efficiently over long distances. Severalsizes available.

4 Radio Service -Dealer, Jane, 1943

THE speed with which an ex-perienced radio serviceman can

often localize receiver defects ' isfrequently a source of wonderment,not only to beginners in the field butalso to trained radio engineers. Oftenthe latter do not think of possiblecauses which are encountered in thefield because such troubles are seldomexperienced in laboratory work.Speed in trouble -shooting is not se-cured by sticking to any particularsystem of localizing defects, butrather to a combination of all sys-tems, aided and abetted by a plenti-ful supply of common sense. As ineverything else, the method to fol-low is that which gives the desiredresults with the least possible expen-diture of time and effort, and throughexperience, a good serviceman almostintuitively follows the proper pro-cedure. In this article we want toshow how it is often possible to ac-complish a lot, in a very short timeby taking advantage of short-cuts.No doubt you are already usingmany such ideas in your own work,but some, we feel certain, will be newto most of us and all will help thosewho more recently entered the serv-ice field.

The first step in trouble -shootingshould invariably' be an analysis ofpossible causes based on the com-plaint. Manifestly it requires notruckload of equipment to determinewhat's wrong with a radio when thecustomer complains that the "partwhich makes it loud and soft" makesa noise when turned, or when welearn that an odor "like burningtar" emanates from the receiver. Weknow, even before we see the set,that in one case a new volume con-trol is going to be required and inthe other, that there is somethingvery, very wrong with the powertransformer. And we find out thatthe customer who insists that all thetubes are burned out because theydon't light when the set is switchedon is almost never right. If it's ana-c/d-c set, we'll check first the line -cord resistor, if one is used, and thepower switch. In every case, wecheck first the most likely cause,based on analysis or experience, thenwe proceed to look for other possiblecauses in the order of their proba-bility.

Inoperative SetsLet's suppose that the set is in-

operative. Usually the customer willtell us whether or not the tubes getwarm when the power switch isturned on. If they don't, then thefirst steps necessary are to determinewhether or not power is getting tothe set. Many servicemen save time

TROUBLE -SHOOTING

SHORT-CUTS

by

John H. Potts

at this point by plugging a tubechecker-using a double plug-intothe same wall receptable in which thereceiver was plugged, inserting thereceiver plug into the double plug.Snapping on the switch of the tubechecker tells us immediately whetheror not power, is available at the re-ceptacle and at the same time we areall set to check the tubes, a necessaryoperation no matter what the causeof receiver failure if we are to beable to give an intelligent estimateregarding the cost' of the repairs.

Short-circuits usually cause heat,especially, in circuits where poweris normally carried. Thus a touchof the finger on the case of a power

transformer will often tell whetherlack of operation is due to a shortor an open circuit. There is usuallya slight trace of hum present in-allreceivers; listening for this huMgives a quick indication of the pres-ence or lack of power in the receiver,when the speaker is OK.

If power is present and there isno quick; obvious indication of thecause of the trouble, it's a good ideato check the rectifier tube with thetube checker. Before replacing thetube in its socket, check the resist-ance from the cathode or filamentsocket terminal in the set to ground.If a short circuit or abnormally lowresistance to ground is indicated, the

Fig. 1. Trouble -shooting is simplified by first localizing the trouble in a majorsection of the receiver. Such sections are shown numbered in the order of test

by the signal tracing method.


1.5 MEG.

400,000

100,000

8.0 MEG.

5000'(CALIBRATING ADJ.)

76

CO'

27 OW

+8200 V.

2000

0-1 MA.

10,000(ZERO

ADJ.)

6000

rectifier tube should not be replacedand further trouble -shooting shouldfollow without attempting to operatethe receiver. If an open circuit isindicated-which would be normal ifthere were no bleeder or voltagedivider circuits across the B supply-the tube may be replaced and testscontinued. Never replace a blown25Z5 without making this test.

If accessible, the grid cap may bemomentarily disconnected from thedetector -first a -f tube; this shouldresult in a loud hum in the speaker,which will serve to show that theaudio section of the receiver isoperative. With the volume controlset to maximum, thereby increasingthe background noise level, touchingthe finger to the mixer grid shouldcause an increase in noise if the i-fand mixer sections are working. Ifthere is still no evidence of a signal,we would first suspect the oscillator-or the oscillator section of a con-verter, if no separate oscillator isused.

Checking OscillationTo check the oscillator, we measure

the voltage from the oscillator gridto ground. If the oscillator is func-tioning, a negative voltage will bedeveloped across the oscillator gridleak; if not, then the circuit is dead.

What is the most likely cause offailure to oscillate? Generally a de-fective tube, and as our tube checkeris already hooked up, we can checkthe tube first. If the tube checksOK, and proper voltages are presentin the set, we will want to take alook at the oscillator tuning con-denser, particularly if we are dealingwith a midget receiver-often therotor plates become shorted to thestator, especially if the set is drop-ped or knocked over. Then we'dcheck to see if the padder or trimmerwere shorted. If the weather hadbeen damp for a prolonged period,we'd be inclined to suspect poor im-pregnation in the coil. Next, wewould look into the corrections at thecoil terminals, at the socket, etc. Wewould reserve for the last checkingof fixed mica condensers-seldomdoes anything happen to them.

Fig. 2. Diagram ofa typical electronicvoltmeter such asused in conjunc-tion with signal -tracing equipment.

In many instances troubles may beaccurately diagnosed with no testapparatus whatsoever. In a goodmany receivers, particularly wheretuned r -f stages are employed,squeals and howls occur when thetuning dial is rotated while the re-ceiver is operating. The volume isnormal. Such troubles are caused bydefective rotor contacts to the gangsections of the tuning condenser.Normally all that is necessary to cor-rect the trouble is simply to removethe contact clips, bend them so asto increase the tension, and replace.If the receiver is, operated in a sec-tion where dampness is prevalent, afilm of corrosion may have formedover the contacting area of the clip;this may be cleaned off with sand;paper-never use emery cloth on anyreceiver. Emery gets into parts andcauses grounds or noise.

AVC Trouble SourceThe foregoing is a simple and fre-

quently encountered trouble. Not sosimple nor so often found is the con-dition apparent when tuning where-by it becomes difficult to tune froma strong station to a weak one with-out having to wait momentarily for

the weak station to build up tonormal volume. As a result suchweak stations may be passed over.This trouble is caused by too long atime constant in the avc circuit. Itmay result when an 0.1 mfd con-denser has been substituted for a.01 mfd one as an avc bypass. Oftensuch receivers have a previous his-tory of intermittent operation andmany servicemen make a practice ofreplacing all small bypasses in suchreceivers, without bothering to testthem, assuming that the cause isa defective bypass and it takes lesstime to replace the condenser than toundertake to test each one. The as-sumption is made that an excess ofcapacity can cause no difficulties inbypassing, therefore the common 0.1size is frequently substituted forsmaller values which may not im-mediately be at hand. The time takento charge and discharge such con-densers is appreciable, and the highvoltage charge which these conden-sers accumulate when the set istuned to a strong station holds overwhen quickly tuning to a weak sig-nal. AS a result, the high avc biasfrom the strong signal lowers thesensitivity of the set to a point wherethe weak signal becomes inaudibleand is passed over.

Another trouble resulting fromthis cause occurs when tuning froma weak station to a strong one. Inthis case it takes a noticeable periodfor the avc bypasses to charge. Dur-ing this period the strong signalcomes in with a bang tapering offrapidly in signal strength as the avetakes hold. The remedy in such casesis obviously to reduce the capacityin the circuit. While the same effect

(Continued on page 26)

"Young man-is this a business or social call?"

6 audio Service -Dealer, June, 1943

FOR SALE-Emerson 6 volt "B"power eliminator. Make offer. JohnKujan, 735 Horne St., Bronx, NewYork, N. Y.

IN THE MARKET-for 3" Oscillo-scope. Describe fully, and nameprice. Wimberley Radio Service,Hayti, Mo.

WANTED-Cathode ray tube, anysize, new or used; or used oscillo-scope, preferably hickok, RCA, orDu Mont. H. Kelley, 5915 HelenAve., Detroit, Mich.

SURPLUS SHOP EQUIPMENTFOR SALE-Having retired fromthe service business, I offer a widevariety of equipment for sale forcash. This includes microphones,transformers, rectifier tubes,transmitting tubes, receiv ingtubes, condensers, relays, metersof many types, and a 5 - tubesuperheterodyne receiver. Writefor complete list. Robert W.Wood, 10950 Longview, Detroit,Michigan.

TEST EQUIPMENT WANTED -"Jumbo" panel meter with 5" or 6"vane; communications receiver suchas National FBXA. Will trade otherequipment, auto radios, or what doyou need? A. H. Mekeel, 9 MarpleRoad, Poughkeepsie, N. Y.

FOR QUICK SALE-Clough BrengleType VE unimeter, portable type;AC volts 0 to 750; DC volts, 1 to1000, DC mils., 1 to 1000, ohmmeter,1 ohm to 3 meg., first-class condi-tion-$25; also small 5c to $1 Na-.tional cash register just reconditioned-$35; and Rider's Manuals 1 to 13,complete, regular price. Act prompt-ly. Nick Shuler Radio Service, Gon-zales, Texas.

WANTED FOR CASH-Power sup-plies or component parts for same atfrom 1500 to 3000 volts and about300 ma.; also 2 HK -254 or similartubes and RCA 954, 955, 956. Wil-liam R. Kennedy, Physics Dept.,Montana State College, Bozeman,Montana.

WILL BUY-Good used sound equip-ment, amplifiers, microphones, P.M.speakers; also vacuum tube ohm-

meter or volt - ohm - meter, factorybuilt, at a reasonable price. SoundService, Inc., 11th & Quaker, Tulsa,Oklahoma.

WILL BUY OR TRADE-Want pre -selector, analyzer, 8 M.M. projector;have tubes, cameras, meters, speak-ers, new filter blocks. G. Samkofslcy,110 Wilson St., Brooklyn, N. Y.

FOR SALE - Supreme, model 500automatic tube and set tester; 100%working order except for copper ox-ide rectifier-$35 cash. Leon D.Markham, St. Louis, Michigan.

WANTED-Supreme audolyzer, mod-el No. 562, Supreme signal generatormodel No. 561, Sprague Tel-Ohmike,Volt-Ohmyst, or similar instruments;also good tube tester for testing lat-est tubes. Must be in good condition.Give complete description and price.R. Flockhart, Mt. Vernon, NewYork.

FOR SALE-Keuf fel & Esser 18 -piece Drafting set in wooden case.First $25 takes it. M. Cimorelli,Catskill, N. Y.

URGENTLY WANTED - Will paycash for radio test equipment, VOM,tube tester and other parts; Hickokpreferred but any make considered;also Rider's Manuals from No. 6 to13 incl. What have you for cash?Edw. j. Danaher, 134 Merrimac St.,Buffalo, N. Y., c/o University RadioService.

RIDER'S MANUALS WANTED -Volumes 10-11-12 and 13. State con-dition and price. Fred Hartmann,32-26 - 54th St., Woodside, L. I.,New York.

URGENTLY NEEDED-Volt-ohm-meter and tube tester, also parts.Cash promptly. Sgt. LawrenceA. Steinberg, 316 East 15th St.,Sioux Falls, So. Dak.

FOR SALE-Metal rack for PrecisionE-200 and 954, $17; misc. radioparts; Radio News and Radio -CraftMagazines; Ranger free point testerwith space for v.o.m. in ,metal cab-inet, $5. T. Wojciechowski, 2837Fulton St., Brooklyn, N. Y.

Your own ad run FREE!The "Trading Post" is Sprague's way of helpingradio servicemen obtain the parts and equipment theyneed, or dispose of the things they do not need dur-ing this period of wartime shortages. Send in yourown ad today-to appear free of charge in this or oneof the several other leading radio magazines on ourlist. Keep it short-WRITE CLEARLY-and con-fine it to radio items. "Emergency" ads will receivefirst attention. Address it to:

SPRAGUE PRODUCTS CO., Dept. RSD36North Adams, Mass.

NEEDED IMMEDIATELY - Alltypes of test equipment, in goodcondition, for cash. Will sell ortrade precision 5840 K.C. cry-stals; also 12SA7, 12SQ7, 35L6,80 Tubes. L. C. Woodard, Sig-nal Section, 328th Sub -Depot, Ft.Sumner, N. M.

WANTED-Condenser, analyzer and0-1 ma, milliammeter. Give fulldescription, condition and price.Charles Morehead, Box 22, Flat Lick,Ky.

OSCILLOSCOPE WANTED - Statemodel, condition, price. G. Boles,315 - 51st Street, Brooklyn, 20, N. Y.

WANTED AT ONCE-Urgently need1/100 ampere meter fuses. Will paycash. Daniel L. Schacher, 4608Forbes St., Pittsburgh, Pa.

WANTED-Meters, test eqpt. preci-sion resistors, copper -oxide rectifiers,switches, receivers, neon bulbs tools,manuals, motors, pick-ups, calciminepaint, brushes, etc. Describe fully.Roby's Swapmart, 3569 CottageGrove Ave., Chicago, Ill.

HOME RECORDER FOR SALE-G-Eportable JM-7 connected for twomikes. One 7 -tube 6L6 output, 30 -watt amplifier, open case. Priced.both for $65. R. R. Reid, Parkersburg, Iowa.

HERE'S THE PATRIOTIC WAY CONDENSERDs EEFCE TC VNE

When you find one bad section in a multi -section dryelectrolytic condenser, don't replace the entire unit! Mostdefective sections can be replaced by using a Sprague Atomof the proper capacity and voltage, as illustrated here. TheAtom can either be fastened by tape to the multi -sectionunit, or simply held in place by means of its sturdy wireleads. You'll save time and money-and you help conserveessential war materials as well!

