sf,rvice dealer

SF,RVICEDEALER

Official U. S. Navy Photograph. Svc Page I,

November, 1942

Have you a few well-read and well -beloved books inyour library that you wouldn't part with at anyprice? We suggest you add another ...because onceyou've read even a few chapters, you'll agree withhundreds of radio servicemen, engineers, amateurs

.. the new MYE TECHNICAL MANUAL is abook worth owning.Many hundreds of copies of this book are being dis-tributed to military radio instructors ... in trainingcenters of the Army, Navy and Marine Corps, includ-ing the Air Forces. Once you glance through thislist of chapter headings, you'll understand why.

1 Loud Speakers and Their Use2 Superheterodyne First Detectors and Oscillators3 Half -Wave and Voltage Doubler Power Supplies4 Vibrator and Vibrator Power SuppliesS Phono-Radio Service Data6 Automatic Tuning-operation and adjustment7 Frequency Modulation8 Television-suggestions for the postwar boom9 Capacitors-how to overcome wartime shortages

10Practical Radio Noise Suppression11 Vacuum Tube Voltmeters12 Useful Servicing Information13 Receiving Tube Characteristics-of all American

tube typesJust one suggestion. We know you'll want a copy ofthis manual eventually. It contains 392 pages ofinformation as down-to-earth as a soldering iron, asindispensable as a voltmeter. It's beautifully bound,

A BookWorth Owning...

with hard cloth covers. It's worth far more than itsprice, $2.00 net to servicemen.

But the supply for civilian use is limited. It will payyou, in the time, effort and money this book cansave you now, to waste no time in going to yourMallory Distributor to reserve a copy. Order yourMYE TECHNICAL MANUAL today!P. R. MALLORY & CO., Inc., INDIANAPOLIS, INDIANA

Cable-PELMALLO

Approved Precision Products

Vol. 3, No. 11 * November 1942

PUBLISHER

SANFORD R. COWAN

Managing EditorM. L. MUHLEMAN

Contributing EditorsJOHN H. POTTS JOHN F. RIDER

"On Leave"

News AnalystA. N. BELKNAP

Circulation ManagerR. ALAN

Special RepresentativeLEE ROBINSON

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

SERVICE1-DEALERSOUNDMAN AND JOBBER

Rec. O. S. Pat. Oft.

.,41 indexAerovox CorporationHigh -voltage CapacitorsAircraft Radio LabsInstruments WantedArmy, U. S. Signal CorpsEnlistmentsBrach Mfg. Corp., L. S.AntennasBurtt, W. R.Tubes WantedCentralabResistors, Controls, SwitchesClarostat Mfg. Co., Inc.P.A. ControlsElectro-Voice Mfg. Co., Inc. 27MicrophonesGeneral Industries Co., ThePhonograph MotorsGuardian Electric Co.Relays

International Resistance Co. 11Fixed and Variable ResistorsLafayette Radio Corp. 27Replacement Parts and KitsMallory & Co., Inc., P. R. ...2nd CoverNew MYE Technical ManualMeck Industries, John 31Audiograph Sound EquipmentMeissner Mfg. Co. 21Radio Training KitsRacon Electric Co. 4Horns, Trumpets, SpeakersRadio Servicemen of America, Inc.Brandex and Service NotesRaytheon Production Corp. . .4th CoverRaytheons Have EnlistedRider, John F. 22Rider Books & ManualsSignal Corps, U. S. Army 3EnlistmentsStandard Transformer Corp. 25TransformersTriplett Elec. Instru. Co. . . . .3rd CoverThin Line InstrumentsU. S. Treasury Dept. 24Pay -Roll Savings PlanVaco Products Co. 29Screw DriversWard Leonard Elec. Co. 31Relays, Resistors, Rheostats

ContenL431 Editorial:

Tube Shortage-Selective Service . 2

32 Noise Generators 5By John H. Potts

3 CIRCUIT COU RT-RCA-Phono radio frequency

25 compensation circuits 8

Silvertone 7072-8 tube, 2 band32 a -c phono recorder 9

RCA-Radiola 522-'Superhet 1031 Silvertone 7167-8 ube, 2 band

Super with pre -selector 10

28 Thinking Ahead 13By J. J. Kahn

Shop Notes 14Philco PT -15; Modulation hum

28 934; Vacuum phototube characteristics2AP1; High -vacuum Cathode-ray tube

29 935; Vacuum phototube, ultraviolettype

5R4-GY; Full -wave rectifier tube6J6; Twin triode, miniature type6AG5; R -F amplifier pentode, minia-

ture1C21; Cold -cathode Gas -triode

Technical Service Portfolio-XXIV 15Resistors and Volume Controls

My Log 20By San D'Arcy

Help Wanted 26

Tube Substitution ChartSuitable for framing, this chart

32 makes the replacement of dis-continued tubes simple.

Cover ctare(Official U. S. Navy Photograph)

RADIO OPERATOR

The radio operator aboard a U. S.Navy Bomber plays a most vitalpart. He gets an invaluable train-ing that will serve him well in thepost-war era. The Navy needsradiomen. See "Help Wanted", page26.

30

Entire Contents Copyright 1942 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, November, 1942

editorial....

Critical Tube ShortageA recent W.P.B. survey indicated that nearly

50 million tubes were on jobbers' shelves or inservice -dealers' stocks. Normally such a volumeof tubes would serve civilian requirements for ayear. Now it is evident that actually less than 15million tubes are "in inventory"-the bulk of theseare slow -movers, worthless for replacement use.

Meanwhile the entire output of all tube manu-facturers is going into the war effort. No civilianuse replacement tube production is scheduled foran indefinite time. The 10 thousand radio service -dealers, who still function as such, face trying daysindeed. Between 2 and 3 million sets are becominginoperative monthly, even if circuit revisions areresorted to, due to the tube shortage alone. Setsto be repaired are piling up on service benches.

The general public has no idea of the situation'sacuteness-that a "radio black -out" impends.Broadcast stations realize how close to disasterthey are; audiences falling away as though struckby a plague. Being "organized" the broadcastersmay yet salvage a critical situation. But whileprice ceilings are in effect tube manufacturers willleave well enough alone. Even if they had facilitiesand could make tubes for civilian use now thesewould have to be sold for less than their cost price.Present tube prices were based upon huge produc-tion run economies no longer possible. We hopeO.P.A. will realize this and afford the relief needed.Some one, somewhere had better do something ina hurry because the general public simply will notstand for a curtailment of radio. Hell is about tobreak loose, and don't say no warning was given.

Inviting the UndertakerOne of radio's leading "dealer" publications has

just published the most fantastic suggestion evermade for service -dealers' consideration. Says ourcontemporary, in effect, "go after juke box repairwork !" Say we, "LAY OFF or you'll risk a bustedhead." Juke box servicing is "organized," in nouncertain manner, and any outsider who butts inbecomes a prospect for a roughing up. Well, itjust goes to show you how little those "merchan-dising -minded" editors, sitting behind polisheddesks in New York City, know about the realworkings of radio from a technical and practicalside. (In addition, the Petrillo ban has stoppeddelivery of new recordings. Jukes rely upon new,popular tunes, and without them jukes are doomedto hasty obsolescence.)

"Dealer, be alert to the profits of servicing" saysthe retailing -minded editors who are grasping fora floating straw, trying to get dealers service -workminded-and they climax the entire nonsensicalarticle with this classic observation : "get afterjuke box servicing-even gas ration boards con-sider jukes necessary for public morale." Whatutter tripe ! If anything, gas rationers will refusea "C" card to servicers who diddle away gasolinetrying to get to jukes while thousands of tax-payers' receivers are piling up awaiting pickupand the parts needed for their repair.

Favoritism Again Selective Service Headquarters issued a list of92 essential occupations recommended for defer-ment. Photo -radio operators (facsimile), record-ing engineers and broadcast station repairmen areincluded in the list, but not mere radio servicemen-the chaps who are striving to keep civilian setsplaying and war -plant or ship -yard public addressand paging systems operating to speed-up produc-tion. Discrimination or oversight?

Tabloid newspapers and wire services, the primeusers of radio relayed photos, employ automaticequipment so simple and fool -proof that even chil-dren can be quickly trained to operate them effi-ciently. Why defer. wire servicemen and not radiorepairmen?

Skilled technicians are required for broadcaststation maintenance work. But what good will itbe to keep BC repairmen on their jobs so theirstations can broadcast beautifully modulated sig-nals to millions of dead receivers lying idle inhomes-dead sets because radio servicing man-power is being drained to the home -front dangerpoint. Not enough servicemen are left to carry onthe volume of work !

A transmitter without sets to receive its signal islike a car without wheels-worthless. Why theSelective Service deferment favoritism to broad-cast station servicers and none for civilian mainte-nance men?

Solder Can Be Had For months many radio parts and materialshave been hard to get. Solder, the most vital ofall materials for a radio maintenance man, hasbeen the scarcest item on the list, and for a peculiarreason. Radio jobbers formerly didn't bother muchabout solder as a stock item. Servicemen usuallybought it from 5 & 10's or hardware stores. (Gen-erally they bought the wrong alloy or type andmade their work doubly difficult) . Freezing of job-ber inventories complicated the situation becausejobbers couldn't buy what they formerly didn'tstock. PD -1X now comes to the rescue. We areadvised by a solder manufacturer that jobbers us-ing PD -1X forms can obtain enough solder to meetemergency requirements. We learn the hard way,don't we?, Jobbers-get busy! Servicemen, buysolder from radio jobbers exclusively henceforth!