Atoms are made in a complete line of capacities and voltages.as well as in many combinations.

FOR SALE-Abbott TR-4; 2-810tubes; 2-809 tubes; 1-815 tube; 26albums popular records; 3-954's;1-9002 and socket, also meters andparts. Write for list. G. V. Sawyer,37 Cleveland Ave., Devon, Conn.

WANTED-Jewell 199 set analyzer;ditto No. 444: Jewell 57 D -C volt-meter., 0-50 volts and 0.50 amps.:Test -O -Phone test unit; RCA serv-ice tip file and supplemental cards;RCA. 156A tube checker, counter orportable type 156; Rider-Chanalyst;RCP tube checker model 309S or309SC; Triumph A & B batterytester, model 630; GTC portapowerunit for 1% volt radios, Model Uor G; pair 7" Klein's pliers No. 201-7NE; back copies of Radio News,Radio Craft, Radio Today. Describefully and name best cash price. How-ell's Radio Service, Anna, Texas.

FOR SOUTH PACIFIC USE-An-xious to buy Echo -phone EC -1Receiver. Urgently- needed. Mustbe in good condition. Have youone to sell for a boy "overthere"? Write T -Sgt. J. E.

M.C.S. Det., Quantico,

Illustrating how a Sprague Atom Type UT -8(8 mfd. 450 volt) replaces the 8 mfd. 450 -voltsection of a 3 -section condenser rated at 8mfd. 450 V.; 8 mfd. 300 V., and 20 mfd. 25 V.:

(A) Cut lead to defective section andtape end.

(14 Connect cut circuit lead to positive(4-) side of Atom.

(C) Connect Cathode (-) aide of Atomto common minus lead of multi -section condenser.

SPRAGUE CONDENSERSAND KOOLOHM RESISTORS

Obviously, Sprague cannot assume any responsibility for, or guarantee goo ds etc. which might be sold or exchanged through the above advertisements.


THE

SUPERHETERODYNERECEIVER PART 2

ConvertersA converter serves to combine the

incoming r -f signal with that of thelocal oscillator signal and to supplya third frequency lower than the r -fsignal but still retaining the modu-lation form that was present in the,r -f. The simplest converter is thetriode. In this type converter we de-pend on the non-linear detector ac-tion of the triode when biased to cut-off. The tube is normally biased tonearly cut-off and enough local oscil-lator voltage is impressed to increasstthe plate current above the valuewith no excitation present. The tubethen operates on the non-linear por-tion of the characteristic curve andhas maximum conversion efficiency.A simple triode converter circuit isshown in Fig. 9.

Besides the triode converter, mod-ern superheterodyne receivers veryoften employ such converters as thePentagrid Converter Tube. This is afive grid tube combiping the functionof the local oscillator and detectorin one tube. The schematic of sucha tube, either a 6A7 or a 6A8 isshown in Fig. 10. Grid 1 acts as anoscillator control grid. Grid 2 actsas the oscillator plate. These twogrids are connected as in any tunedgrid plate feedback amplifier. Thebias is obtained by grid leak and

Fig. 9. Triode Converter

by Oscar E. Carlson

blocking condenser. Grid 2 is nor-mally supplied with about a 200 voltpositive potential with' respect tocathode.

The oscillator action is similar tothe,,conventional triode but the ac-tion within the tube is not completed.Grid 2 is not a solid plate and elec-trons pass through it. The electronspassing grid 2 vary in accordancewith the oscillator anode current andtherefore we may think of the spacearound grid 2 as being a virtualcathode, or varying source of elec-trons. Grid 4 then becomes the con-trol grid of a screen grid tube uponwhich the signal voltage is im-pressed. Grids 3 and 5 are connectedtogether, one on each side of thiscontrol grid. This accomplishes twopurposes. Grid 3 acts as an acceler-ating grid to draw electrons beyondgrid 2 and under the influence ofgrid 4. Grid 5 acts to shield the con-trol grid 4 from the effect of theplate just as in any screen grid tube.Grids 3 and 5 are maintained posi-tive with respect to cathode by about100 volts. The plate is made positiveby 250 volts and connects to the .out-put circuit just as in any amplifier.The desired mixing acton is accom-plished in the electron stream in-stead of in the tuned grid circuit asin the conventional first detector andoscillator. The plate circuit is tunedto the i-f frequency and amplified bythe i-f amplifier stage, or stages.

Fig. 10. Pentagrid

ConverterG5G4G3Ge

DetectionDiode detection is the nearly uni-

versal type of detector in use today.Detection is simply the rectificationof the r -f signal so that only themodulation component will remain.An RC combination in the cathodecircuit is the load across which theoutput 'voltage is developed. Theproper combination of R and C isvery important as for a given modu-lation frequency and large value ofR, if' C is small the filtering actionis inadequate and a large r -f corn-potent will be present and the effec-tive signal amplitude will be de-creased. If C is too large it will notdischarge rapidly enough and athigher modulation frequencies theoutput voltage will not follow the de-crease of the modulation envelopeto the lower limits thus flatteningout the lower alternation of the sig-nal voltage and resulting in, distor-tion. C and R must be sufficiently


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Fig. 11. Diode detector.

small so that the discharge of Cthrough R is at least as rapid as themodulation amplitude decreases dur-ing a cycle. Fig. 11 illustrates a sim-ple diode detector. To determine theproper value of either C or R to usewith the circuit we pick some arbi-trary value of either. In that case,for proper operation:

c,iff R,1 1

kR±R. (R±ROIC-1where

0)8 is 27r X the modulation fre-quency in c.p.s.

Ro is the grid load resistor offollowing tube.

R is the diode load resistor.C is the filter capacity.K is the percentage of modula-

tion expressed as a decimal.

In practice Xo/R should not be lessthan 3. R may be 250,000 ohms andC from 50 to 100 micro -micro -farads.

Another type of detector that wasonce very popular but is now seldomused is the Plate Detector, or LinearDetector. A linear detector developsa rectified output proportional to theamplitude of the input voltage anddetection is accomplished by workingthe tube with such plate and biasvoltages that the Eg-Ip character-istic curve is essentially linear andthe entire_half of the cycle is cut offwithout altering the shape of theupper half.

This detector is illustrated in Fig.12. It is nothing more than a class

Fig. 12. Plate or linear detection.

B amplifier with the plate circuit soarranged as to suppress the carrierfrequency while accepting and pass-ing on to the next tube the modula-tion frequency component. As suchthe tube must be biased to almostcut-off and a large plate voltage mustbe -used to give an essentiallystraight characteristic curve.

When the tube is biased to nearcut-off and a large alternating volt-age is applied to the grid, there willbe a pulse of plate current duringeach positive half cycle of the ap-plied voltage and no plate currentduring the negative half cycles. Dueto this high bias no grid current,flows during the signal and there isno loss of selectivity in the preced-ing r -f or i-f circuit as with gridleak or diode detection.

Audio AmplifiersThe two general types of audio

amplifiers in use for radio receiversare the class A and the class B am-plifiers. The class A amplifier oper-ates in such a manner that the formof the power supplied to the plateload circuit is essentially a reproduc-tion of the grid excitation voltage,that is, the plate current varies di-rectly with the grid voltage. Thus,since the tube is operated well withinthe linear limits of the character-istic curve, the plate voltage alsovaries in the same form as the gridvoltage. Usually, the tube is oper-ated in the center of the straightportion of the Eg-Ip curve and thegrid is not permitted to swing eitherpositive or into the lower bend of thecharacteristic curve.

Plate current for the class A am-plifier flows at all times and the volt-ages are such that the tube operatesas a linear amplifier. The amountof second harmonic distortion thatis present in the output that was notpresent in the input is taken as ameasure of the distortion and isusually limited to less than five per-cent (5%).

Whenever the plate cui-rent, dueto excessive excitation extending be-yond the straight portion of thecharacteristic curve or to a flow ofgrid current,' is distorted out of theform of the input voltage variations,harmonics result in the output. Theamplifier characteristics are low effi-ciency and low output with a largeratio of power amplification. Thelow efficiency is due to the fact thatplate current flows during the full360 degrees of the excitation cyclethus causing a continuous expendi-ture of power within the tube. Fig.13 illustrates the action of a normal-ly operated class A amplifier tube.Low output is due to the fact that

Fig. 13. Graphical analysis of a class Aamplifier tube.

high excitation cannot be used, asexplained above. The theoreticallimit of efficiency is 50%.

Due to the low operating efficiencythe plate .power input must be keptcomparatively low due to the largeproportion of the input being dis-sipated within the tube itself. Thehigh ratio of power amplification isdue tb the fact that high excitationvoltages cannot be used and conse-quently the power requirements forexcitation are very low.

Class A audio amplifiers may beused as first audio driver stages fora succeeding class A power amplifieror class B power amplifier.B output tubes are employed aninterstage coupling transformer isrequired to couple the driver stageto the power amplifier. A phase in-verter can be used for such coupling.We shall not, however, cover suchan arrangement in this article.

If the class A driver stage is fol-lowed by a class A power stage, re-sistance capacitive coupling is usual-ly used. Such an arrangement isshown in Fig. 14. The function ofsuch a coupling arrangement be-tween stages is merely to allow thetransfer of the signal component ofthe plate voltage from the drivertube to the grid circuit of the suc-ceeding stage. The de plate voltage


Fig. 14. Resistance capacity coupledclass A amplifiers.


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SECTION XXXI

ELECTROLYTIC CONDENSERS

DESPITE the fact that failureof electrolytic condensers is one

of the most common causes of radiotrouble, it is also true that this typeof condenser represents one of thegreatest improvements in radio com-ponent parts design to have occurred

1 in the past fifteen years. It is dueprincipally to electrolytics thatradios are now substantially hum -free, yet are compact and light inweight. Better hum filtration hasresulted in better audio systems andconsequently, improved fidelity.Higher gain p.a. apparatus, result-ing from the improved filtering effi-ciency of electrolytics, enables bettermicrophones to be used and there-fore more natural reproduction isachieved. In industrial applications.high -capacity electrolytics are usedto start capacitor motors, which arequite generally used in theater andother installations because of theirquietness in operation. The electro-lytic has given us, for better or forworse, the a-c/cl-c midget.

In a great many cases, the electro-lytic is more sinned against thansinning, insofar as troubles in serv-ice are concerned. Extremes of heatand cold affect any, units containinga liquid or moist component._ Elec-trolytics are no exceptions. Yet wefind such condensers jammed in closeto hot rectifier tubes or pressed innear or even against the scorching

heat of a line voltage -dropping re-sistor, so frequently located alongthe back of small midget a-c/d-c re-ceivers. In the early days of electro-lytics, when electrolytes were not sowell understood, the combination ofpoor set design and excessive heat-ing of the electrolytic occasionallycaused so much gas pressure withinthe condenser that explosions re-sulted. This was particularly thecase with the older wet electrolytics,which were fitted with a vent fromwhich the gas could normally escape.When this vent became clogged up,there was no other release for thepent-up gas, except to "pop." Im-provements in condenser designhave overcome this trouble, but theneed for avoiding abuse of the con

AS CI-:VrEMatal

NEGATIVEELECTROD

FILM ON ANODE

ANOD POSITIVELECTRODE

Fig. 1. In ansulating film

electrolytic condenser, an in -is formed on the anode, as

shown.

denser in order to obtain maximumlife and operating efficiency is justas essential as heretofore.

Electrolytic Advantages-Limitations

To get a better idea of the prob-lems involved in the design of elec-trolytics, and of their advantagesand limitations, let us first considerFig. 1, which shows essentially howsuch condensers are made. The posi-tive electrode is aluminum, and thenegative electrode is generally, butnot always, of the same metal. Inbetween these electrodes is placed anelectrolyte, which is either in liquidor paste form. In most modern con-densers, the paste form electrolyteis used. When a voltage is appliedto the electrodes, an electro-chemicalaction takes place, much like thatwhich occurs in an electro-platingbath. However, instead of a platingbeing formed, a thin film of insula-tion is deposited on the positive elec-trode. This film serves as the di-electric for the condenser in thesame manner 'as mica and wax -im-pregnated paper serve in other typesof condensers. Principally becausethis film dielectric is so microscopic-ally thin, the capacity obtained fora given area of electrode is verylarge-much larger proportionatelythan for the same area when micaor paper are used.


TECHNICAL SERVICE PORTFOLIO * SECTION XXXI

The resultant capacity after form-ing is dependent not only upon thearea of the electrodes but also uponthe forming voltage and the, type ofelectrolyte employed. The lower theforming volthge, the thinner the filmand the higher the capacity. That iswhy low -voltage electrolytics of veryhigh capacity can be made in suchsmall sizes.

There are other methods of in-creasing the capacity of the con-denser, without reducing the form-ing voltage. One such is by etchingthe surface of the anode. This isdone either chemically or mechani-cally and produces minute corruga-tions in the aluminum foil and there-by increases the effective area ofthe condenser surface. It is neces-sary to use a high forming voltageif the condenser is to be subjectedto high voltages in service, since thethinner films which result at lowerforming voltages will not withstandhigh operating voltages. Then thereis the fabricated plate method bywhich means an exceptionally highplate surface is obtained mechanical-ly to greatly increase capacity insmall units.

The types of electrolytes used areto a certain extent trade secrets, andvary with the forming voltage, ulti-mate capacity desired and type ofconstruction. In many condensers,the electrolyte is, or used to be, so-dium or ammonium borate dissolved,with boric acid, in water; or a dilutesolution of sulphuric acid. Some-times the condenser is partly formedwith one type of electrolyte and theforming process is completed withanother type.

Note that the film thus formedappears only around the positivefoil. If the polarity is reversed, thefilm will be destroyed and the con-denser will be ruined. In alternatingcurrent circuits, where the current

CC

0CC

>-

U

N

continually reverses, electrolyticsare unsuitable, as ordinarily con-structed. You may wonder why theyare able to operate in power supplyfilter circuits because of the humwhich is normally there. However,we should remember that this humis not an alternating current, but apulsating one. And there is no ob-jection to using electrolytics in cir-cuits where a pulsating current ex-ists. Also, in testing, it is necessaryto use an alternating current as acurrent supply source for a bridge;in such cases a polarizing voltagewhich is sufficiently high to makecertain the anode foil of the con-denser is never negative is used.When the supply voltage for thebridge is very low-less than 2 or 3volts - it is possible to omit thepolarizing voltage without causingbreakdown of the anode film, butmeasurements made under theseconditions do not yield the same re-sults which are obtained when theproper polarizing voltage-equal tothe normal d -c working voltage ofthe condenser-is employed.

Effect of Varying TemperatureWe have stated that the capacity

of an electrolytic condenser is af-fected by the operating temperature.An idea of the magnitude of thechange with temperature may be ob-tained from a consideration of thegraph, Fig. 2. This represents thechange in capacity of representative10 mfd condensers of the plain andetched foil varieties over a widetemperature range. Note that aplain foil condenser which has a ca-pacity of 10 mfd at normal roomtemperature drops to nearly 1 mfdat 40 degrees below zero. And theetched foil type, of similar capacityat normal room temperature, loseshalf its capacity at minus 40 degreesFahrenheit. While most of us don't

BA-10 MFLT ETCHED FOIL CONDENSER

B- 10 WO PLAIN OIL CONDENSER

0-40 -20 0 20 40 60 80 100 120

AMBIENT TEMPERATURE, DEGREES F.110 100

Fig. 2. The capa-city of electrolyticcondensers de-creases at lowtemperatures, as

shown.

Fig. 3. The power factor creates lossesin a condenser equivalent to thoseresulting from series resistance (as in Aabove), or shunt resistance (as in B).

feel like sitting around, listening tothe, radio, when the temperature inthe room is anywhere near 40 de-grees below zero, even lower temper-atures are frequently encountered inhigh -altitude bombing planes, and infield operations in Arctic regions.When electrolytics are used undersuch conditions it is necessary toselect a condenser with sufficient ex-cess capacity to make up for the losswhich occurs at low temperatures.

Although the capacity increases athigher temperatures, it is not to beassumed that operation at tempera-tures above normal is favorable tothe performance of electrolytics.Quite the reverse. As we have men-tioned before, every electrolytic con-tains a certain amount of moisture,regardless of the type of electrolyteemployed. At high temperatures thismoisture evaporates more rapidly-the condenser "drys out"-the ca-pacity eventually decreases and poorfiltration results. Further, the aver-age life of the condenser is greatlyreduced, more frequent breakdownsoccur, the power factor is consider-ably increased. In general, the per-formance as a whole is considerablyworse than at low temperatures. Thesame drawbacks are likewise experi-enced, though not to so great an ex-tent, with all types of wax or oilimpregnated paper condensers.

Power FactorThe effect of an increase in power

factor in a condenser is similar toan increase in the series resistanceof the condenser, as represented byR in Fig. 3A, or to a decrease inthe shunt resistance, shown in Fig.3B. Both these factors representlosses in filtering efficiency; in seriesresistance, because the impedance ofthe condenser is increased so thatmore of the current to be bypassedpasses along through the externalcircuit to which the condenser isconnected rather than being appliedto the condenser. And, insofar as

14 Radio Service -Dealer, Jane, 1943


the shunt resistance is concerned.this serves to limit the amount ofcharge which the condenser can re-ceive and hold in a given time andthus reduces its ability to store en-ergy, which is a measure of con-denser efficiency.

In general, electrolytic condensersare not as efficient as paper con-densers insofar as bypassing is con-cerned, assuming that we are com-paring two condensers of equal ca-pacity, because the power factor ofelectrolytics is normally far greaterthan that of paper condensers -usually about 10 or more times asgreat. But if we compare these twotypes of condensers on the basis ofphysical size, we find that an electro-lytic can be made in a small frac-tion of the space required for astandard paper condenser of equiva-lent capacity or filtering efficiency.

Filtering EfficiencyWhen we speak of filtering effi-

ciency, we refer of course to low -frequency filtration, such as is re-quired in power supply circuits nor-mally found in home radios. Theelectrolytic is not efficient as a filterof radio frequencies, and occasion-ally circuits are encountered inwhich poor operation results becauseof the attempt to use an electrolyticboth as an r -f and a -f filter.

Such a circuit is shown in Fig. 4.Here the filter condenser' CI, acts notonly as a bypass for hum frequen-cies in the power supply, but also forradio frequencies present in theplate circuit of the i-f amplifierstage shown. When the electrolyticis fresh, it may serve both thesefunctions satisfactorily; but longbefore it has reached the end of itsuseful life as a hum filter for thepower supply it has become uselessas an r -f filter. The result is fre-quently oscillation or low volume ofoutput in receivers so afflicted. Nowthat electrolytics are so scarce, it is

! worthwhile to prolong their life byshunting them with paper condens-ers -0.1 mfd or thereabouts, whenthey are still sufficiently good toserve as hum filters. The paper con-denser will take care of r -f bypass-ing. CBI? demonstrates this applica-tion.

Electrolytics are characterized byhigh leakage, up to about 1 ma permicrofarad of capacity, which is notpresent in paper or mica condensers.As a result, electrolytics cannot beused as coupling condensers in re-sistance -coupled amplifier stages.Further, electrolytics should not be,

but often are, used as screen by-passes in a -f stages. An example isshown in Fig. 4, where the screenbypass condenser' CB is an electro-lytic. Here the effectiveness of thecondenser, and in fact the perform-ance of the entire circuit, is de-pendent upon the amount of leakagepresent in the condenser CB. Whenthe leakage is high, it serves as aresistance which forms a voltage di-vider with the screen series resistor.As a result, only a portion of thenormal screen voltage reaches thescreen; the gain of the tube and cir-cuit is reduced, overload and distor-tion occur. There is no simple rem-edy other than replacing the electro-lytic with a suitable paper condens-er. If the screen resistor is high invalue-it is usually 0.1 megohms ormore-a paper bypass of 0.25 mfd isnormally adequate.

Condenser Testing

Nowadays when test equipment ishard to get, it is often necessary toimprovise some simple method oftesting electrOlytics which will tellus just how bad they area One meth-od, adaptable to power supply filtercondensers of the commonly used 8mfd type, is shown in Fig. 5. Thisis a perfeCtly ordinary power sup-ply, which is normally connected toa working radio receiver, but towhich has been added a means ofcomparing the electrolytic condenserC2, already in the power supply,with another which we want to test,designated as Cx. By manipulatingthe switch S1, either C2 or Cx (both

TO RECTIFIER TO RECEIVER

C2 Cx

Ci Si

RI

Fig. 5. The performance of an electrolyticcondenser can be quite simply checked bycomparison with another, as shown above.

nominally the same) serves as thefinal section filter of the power sup-ply, and we can judge by listeningto the result in the speaker as tohow well the condenser Cx performswith respect to C2. In this circuit,R1 and R2 are the same value-about 10,000 ohms or more. Whenthe switch Si !is turned to short outR1, C2 serves as the filter condenserand the power, supply functions nor-mally. When Si is turned to shortout R2, then Cx replaces C2 as thefilter and the performance of Cx canbe compared with that of C2. R1 andR2, when in series with the con-densers with which they are asso-ciated, serve so to limit their effec-tiveness as bypasses that the con-densers may be considered to becompletely out of ,the circuit. It isnecessary to use these resistors be-cause, if we simply switched fromone condenser to the other, a heavydischarge would take place through

Fig. 4. An electrolytic may be required to bypass radio -frequency, as well asaudio -frequency, currents. Better results are obtained by using an auxiliary

condenser, Crf, to handle the r -f currents.



Fig. 6. Both capacity and leakage can bechecked with this simple circuit.

the switch contacts which wouldruin them in a short time.

A simple method of checking ca-pacity and leakage, assuming that acopper -oxide rectifier type of meteris available, is shown in Fig. 6. Thetransformer shown in a type de-signed for heating tube filaments,with a secondary of 6.3 or .morevolts. The battery voltage-a powersupply with filtered d -c output canreplace the battery-serves to polar-ize the condenser and thus enablesaccurate capacity readings. Further,it enables us to determine the leak-age present in the condenser undertest.

In operation, the switch S1 isopened so that no a -c voltage is ap-plied to the circuit. R1-which maybe 1000 or more ohms-serves tolimit the current in the circuitshould the condenser under test beshorted. The reading on the meterindicates the leakage current in thecondenser. This should not exceedapproximately 1 ma plus .05 ma permicrofarad of capacitance (1.40 mafor 8 mfd). After the leakage hasbeen noted, S6 is switched to apply

POLARIZINGVOLTAGE

Fig. 7. For accurate measurements of ca-pacity and leakage, this bridge circuit has

come into general use.

the a -c test voltage to the circuit.R2 is adjusted until the proper read-ing, predetermined by calibrationwith other condensers of known ca-pacity, has been obtained. The valueof R2 depends upon the meter used-if from an analyzer, R2 may rep-resent the a -c current range shunts.

Bridge CircuitsA standard bridge circuit for

measuring capacity and leakage ofelectrolytic condensers is shown inFig. 7. In this schematic, Cx is theunknown condenser under test, Csis the standard condenser, Rpf is theseries resistance which enables pow-er factor determination and R2 andR1 are balancing arms of the bridge.The resistor R3 is not a part of thebridge circuit, but has been addedin order to enable measurement ofthe leakage current. Actually thisresistance may be omitted if we arecareful to make certain that themeter is shunted by Rs when thed -c polarizing voltage is applied tothe condenser under test. If the con-denser has not been recently in use,adequate time for forming (up toone-half hour at full polarizing volt-age) should be allowed before test-ing.

The formulaR2

Cx =- - CsR1

shows the condition under which thebridge is balanced. When Cs is equalto 1 mfd, Cx in microfarads is equalto R2/R1. Thus when R2 is 10,000ohms and R1 100 ohms, R2/R1equals 100 and the capacitance ofthe condenser under test would thenbe 100 mfd, which represents themaximum range of the bridge. Thisrange may be increased to 1000 mfdeither by increasing R2 to 100,000ohms, or decreasing R1 to 10 ohms;the latter is preferable. Except forvery special applications, such asthe measurement of starter condens-ers and others used in industrial ap-plications, it is not likely that anyneed for a range greater than 100mfd will be required. If R2 is cali-brated down to 10 ohms,, the mini-mum value of the capacitance whichcan be measured will be 10/100times 1 mfd or 0.1 mfd. Smallervalues can be checked by increasingthe resistance of R1 so that thefractional capacity is greater. Forexample, if R1 is 1000 ohms, thenunder the same conditions capaci-tances of '.01 mfd :can be checked.For' still lower values, Cs can be re-

duced to 0.1 or less and the mini-mum value of capacitance measur-able will be proportionately less. Thebridge is adaptable to all types ofcondensers.

The power factor range can bedetermined from the formula (ap-proximate)

Power Factor (per cent) =100x2x6.28x6OxRpfxCs

when the test frequency is 60 cyclesand the power factor is such thatthe resistance is small in comparisonwith the reactance of the condenser.When Rpf is 1500 and Cs is 1 mfdthe power factor is equal to 100x2x6.28x60x1500x.000001, or about56%. (In this formula Cs is infarads and 1 mfd therefore equals.000001 farads). It is assumed thatthe resistance of Cs is negligible,which will be the case of a high-grade paper type condenser is em-ployed. Other values of power fac-tor will be proportionate to the valueof Rpf used.

Another type of bridge which mayalso be used for capacity, power fac-tor and leakage measurements isshown in Fig. 8. This is quite simi-lar to Fig. 7 in its manner of func-tioning and the bridge arm and con-denser standard values should bethe same as in the circuit of Fig. 7.Care must be taken that the signalsource does not have capacity toground, as would be the case if afilament transformer were used,otherwise inaccuracies in measure-ment will occur and difficulties in

SIGNALSOURCE

Fig. 8. This bridge circuit is somewhatsimilar to that of Fig. 7, but the d -c pol-arizing voltage is located differently in thecircuit. Constants for the resistors and

condensers are the same as in Fig. 7.

16 Radio Service -Dealer, ne, 1943


balancing will be encountered.With reference to the signal

source, a filament transformer, thesecondary of which feeds the bridge,will serve nicely in connection withany power supply source, consistingof a conventional rectifier and filtercircuit, to supply the d -c polarizingvoltage. Alternatively a special pow-er supply, which combines both a -cand d -c in a single unit may be used.This is accomplished by using apartly filtered half -wave power sup-ply, as shown in Fig. 9. As shown,the polarizing voltage is takenoff the high side of a 50,000 -ohmresistor, which serves as a load cir-cuit for the power supply. This re-sistor is bypassed by a single 1-mfdpaper condenser, scarcely sufficientbypassing to remove more than thehigher harmonics of the rectifiedvoltage. As a result, considerable60 -cycle ripple is present in the out-put voltage, and this ripple is putto work by serving as the signalsource for the bridge.