SRC

2 Radio Service -Dealer, November, 1942

Some day American 'voices will rock theImperial Palace in Tokyo and cause the defensesof Berlin fo tremble. They will be fhe voicesof U. S. Army radio men, relaying commandsfor the final attack. Will yours be one of them?

IN THIS fast-moving war, words are weapons.Split-second communications are vital to thetiming and teamwork that win battles. Asone of Uncle Sam's radio soldiers, you notonly see action - you help to guide anddirect it!

In Army communications, your oppor-tunities for heroic service are limitless. Atthe same time, you receive training and ex-perience that will be invaluable for a suc-cessful after -the -war career. You learn howto assemble, install and operate the mostmodern radio transmitters, receivers,"Walkie-Talkies," "Electronic Sentries" andscores of other closely guarded secret de-vices-pioneers of future industries-whichcombine today to knit the whole Army intoone hard -fighting unit.

Any man, physically fit, from 18 to 44, inclusive,may enlist. Licensed radio operators and radio,telegraph and telephone workers may enlist foractive duty at once. They may advance rapidlyup to $138 a month, plus board, shelter anduniforms, as they earn higher technical ratings.

Men of 18 and 19 may choose enlistment inthe Signal Corps without any previous trainingor experience.

Those without qualifying experience, who en-roll full time, may enter the Signal Corps En-listed Reserve for training with pay. GraduateElectrical Engineers may apply for immediatecommissions in the Signal Corps.

Civilians over 16 years of age may attend aSignal Corps School, and will be paid not lessthan $1020 per year for full-time training andfuture service with the Signal Corps. Apply U. S.Employment Bureau or U. S. Civil Service.

Incons

"KEEP'EM FLYING!

USARAIY% RECRUITING AND INDUCTION SERVICEtears

GVeisniteromr,,w,oriftethtehesenrzeesct oUm.mSa.ndArnmeayreRstecyrouuitinogr panrocicuIrnedmuecInductionnA17-2wrAit.eG.too:,`W'Tabsehington

CommandingDc.

Radio Service -Dealer, November, 1942 3

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AT SEA RACONS dependably serveSteamship Lines., the MaritimeCommission, Coast Guard and Navyships.

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PAGING HORN

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GENERATORS

T0 many it may seem at first alittle difficult to realize that

noise in any form can be of anyvalue in radio servicing. But, aftera moment's consideration, it will be-come evident that many operationsand tests are now being made in thefield in which noise alone providesthe signal source. This noise maybe atmospheric or man-made static,for which no service apparatus is re-quired. This we utilize when we ad-just the regeneration control of amidget receiver. Or it may be pickupnoise resulting when we touch the'grid of a tube in a high -gain, high-impedance circuit, such as we findin a -f amplifiers of most sets. Ineach case the noise gives us infor-mation regarding the. performanceof the circuit or circuits involved.Such tests are often the easiest andquickest methods to use, and aretherefore the most efficient.

Apparatus designed to produceelectrical noise has been in use fortest and adjustment purposes inradio factories for some years, butlittle information regarding its ap-plication in the service field has beenpublished. At the present time,when the demand for service is atits greatest, it seems particularlyadvisable to discuss any methods ordevices which promise to increase

Italia letvicinf

by John H. Potts

our efficiency. Because noise gen-erators are simple to design andconstruct, and have very definite ad-vantages in many service applica-tions, we believe that many will beinterested in hearing about them.But, first, a word about their appli-cations.

All -Band Noise GeneratorIn general, a noise generator is of

greatest value in providing a testsignal which extends over a verywide band of frequencies so thattuned circuits may be quickly tested

Fig. 1. A simple relaxation os-cillator. RI is a limiting resistor.


for operation without the need fortuning to a specific frequency, as isthe case when a test oscillator orsignal generator of the conventionaltype is employed. Since the type ofnoise generator in which we are in-terested produces a signal whichcovers not only the r -f band, but alsothe i-f and audio ranges, it becomespossible to inject such a signal in anycircuit in any receiver and thus dis-cover, from the response in thespeaker (or the lack of it) whetheror not the circuit under test is oper-ating. It becomes possible to feedsuch a signal to the antenna circuitof .a multi -band receiver and get aquick check of the relative sensitiv-ity of each band by simply notingthe strength of the output signal asthe tuning condenser is rotated overeach of its tuning ranges. "Deadspots" are revealed immediately,which might ordinarily be over-looked. In i-f circuits, preliminarytuning adjustments may be made ofcircuits badly out of line; this willbe of especial value when a replace-ment, not accurately pre -tuned, isbeing used. The padding condenserin an oscillator circuit may be ad-justed properly without rocking thegang condenser.

The simplest device for such testpurposes is a small buzzer. One was

5

Fig. 2. The wave shape obtainedfrom an oscillator of the type

shown in Fig. 1.

on the market a few years ago butits power output limited its useful-ness. A circuit such as that shownin Fig. 1 is adaptable to a widerrange of application. This consistsof a so-called relaxation oscillatorand operated on the following prin-ciple : When the condenser C ischarged to a voltage sufficient tocause the gas in the neon lamp orglow tube to ionize, the lamp lights.The lamp then forms a very low re-sistance path for the condenser todischarge and the condenser voltagedrops until the extinction point ofthe lamp is reached. Then the lampno longer forms a conducting shuntfor the condenser, so the condenserstarts to charge again. This cycleof charge and discharge is repeatedat a rate determined primarily bythe resistance and capacity in thecircuit. The resulting wave form isillustrated in Fig. 2.

Vacuum -Tube CircuitsA method of accomplishing sub-

stantially the same result with a va-cuum tube is shown in Fig. 3. Thisis a negative -conductance circuit inwhich oscillation is produced due to

Fig. 3. A single -tube relaxation os-cillator of the negative conduct-

ance type.

the negative resistance characteris-tics resulting when the screen gridof a pentode is operated at ,a highervoltage than the plate. Actually theactive tube elements of this oscillatorare the screen and suppressor. Thecontrol -grid potential governs thestrength of oscillation, as does thebias on the suppressor. The platevoltage is not critical, but is alwaysless than the screen voltage. In thiscircuit, as in the preceding one, theoscillation frequency is mainly de-pendent upon the values of C and R-in this case, of R1 and R2. Thewaveform of the output is likewisesomewhat dependent upon the con-stants used, as well as upon the tubevoltages. When experimenting withthis circuit, it will be found thatthe poorest waveform (and we wanta poor waveform for this purpose)will be obtained when the tube oscil-lates violently. This is secured byoperating the control grid at zerobias and by adjusting the screen andsuppressor voltages for maximumdepth of oscillation.

A better method of obtaining thetype of waveform most suitable fortesting over a broad band of fre-quencies is shown in Fig. .4. This isa typical multivibrator circuit whichconsists of two resistance -coupledtriode amplifiers, in which the outputof one feeds into the input of theother. As in the other circuits, thewaveform and the frequency dependupon the constants employed. Forour purposes, a square wave is mostdesired, since this wave shape indi-cates a signal with harmonics ofmaximum strength over a very wideband. The fundamental frequencyshould preferably be somewhere be-tween 400 and 1000 cycles.

Coupling SystemTo get the most value out of any

of these circuits in this application,we need some means of coupling theresulting test signal to the receiver.If we connect to one of the grid cir-cuits, we can, to be sure, feed thesignal to any high -impedance circuit

$1.00 PAID FOR SHOP NOTES

Write 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 with stamped and addressed

return envelope.

in a receiver, but the loading effectwhich results when we connect to alow -resistance circuit is often suffi-cient to stop oscillation in the testapparatus. To avoid this, it is ad-visable to use a sort of buffer tubebetween the multivibrator and thetest apparatus. This may take theform of an amplifier, such as isshown in Fig. 5. The audio choke inthe output circuit forms a high -im-pedance load for the audio frequencyfundamental, generated by the multi -vibrator. The r -f choke in seriesprovides a high impedance for thehigher harmonics of the multivibra-tor signal. Any tube may be used forthe purpose; a type 45 is shownsimply because it is readily avail-able and is low in cost. In one com-mercial instrument, the buffer tubeconsists' of a 955 acorn, chosen be-cause its low inter -electrode capaci-tances make it possible to get themost output from the higher har-monics, which are weak in any event.

Fig. 4. A typical single -tube multi -vibrator circuit. Two triodes, type76 or equivalent, may be substi-

tuted.

The buffer amplifier just describedmay be used with any other multi -vibrator circuits described. Connec-tion is made to the "high" side ofthe input circuit through the block-ing condenser, as shown.

To apply this test method, let usconsider the block diagram, Fig. 6.This is assumed to represent a radioreceiver which is inoperative, orwhich gives weak response. Beforeservicing a receiver with such symp-toms, we shall take it for grantedthat the power -supply voltages havebeen checked, and that a check of thewattage consumption of the entirereceiver indicates that no seriousoverload exists.

Testing ProcedureTo proceed, then, the multivibrator

signal is fed first to the grid of theoutput tube in the receiver, point 1in the diagram. If no signal is heard,


the fault is immediately isolated tosome component in this stage. Or, ifthe signal is weaker than it shouldbe, then in the case of a receiverwhich is merely weak but not inop-erative, we should stop and check thespeaker, output tube and other com-ponents in the output stage.