A further advantage of this typeof power supply is that the currentis limited by the grid potential ofthe type 45 half -wave rectifier. Whenthe grid is at ground potential, littlerectified current is available for theload, 50,000 ohms, and for thebridge, so the voltage is low. Atmaximum setting, when S1 is joinedto point 1 through the tap switch,the grid is at the same potential asthe plate and maximum rectified cur-rent flows. Consequently the voltageacross the load is high. By thismeans it is possible to secure a widerange of polarizing voltages withoutusing a tapped transformer. Also,the need for a tapped voltage divideris avoided. And the fact that thesame load resistance is always pres-ent means that a definite ratio ofhum to polarizing voltage is main-tained. An arrangement of this typeis used in the Aerovox capacitorbridge.

Some means of detecting bridgebalance will also be required. Sincethe signal frequency is 60 cycles,phones are not desirable becausethey are relatively insensitive atthis frequency. By using an ampli-fier which tends to amplify the 60 -cycle frequency and attenuate highfrequencies, a sharper balance is ob-tained. Such an amplifier is illus-trated in Fig. 10. If the choke L andthe, condenser C in the input circuitare chosen to resonate at 60 cycles(a 10 -henry choke and an 0.5 mfdcondenser will do the trick) a highvoltage at 60 cycles will be developed

across C, which will be fed to thegrid of the 6J5. There will be rela-tively little signal response at higherfrequencies and what does getthrough may be further reduced bythe bypass condenser (.01 mfd)across the grid circuit of the 6K6.A loudspeaker or copper -oxide meterwill then serve well as a detector.The bridge is balanced when thesignal heard or indicated is at aminithum. The bridge transformermay be any audio type for inter -stage use-a 1:3 step-up ratio issatisfactory.

Since the purpose of this testingis to determine whether or not thecondenser in question is satisfactoryfor use, the problem of setting limitsbeyond which a condenser should berejected arises. And this dependsupon a number of factors. Some ideaof what to expect in new condensersmay be gathered from the specifica-tions which have been set up forthe Victory line of electrolytics,which will be standard for the dura-tion. These are listed below:Leakage -1 ma, plus .05 ma per mfdPower Factor

25 V. and 50 V., DCW 25%150 V. to 250 V., DCW 20%450 V. DCW 15%

Capacity ToleranceMinus 15% to plus 200%

The higher power factors are en-countered, as indicated, in the lowervoltage bypass electrolytics. Sincethese are normally used as cathodebypasses and therefore shunt resis-tors of low value, neither the leak-age nor the power factor considera-tions arc as important as in thehigher impedance circuits. The aver-age run of new condensers will bewell within the above limits in everyrespect. For use in power supplycircuits where only low frequencyhum is a consideration, a power fac-tor has high as 50% will cause a lossin filtering efficiency in a standard

Fig. 9. This unique power supply furnishesboth d -c for polarizing purposes and a -c

for bridge tests.

power supply circuit of only around15%, as compared with that pro-vided by a perfect condenser. Usual-ly, however, high power factor is ac-companied other deficiencies, suchas high leakage and low capacity,which combine to render the con-denser unsatisfactory. Naturally, acertain amount of judgment must beexercised; if a condenser still per-forms acceptably in the circuit inwhich it is employed, but shows highleakage, power factor and low capac-ity on test, one may be certain thatit is likely to require replacement inthe very near future. Consequentlyit had better be done immediatelyrather than to wait for what is like-ly to be a "no -charge" call-back.

In testing condensers for indus-trial use, such as the motor -startingvariety, severe heating will resultif the power factor test shows above20% power factor. Such condensersshould measure close to their ratedcapacity-within 20%, at least, forsatisfactory service. In radio re-ceivers, we really don't care howhigh the capacity is (for filter cir-cuits). The higher the capacity, thebetter the filtration.

L

TOBRIDGE

TRANSF.

0.56J5 (6c5) 0.1 6K6

+8180-300 V.

Fig. 10. This bridge amplifier is especially suited for use with capacitancebridges employing a 60 -cycle signal source.

Radio Service -Dealer, June, 1943 1i

BATTERY PRODUCTION.

AND "MR" TUBES

THAT there is a shortage of re-placement tubes is well known.

That farm radios are becoming inop-erative in droves because there areno batteries is likewise commonknowledge. That radio is daily be-coming a most important factor indisseminating vital news events, cropcontrol news,' changes in rationingand other governmental regulationsis likewise factual.

Many radio service -dealers andjobbers have wondered how long itwould be before there would be a re-sumption of deliveries of batteriesfor farm radios. The answer came,like a bombshell, from War Produc-tion Board on May 17th. So therecord may be clear, here is the com-plete release:

WPB Release 3570"Production of radio batteries

has been boosted to a rate of 425,000a month, the Consumers DurableGoods Division of the War Produc-tion Board announced May 17th. Thisexceeds the pre-war volume, the Di-vision said in reporting on WPB'sprogram to bring relief to farmersin non -electrified areas of the nationwho have felt the battery shortagemost severely. These rural dwellersdepend upon battery radios for dailywar and food program news, as wellas for entertainment.

"Initiated in mid -March, the bat-tery program, at the present rate ofproduction, and if continued overa twelve-month period would easilycover normal requirements for the3,200,000 radios that are estimatedto be on farms. The present month-ly rate-more than double the mid -March output-is 50,000 more thanthe 1941 average monthly output of375,000 radio batteries for the2,700,000 sets estimated on farmsthat year. It is impossible to statenow whether the present rate of pro-duction can be continued indefinitely.

By San D'Arcy

"Breaking down these compara-tive figures reveals that in 1941 theproduction allowed an annual use of1.4 batteries per radio per year. Thecurrent rate if continued, wouldexceed this allowance, and permit1.62 battery sets per radio.

"This indicates one of the pur-poses in WPB's program-to accom-modate increased daily use of radios.Reports indicate that farm radiolistening -in time has increased abouttwo hours a day. The goal of thesupply program is not only to meetnormal requirements, but to satisfyan abnormal anticipated need for2.0 batteries per radio per year.

"Two factors in this supply prob-lem dim the brightness of today'spicture. One is the abnormal back -

"No service shop in town will tell mehow long it will be before I can get this

set repaired. Can you tell me?"

log of radio battery requirementswhich has accumulated in the lastnine months of curtailed production.It will take some time to balancesupply and demand with such aninitial handicap.

"The other is the uncertainty ofmaintaining present revived pro-duction. Facilities, manpower, andthe critical materials that are in-volved in the production of radiobatteries, are subject to prior claim-ants including the Army and Navy..The present reversion to civilianproduction is possible through atemporary lag in prior claims. Forthis reason it is not possible to pre-dict how long production will con-tinue at the present rate, whether itwill be increased, or cut back again."

It is unnecessary to spend muchenergy analyzing the WPB an-nouncement. Batteries are now be-ing made and delivered to jobbers.

It is possible that deliveries ofbatteries may continue without seri-ous interruption-or the materialsshortage may again become acute.

"MR" TubesIf it could work the WPB L-265

order would clean up a messy situa-tion insofar as replacement tubesare concerned. There simply are notubes for civilian radio sets now, butunder L-265, as amended, there couldbe, IF tube makers can find the fa-cilities for producing the "MR"tubes. There is the catch! We un-derstand that government agenciesplan to purchase about 120,000,000tubes for the military services with-in the next year. Tube productionfacilities, as now established andworking at peak capacity, are limitedto a maximum output of only 110,-000,000 tubes annually. If UncleSam needs for himself 10% moretubes than tube makers can pro-duce, how can there be a surplus of



SIGNAL CORPS TRAINING KITS

Part 2.

VHE thrill which all of us haveI experienced in building our first

radio is something we never forget.The magic in being able to connecttogether a few simple componentsand convert unseen, intangible wavesinto familiar voices and music isever fascinating, the more so whenwe do the work ourselves. Becauseof this, thousands of radio traineesin the Armed Forces are finding thatthe long hours in the training schoolsoften pass all too quickly, thougheach man looks forward eagerly tothe time when the last connectionhas been made and the radio he hasbeen assembling is "perking." Be-cause no two radios are ever precise-ly the same, each man knows his isan individual, custom-built job, eventhough he uses the same hook-up as

0 others. And there is always the pos-sibility that a little added care inshortening a connection, or makinga better soldered joint, or in rear-ranging the wiring, will make hisradio work a little better than thebest of the others.

In the Signal Corps traininggroups many radio kits are employ-ed, ranging from the simplest one -tube types for beginners to a highlyefficient five -tube broadcast super-heterodyne. Some of the simplerkits are ideal for experimental pur-poses around the shop and for teach-ing undergraduates in high schools.Many servicemen are utilizing theirspare time in instructing juniorclasses in such work. The more com-plicated kits serve as perfectly goodreseivers, when assembled, which willequal or surpass the results obtainedfrom many commercial models. Nowthat standard commercial types arepractically extinct, these kits lookto be a way out for those who haveno receivers now.

Single Tube ModelsThe single tube receiver kit uses

) a 1E4G tube in a simple regenera-tive circuit, and will be found re -

Radio Service -Dealer, June, 1943

By J. P. Hollister

markably efficient in pulling in dis-tant stations. It is assembled on asteel chassis, which fastens to asteel panel. Both parts are availablealready punched for assembly of theparts.

The schematic of the 1 -tube kit isshown in Fig. 1. A tickler -feedback

circuit is employed, the coil plugginginto a specially designed, 5 -prongsocket. A 10,000 -ohm potentiometerserves as regeneration control. The1E4G filament is heated directly bya 1.5 volt dry cell. Although the fila-ment of this tube is rated to operateat 1.4 volts, it is so designed that it

0

0Ant

0GndA --

Regeneration

00005PLUG-IN COIL

ss's.

,, 5 MegI/4w

IE4G

ofe

Regeneration Control10M ohm

NANTA.Ar 0.-4 Switch

C

11 Tuning

s'T1.l

A+ 5v 81-45v. Phones

Diagrams show bottom view oftube socket and coil socket

Panel Screw10M ohm Regeneration

Control

To stotor terminalof condenser

CoilSocket

Yellow

Green

Ant Gnd. A+ 8+A- B- 1.5v. 45v

Hole Plug

Panel Screws

4-110,II)Tuning condenser mounting screws

ue

Phone Jocks

9 ---I

Fig. 1 (above) , Schematic of the 1 -tube receiver kit and below (Fig, 2), thechassis layout.

19

QP

LUG

-IN

CO

IL

0 0 0

.090

9511

IE4G

5 M

eg.

I/4w

.01

r 20

0

0 0

An.

Gnd

.,A-,

8-,

C+

Reg

ener

atio

n

Pan

el

Scr

;S

witc

h Yel

low

Gre

enT

o S

tato

r P

late

sof

Con

dens

er

IE4G

Bla

ck

Aso

Tun

ing

IOM

ohm

flbge

nera

tian

Con

trol

Ant

.G

nd. A

i-B

+A

-8-

15v

90v.

0 0

A+

I.5v .0

1 m

fd. 2

Cl0

y

0T

unin

g co

nden

ser

mou

ntin

g sc

rew

s

-7.5

Y

Gre

en

2 O

C 2

V

I C

5G

B -

1-90

v. C

-7.

5v.

Hol

e P

lug

Tub

ing

Ay\

*)C

o.

Pho

nes

onel

Scr

ews

IC5G

Red

Pho

ne J

acks

el lo

w

Blu

e

C+

may

be

wor

ked

at 1

.5 v

olts

with

out

usin

g an

y fi

lam

ent r

heos

tat o

r ba

l-la

st r

esis

tor,

yet

will

hav

e sa

tisfa

c-to

ry li

fe.

As

the

fila

men

t dra

in is

smal

l, on

ly .0

5 am

ps, l

ong

A b

atte

rylif

e m

ay b

e ex

pect

ed. T

his

tube

isfa

r be

tter

than

som

e of

the

earl

ier

5 -v

olt t

ubes

whi

ch u

sed

to b

e em

-

Left-

Fig

. 3(

top)

-S

chem

atic

of t

he 2

-tu

be r

ecei

ver

kit a

ndbe

low

(Fig

.4)

, the

chas

sis

layo

ut.

Not

eth

at th

e sa

me

chas

sis

is u

sed

as fo

r th

e1

-tu

be r

ecei

ver.

Rig

ht-F

ig.

5(t

op)

-Sch

emat

icof

the

3 -t

ube

rece

iver

and

belo

w(F

ig.

6),

the

chas

sis

layo

ut.

Thi

sre

pres

ents

the

com

-pl

ete

chas

sis

asse

mbl

yof

whi

ch th

e 1

and

2 -

tube

kits

are

abb

revi

-at

ed e

xam

ples

, tho

ugh

com

plet

e in

them

-se

lves

.

ploy

ed in

suc

h ki

ts a

nd e

xcel

lent

resu

lts m

ay b

e ex

pect

ed.

Tw

o sm

all 2

2.5

-vol

t B b

atte

ries

-or

a s

ingl

e 45

-vo

lt ba

ttery

-com

plet

eth

epo

wer

supp

lyre

quir

emen

ts.

Hea

dpho

nes

of a

ny ty

pe, h

avin

g an

impe

danc

e of

200

0 oh

ms

or m

ore,

pre

-fe

rabl

y, m

ay b

e us

ed.

If c

ryst

al

Ant

PLU

G-I

N C

OIL

Gnd

.

.000

25

Rei

g°4r

a-e°

hTto

riN.