However, if a normal signal isheard in the speaker when we feedto the output tube grid-and we candetermine what is normal by testson a few normal receivers-we con-tinue with our tests by feeding thesignal to the second test point, whichis designated as point 2 and is lo-cated at the input to the first a -fstage. The signal should be muchstronger when fed to this point, be-cause of the gain which is obtainedin the first a -f stage. If no signal,or a weaker signal, is obtained thenwe know that some component inthis stage is at fault. Note that wehave eliminated the last stage as asource of trouble as the result ofour first test, so we need confine ourinvestigations solely to this stage.

Our next step, assuming that thesignal strength obtained by feedingto point 2 was normal, is to checkthe last i-f and detector stages. Thisis done by feeding the signal to point3. No adjustment of trimmers shouldbe made; the signal is "broad"enough so as to ride through, eventhough the trimmers in a singletransformer are badly out of adjust-ment. If the signal is weak-and thecomplaint is weak reception-the na-tural tendency to try readjusting thetrimmers to increase the signal out-put should be resisted until the com-pletion of the test routine.

The next test point, number .4, isat the input of the preceding i-fstage. This is tested in the samemanner as just described. Thereshould be considerable gain in signalstrength between these stages, butthis will be offset by avc action, as-suming the receiver is so equipped.If a "magic" eye or other indicatorof signal strength is used in the re-ceiver, the increase in signalstrength should be apparent.

The signal is next fed to point 5,the input to the mixer or converter.Since this circuit is normally oper-ating at radio frequencies, it is wellto tune the gang condenser to thelow -frequency end of the dial, somaximum signal strength will be ob-tained. Some gain should be ob-tained, though it will not be large.It is interesting to note that the sig-nal will ride through when fed topoint 5, whether or not the oscillatorsection of the receiver is operating.In the latter case, the mixer simplyfunctions as an i-f amplifier tube. In

the case of a converter tube, thisshould be kept in mind, because itfrequently happens that only the os-cillator section is inoperative.

Our last test calls for feeding thesignal to the antenna circuit. Thisembraces a test of the complete re-ceiver. If the response is normal atthis point, we should concentrate ourattention on the set oscillator circuit,checking the voltage across the oscil-lator grid leak with an electronicvoltmeter, or connecting a milliarn-meter in either the plate, grid orcathode circuit of the oscillator andnoting whether touching the gridcauses a change in the meter read-ing. If it doesn't, the oscillator is notfunctioning.

Use In AlignmentThese are the general tests and

routine in trouble shooting with thenoise generator. In alignment work,the noise generator has been founduseful when called into service foradjusting the r -f trimmers and pad-ders. The procedure is to align thei-f sections in the customary fash-ion with a signal generator. Afterthis is done, the multi -vibrator sig-nal is fed to a point correspondingto point 5 in Fig. 6, at the input tothe converter tube, and the receiverdial is turned to the high -frequencytrimmer adjustment point, as speci-fied in the manufacturer's servicenotes. The oscillator trimmer is thenadjusted until maximum output isobtained. Then the dial is turned tothe low -frequency padding point andthe padder is similarly peaked. Theoscillator trimmer should be re-checked, but reports from the fieldindicate that this is seldom morethan slightly out of adjustment. Norecheck of the padder should berequired.

The feature of this method is thatthe rocking of the gang condenser,formerly essential in adjusting the


Fig. 5. This amplifier acts as a buf-fer tube and may be used with anyof the relaxation oscillators described

in this article.

padder, becomes unnecessary. Ther -f stages are adjusted as usual, witha signal from the customary testoscillator or signal generator.

Note that the multivibrator doesnot supersede tl'.e signal generator.It will always be necessary to have asignal source which provides ac-curately known frequencies. But itdoes simplify testing by the signal -tracing or signal -substitution meth7ods by eliminating the need forretuning each time we enter a circuitadjusted for a different frequency.

While we have described only theadaptability of the noise generatorto trouble shooting without a signal -tracing instrument, it should beunderstood that the noise generatoris likewise suitable as a signal sourcein conjunction with such instrumentsas well.

As with any other new method, itmust be realized that a certainamount of time will be required be-fore the maximum in results will besecured. But those who have perse-vered with such devices as we havehere outlined, have found the timewell spent.

Fig. 6. A block diagram of a representative superhetero-dyne receiver. The numbered points represent equivalent

test points in an actual receiver.

7

Circuit Court.

Fig. I . Phono compensationcircuit with series equalizer

T HE day is fast approaching-if itis not already here-when a large

part of radio service work is goingto fall into the class of "hay -wire"repairs. We mean by this that theserviceman will have to redesignparts of receiver circuits on his ownhook, if the receivers are to continuein operation at all.

In many respects, the job is goingto be easier in the larger receivers.If an i-f tube goes west, and cannotbe replaced, the entire stage can beby-passed, if the receiver has morethan one i-f stage; and the receiverwill still be satisfactory for local re-ception. Likewise, one side of apush-pull power amplifier can be putup in moth balls for the duration, ifa replacement tube is not available,providing the serviceman does a bitof redesigning in the stage involved.

The job will not be so easy in thesmaller receiver, for the less expen-sive set has practically nothing in itsmakeup that could be classed as non-essential. Here it is necessary to re-design the circuit to fit a tube typeforeign to the set, where an exactduplicate cannot be obtained.

But, on the whole, there are manystunts that can be pulled, even in thesmaller sets, to "keep people on theair." Study circuits and make use ofyour tube manual, and you'll be sur-prised what you can get away with.

goo

F'g. 2. Phono compensationcircuit with shunt equalizer

Tone CompensationBecause of the widely varying fre-

quency characteristics of varioustypes of audio amplifiers with whichcrystal pickups may be used, it maybe desirable in some cases to makerefinements in the pickup circuit tocompensate for the characteristics ofthe amplifier. In Figs. 1, 2 and 3are shown three methods, worked outby RCA, by which varying degreesof compensation are obtainable.

In the circuit of Fig. 1, the low-frequency response may be increasedby increasing the value of the pick-up load resistor RI. On the otherhand, high -frequency response maybe increased by increasing the valueof condenser Ci. Thirdly, the volt-age output may be increased by in-creasing the value of R3 with respectto the total value of R2 plus R3. Theresistor R2 and condenser C/ con-stitute a series equalizer.

In Fig. 2, the low -frequency re-sponse -may be increased by increas-ing the value of Ri. The high -fre-quency response may -be increased byincreasing the value of R2. The out-

R cz

Fig. 3. Another form of phono com-pensator with shunt equalizer

put may be increased by decreasingthe value of Ci which, in conjunc-tion with R2, constitutes a shunt-type equalizer.

In Fig. 3, increasing R1 increasesthe low-frequendy response. Increas-ing R2 increases the high -frequencyresponse. Increasing the value of C/with respect to the total value of Ciplus C2 increases the output.

The "center" values for the con-densers and resistors in all three cir-cuits correspond to the values nor-mally employed in such compensationnetworks. Arbitrary values can beselected from phono-radio sche-matics, and thereafter altered to suitthe ear and the pickup voltage out-put required.


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RECI

SELECTOR SWITCH GOWN IN ',MIKE RADIO RECORDING'POSITION

Fig. 4. Schematic diagram of Silvertone Model 7072 receiver

Silvertone 7072This late Silvertone model is an

8 -tube, 2 -band a -c super with push-button tuning and record - changingrecorder. The complete diagram isshown in Fig. 4..

The loop, L4, is designed forstandard -band "loop" reception only.Its primary is in series with the pri-mary of the short-wave antennatransformer L2, and is shunted bycondenser Cl so that it is not effec-tive in the short-wave range. Thesecondary or loop proper is in serieswith the loading coil L1, the totaladditive inductance having the prop-er value for standard -band coveragein conjunction with the tuning con-denser C33. The loop may be usedas a pickup in the short-wave band,in lieu of an external antenna, but inthis case is not tuned, the loop turnsfunctioning as a capacitive antenna.

The 6J5GT converter oscillator iscathode coupled. The oscillator sig-nal is fed to the cathode of the 7117first detector through condenser C13,with the voltage build-up across the7117 cathode resistor R30. Voltagefrom the grid circuit of the oscil-_lator tube is introduced into the avccircuit, and therefore on the detec-tor diode, through the 10-meg. resis-tor R25. The resultant rectified volt-age provides an initial bias on thefirst detector and i-f tubes.

The 6Q7GT is used as second de-tector and mike amplifier. Since thetriode of this tube feeds into the vol-ume -control circuit when switch S7is in the recording position, the vol-

t time control R3.4 is used to adjustmike input gain.

The phono pickup circuit is equal-ized, and the volume control is of theusual compensated type.

The triode of the 6SQ7GT is usedas the a -f voltage amplifier, and isresistance -coupled to the 6K6GT out-put tube. One diode in this tube isemployed as an a -f rectifier, to pro-vide control voltage for the grid ofthe 6135. Voltage is picked off theplate of the 6K6GT and fed to the6SQ7 diode through C.4.1 and R4.The resultant rectified voltage ap-pearing across R21 operates the eyetube which functions as a volume -level indicator.

One push-button switch is em-ployed for tone control in the platecircuit of the 6SQ7GT a -f voltageamplifier.

Radiola 522The circuit of this late RCA job,

shown in Fig. 5, -applies to 1st pro-duction Chassis No. RC -1001C and2nd production Chassis No. RC -1022 -

Address Change?Notify RSD's circulation de-partment at 132 West 43rdStreet, New York City ofyour new address 2 or 3weeks before you move.The Post Office Departmentdoes not forward magazinessent to a wrong address un-less you pay additionalpostage. We cannot dupli-cate copies mailed to yourold address. Thank You!

A. Slight changes were made in the2nd production run, and these areshown in Fig. 6.

The circuit is conventional, incor-porating such tricks of the trade asan open-ended winding on the oscil-lator coil instead of a grid condenser,and a stop on the volume control sothat the resistance of the control be-yond the stop may be used as the"resistor" in the i-f filter, the re-mainder of which is made up of thecondensers C// and C12. And thestunt of improving frequency re-sponse and reducing distortion bythe simple expedient of leaving offthe power -tube cathode by-pass con-denser and using another of muchlower value, connected from plate tocathode, to provide additional inversefeedback.

This receiver employs an iron -corei-f transformer between mixer andi-f tubes, and an air -core unit coupl-ing the i-f tube to the 2nd detector.But both transformers are adjustedby means of trimmer condensers.

Note that with an electrodynamicspeaker, the power -tube plate supplyis also filtered. It has long been thepractice in small receivers using p-rndynamics, to connect the power -tubeplate supply lead directly to the cath-ode of the rectifier. This wasn't bad,but neither was it particularly good.

We've always liked the simplephono-connection arrangement inthese receivers. With the exceptionthat there is some possibility of sig-nal break -through in the 12SQ7 tube,the method is neat. The pickup volt-age output is applied directly acrossthe grid resistor R3, and volume con-


trolled from the record player. Thereceiver volume control is turned allthe way down which precludes signalpickup from the diode output circuit,and also grounds C3. This reducesthe pickup output somewhat, butthere is always more than enoughoutput available.

Silvertone 7167Though this 8 - tube, 2 - band a - c

super has no r -f stage, it does have,1) a rotatable loop, which providesa form of selectivity, and 2) a pre -selector circuit in the broadcast -bandrange. The complete circuit is shownin Fig. 7.

The pre - selector is composed oftwo sections of the three -gang con-denser, VC, the loop antenna, theloading coil L4, the pre -selectorcoupling coil L3, and the translatorcoil Ll. This arrangement providesadequate selectivity without the useof a tuned r -f stage.

In the short-wave band, a separateshort-wave antenna transformer, L2is employed. The frequency range of

12SA7 I SC47ISM DET 8050. ?Ho TS AF -AVC

2ND.1..ETRANS.

-C1.01 AMC.

vOL.CoHT4500.000 C3

OTHERWISE SWFSTOP AT .0250.000

AS RADIOL S22 (RC 1001 C)

R54.7 MEG

Fig. 6. Circuit changes made in 2nd pro-duction of RCA Radiola 552 receiver

the oscillator coil, L5, is shifted to ahigher band by means of a tap on thegrid coil, controlled by the wavebandswitch.

The triode section of the 7E6 func-tions as a tickler -feedback oscillator.Coupling to the grid circuit of the7117 translator is by means of a gim-mick wound around the lead to theplate of the oscillator tube.

One diode of the 7E6 is used as abias control. Oscillator voltage ap-pears on the diode plate by cathodeemission, and the resultant rectified

voltage appears across resistor R3.This negative voltage is applied tothe avc line through resistor R4, andconstitutes an initial bias for thetranslator and i-f tubes. When a sig-nal is tuned in, avc voltage is devel-oped in the load circuit of the second -detector diode. This comparativelyhigh negative voltage also appears onthe 7E6 bias control diode, thus re-pelling the flow of electrons to thediode and removing the initial bias.The condenser C8 across the biasControl diode load resistor .R3 func-tions as a radio -frequency bypass.

Regeneration is introduced in thei-f stage by means of a third wind-ing on the second i-f transformer.The regeneration takes place in thescreen circuit.

Grid bias for the triode section ofthe 6SQ7GT is provided by means ofa bias cell connected in series withthe grid resistor R25. A continu-ously variable tone control appearsin the plate circuit of this, same tube,and additional, push-button tone con-trol is provided in the circuit of the

(Continued on page _12)

ANT

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Fig. 5. Schematic diagram of RCA Radiola 522 receiver. See Fig. 6 for production change


RESISTORS

IRC flies the flag of theArmy -Navy Production Award

for "High Achievement"

WWY? ... Results of a nation-wide surveyconducted by a wholly independent researchorganization disclosed that Executives and Engi-neers in the electronic industries overwhelminglyprefer IRC resistors. In voting them "superior"by a plurality of more than two to one, thesespecific reasons were cited-

BECAUSE . . . IRC offers "bestproduct" and "most complete line."

INTERNATIONAL RESISTANCE COMPANY401 N. BROAD STREET PHILADELPHIA


CIRCUIT COURT(Continued from page 10)

compensated volume control R18.One 2 -position switch provides high -frequency boost, and a second 2 -posi-

tion switch provides bass boost. Bothswitches control resistance and ca-pacity voltage dividers common tothe volume -control circuit.

A second 6SQ7 is employed as aphase inverter in a purely conven-

tional circuit. The push-pull powerstage incorporates inverse feedback,the common cathode resistor beingunbypassed. Additional feedback isprovided by voltage feed from platesto cathodes via condensers C33 -C34.

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TARGET FOR TONIGHTI

et.Your Business? - =z

Maybe they won't actually come and drop a bomb on your business, butthe Axis war lords have their eye on it, just the same. They want to wipeit out as a competitive force-or take it over lock, stock, and barrel. Hereis a threat that you can reply to now, today, and in no uncertain terms-by buying War Bonds to the very limit of your powers, that our armedforces may have the guns, tanks, and planes they need to crush the Axisonce and for all.

THE GOAL: 10% OF EVERYONE'S INCOME IN WAR BONDSEvery American wants the chance to help win this war. When you installthe Pay -Roll War Savings Plan ( approved by organized labor), you giveyour employees that chance. For details of the plan, which provides forthe systematic purchase of War Bonds by voluntary pay -roll allotments,write: Treasury Department, Section S, 70912th St. NW., Washington, D. C.

Buy War Savings BondsThis space is a contribution to America's All -Out War Program by

RADIO SERVICE -DEALER


THINKING AHEAD

an Jetviciny "radio labby Jerome J. Kahn

0 UR Administration and the va-rious divisions of the govern-

ment consider home radio receivingsets an esesntial part of the war pro-gram. Efforts have been constantlymade to clarify the problems relativeto the procurement of materials forthe further maintenance of thoseradio sets.

The present program, the PD1Xforms filled in by jobbers, will serveto acquaint the War ProductionBoard with the exact status of theinventories of replacement parts, andwill provide the vehicle upon whichthe radio section of WPB may pre-sent to the various material sectionsand requests for allocations of mate-rials to produce the much talkedabout 'Victory Lines' of replacementparts or components.

Suppose that as of today or to-morrow this allocation program wasapproved by the various departmentswithin WPB ! What next? When Iask what next, I am pondering overthe problem of man power to prop-erly utilize these replacement partsand get them into the inoperativehome receiving sets to provide theproper types of reception the Ad-ministration is anxious to see theradio industry provide 'John Q. Pub-lic' from broadcasting station downto serviceman.

Servicemen's Ranks DepletedVery bluntly, the continued re-

quests of the Army Air Force forradio men, the Signal Corps cam -

The author of this article is president of Standard Transformer Ccrp., adirector of RMA, Chairman of the RMA Priorities Committee and a member of theRadio Replacement Parts Industry Committee working with WPB. Much of his timeand energy is now devoted towards obtaining a steady flow of replacement partsfor service -dealers' use.

Here he outlines a Plan of Operations that merits consideration, especially inthose territories where servicing man -power has been depleted; or where job-bers, having but little priority -rated business, are "considering" entering theservicing business.

The prime object of the Priorities Committee is to assure the utilization ofevery bit of man -power, conserve materials to the maximum degree and spreadservicing and parts so that they will be uniformly available to all set owners.

paigns to enlist radio servicemen, theNavy's enlistments of qualified radiomen, as well as the draft have fallenshort of their quotas and as wellhave left our radio serviceman'smarket badly depleted of qualifiedmen, competently equipped to prop-erly service a receiver. If these partswere available, where would the serv-iceman come from that could prop-erly use them? This presents theproblem of correlating all the facts,material, and man power into oneunified program so that the properservicing may be accomplished.There are several ways in which thiscould be done. One would be to havethe public service or utility com-panies handle the servicing of homereceivers. My thought, however, isthat for the duration of the war amobilization of servicemen, dealers,and radio parts jobbers, might an-swer our problem and keep the serv-

icing of radio receiving sets in thefield where it belongs.

The writer is of the opinion thattime saving primarily is the essenceof defeating this difficulty we arenow facing in the servicing problem.We know the average radio set canbe repaired in a few moments. Thegreater portion of time is spent inmaking the call, analyzing the trou-ble, and toting back and forth ofthat particular receiver to the shopto permit the efficient installation ofwhatever part or parts may be re-quired.

Our first problem, then, is to savethat time devoted in making theservice calls, picking up and deliver-ing the defective units. My planwould call for the set user to bringhis radio set into the dealer or serv-iceman's place of business and afterit has been repaired to pick it up.