Con

trol

/AP

Pan

el s

crew

_S

witc

h

Sta

tor

term

inbl

of

Tun

ing

Con

dens

e

PLU

G-I

NC

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GR

EE

N

DR

OW

N

GR

EE

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&If

00°0

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4G

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5G

Reg

ener

atio

nV

olum

eT

unin

g

Tub

ing

500M

-oh

mV

olum

eC

ontr

ol

.01

mfd

. 200

v.

Tun

ing

Con

dens

erM

ount

ing

Scr

ews

16m

fd. 2

00 -

volt

Ele

ctro

lytic

BLA

CK

GR

EE

N

Yel

low

I E4G

Tub

ing

An

.G

nd.

A+

8+

Tub

ing

El

16 m

fd20

0 v

Bot

tom

vie

w s

how

non

all

sock

ets

Shi

elde

d

Sol

der

lug

Wire

to s

hiel

d

5

0

I H5G R

ED

GR

EE

N

Gre

en

Red

A -

B -

C+

I.5v

.90

v.C

-7.

5v.

icLL

ow D

oi Pho

nes

it

Pan

el

scre

w

IC5G

Yel

low

head

phon

es a

re u

sed,

how

ever

, it w

illbe

nec

essa

ry to

shu

nt th

em w

ith a

na

-f c

hoke

, and

pla

ce a

n 0.

1 m

fd c

on-

dens

er in

ser

ies

with

the

phon

es,

The

cho

ke s

erve

s as

a p

ath

for

the

d -c

bat

tery

vol

tage

to th

e pl

ate

ofth

e tu

be a

nd th

e bl

ocki

ng c

onde

nser

keep

s th

e B

sup

ply

volta

ge o

ff th

e

crys

tal p

hone

s.T

his

prec

autio

n is

not n

eces

sary

with

the

usua

l mag

-ne

tic ty

pe p

hone

s. T

he w

irin

g di

a-gr

am is

sho

wn

in F

ig. 2

.

Mul

ti -T

ube

Mod

els

The

two

-tub

e ki

t, sh

own

in F

ig. 3

,is

sub

stan

tially

the

sam

e as

the

one-

tube

mod

el, b

ut a

sin

gle

-sta

ge a

udio

ampl

ifie

r is

add

ed, w

hich

ser

ves

toin

crea

se th

e vo

lum

e co

nsid

erab

ly, a

sw

ill b

e ne

eded

for

far

-di

stan

t sta

-tio

ns o

r w

hen

oper

atin

g w

ith a

sm

all,

inef

fici

ent a

nten

na. T

he s

ame

chas

sis

and

pane

l are

use

d as

for

the

one

-tu

be jo

b, s

o on

e ca

n st

art w

ith th

e

smal

lest

kit

and

add

to it

, with

out

rebu

ildin

g or

dis

card

ing

any

part

s.T

he w

irin

g di

agra

m f

or th

is jo

b is

show

n in

Fig

. 4.

Max

imum

res

ults

fro

m th

is ty

peof

kit

are

obta

ined

whe

n th

ree

tube

sar

e us

ed. T

he r

esul

ting

rece

iver

is a

rege

nera

tive

dete

ctor

with

a tw

o -

AN

T

.000

25P

LUG

-IN

CO

IL

Bin

ding

Pos

tC

hass

is-

ut-Lug

Bak

elite

Was

her P

hone

s

Gre

en to

Sta

tor

Ter

min

alof

Tun

ing

Con

d.

.01

1000

IOM

ohm

Reg

ener

atio

nC

ontr

ol w

ith s

witc

h

Lug

tobe

bet

wee

nso

cket

and

chas

sis

6v. A

C

Sw

itch

on'

Reg

ener

atio

n 1.

-4C

ontr

ol

1M/ V

..34

0 oh

ms

in li

ne c

ord

-05

T40

0

All

resi

stor

s or

e 1/

4 w

att

stag

e au

dio

ampl

ifie

r. I

n th

e ci

rcui

tsh

own

in F

ig. 5

, the

com

plet

e sc

hem

-at

ic f

or s

uch

a re

ceiv

er is

. sho

wn.

The

11I

5G h

igh

-mu

trio

de a

cts

asth

e fi

rst a

-f

ampl

ifie

r, g

ivin

g a

gain

of a

bout

20.

Thi

s fe

eds

into

the

1C5G

out

put t

riod

e w

here

fur

ther

ampl

ific

atio

n ta

kes

plac

e. A

wir

ing

Left-

Fig

. 7(t

op)

- S

che-

mat

ic o

f the

2 -

tube

a-c

/d-c

Tra

inin

gK

itan

d be

low

(F

ig.

8), t

he c

hass

isla

yout

.

Rig

ht-

Fig

.9

(top

) -

Sch

e-m

atic

of t

he 3

-tu

be a

-c/d

-cT

rain

ing

Kit

and

belo

w (

Fig

.10

), th

e ch

ass-

is la

yout

.T

his

empl

oys

the

sam

e ch

assi

s as

the

2 -t

ube

re-

ceiv

er.

Ant

Bin

dng

s

diag

ram

of

this

layo

ut is

sho

wn

inFi

g, 6

.If

des

ired

, a s

mal

l p.m

. dy-

nam

ic o

r m

agne

tic lo

udsp

eake

r m

aybe

use

d w

ith th

is r

ecei

ver.

In a

ll th

ree

of th

ese

rece

iver

s, a

d-di

tiona

l wav

eban

ds m

ay b

e co

vere

dby

sub

stitu

ting

othe

r pl

ug-i

n co

ils.

(Con

tinue

d on

pag

e 28

)

Ant

.P

LUG

-IN

0002

5C

OIL

.000

05

©A

nt.

Coi

l

7

360

rnm

fd

76

0110

00

Sw

itch

onR

egen

erat

ion

Con

trol

340

ohm

s in

line

cor

d

2 U-1

15

Ow

T

05

1400

AI

resL

tors

ore

1/4

wat

t

10M

ohm

Reg

ener

!ion

Con

trol

Bla

ck

Gre

en to

Sta

tor

Ter

min

al o

fT

unin

g C

onde

nser

)0;

si'6

1a

,0

4)ro

Bla

ck--

Lug

to b

e be

twee

nv

)so

cket

and

6v.A

-d/(R

ed

Red

/

05m

fd. 4

00v.

Bin

ding

Pos

t

Was

her

Ext

rude

dW

ashe

r

hass

is

Ug

Blo

ckB

e A

C2v

AC

%*?

A 0

L1 ®

Le)

0ts

-5.

tr

.25m

fd.

8-8

mfd

. 150

w.v

.E

lect

roly

tic _

rm.ti

Red

..--

----

- --

--- -

----

---

o' oi oi 01

of the driver tube must be isolatedfrom the grid circuit of the succeed-ing tube so that grid may be nega-tive with respect to its cathode andconsequently not draw grid current.

The coupling condenser, or deblocking condenser, is the controllingfactor of the low frequency responseof the audio amplifier. The largerthe value of this condenser, the low-er will be the impedance offered tothe passage of low frequency audiovoltages. This condenser is usuallyso chosen that the lowest frequencypassed by the circuit will be on theflat portion of the amplifier responsecurve which would include the high-est frequency that we wish to am-plify.

The class B amplifier operates insuch a manner that the power out-put is proportional to the square ofthe grid excitation voltage. The gridis biased to the cut-off point. Littleor no plate current flows during pe-riods of no excitation. Plate currentflows only during the positive alter-nation of the excitation cycle. Inorder to increase the power outputthe grid may be allowed to swingpositive on excitation peaks. If thisis done, suitable filters must be usedto remove harmonics from the out-put circuit. With the use of highplate voltage and bias the dynamiccharacteristic of the tube is fairlystraight to the cut-off valueand the slight amount of distortiondue to this curvature is not objec-tionable.

Fig. 15 shows the typical opera-tion of one class B amplifier tube.To utilize such tube circuits in audiofrequency work it is necessary tooperate two tubes in a so-called"push-pull" circuit. This is necessi-tated to achieve a reproduction ofthe input voltage, since each tube re-produces only half an excitationcycle. The tube grids are connectedto the extreme ends of a centertapped secondary on the input, orinterstage, transformer. This allowsthe two tubes to be alternately ex -

Fig. 15. (a) Graph-ical analysis of aclass B amplifiertube. (B) Push-

pull circuit.

cited so that we achieve in the out-put circuit a reproduction of the in-put voltage.

The characteristic of such an am-plifier is fairly high efficiency andoutput with a relatively low ratio ofpower amplification. This is due tothe power required to produce thelarge excitation necessary. The min-imum efficiency of such an amplifieris about 32% and the maximum effi-ciency attainable is about 78%.

Automatic Volume ControlTo keep the receiver gain constant

with varying signal intensities a sys-tem known as automatic volume con-trol (AVC) has been in use for sev-eral years. The principle is verysimple. A portion of the amplifiedi-f signal supplied to the second de-tector rectified, passed through aresistor of proper value and the devoltage drop across this resistor isapplied as additional bias for the r -fand i-f tubes. As the signal voltageincreases the rectified currentthrough the resistor increases. Thisincreases the bias on the controlledtubes and thus decreases the gain.To accomplish this it is necessarythat the second detector, if to beused to provide both audio voltage tothe audio amplifier and negativevoltage to the controlled tubes, behooked up as a negative rectifier.That is, we must connect the cathodeto ground so that is the positive sideof the circuit and our negative volt -

"Can you fix this by Oct. 8th?"

$1.00 PAID FOR SHOP NOTESWrite up any "kinks" or "tricks -of -the -

trade" in radio servicing that you havediscovered. We will pay $1 in DefenseStamps for such previously unpublish-ed "SHOP NOTES" found acceptable.Send your data to "Shop Notes Editor,"RADIO SERVICE -DEALER, 132 W. 43rdSt., New York City. 'Unused manu-scripts cannot be returned unless ac-companied by stamped and addressedreturn envelope.

ages will then be taken off the highend of the voltage divider. The audiovoltage is fed from the variable tapof this resistor to the audio stagesand the rectified voltage that is to beused as AVC voltage is filtered by anRC combination and passed on tothe controlled tubes. Such an ar-rangement is shown in Fig. 16.

Fig. 16. Automatic Volume Control.

The output of the last audio stagemay be fed through a suitable out-put transformer to a loud speakerof either the Dynamic or PermanentMagnet Type.

We have covered briefly so far thevarious components of a superheter-odyne receiver. The omission, youmay have noticed, is the power sup-ply for the receiver. Since this isusually well understood by most stu-dents and technicians it will not beincluded in this article. For thosewho do not feel sure of power supplyoperation a bibliography will befound at the end of this article. Thisbibliography covers texts dealingwith pertinent subjects related toradio receiver and other theory.

Bibliography:Fundamental of Radio-TermanPractical Radio Communications

-Nilson and HornungElements of Radio-Marcus and

MarcusAutomatic Volume Control -

RiderRadiotron Designers' Handbook

-Distributed by RCA.


OfficialU. S. SignalCorps Photo

*Mr. L. H. R., a Service -Dealer in Detroit,Mich., wrote this.

We have hundreds of cordial letters likeit in our files.

Richard Alan,Circulation Mgr. of "RSD."

Answering YourProblems!

"MORE FOR YOUR MONEY"*"Several magazines claim they are doing a terrific pub-lishing job for radio servicemen and dealers. One evenclaims that it alone is responsible for helping to keep theradio service business alive during these trying times.That's baloney! I've found only one radio magazine thatreally knows what our problems are and is trying to dosomething to help us. Yes, it's 'Radio Service -Dealer' thatdelivers what we want-so please keep it up! "RSD" givesme much more for my money so I gladly pay you $2 fora year's subscription rather than subscribe to other maga-zines that charge less, claim too much and deliver toolittle." (Signed L.H.R.)

TEAR OUT AND MAIL TODAY.RADIO SERVICE -DEALER132 West 43rd Street, New York City, N. Y.

Sirs: Here is my 0 check (or 0 money order) for Enter my sub-scription order to RSD for the next issues. (12 issues cost $2.-24 issues cost $3.) (Canadian and Foreign subscriptions are $3 annually.)

Name (print carefully)

ADDRESSOWNER

CITY STATE I am SERVICE MGR.SERVICEMAN

FIRM NAMEIS YOUR FIRM A: SERVICE -DEALER 0 JOBBER D MANUFACTURER

IF IN SOME OTHER BUSINESS, TELL WHAT IT IS:


LAST YEAR'S BONDS GOT US STARTED

F

TN

.41(' Last year saw nearly 30,000,-000 workers voluntarily buy-

ing War Bonds through some 175,-000 Pay -Roll Savings Plans. Andbuying these War Bonds at anaverage rate of practically 10% oftheir gross pay!

This year we've got to top allthese figures-and top them hand-somely! For the swiftly acceleratedpurchase of War Bonds is line ofthe greatest services we can renderto our country . . . and to our ownsons . . . and our neighbors' sons.Through the mounting purchase ofWar Bonds we forge a more po-tent weapon of victory, and buildstronger bulwarks for the preserva-tion of the American way of life.

"But there's a Pay -Roll Savings

Plan already running in my plant."Sure, there is-but how long is

it since you've done anything aboutit? These plans won't run withoutwinding, any more than your watch!Check up on it today. If it doesn'tshow substantially more than 10%of your plant's pay -roll going intoWar Bonds, it needs winding!

And you're the man to wind it!Organize a vigorous drive. In just6 days, a large airplane manufac-turer increased his plant's showingfrom 35% of employees and 21/2%of pay -roll, to 98% of employeesand 12% of pay -roll. A large WestCoast shipyard keeps participationjacked up to 14% of pay -roll! Youcan do as well, or better.