(Continued on page 21)


Shop NotesCard 1

PH I LCO PT -15(Constant or Bad Modulation Hum)

Hum in these models is usually caused by high re-sistance shorts due to faultyinsulation in the bakelite, asbetween tube sockets andchassis, and leakage betweenwindings of antenna coil. Toremedy, alter antenna cir-cuits as shown. Bond one side ORIGINALof a -c line direct to chassis.Dry moisture out by heatingset several hours after cov-ering it with a heavy cloth.Several bondings may be re-employs a magnal 11 -pinGulliver.

AVC

ALTERED

Card 32AP1

High Vacuum Cathode -Ray Tube

The RCA-2AP1 is a high -vacuum, cathode-ray tube902 except that it has sepa-rate leads to all deflectingelectrodes and the cathode,employs a magnal 11 -pinbase, and can be operatedwith higher anode voltages.

Card 55 R4-GY

Full -Wave High -Vacuum RectifierThe RCA-5R4-GY is a coated -filament type of full -

wave, high -vacuum rectifier1302

having a maximum peak in-verse voltage rating of 2800 Pp!

volts, a peak plate currentrating of 650 milliamperes,and a maximum d -c outputcurrent rating of 175 milli-amperes when a choke -inputtype of filter is used. The5R4-GY has a micanol base.

NC KEY

G-5 TF

Card 76AG5

R -F Amplifier Pentode (Miniature Type)The RCA-6AG5 is a heater -cathode type of r -f pen-

tode with a sharp cut-offcharacteristic and a highvalue of transconductance.Having miniature con-struction, the 6AG5 is use-ful in compact, light-weight equipment as anr -f amplifier up to about400 megacycles, and as ahigh -frequency intermedi-ate amplifier. It has lowinput and low output ca-pacitance.

K, G3

INTERNALSHIELD

7BD

K, G3

INTERNALSHIELD

934Vacuum Phototube

The RCA -934 is a small high -vacuum.tended primarily for use insound and facsimile equipmentbut it is also suitable for light -operated relays and light -mea-suring equipment. Its S4 photo -surface has exceptionally highresponse to blue and blue-greenradiation and negligible re-sponse to red radiation. Dimen-sions: 2 15/32" long x 23/32"diameter.

Care 2

phototube in -

DIRECTION OF LIGHT

NC H(-)

K = CATHODENC = NO CONNECTIONP = ANODE

Card 4935

Vacuum Phototube-(Ultraviolet-Sensitive Type)The RCA -935 is a high -vacuum phototube possessing

extraordinarily high sensitivityto radiant energy rich in blueand near ultraviolet and will re-spond in the region down toabout 2000 Angstrom units. Be-cause of its excellent stability,consistency of spectral response,and extremely high sensitivity,the 935 is particularly suitedfor use in measuring ultra-violet absorption of gases andliquids.

DIRECTION OF LIGHT

NC

K

NCP

= CATHODE= NO CONNECTION= ANODE

Card 66J6

Twin Triode (Miniature Type)The RCA -6J6 is a Miniature twin triode having

two grids and two plateswith a common cathode in-directly heated. The twinunits may be operated inparallel or in push-pull. Withpush-pull arrangement ofthe grids, and with the platesin parallel, the 6J6 is par-ticularly useful as a mixerat frequencies as high as 600megacycles. It is also usefulas an oscillator. 7BF

Card 81C21

Gas -Triode

The RCA -1C21 is a cold -cathode, glow -dischargetriode designed for use primari-ly as a relay tube. The dischargecan be initiated with a verysmall amount of energy appliedin the grid circuit. It is similarto the type 0A4 -G but is moresensitive.


`ITIMINItg128171M `,.1q21? o 1

SECTION XXIV

Resistors and Volume Controls

I N PEACETIME the matter of re-placing defective resistors or vol-

ume controls is simple; you just findout what is called for in the sche-matic and make a replacement withan exact duplicate chosen from yourown stock or at your jobber's. Butnowadays things are different; wecan't always pick out just what weneed for a given job because partsare scarce and are becoming scarcer.And, to make it still harder, thereseems to be a greater demand forradio servicing now than at any timein the past fifteen years.

In some respects these difficultiesare helpful rather than otherwise.All of us are going to have to do alot more thinking than we did be-fore. And that means we are boundto learn a lot- more about radio serv-icing than we would have if we fol-lowed the same old routine.

We are going to ask ourselves ifthis business of replacing a defectiVepart with another of precisely thesame characteristics is necessarilythe proper thing to do. For, we arelikely to conclude, if the original partwouldn't stand up in the circuit, howdo we know that an exact duplicatewill be any better? Maybe-if weare servicing- without a schematic-the part we are replacing is not theproper value due to some error onthe part of another serviceman.Maybe the schematic itself is in er-ror, or the designer may not have al-lowed a sufficiently good safety fac-tor in his wattage rating.

To answer these doubts we mustbe able to sit down and work outsome of these design problems our-selves. We will find the time wellspent, because as time goes on and

parts become scarcer, we are goingto be obliged to do a lot of thingswhich aren't immediately necessary.We are going to have to redesign cir-cuits to use parts and tubes whichare obtainable to replace those gonefor the duration, to reduce set oper-ating voltages to reduce strain onweakening components, to changeover from avc to manual volume con-trol and lots of other things whichwould be unthinkable under normalconditions.

Molded Resistors

Because we cannot handle any de-sign problems intelligently withoutdefinite knowledge of the character-istics of the components we have towork with, let us first consider thedata given in Table I on fixed moldedcomposition resistors, what we gen-erally call carbon resistors. We be-lieve this is the first time these im-portant characteristics have beengiven in any service literature, yetfamiliarity with them is vitally im-portant in many aspects of radioservicing, as well as in design work.

The wattage ratings are familiarenough, of course. But we wonder

how many servicemen know that thewattage rating is definitely tied inwith other characteristics whichmust be simultaneously considered inchoosing the proper rating. For ex-ample, note that a 1/2 -watt resistor isdesigned to operate at a temperaturenot to exceed 90° C. (194° F.). Thetemperature rise at rated load isgiven as 40° C. (104° F.). Thismeans that, under rated load, thetemperature of the resistor will be40° C. hotter than the ambient, orsurrounding, temperature. Thus, ifthe air temperature around the re-sistor is 20° C. (68° F.) the actualtemperature of the resistor underrated load will be 40 plus 20 or 60° C.This is all very well, since the maxi-mum operating temperature is notreached. But if the resistor hap-pened to be mounted on the termi-nals of a power transformer, wherethe temperature of the winding un-der load frequently rises to 90° C. oreven higher, it is possible for themaximum operating temperature ofthe resistor to be reached evenhigher, it is possible for the maxi-mum operating temperature of theresistor to be reached even though itisn't being subjected to any load at

TABLE .1

TYPICAL CHARACTERISTICSFIXED MOLDED COMPOSITION RESISTORS

Wattage Rating 1/2 watt 1 watt 2 wattsMaximum Operating Temperature 90°C ..90°C 90°CTemperature Rise at Rated Load 40°C 50°C 62°CTemperature Coefficient per °C 0 12% 0 12% 0 12%Voltage Coefficient 1% change per volt) ..0.03% 003% 0.03%Resistance Variation with Age 21/2% (ay.)Maximum D -C Voltage 350

...21/2% (ay.)350 350

21/2 cY0 ( ay. )

Resistance Variation- due to Humidity.... 5% (ay.) 5% (ay.) 5% (ay.)Noise (microvolts per volt) 2 to 10 2 to 5 1 to 3Tolerances 5%-10%-20%..5%-10%-20%.. 5%-10%-20%


TECHNICAL SERVICE PORTFOLIO * SECTION XXIV

Fig. 1. Illustrating distribution of cur-rents in an electric circuit; it's prac-tically the counterpart of Fig. 2.

all. These considerations are par-ticularly important in the tropics,but should be kept in mind even inour climate don't let a resistor gettoo hot. Along these lines, it is agood idea not to hold a hot ironagainst a small resistor when solder-ing - many have been damaged inthis manner.

The temperature coefficient of theresistor is important when it is usedas a voltage divider or multiplier intest instruments. The coefficient0.12% per degree C. means that foreach degree centigrade change intemperature the resistance value willchange by a factor of 0.12%. Thusa 40 -degree change means a 4.8%change in resistance. If all resistorschanged in the same degree and inthe same direction-that is, positiveor negative-this wouldn't mattermuch, since the proportionate resis-tance of a divider would remain thesame. This, unfortunately, is notalways the case. In the higher resis-tance values a different "mix" is em-ployed than for low values of resis-tors, so the characteristics likewiseare subject to change. In some casesit has been found that higher valuesof composition resistors increase in

Fig. 2. Current distribution in vacuum -tube circuit. Compare this with Fig. 1.

resistance with an increase in tem-perature, while low values decreasein resistance under the same condi-tions.

Voltage CoefficientThe voltage coefficient is the per-

centage change in resistance whichresults when a voltage is applied tothe resistor. If the voltage dropacross a 1/2 -watt resistor is 100 volts,we may expect a change in resistanceof the order of 3.0% since the changeper volt is .03%. This applies tohigh resistances, of the order of 0.5megohm or more. The voltage co-efficient, in any event, is usually neg-ligible in comparison with the tem-perature coefficient.