By so doing, you help your na-

tion, you help your workers, andyou also help yourself. In plantafter plant, the successful workingout of a Pay -Roll Savings Plan hasgiven labor and management acommon interest and a commongoal. Company spirit soars. Minormisunderstandings and disputeshead downward, and productionswings up.

War Bonds will help us win thewar, and help close the inflationarygap. And they won't stop workingwhen victory comes! On the con-trary-they will furnish a reservoirof purchasing power to help Amer-ican business re-establish itself inthe markets of peace. Remember,the bond charts of today arethe sales curves of tomorrow!

You've done your bit Now do your best!

THIS SPACE IS A CONTRIBUTION TO AMERICA'S ALL-OUT WAR EFFORT BYRADIO SERVICE -DEALER


Servicing Facilitated By L-265

OrderBy Charles Golenpaul

IIHE first constructive legislationreleased by the War Production

Board that actually benefits consum-er, serviceman, and jobber, whilecutting red tape to the bone is therecent WPB Limitation Order L-265.

Now for the first time the service-man can really buy those replace-ments he needs in his work. Pre-vious restrictions are swept aside.By submitting the defective part hehas removed from radio or similarassembly, or certifying that he needsthe replacement, he can walk intohis jobber and get that requirementpart. Meanwhile, the jobber in turnshould have no hesitancy in givingthat part to the serviceman sincethe jobber can replace his stock onthis same part -for -part basis.

I like this new Limitation OrderL-265. It's simple. It reduces paperwork to a minimum. And yet it safe-guards the use of our strategic ma-terials as it should. The servicemanmerely collects that part which he isreplacing-or gets a certificate whenhe sells the customer. He does nothave to pass the defective part onto the jobber. He must simply certi-fy that he has collected the, compo-nents in kind, or corresponding cer-tificates. He must keep a record ofthe parts or certificates, and thisrecord must balance with his pur-chases. The junked parts are turnedin at scrap or salvage stations with-in 60 days of their collection.

This new order should work won-ders in wartime servicing. Untilnow, unfortunately, many jobbershave held up on the release of theirmerchandise. They have held out forbetter odds, working under the falseimpression that they could not re-place their stock, although theycould have replaced whatever theysold by filing the PD -1X form. How-ever, the present part -for -part rou-tine now clears up all doubts as tostock replenishrrient within the pro-

-duction scope of the manufacturers.(Italics ours, ED.)

The serviceman did not have to'flash a priority in order to buy re-'placement parts prior to L-265. Thejobber did have to furnish a pri-ority which he obtained through thePD -1X. The difference now with

*Sales Manager, Aerovox Corp.

L-265 is that the jobber can displayhis merchandise and make every ef-fort to sell it, whereas before hedoled out his precious stock only topet accounts. The result was thatsome servicemen were out of luck.And millions of receivers were silentfor want of proper repairs.

The WPB is certainly proving itsintention of keeping American radiosets functioning, to the end that theAmerican people can be kept in-formed and guided and encouragedat every stage in the winning of thewar.

A Hint About

Your Signal TracerBy Robert Boudreaux

' The Sigdal Analyzer or SignalTracer, (whichever You prefer' to callit) 'is more or less misunderstdod bysome servicemen. For that reasonthe' writer undertakes giving some

'light on its -adaptabilities to the mod-ern service shop.

Many hours can be saved with theTracer once the serviceman haslearned -to use it. I remember thetime I bought mine-a friend toldme that Nvould like. it for three orfour months and then I would stopusing it. That was two years ago andI am not thinking of putting it aside.

The Atwater -Kent Model 487whose gain data was published asCard 4, page 29, May 1943 RADIOSERVICE -DEALER, had a funny troublein it. The RF gain was normal up to"the diode detector, but past that itwas extremely weak. By applyingone volt on the control grid with theaudio signal generator tuned for 400cycles per second, there. was a gainof only about 1 to 3 from the grid tothe plate of the 2A6 tube. By placingan 8 mfd. condenser .across fromcathode to ground the gain wouldjump up to normal on the meter withits probe, on the 2A6 tube. Seeingthe voltage go up to normal for thattype tube would encourage a service-man, but the trouble was not foundat that point.

Moving the probe to the 2A5 out-put tube's plate, a gain of about 1 to2 was obtained which was far frombeing right. The solution was foundby placing an 8 mfd. condenser fromscreen grid to ground (chassis) ofthe 2A5 which caused the voltagegain to go up to normal.

Now, you may think that it wouldhave been easier to try the condenseracross the screen grid in the firstplace, and such would be correct hadthere been any hum coming from thespeaker, but in this set there wasno hum, and a stage -to -stage gaintest was the quickest way in whichto isloate the fault.

This is a typical example of howthis wonderful instrument, a SignalTracer, can save hours for you.

OPA On OvertimeHEN an appliance repair shopspecifically offers to do a re-

pair job in overtime hours, the cus-tomer requesting such a special serv-ice, and the work is actually doneduring overtime hours by mechanicswho are paid time and a half, theShop may in most cases charge oneand one-half times its regular cus-tomers' hourly rate, the Office ofPrice Administration

This interpretation applies wherethe seller in March, 1942, the baseperiod under the services regulation(Maximum Price Regulation No.165), actually made an extra chargefor overtime labor or where he didnot regularly supply any overtimelabor as such in March. In the firstcase, the repair shop has its over-time charge in March as a ceilingprice. In the second case, where noovertime was regularly supplied inMarch, the special overtime servicenow becomes a new or different serv-ice, and the maximum price for it isdetermined either by the nearestcompetitor's charges or by the useof the regular percentage marginmark-up formula provided by theregulation.

The only case in which the specialcharge cannot be made is where therepair shop regularly worked over-time in March without making anydistinction in its charges for regu-lar hours and overtime hours.

In all cases, overtime work at anextra charge must be specifically au-thorized by the customer, and theextra charge cannot be made merelybecause employees are worked over-time to finish a job which the cus-tomer intended to have completedwithin regular shop hours.


FOR THAT

MARCHHEA

SERVICEMANSERVO

byFRANK FAX

Is the memory of income tax day stillpainfully fresh? Was the prepara-

tion of the form almost as hard as dig-ging up the scratch to pay?

Well, this is just the time to tell youabout the new Sylvania Business RecordBook. It's a simple week -by -week book-keeping system, specially designed foryour business. Layout was directed byRodman L. Modra, who was formerlyChief Deputy Collector of U. S. InternalRevenue. This tax expert tells how touse it.

Use it in conjunction with Sylvania's3 -in -1 daily Service Forms, and you havea complete record of daily business deal-ings for the year.

And it's useful not only for tax pur-poses. These are days of reports, ques-tionnaires and affidavits that must befilled out. The Sylvania Business RecordBook enables you to answer any quiz theexperts give.

Buy your own bookkeeping service foronly $1. If yourjobber is un-able to supplyyou, write to szdFrank Fax, BUSINESSRECD'

te84Dept. RS -6,SylvaniaElec-tric Prod-ucts Inc.,Emporium,Penna.

XJ1L R P

RDFOR 1

lot CR, RadioSeraice:dn

ORD

Complete bookkeepingsystem with expertinstructions-price $1

SYLVANIAELECTRIC PRODUCTS INC.

RADIO DIVISION

Trouble -Shooting Short -Cuts

(Continued from page 6)

could be secured by reducing the avcfilter resistor values proportionately,this is likely to lead to other diffi-culties.

Occasionally troubles are presentin receivers when the chassis is in-stalled in its cabinet but the setfunctions satisfactorily when re-moved from the console. Many suchcases are due to warping of thewood, which places the chassis understrain and sometimes bends it sothat closely adjacent parts areshorted; or intermittent action be-comes evident when the vibrationsof the speaker, coupled with thewarping, causes intermittent shorts.Sometimes, too, longer mountingbolts are substituted for those norm-ally supplied to hold the chassis inplace and a short results due to theexcess length of the bolt groundingsome portion of the receiver circuit.

In many of the smaller receiversusing a single i-f stage and no r -fpre -selection, strong stations at thelow frequency end of the dial canbe heard even when the oscillator sec-tion of the pentagrid converter is in-operative. In such cases the i-f trim-mers are usually somewhat mis-tunedso that the circuit is even broaderthan usual. Then, when the set istuned to the low frequency end ofthe dial, it functions as a tuned r -freceiver rather than as a super-heterodyne and the low -frequencybroadcast signal rides through. Whenthe gang condenser is tuned to high-er frequencies, the signal becomesprogressively weaker, but no otherstations are brought in.

Occasionally, too, only a singlestation can be tuned in no matterwhere the receiver dial is turned, butfor an entirely different reason. Ifthere is no change in output volumeas the dial is rotated, we can bepretty certain that the trouble ismerely a loose set screw connectingthe dial and condenser shaft.Variants on this theme are condi-tions where the dial bushing is notconcentric with the condenser shaftso that the condenser is turned,while the set screw is loose, but onlyover a portion of the range. In suchcases we shall find that one or morestations tune very broadly whileothers seem to tune normally. Onceexperienced, it is easy to identifysuch troubles when they recur.

Bench Test MethodWhen the set is on the shop bench,

it is convenient to keep in mind the

major sections of the receiver, asshown in Fig. 1. If we break it upinto these sections as has been donein this block diagram, it is simplerto isolate the section in which thefault is present. 'Once we have es-tablished this, it requires merely acheck of the components in the par-ticular section affected rather thana test of the entire receiver.

In either signal tracing or signalinjection, the usual practice is tocheck each circuit or stage in thenumerical order (or the reverse)given in the diagram. Thus, in sig-nal tracing, we would start at theantenna, feeding a signal to the re-ceiver at this point, and check withthe signal tracer the presence or ab-sence of the signal at each succeed-ing point in the order marked. Forsignal injection, we would connectan output meter across the voicecoil and feed the signal to each stage,starting at the grid of the poweroutput tube and working back to theantenna stage. Each time the signalwas injected, we would check to notethe response in the output meter.

Fig. 3. Used in conjunction with the elec-tronic voltmeter of Fig. 2, this rectifying

circuit enables a -c tests to be made.

Instead of this step-by-step meth-od, we can of course take in broadersections of the receiver in much thesame manner as we discussed earlierin this article. That is, we can feeda signal-in the case of the signalinjection method-to the input tothe audio section and note the re-sulting output. If there isn't any-fine, the trouble's in the a -f section.If there is output-equally fine, weknow we should look elsewhere forthe trouble.

In the case of signal tracing, wedo just the reverse. We feed the sig-nal to the antenna and check at thesecond detector to see if the signalhas progressed through the r -f andi-f stages. If so, then we know thetrouble's in the a -f section.

Of course, again, much can be donewithout instruments. For instance,if there is a tuning indicator on theset, we need not hook up a signal


tracer to find if there is any responseup to the second detector. If there isno signal, we will get no indicationon the magic eye or other indicator,when we feed a signal to the antenna.Naturally, this isn't the whole story;perhaps the indicator isn't working,perhaps there's something wrong inthe avc system. Maybe, too thepower supply isn't delivering anyjuice. But if we do get a healthyclosure of the eye when we apply anormal broadcast signal to the an-tenna imput, we can be pretty cer-tain that we'll save time by lookingin the audio system for the trouble.

The above is based on the assump-tion that the receiver under test isinoperative or, at least, almost so. -

If the trouble is noise, or hum, oroscillation, or any of the other an-noying manifestations peculiar toradios, then we still follow sub-stantially the same method, but in-stead of looking for a replica of asignal fed to a point in the receiver,we look for the presence or absenceof the noise or other abnormal soundin the section under test.

A circuit diagram of an electronicvoltmeter similar to that used in theRider Chanalyst is shown in Fig. 2.This covers from 0.2 to 500 volts infour ranges. A special scale is re-quired, so calibrated, that the zero isin the center. The principle of opera-tion has been described before, butfor the benefit of newcomers let usgo over it again. A milliammeter inthe cathode circuit of a type 76 tri-ode is adjusted to read half scale(0.5 ma) by means of the 10,000 ohmzero adjusting rheostat and the6000 ohm calibrating adjustment, thelatter being adjusted only whentubes are changed. If we now applya positive voltage to the grid of thetype 76 tube, the cathode current willincrease and consequently the meterreading will be higher; if we apply anegative voltage to the input thecathode current will decrease and themeter pointer will accordingly swingtoward zero. Thus in measuringpositive voltages, with respect to -ground, the meter reading increasesand for negative voltages it de-creases. At full sensitivity, 5 voltspositive swings the pointer to fullscale and 5 volts negative swings itto zero. The voltage divider in theinput circuit enables the four rangesto be covered.

This meter is automatically pro-tected against excessive overload ordamage. If a high negative voltageis applied to the input, the meterpointer swings to zero; it cannotread less, because the negative volt-age simply drives the cathode cur-rent to zero. If an excessive positive

voltage is applied, the meter pointermay swing off scale, but the currentis limited by the voltage dropthrough the 27,000 -ohm plate re-sistor, and cannot become sufficientlygreat to burn out the coil.

The electronic voltmeter is adaptedonly to checking d -c voltages. It isused with a shielded cable and probepoint. In series with the probe is a1-megohm resistor. In combinationwith the 10-megohm input, this givesa total input impedence of 11 meg-ohms, so the loading on the circuitunder test is very small.

This instrument is most useful forchecking d -c voltages in high impe-dence circuits, such as the plate and

grid circuits of resistance -coupledamplifiers, the oscillator grid voltageresulting from rectification, screenvoltages, etc. It may be adapted toa -c tests by using a diode or triodein a circuit illustrated in Fig. 3. Thecircuit under test is then coupled tothe diode input and the output of thisrectifying unit is coupled directlyto the electronic voltmeter. The inputvoltage divider of the electronic volt-meter had best be removed to in-crease the sensitivity. The calibra-tion for a -c will not be the same asthat for d -c.

These two units will come inhandy for a multitude of tests insignal and other circuits.

In plane -to -plane -to -base communica-tion as demonstrated in the AleutiansKen-Rad Electronic Tubes guide andguard our forces in the air on theland and sea In all allied maneu-vers everywhere instant communi-cation knits together our combat units"Coordination through communica-tion" - that's the success story nowbeing recorded in every globalquarter Knowing this Ken-Rad'sarmy of service men dealers anddistributors are glad to wait for

their full quota of Ken-Rad tubesNone of us - ever! - will keep Vic-tory waiting one needless second

E ICRADRADIO TUBES INCANDESCENT LAMPS TRANSMITTING TUBES

OWENSBOR....) KENTUCKYRadio Service -Dealer, June, 1943

PAINE1111111111i,

27

for PermanentResistanceToday andTomorrow . .

Consistent performance day -

t after -day under a wide rangeof operating conditionshas proved the dependability

I of Ohmite Resistors. Thisrugged quality has enabledOhmite Brown Devils andDividohms to keep ex-isting installations goinglonger. It has also made

I them especially well fit forIi

today's wartime applica-I tions ... and tomorrow's

Ipeacetime needs.

Handy Ohm's Law Calculatorit

Figures ohms, watts, volts,amperes-quickly, accurately.Solves any Ohm's Law prob-lem with one setting of the.slide. Send only 10c in coin forhandling and mailing. (Alsoavailable in quantities.)

OHMITE MANUFACTURING CO.4847 Flournoy St. Chicago, U. S. A.

28

Signal Corps Training Kits


Coils are available to cover the fol-lowing short-wave ranges :

70 to 200 meters35 to 70 meters15 to 35 meters

as well as the standard broadcastband of 545 to 1500 kc.

AC -DC Models

There are many who prefer to doaway with batteries, and for suchac -dc kits are available. These func-tion similarly to the battery models,although different tubes, componentsand more care in layout and opera-tion are required. The circuit is thesame as for the battery types, inso-far as the detector is concerned, and

the same coils may be employed tocover the ranges given for the bat-tery models.

A schematic of the two -tube ac -dckit is shown in Fig. 7 and the cor-responding wiring diagram in Fig. 8.The first type 76 tube is employedas a regenerative detector in thesame type of circuit used for thebattery -operated kit. The secondtype 76 tube has its grid and platejoined, and serves as a diode half -wave rectifier. The 20,000 -ohm re-sistor in its cathode circuits acts asa filter resistor and is bypassed bythe two 8 -mike electrolytics, whichserve to remove most of the hum.

The three -tube ac -dc kit, shown inFigs. 9 and 10, is similar to that justdescribed, but has a single -stage re-sistance -coupled audio amplifier add-ed. The type 76 tube has greater

Broadcast Superheterodyne I.F.=-06

12SA7 BIi 01706 Green ,I2SK 7 t 0 7136 Grben 12S07 02a

8.., 81 8a

Lim h ... ..,B E

1970001710

era

BlocBlock

/Red

Ground condenser from, W rhotenpin of lierible wire

of S rill,

3 Meg

01708 0170612 07 1261(7 2SA

777ihMmEM

002600.

Switch on VolumeCon. 01

12SQ7

12SA7

12SK7

50LAGT

352567

501_6GT 400v. Blue

102400. Red

Speoke

Specker Field

E"' Yellow

20-20150wv

05 400

110v AC -DC

35Z5GT

Bloc

Red 65wnlle

77 t/ "4 is

e

35Z 5GT

.6146Th_

50 Bloc

ellow

19701

- - -26-20m14

t50Electrolytic =_

Lighl

0

500 M ohmVolume Control

With Switch

Rea

See Fig

To 1100 AC -DC

Red

Oco Coil01710

125A7

See Me

Ootvd_To Loop Ant To Aol

NOTES ..er Lug -0 on Om Cog is to be soldered Marshy to lug no 6 on 12 SA7 5001481"El" Wire from outside Ant as heisted with Green wire from no 13 lug on 12 SA7 socket to Motor

00PM on rem section of Timing Gond"C Wire from lug on Os< Coil to stator gloms on front section of Tonang Gond

Fig. 11. (above)-This 5 -tube a-c/d-c receiver meets the need not only for anadvanced training kit but also as a home receiver for custom-built installations.

Fig. 12 (below)-shows how easy it is to follow the wiring.


power output than the small batterytubes used in the battery -operatedkit, and adequate power will befound available to operate a midgetspeaker, preferably of the magnetictype, on strong signals.

Because one side of the a -c line isgrounded, particular care must betaken in operating these ac -dc mod-els. If the metal chassis is placedwhere it may touch other metal, suchas a radiator, pipe, etc., there is apossibility of crossed grounds re-suiting which will damage the appa-ratus or blow out the line fuse. Donot touch any of the metal partswhen the set is in use without mak-ing certain that no grounds may re-

' suit. These kits should be reservedfor the use of more advanced stu-dents who will understand the needfor such precautions, which are notpeculiar to these particular kits butapply also to an ac -dc chassis.

The 5 -tube ac -dc broadcast super-heterodyne circuit shown in Fig. 11follows along the design lines of thebetter commercial receivers. It willtherefore serve not only for train-ing advanced students but also as anexcellent item for dealers and serv-icemen who need a chassis for cus-tom-built installations. The tubelineup assures adequate sensitivityand power output, and its adaptabil-ity to modern apartment house usein large metropolitan centers is ob-tained through the use of a built-inloop antenna. The sensitivity is highenough so that the average fieldstrength of local stations will pro-duce full power output, and, forweak, distant stations, an externalantenna may be employed, coupled tothe loop by twisting around one ofthe loop leads.

In this receiver, the 12SA7 pen-tagrid converter is coupled to asingle 12SK7 i-f stage operating at456 kc, thence to a 12SQ7 detector,avc and 1st a -f amplifier. The pow-erful 50L6GT beam power outputtube feeds a dynamic speaker, thespeaker field of which serving- as afilter choke. The. 25Z5GT rectifiershas its 'he'ater tapped to providethe proper voltage for the pilot light.The negative voltage developed atthe oscillator grid, when oscillating,is coupled to a voltage divider cir-cuit formed by a 15-megohm 3-meg-ohm and 500,000 -ohm resistor (thevolume control) in series, and thevoltage resulting at the junction ofthe 15- and 3-meg. resistors is em-ployed as a bias for the 12SA7 and12SK7, in addition to that providedby the avc system.

By this unique feature, the normalincrease in oscillator voltage whichoccurs at the high -frequency portionof the tuning range and which re -

INSTRUCTORS!Send for this NEWFREE BROCHURE

( RADIO TRAINING KITSLa fa ye tt e' s Special Department for handling the needs of

instructors and school management has juit prepared this new brochure toaid schools in their government training courses. We are helping Uncle Samto teach radio and we can help you too.

Lafayette Radio is headquarters for all radio and electronic partsand equipment of every nationally known manufactUrer in the. field. Asingle order, no matter how large or how small, will bring prompt deliveryon all your requirements.

Send for your free copy of "Radio Training Kits" brochure today.

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-Quick Deliverieson Radio and Electronic'Parts aoaoal Equipment"

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Radio Service -Dealer, June, T 1943 29

for PermanentResistanceToday andTomorrow ..

Consistent performance day\after -day under a wide range

II of operating conditionshas proved the dependabilityof Ohmite Resistors. Thisrugged quality has enabledOhmite Brown Devils and

I Dividohms to keep ex-isting installations goinglonger. It has also made

I them especially well fit fortoday's wartime applica-

I dons . and tomorrow'speacetime needs.

Handy Ohm's Law CalculatorFigures ohms, watts, volts,amperes-quickly, accurately.Solves any Ohm's Law prob-lem with one setting of theslide. Send only ioc in coin forhandling and mailing. (Alsoavailable in quantities.)

10cOHMITE MANUFACTURING CO.4847 Flournoy St. Chicago, U. S. A.

28

Signal Corps Training Kits


Coils are available to cover the fol-lowing short-wave ranges :

70 to 200 meters35 to 70 meters15 to 35 meters

as well as the standard broadcastband of 545 to 1500 kc.

AC -DC Models

There are many who prefer to doaway with batteries, and for suchac -dc kits are available. These func-tion similarly to the battery models,although different tubes, componentsand more care in layout and opera-tion are required. The circuit is thesame as for the battery types, inso-fak as the detector is concerned, and

the same coils may be employed tocover the ranges given for the bat-tery models.

A schematic of the two -tube ac -dckit is shown in Fig. 7 and the cor-responding wiring diagram in Fig. 8.The first type 76 tube is employedas a regenerative detector in thesame type of circuit used for thebattery -operated kit. The secondtype 76 tube has its grid and platejoined, and serves as a diode half -wave rectifier. The 20,000 -ohm re-sistor in its cathode circuits acts asa filter resistor and is bypassed bythe /two 8 -mike electrolytics, whichserve to remove most of the hum.

The three -tube ac -dc kit, shown inFigs. 9 and 10, is similar to that justdescribed, but has a single -stage re-sistance -coupled audio amplifier add-ed. The type 76 tube has greater

Broadcast Superheterodyne I.E=456

12SA7 /Blue 01706 Crewe, )12SK7

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01708 0170612507 12567 12SA

Switch on VolumeCost ol

12507

12567

12567

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352561

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20- 20T 705 14001

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C". tP-11 Vrthite Pilot Light,

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=.05 400o

0 II Black

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12517

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12547

To.To Loop AntOutside

NOTES "A" Lug Y on ()sc. col is to be soldered directly to lug no.6 on 12 SAT socket"8" Wire from outside Ant is twisted with Green wire from no. 8 lug on 12 SA7 socket to stator

plates on rear section of Tuning Gond"G" Wire from lug on Osc Coil fo stator plates on front section al Tuning Gond

Fig. 11. (above)-This 5 -tube a-c/d-c receiver meets the need not only for anadvanced training kit but also as a home receiver for custom-built installations.

Fig. 12 (below)-shows how easy it is to follow the wiring.


power output than the small batterytubes used in the battery -operatedkit, and adequate power will befound available to operate a midgetspeaker, preferably of the magnetictype, on strong signals.

Because one side of the a -c line isgrounded, particular care must betaken in operating these ac -dc mod-els. If the metal chassis is placedwhere it may touch other metal, suchas a radiator, pipe, etc., there is apossibility of crossed grounds re-sulting which will damage the appa-ratus or blow out the line fuse. Donot touch any of the metal partswhen the set is in use without mak-ing certain that no grounds may re-sult. T-hese kits should be reservedfor the use of more advanced stu-dents who will understand the needfor such precautions, which are notpeculiar to these particular kits but

I apply also to an ac -dc chassis.The 5 -tube ac -dc broadcast super-

heterodyne circuit shown in Fig. 11follows along the design lines of the

' better commercial receivers. It willtherefore serve not only for train -ing advanced students but also as anexcellent item for dealers and serv-icemen who need a chassis for cus-tom-built installations. The tubelineup assures adequate sensitivityand power output, and its adaptabil-ity to modern apartment house usein large metropolitan centers is ob-tained through the use of a built-inloop antenna. The sensitivity is highenough so that the average fieldstrength of local stations will pro-duce full power output, and, forweak, distant stations, an externalantenna may be employed, coupled tothe loop by twisting around one ofthe loop leads.

In this receiver, the 12SA7 pen-tagrid converter 'is coupled to asingle 12SK7 i-f stage operating at456 kc, thence to a 12SQ7 detector,avc and 1st a -f amplifier. The pow-erful 50L6GT beam power outputtube feeds a dynamic speaker, thespeaker field of which serving as afilter choke. The, 25Z5GT , rectifierhas its .13.6atei tapped to, providethe proper voltage for the pilot light.The negative voltage developed atthe oscillator grid, when oscillating,

l.

upledtoby avoll5tamgeegodbbaivide3rceigr--cir-cuit formedohm and 500,000 -ohm resistor (thevolume control) in series, and thevoltage resulting at the junction ofthe 15- and 3-meg. resistors is em-ployed as a bias for the 12SA7 and12SK7, in addition to that providedby the avc system.

By, this unique feature, the normalincrease in oscillator voltage whichoccurs at the high -frequency portionof the tuning range and which re-

INSTRUCTORS!Send for this. NEWFREE BROCHURE

( RADIO TRAINING KITS

)43;,,11)10

treaulotoItzttilt

Lafayette's Special Department for handling the needs ofinstructors and school management has just prepared this new brochure toaid schools in their government training courses. We are helping Uncle Samto teach radio and we can help you too.

Lafayette Radio is headquarters for all radio and electronic partsand equipment of every nationally known manufacturer in the field. Asingle order, no matter how large or how small, will bring prompt deliveryon all your requirements.

Send for your free copy of "Radio Training Kits" brochure today.