The resistance variation with ageis a sort of settling of the composi-tion which occurs while the resistoris resting in stock as well as after in-stallation in a set. This may resultin an increase in resistance or a de-crease; generally the former for highresistance values and _the latter forlow values, as with temperature va-riations, but' this varies with resis-tors of different makes.

The d -c voltage rating is the maxi-mum voltage which should be appliedto a given resistor, regardless of itswattage rating. We might figurethat a 10-megohm, 1/2 -watt resistorcould well be used with 1000 voltsacross it because the resulting watt-age dissipation would be only 0.1watt - well within its rating. Butactually we should not apply morethan 350 volts to its terminals if wewant to keep out of trouble.

Noise results when a voltage is ap-plied across a resistor or when theresistor is used as a plate load. Thisnoise is small in comparison withtube noises, in most cases, but never-theless it is a limiting factor in highgain p.a. amplifiers. The noise iscaused by imperfect cohesion of themixture used in making resistors andis more prominent in small resistorsthan in larger ones. Thus, for lownoise, it is always best to use a re-sistor of high wattage rating. Thistype of noise is not present in wire-wound resistors, which are accord-ingly preferable for high -qualityamplifiers where low noise is impera-tive. It must always be remembered,though, that as stated, tube noisesare generally greater unless specialprecautions are taken, such as oper-ating at sub -normal operating volt-ages.

Dampness causes a change in re-sistance in any molded composition

resistor. However, it must be re-membered that in normal operationthe interior of a radio receiver tenasto get pretty warm, and this increasein temperature lowers the relativehumidity so that the parts dry outrapidly. In most cases, resistors thenregain their normal rating so thiseffect is not of much consequence inpractical work. It is a good idea tokeep this point in mind when check-ing resistance values in damp weath-er when the set has been inoperativefor an appreciable period - it maysave your finding that resistorswhich appear to be of the wrongvalue are perfectly all right underoperating conditions.

TolerancesTolerances are frequently misin-

terpreted. Many people have the ideathat such -and -such resistors are bet-ter than some other make becausethe values of resistance are some-times closer to their ratings thanOthers. This is purely a matter of se-lection and has nothing whatsoeverto do with the quality of the resistor.If you must have, and are willing topay for, resistors having a close tol-erance, you need merely specify thiswhen buying. For a 5% tolerancerating, a resistor nominally rated at100 ohms may be of any value from95 to 105 ohms; for a 20% tolerance,from 80 to 120 ohms. In most re-ceiver applications, a tolerance of20% is close enough for plate, cath-ode or grid resistors, avc circuits, di-ode loads, and volume controls. Forfixed biases applied to control -gridcircuits, a closer tolerance is some-times required. When tolerancescloser than 5% are required, it is ad-visable to use wire -wound resistorsbecause the latter are far more stablethan composition types. This is ap-parent from a study of the variablesshown in Table I. However, for high

RI

R2

Fig. 3. Text explains fully the methodfor determining values of cathoderesistor RI and screen resistor R2.



resistances, it will often be foundthat the cost of wire -wound types isprohibitive. Except in laboratorytest equipment, wire -wound resistorsare usually chosen because they areavailable in greater wattage ratingsfor a given size rather than for theirgreater stability.

In every circuit using resistors andpotentiometers we are concernedwith voltages and currents, eithera -c or d -c, or both. Therefore, inmaking replacements, our problemis to restore the original voltagesand currents. Insofar as tube oper-ating voltages are concerned, in theabsence of a schematic or servicenotes we may determine the requiredvoltages from any tube manual orchart. The a -c voltages in which weare interested are usually signal volt-ages; those we shall take up later on.Once we know what voltages are re-quired, the resistance value need forreplacement can be determined bysubstitution or by calculation.

Often it is quicker to find theproper resistance value by substitu-tition, using a calibrated wire -woundpotentiometer for this purpose andadjusting it until the proper voltagesare restored. But this method is opento criticism because often when thisadjustment is being made other com-ponents in the receiver, such as thetubes, may not be up to normal rat-ing with the result that we adjustthe voltages for a condition whichdoes not represent those presentwhen everything is as it should be.Further, this method does not workout well with low -current, high -resis-tance circuits, such as plate andscreen resistors, where voltages arehard to measure accurately. In anyevent, it is important to be able tocalculate the required values, and aknowledge of the proper way totackle such problems will be of valuenot only in service work, but in anytechnical work along radio lineswhich one may want to enter.

Current Distribution

Most servicemen understand thesimpler applications of Ohm's law,but many do not realize that thesesimple fundamental principles maybe applied to the most complex cir-cuits. In Fig. .1, which is a ratheracademic presentation of a problemin the distribution of currents in atypical electric circuit, we may notat first realize that this representsvery closely the distribution of cur-rents in a vacuum tube amplifyingcircuit. Meters are shown in each

Fig. 4. Typical re-ceiver power -sup-ply filter circuit.RI is a voltage -dropping resistorwhich serves to re-duce effective tubevoltages.

A.C.POWER

SUPPLY :ado+B, POWER TUBE

TOALL OTHER

TUBES

R2 R3 +B

circuit for clarity. Three currentsare designated-i 4 and i3. All aresupplied from a single voltage sourceas indicated. The current throughR1 and R2 is shown as i and is in-dicated on the meter M4. No portionof this current passes through R4,therefore the current 4 indicated onM2 may be considered as an entirelyseparate circuit from that of R1 andR2 and the current may be calculatedwithout considering Ri or R2. But,as the current for R3, indicated onM3, must pass through R1 in order,to reach R3, the voltage across R1will be dependent upon both currents,4 and is. Again, however, each cur-rent may be calculated separately.Thus we can determine how muchcurrent is represented by i5 if weknow the values of R1 and R3, andthe voltage. And we can find out thesame for 4 if we know what R1 andR2 are. To find the voltage dropacross R1, we add the currents 4 and4. Then the voltage drop is obtainedby Ohm's law.

Let's take an example. The bat-tery voltage is 300, R. is 30,000ohms, R2 is 100,000 ohms and R3 is100,000 ohms. We will assume thatwe have to select a resistor for Riwhich will provide 100 volts acrossR2. This same voltage will of courseappedx across R3, since the two arein parallel. When the voltage acrossR2 is 100, the current i, through R2will be equal to 100/100,000 (corre-sponding to E/R) or .001 ampere,which is 1 milliampere. The currenti5 through R3 will likewise be 1 mabecause the resistance of R3 is thesame as that of R2. The currents 4plus i, which pass through. R1 arethus equal to 2 ma. In order to re-duce the 300 volts to 100, the resis-tor R1 must cause a 200 -volt dropwhen 2 ma are flowing through it.Applying Ohm's law (R = E/I)200/.002 = 100,000 ohms.

Note that R4 doesn't enter the pic-ture at all in these calculations. Andif any number of additional circuitswere added we would have no needto consider them either in determin-ing what is required for any circuitwhere no portion of the current in

another circuit passes through it. Ifwe want to find the current in R4, wecan ignore the currents in R1, R2and R3, because none of the currentsin these circuits pass through R.4.Thus 4 would be equal simply to300/30,000 = .010 ampere = 10 ma.The total current drawn from thebattery,, i, + 4 + 4 would thus beequal to 1 + 1 + 10, or 12 ma.

Tube CircuitsIn Fig. 2, the same circuits shown

in Fig. 1 are represented, but we arenow showing tube circuits as por-tions of the load, rather than the re-sistors R3 and R4. Thus we see thatthe current 4 in Fig. 1 may be con-sidered to represent plate currentand the current is screen current.Because the total current in any tubemust return to the cathode, the sumof. the screen and plate currents, 4and i3, represents the cathode cur-rent. The only current which doesnot pass through the cathode circuitis i which represents the current inthe voltage -divider circuit. It is im-portant to realize this, because itmeans that a voltage divider acrossa battery will draw current at alltimes, whether or not the tube, inthe circuit shown, is operating.

We see from Fig. 2 that the screenand plate circuits of an operatingtube can be considered as resistorssimilar to R3 and R4 in Fig. 1. Of-ten, in modern circuits, the voltagedivider is eliminated and we need tocalculate the value of resistor neces-

+B , POWER TUBE TO ALLOTHER TUBES

E d.c,

III I III I+B

Fig. 5. With a choke filter only thed.c. resistance of chokes need be con-sidered in determining output voltages.



Fig. 6. Audio circuit in which a.c. volt-ages must be considered; across RI, R3and R4, for instance.

sary to supply a given screen voltage.For example, in Fig. 3, we might berequired to determine what value R2should be. Let's assume the tube tobe a 6K7. The plate voltage is 250and the screen voltage, according tothe tube manual, should be 100. Thescreen current, as listed in the man-ual, is, 1.7 ma. To find the value ofR2, then, we must calculate what re-sistance is required to reduce 250 to100 volts at a current of 1.7 ma, of.0017 amp. This means that a 15v -volt drop is required. Since R equalsE/I, 1? would be equal to 150/.0017or 88,000 ohms (approximately)This value is not critical becausescreen currents vary among tubes,and other compensating factors willtend to keep the performance normalwhen the voltage varies.

The cathode resistor RI is calcu-lated similarly, except that bothscreen and plate currents enter intothe picture. For the 6K7, the platecurrent would be 7 ma and the screencurrent, as we have seen, 1.7 ma.The sum thus equals 8.7 ma. Sincethe cathode bias determines the gridvoltage, which should be in this case-3 volts, we find RI by dividing 3by .0087. This equals 345 ohms (ap-proximately). Thus 350 ohms hasbecome a common value, in many de-signs.

In Fig. 4 and Fig. 5 are shown

typical power - supply filter circuits.In Fig. 4, R1 serves as a voltage-dropping resistor through which allthe current in the supply circuitmust pass, as it acts as a return cir-cuit for all rectified current. ThroughR2 will also flow the current for allcircuits, with the exception of thesmall leakage current which passesthrough the first section filter con-denser. Through R3 flows all currentexcept that for the power stage,which we see is taken off at the junc-tion of R2 and R3.

The analysis of Fig. 5 may be car-ried out the same as for Fig. 4, ex-cept that for d -c voltages we needconsider only the d -c resistances ofthe chokes in the filter circuit.

Wattage CalculationsIn the preceding examples we have

considered only voltages and cur-rents. From these we have been ableto calculate resistance values. Forwattage ratings, we can determinethe wattage dissipation by the for-mula E2/R = W. Thus when thevoltage is 300 and the resistance is30,000 ohms, the wattage dissipationis 3002/30,000, or 90,000/30,000,which equal 3 watts. Or, if we arebasing our calculations on currents, itis equal to 12 X R. Thus, for a 10 -macurrent in a 30,000 -ohm resistor, thewattage dissipation would be .0102 X30,000 or .00010 X 30,000, which alsoequals 3 watts.

The mathematical method of de-termining wattage dissipation justdescribed is of course well known tomost of our readers. However, whatis not generally appreciated is thatsome safety factor must be allowed.We must reckon that the unforeseenfailure of some related componentmay seriously increase the current ina circuit so that resistors will besubjected to considerable overload.Further, as we have seen, temper-ature and other factors limit the cur -

Fig. 7. Typical detector -amplifier circuit. The d-c across RI and R2must be considered, as these resistors form the diode load circuit.

Fig. 8. In this circuit the volume con-trol R2 also carries d.c., and is there-fore subject to early breakdown.

rent which may be accommodated re-gardless of the wattage rating. Agood rule is to choose a 1/2 -watt re-sistor for all wattages of 1/4 or less;1 watt resistors for 1/2 watt to 1/4watt and 2 -watt resistors for anyvalues between 1/2 and 1 watt. Somedesigners always choose a resistorhaving at least four times the watt-age rating which would be theoreti-cally required.

A -C Voltage Considerations

So far, too, we have consideredonly d -c voltages. We must remem-ber that, in many circuits, the a -cvoltage across a resistor may far ex-ceed the d -c potential. In Fig. 6, forinstance, we may apply a much largersignal voltage to the input controlRI than we would think of usingwere d -c voltages involved. An ordi-nary carbon -type volume control, ofthe small varieties used in radios,has a rated wattage dissipation ofbut 1/2 watt; it is quite easy for thisvalue to be exceeded when a low -re-sistance control is being used. Weshould always consider the signalvoltage which will appear across anyresistor or control. Thus, signal volt-ages will appear across R.1, R3 andR.4 in Fig. 6. Of course, there willalso be a slight signal voltage acrossR and R2, but in these circuits it willbe small because, in the case of R,the grid input circuit is of such ex-tremely high input resistance thatthe current through R is limited topurely a capacitive current, and isfurther reduced by the bypassing ac-tion of C. This circuit, of course, isused to increase the high -frequencyoutput. In the case of R2, its associ-ated bypass condenser reduces thesignal voltage to a negligible value.The signal voltage developed acrossthe plate load, R3, causes a variationin the effective voltage in the circuitderived from the supply circuit. This



Fig. 9. Alternate volume -control circuitto replace avc and diode detector whenthe latter type of tube is unavailable.

signal voltage will be substantiallythe same as that across R4.

Fig. 7 represents a typical radioreceiver detector -amplifier circuit.R1 and R2 are subject to applied d -cvoltages resulting from rectificationof signal voltages. The value seldomexceeds 50 volts and, because the re-sistances used are ordinarily high,the rectified current is small and thewattage dissipation correspondinglylow. Such a circuit usually causeslittle trouble. However, it must beremembered that the volume controlmust be of 2 to 10 megohms resis-tance to avoid appreciable distortion.

Fig. 8 represents a modification ofFig. 7 which is quite often found inlow-priced receivers. The volumecontrol appears in the diode circuitrather than in the grid circuit. It ispossible, with this form of connec-tion, to use a lower resistance volumecontrol, usually 1/4 megohm, while R3may be 10 or 15 megohms. However,the rectified d -c across the control,absent in the circuit of Fig. 7, tendsto create noise so that more frequentreplacement may be required thanwith the preceding circuit. All vol-ume controls are likely to becomenoisy quicker if they are used in cir-cuits in which d -c is present.

There are times when it will befound difficult to obtain the propercontrol replacements for one or theother of the two circuits shown(Figs. 7 and 8). When a control forone is available, it may be useful toknow that the other circuit may bemodified so it may be used.

Alternate Controls

There are occasions when it maybecome necessary to eliminate theavc circuit in a receiver being re-paired because no combination diode -triode or diode -pentode tube can be

obtained for replacement purposes.In such cases, volume control may beeffected by using the circuit of Fig.9. The control resistance may be 15,-000 ohms or thereabouts. R1 is theusual cathode resistor.

Combination volume and tone con-trols, formed by using filter circuitsin conjunction with tapped volumecontrols, as illustrated in Fig. 10,provide an excellent method of im-proving the performance of receiv-ers with unsatisfactory tone qualityin that the low -frequency responsemay automatically be increased asthe volume control setting is reduced.Representative values may be foundin set manuals. This makes up forthe apparent falling off in lows atlow volume. This effect is purelypsychological, so the compensationintroduced by the special control andits, associated circuits is not subjectto the criticism which has so oftenbeen brought against the older, con-ventional type of tone control.

In choosing replacement controls itis well to keep in mind that taperedcontrols which show abrupt changesin resistance at any point are likelyto become noisy at that point. Ataper which will last in serviceshould have a curve which slopessmoothly into the steep portion re-quired for proper audio grid control.Such a control may, not initially seemquite as good in operating qualitiesas one with a more abrupt slope, inthat the increase in volume as thecontrol knob is rotated is not quiteso uniform, but a control of this typewill usually outlast the other.

It is well to avoid, at all times,using a carbon -type control if anycurrent is to be 'taken off the movingarm. Most controls are designed towork into circuits which require noappreciable current; consequently

Radio Service -Healer, November, 1942

Fig. 10. Combination volume- andtone -control circuit for improving bassresponse at very low volume levels.

the contact to the control element isoften simply a very small surface,which quickly develops poor contactwhen subjected to excessive current.This is especially true of high -resis-tance controls. In any applicationswhere current -nust be taken fromthe moving arm, it is best to usewire -wound controls.

Volume controls of the carbontypes are subject to humidity trou-bles just as are resistors of the samecomposition. Care should be takennot to store them in damp places.But do not try to seal them up com-pletely. If this is done, then moist-ure inside the case may condense onthe composition element and causeserious trouble.

Checking Noise

A circuit for checking noise ineither controls or fixed compositionresistors is shown in Fig. 11. Noiseis expressed as "equivalent noisevoltage" in engineering terms. Justwhat this means is apparent from astudy of the test circuit. Thus, whenwe apply a d -c voltage across Rx, inFig. 11, a certain amount of noise is


Fig. 11. Test setup for checking noise in composition fixed re-sistors or potentiometers. It operates on the substitution method,where the noise in one circuit is compared with that in another.

19

I T'S midnight. My head and feethurt. For a long time I've owed

myself a little rest, and this is it!I feel like reminiscing, so, as RedSkelton would say, "I'll dood it!"Yes I will, if my nerves will justquiet down.

Gosh, in the good old days my pardJerry and I used to do a lot of remi-niscing. We'd sit here in the shopfor hours, after knocking off, talkingabout the gals we knew and thethings we did. Most of 'em werefoolish things, but fun. You knowwhat I mean ! But tonight it's dif-ferent. I'm so dag nabbed tired andgroggy from Girls, Girls, Girls thatI don't even want to think of 'em.

Not so many months ago Jerryand I would jump in Liz and take aride around town picking up fouror five chassis. That was a day'swork for us. If there was a realrush on one of us would stick to thebench and the other would do thehot -footing. Those were seven sets -to -repair days. Big days they were,too, for on seven repair jobs a dayJerry and I could make nice sugar.That is, we thought we were mak-ing good dough then.

MY LOG

by San D'Arcy

I remember the Saturday night,not long ago, when Jerry and Ichecked the till and figured theweek's take. We found ourselveseighty bucks to the good. Thatmeant forty apiece, and boy, were werolling in clover! We were big -shots, so out for a bottle of two -fiftyRye we went. That bottle only lasted

two hours, but as I remember it, thehang -over lasted two days. And asI sadly recall the situation, half adozen of our repair jobs came backbecause in our misery we had for-gotten to solder connections, or haddelivered the wrong sets to thewrong people.

Jerry and I don't have time forsuch nonsense now -a -days. But con-fidentially speaking, our big job nowis to make sure that our bench work-ers keep their minds on their jobsso that the customers get a squareshake. Since I hired Elaine twoweeks ago, it's been quite a prob-lem. She is a problem and so areour two new benchmen. If it getsmuch worse I'll have to make up mymind and try to find new mechanics.Elaine is so cute I don't think I'dhave the nerve to fire her. But shedoes the darndest things! You'dthink a girl like that would know,by this time, how to solder leadstogether.