Steatite Insulators Ceramic Trimmers High Frequency

Circuit Switches Volume Controls Ceramic Capacitors Wire Wound Controls Sound Projection

Controls

write now-address:{SchoolSale Division

901 IV est Jack on BoulevardChu agu, Illinois "

Dept. 61{3

-Quick Deliveriesoffo ilgagalio and Electronic'Paarg. sand Equipment"

Radio. Service -Dealer, June, 1943 29

Those super -sealed Aerovox paper tubu-lars are just as good as they look. Be-neath that colorful yellow -black -and -redlabel jacket, you'll find an extra -generous-ly -waxed cartridge for maximum protectionagainst moisture penetration. Likewise theextra -generously -waxed ends neatly milledand with pigtail leads that won't workloose. In all climes-from frigid Arctic totorrid tropics, these paper tubulars are es-tablishing new performance records. 400,600, 1000 and 1600 v. D.C.W. Popular ca-pacities. Ask Our Jobber ...Ask for these Aerovox paper tubulars. Ask forother wartime capacitors you need. Ask for ourlatest "Victory" catalog-or write us direct.

INDIVIDUALLY TESTED

AEROVOX CORP., NEW BEDFORD, MASS., U. S. A.

In Canada: AEROVOX CANADA LTD., HAMILTON, ONT.

Export: 100 VARICK ST., N. Y. C. Cable: `ARLAB'

VICTORY LINEAerovox Condensers, ConsolidatedResistors, Ductone Recording Blanks,Ken-Rad Radio Tubes, LeotonePickup Needle Screws, MuellerBattery Clips, Wright, Inc. Speak-ers, Walsco Knob Springs, DialDrive Springs, Radio Set Screws,Radio Cement, Snap -in Trimouts,Scratch Removing Polish, RadioTroubleshooters Handbook 3rd Edi-tion, $5.00 Postpaid.

Established 10 YearsPrice List Free To Dealers

Advance Deposits On Tube OrdersAccepted

Interested in Sub -Contracts

Anchor Radio Distributing Service Co.Box 21 Ithaca New York

sults in a greater negative potentialat the oscillator grid, due to rectifi-cation, is put to work to increase thebias on the 12SA7 and 12SK7 tubes.This reduces slightly the sensitivityat this end of the range (where itwould normally be higher) and thusproduces a more uniform degree ofsensitivity throughout the tuningrange. On strong signals, this bias-ing of the grids is further augmentedby the avc action, which is accom-plished in the usual manner throughthe medium of the 12SQ7 diodes.And, for weak signals, the avc actionis rendered less effective due to thedecreased gain resulting from theoscillator biasing, so that the netresult is a slight increase in sensi-tivity over and above that whichwould normally result from the ap-plication of this system, were theavc to act with the same effective-ness as with stronger signals. Whichis just what we want.

The tuning range is from 540 kcto 1600 kc. The oscillator section ofthe two -gang tuning condenser isspecially shaped to provide the properfrequency difference without the useof padding condensers, thus simplify-ing the aligning problems, which

simmer down to a matter of adjust-ing the oscillator trimmer at 1400kc, the test signal being fed to theloop by means of a small auxiliaryloop connected to the test oscillatoroutput and placed several inchesaway from the receiver loop, toavoid interaction between the two.

Because the power line is con-nected directly to the chassis, a non-metallic cabinet and non-metallicknobs must be employed to avoid anypossibility of a person making con-tact with any metallic portion of theset. The back of the set should also,be protected against inquisitivefingers, yet ventilation should be pro-vided. Take care that the mountingscrews are insulated and, in servic-ing, do not attempt to remove thechassis from the cabinet before dis-connecting the power plug from thewall receptacle. These precautionsare standard with all ac -dc receivers.

All of these kits described in thisarticle are available from the Miess-ner Manufacturing Company,through whose courtesy, plus that ofthe Signal Corps, we have been per-mitted to reproduce the schematicsand layouts.

S. N. Shure accepts the Army -Navy "E" Burgee awarded to Shure Bros.,"Microphone Headquarters."

WESTERN S -M GROUP CHANGES TITLE>> >> The Sales Managers Club, WesternGroup, a trade association of radioparts manufacturers which has been inexistence for over ten years, haschanged its name to the Association ofElectronic Parts and Equipment Manu-facturers, to be known in the trade as"E. P. & E. M." The Association,which now has over fifty members, hasmade this change so as to be readilyidentified with the industry which itrepresents. There will be no changein the functions of the organization.The group meets on the second Thurs-day of each month in Chicago, and has

been a potent factor in radio industrymatters. It is currently rendering aservice to its members on prioritiesproblems, price controls, governmentcontracts and regulations, and man-power problems. It is also givingearnest consideration now to post warplanning. The present chairman of E.P. & E. M. is Mr. Jerome J. Kahn. TheSales Managers Club, Eastern Group,has not changed its name but will con-tinue its identity and affiliation withthe Western Group as heretofore.

BUY MORE WAR BONDS


NEW TRAINING KITS BROCHURELafayette Radio Corporation's Spe-

cial Department for handling the needsof instructors and school managementhas just prepared this new brochure toaid schools in their government train-ing courses.

Lafayette's engineers have expresslydesigned the kits mentioned in thisfolder to fit present training programs.Starting with fundamentals and prog-ressing to basic receiver and trans-mitter operation, a progressive train-ing program may be built up aroundthese kits. Lafayette Radio Corpora-tion, 901 W. Jackson Blvd., Chicago,Illinois.

BOOK THAT "SELLS" SOUND

A 24 -page book on "Music and Man-power," has just been released by Oper-adio Manufacturing Company, of St.Charles, Illinois.

1110,41" `'4'''1549f101

Treating the subject of industrialmusic as a production factor both his-torically and currently, the book repre-sents important reading to any execu-tive concerned with the problem ofmaintaining or increasing war produc-tion in the face of a dwindling man-power supply.

Although only a limited edition hasbeen printed, a copy of "Music andManpower" will be sent gladly to anyexecutive addressing Operadio Manu-facturing Company, St. Charles, Illi-nois.

G. E. EXPANDS ITS NEWS PROGRAM

The General Electric Company ex-panded its radio news service\ to thepublic from three to six nights a week,and increased the number of stationson the Columbia Broadcasting Systemcarrying this news program from 60 'to 117, when it began sponsoring the

VSEPRODUCT

roR BEST RESULTS

A TYPEAND SIZEFOR EVERY RU/190E41'T

CLFIROSTAT

MFG. tn.,0FIXED,

VARIAfitt.ANDANYOMATIC

RESISTORS28 S2RopMTrSth SYRCET

A v..U. s

MADEIA U.1

10 -minute news program, "The WorldToday" 6:45-6:55 P.M., EWT, on May31. This was announced by Dr. W. R.G. Baker, Vice President of the com-pany in charge of G.E.'s ElectronicsDept. The new program supplants theformer news program sponsored byGeneral Electric, carried at 6 P.M.,EWT, for over a year on CBS.

.Boob to* those

GREEN caidems4* Although Clarostat is now100% on war work, Clarostatjobbers still have a stock ofessential Clarostat replacements.And those civilian Clarostatsfully reflect the performance,dependability and reputationdemanded by our armed forces.* So look for the green Clarostatcarton. It is your gucrantee ofgetting "tops" in cortrols andresistors.

Are ,You Moving?Notify RSD's circulation department at 132 West 43rd Street, New YorkCity of your new address 2 or 3 weeks before you move. The Post OfficeDepartment does not forward magazines sent to a wrong address unlessyou pay additional postage. We cannot duplicate copies mailed to yourold address. Thank You!

TRANSFORMERSFirst Choice of Servicemen!

STANDARD TRANSFORMER CORPORATION

1500 NORTH HALSTED STREET... CHICAGO


U. S. ARMYSIGNAL CORPSU. S. NAVYAPPROVED

NAF-1136-1P1,68, PL -54PL -55, JK-26

JK-48, PL -291NAF-212938-1

Prompt Deliveries

UNIVERSAL MICROPHONE CO., LTD.424 WARREN LANE

INGLEWOOD, CALIFORNIA

TRIPILETTfr,riatZ,e;se._

TESTERSPodet

213e

MODEL

666H

VOLT-OHM-MILLIAMMETER

Although some older designs are no longerobtainable, several alternate models are avail-able to you under Government requirements.TRIPLETT ELECTRICAL INSTRUMENT CO., BLUFFTON, OHIO

R. C. Sprague (right) president of SpragueSpecialties Co. and Sales Manager HarryKalker of Sprague Products Co. extendmutual felicitations occasioned by the

Army -Navy "E" award to Sprague.

"MR" Tubes(Continued from page 18)

tubes for civilians? We are old-fashioned in one respect-we stillbelieve that two plus two equals four.WPB don't add that way.

The obvious solution rests withthe military agencies. If they needmore tubes than can be produced,some means of expanding tube pro-duction facilities should be tried. IfWPB is convinced that the ArmedServices will require 110% of thepotential output, and that no ex-pansion of tube facilities is to bemade, WPB state thefacts and not evade the issue byputting out some bait in the formof orders about "MR" tubes-tubesthat will never be made.

To actually get badly needed bat-teries (and replacement tubes) intothe sets of civilians only one man-ner of procedure is necessary, to ourway of thinking. WPB should de-termine what minimum limits of re-placements can be made for civilian'sexclusive use, and then WPB shouldendeavor to obtain allocations ofneeded materials and production fa-cilities so the units in question canbe produced. Then the manufac-tured items should be ear -markedfor distribution to jobbers in equit-able manner-and the latter shouldendeavor to get the components intouse in civilian radios as quickly aspossible. Let's try to keep oneradio in every home in working or-der. With wisely determined allo-cations and WPB cooperation itmight be achieved.

*CRYSTALS WANTED!

The government needs more quartzcrystals. And so the WPB has sentout a call to all citizens who may ownproperty on which such material maybe located, or who know where any

can be found, to get in touch with theMiscellaneous Minerals Division, WarProduction Board, Temporary "R"Building, Washington, D. C. If samplescan be provided at the same time, theywill be welcome. There should be sev-eral samples of the best crystals ob-tainable from the location.

These crystals are needed for themanufacture of quartz oscillator platesused in radio equipment for the armedforces. At present practically all ofthe quartz used for this purpose comesfrom Brazil.

The Miscellaneous Minerals Divisionwants only separate individual crystals-clusters' groups or grainy masseswon't do. And each crystal must weighat least half a pound, be at least aninch thick and three inches long. Itmust be clear and colorless on the in-side, although light smoky quartz canbe used. But milky quartz, rose quartzand purple quartz (amethyst) are use-less.

FOLDER ON GHIRARDI'S NEWHANDBOOK

Ghirardi's newly revised and ex-panded 3rd Edition "Radio Trouble-shooter's Handbook" containing 744manual -size pages of valuable time-saving data covering all phases ofradio service work is described and adetailed listing of its 75 topic sectiontitles is given in an attractive new 4 -page folder in color just issued by theRadio & Technical Publishing Co., 45Astor Place, New York City.

This colorful folder points out thespecific advantages this new 744 -pageHandbook offers the busy technicianworking under present "wartime" serv-ing conditions-not as a "study book"but as a reference volume which con-tains a gold mine of vital, profitabletime -saving troubleshooting and repairinformation and data that will enablehim to cut corners, save troubleshoot-ing and repair time, train new tech-nicians; repair cheap sets at a profit;handle tough jobs in half the usualtime.

Copies of this new folder are avail-able from local radio supply houses,radio dealers and bookshops, or directfrom the publishers.

C. E. POINTS AHEAD

Two consumer markets that are duefor phenomenal post-war expansion areF.M. radio and recorded music, in thebelief of the General Electric Company.

Aimed at both is the current G -Efour-color full -page magazine adver-tisement entitled "First step in yourchild's musical education . . . an F.M.radio -phonograph," which featuresGeneral Electric F.M. radio -phono-graph combination sets.

Copy is based upon child appeal andchildren's records, which, together with"grown-up" music, are a valuable andnecessary adjunct to getting the child'staste and education off to the rightstart.


moommuseiri) III

MODERN MEASUREMENTS

without mechanical movement

or its limitations

No type better illustrates the indispensablenature of the Electron Tube throughout scienceand industry than the famous RCA Cathode -RayTube. No type better emphasizes the steadilygrowing business opportunities for RCA service-men, dealers, and distributors who make a pointof keeping abreast of the far-reaching develop-ments in applying basic electronic principles tonew jobs.

Used in oscillographs, RCA Cathode -RayTubes are paving the way to higher standards inmeasuring any phenomena that can be trans-formed into electrical impulses-and doing itwithout mechanical movement and its inherentlimitations.

In addition to their better-known applicationsin radio and communications, C -R Tubes areused regularly in such diverse fields as ignition,timing, and adjustment work; acoustics and vibra-tion studies; studies of magnetic phenomena;medical and biological research; aeronauticalengine synchronization; engine -pressure indica-tions, and a host of others.

Such things as these are what we're talkingabout when we say "The Developments of TodayAre but a Promise of the Future"-and this meansfor servicemen and distributors, as well as forRCA itself.

RCA ELECTRON TUBESRADIO CORPORATION OF AMERICA

RCA Victor Division Camden, N. J.

RAYTHEON TUBES AIDMEDICAL SCIENCE!

Dr. Lee de Forest, Inventor of the Radio "Ferer" Machine

As the annals of modern medical sciencepart company with the past, new ideas sup-plant pre-war practices ... the radio "fever"machine is a modern example ... developedby Dr. Lee de Forest for treatment of coldsand respiratory organs ... another advance

RAYTHEON PRO DUNewton, Mass. Los

New York Chicago Atla

in the new electronic era ... made possibleby the use of tubes. Raytheons are dailydoing their duty in new electronic develop-ments ... a part that Raytheons have so suc-cessfully played in civilian life. There is aqualified dependence in Raytheon tubes.

CTION CORPORATION

Devoted to Research and the Manufacure of Tubes for the New Eras. Electronics

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