When I opened the shop at seveno'clock this morning I felt prettygood. There were only seventy oreighty chassis laying around, and ifyou stepped carefully you wouldn'tget snagged very badly. The otherday we had over one hundred andfifty jalopies in work and then wereally had a mess on our hands. Butthe boys, Jerry, Elaine and I gotdown to business and we cleaned upa lot of easy jobs in order to makeroom for the pile of stuff that is ac-cumulating around town. Our hooklooks like it needs an assistant, andI'd buy another if I could, but thereain't another in town, and I'm toobusy to put up a long nail.

But that gal Elaine sort of gumsup the works. In some respects shespeeds up production, and in othersshe ties us up in knots. I could al -



Thinking Ahead OnServicing Radio Sets

(Continued from page 13)

This might even mean that 'Mr. JohnQ Public' might have to take hischassis out of a console cabinet, un-less it were in large combination in-stallations, but during war times, Idon't think that they could objectto this.

Today, if a person wants a re-ceiver to play he must be made torealize that some discomfort andsome effort must be experienced onhis part to provide sufficient time-saving on the part of the servicemanto permit him to devote his valuabletime to the technical aspects of serv-icing the receiver itself and notmerely to that of being a deliveryboy.

Consolidating Technical Work

The second problem would be theestablishing of these collectionagencies wherein the public mightbring their receiving sets for service.The average service -dealer is so busythese days that it may take sometime to get around to actually per-form some operations on the receiver.These servicemen or individual shopsshould effect a mobilization and con-centration of the remaining techni-cal skill into an organization such asthe local parts jobber wherein allservice work could be done by theseconsolidated servicemen. The serv-ice -dealer's store would then act asthe media through which the receiv-er was delivered by the public andthen turned over in quantities to thismaster servicing organization oper-ating over the local parts jobber'sguidance. By having the actual serv-icing done within the parts jobber'sestablishment, it would salvage thetime generally required by the aver-age serviceman to run down and pickup one specific type of tube or one ortwo other miscellaneous parts thatwould go into the service work forthat particular day. Bear in mindthat in order to expedite man power,time is the one element that can besaved.

When one of these sets is deliveredto the master service organization orthe parts jobber, as we have estab-lished him, it would then be turnedover to a master diagnostician whoby experience could in most instancestell within a few minutes just whatis the difficulty, and in many in -

ARE

For many years Meissner Coils havebeen the accepted standard by engineerswho insist upon high quality performance

. Meissner precision coil constructionnever varies . . . they are the best thatengineering research and modern pro-duction methods can make.

When you specify a Meissner Coil youhave the assurance of long, trouble -freeoperating life backed by a name thatis synonymous with precision -builtproducts.

Coils illustrated and described representonly a few of the complete MeissnerCoil line.

See your nearest Meissner distributor today.

MT. CARMEL, ILLINOIS

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Ideal units (or replacement in com-pact midget or auto Radio sets. Coilswound on form 5/s" in diameter, 11/4"long. List price, either type, Anten-na or RF, 50c each.

stances could repair it in making thediagnosis. If difficulty in diagnosisis met, the set could then be turnedover to one man that would be termedin the vernacular as a `piddler', thekind of an individual who has enoughpatience and knowledge to sit downand trace out the circuit and find outjust what is wrong. Thus, servicework would be expedited to a largedegree. Upon completion of the job,the radio service -dealer would thenpick up the sets to be taken back tohis store or the owner could pick uphis at the master servicing establish-ment. Thus, much time would be

saved and this plan may tend tokeep radio service available to thepublic.

Salvage A FactorThe above suggested plan would

also facilitate the reclamation or sal-vaging of used and defective parts.The Radio Section of WPB has askedthat some plan be presented to effectthe most general salvaging of suchdefective units, and it would appearmost logical that were a procedureof this type accepted as a standardpractice for the duration, by havingthe units serviced by the jobbers or


"Sure, I'd Rather Have Roast Beef *. . . but if it's a question of who itgoes to-me or a boy at the front-Brother, I'll eat fish and like it."

People are accepting with ever-increasinggood -grace each days new war -born incon-veniece-VIHEN they know the reason forit.If you explain to your customers how warneeds are taking all new radio parts-howyou have licked a tough situation to gettheir sets into operation without thoseparts-they'll be satisfied with performancethat's a "little less than perfect."Improvising repairs, however, may requireyour eliminating certain stages, substitut-ing for specific resistors, condensers, sock-ets, etc. It may require that you transfercertain materials from one part of a set toanother. But one thing it is always certainto require is a knowledge of exactly whatis inside the set.That's where Rider Manuals help youout-quickly. They save you hours other-wise wasted "guessing out" defects andexperimenting with "possible" methods ofimprovising repairs. They lead you rightto the cause of the trouble and furnishthe facts that enable you to turn out a bigvolume of work in spite of material andlabor shortages.So, reach for one of your thirteen RiderManuals when you begin every job. To-day, it's good sense and good citizenshipto work with the greatest possible effici-ency.

RIDER MANUALSVolumes XIII to VII $11.00 eachVolumes YI to 111 8.25 eachVolumes I to V AbridgedAutomatic Record Changers and Recorders.. 6.00

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2.001.25 *

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*

master servicing organization set-upunder the jobber's surveillance, thesalvaging of materials would be thuseffected in the most important link inthe chain of returning those stra-tegic materials to the melting pot.The question of salvaging is to de-velop directly in proportion to theproximity of our receiving materialallocations and must, therefore, beconsidered as one of the salient ele-ments of the above plan.

Many jobbers throughout thecountry have already been affectedby the shortages reviewed in this ar-ticle. Many jobbers have already

converted to a plan coinciding inprinciple with the above -mentionedoutline in cities such as Pittsburgh,Pa.; Moline, Ill.; Denver, Col.; Oak-land and Long Beach, Cal. In theMiddle West, two other distributorshave written their servicemen ac-counts obtaining their reactions to aplan very similar in nature and out-lining to them the necessity of actionbeing taken promptly. It would bewell, therefore, that the parts dis-tributing groups consider this phaseas an industry problem to perpetu-ate their own organizations.

As time goes on our service prob-

lem is going to become increasinglyacute and if we expect materials tobe freed by the cooperation of WPB,we must also find some way of "un-freezing" the man power so thatthese materials may be used advan-tageously.

Let us try to think ahead of theman power problem in radio serviceand have our own program well es-tablished so that when we receive thematerials we expect we will have aplace to use them!

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In the Glasohm construction the re-sistance wire is wound on a fibre -glasscore and is protected by a fibre -glassbraided covering. The fibre -glass is vir-tually indestructible glass, almost asflexible as silk. The unit can be bentand compacted to fit snugly about partsto be heated, or jammed into very tightspots, in either case providing an effi-cient heating means. Glasohm heatingelements can be made to any requiredlength and provided with any typeterminals. Wattage ratings are from 1to 4 watts per body inch depending onthe application. Operating tempera-tures up to 750° F.

*JOB COST CALCULATOR '

>>>> Pay rolls and job costs can be fig-ured in a fraction of the usual timethrough the use of a new calculator,according to the manufacturers, theBerger -Bricker Company of 433 SouthSpring Street, Los Angeles, California.

Operating on a simple new principle,this device includes all hourly rates ofpay from $0.50 to $1.75 with a half -cent spread between rates. It covers alltime periods up to 104 hours with di-visions of one -tenth of an hour. It ishandsomely made of lacquered woodand easily fits into a desk drawer. Sell-ing price of the new pay roll calculatoris $7.50.


What do you see?The answer, obviously, is nothing. Not one of us in the

field can put our future prospects under aglass and examine them with a real degree of accuracy.

We know there is a serious shortage of replacement parts

and tubes; a condition that will get worse, not better, We

know that many of our competitors have entered some

branch of the Signal Corps; that many more of us will soon

join them. We know we have more work in our shops than

we can comfortably handle; that a bigger backlog willpile up, despite our efforts.

We service -dealers have a vital job to do-buying War

Stamps-and keeping as many civilian sets in repair aspossible. How best can we do this job? By keeping

thoroughly informed on the latest technical servicing pro-

cedure-methods that help save time and materials --learn-

ing tricks that will speed up work without impairing efficiency. What source gives you that type of technicaldata, and information on the latest government "ceilings,"

restrictions, rulings, etc.? The answer is RADIO SERVICE-

DEALER-the technical monthly that practically every

radio servicing organization in the country now subscribes

to or reads regularly . , . yes, RSD, that publication knows

the problems of service dealers and tries to help solve them,

TEAR OUT AND MAIL TODAYRADIO SERVICE -DEALER132 West 43rd Street, New York City, N. Y.Sirs: Here is my check (or money order) for S.... Enter my subscription order to RSD for the next issues. (12issues cost $2.-24 issues cost $3.) Canadian and Foreign subscriptions are $3 annually.

Name (print carefully)

ADDRESS FIRM NAME Est. 19

CITY STATE My Position Is: OwnerPlease check whether firm is An independent servicing organization, we do not sell sets. An independent service -dealer (engaged primarily in service work) A service -dealer (does servicing, but is primarily interested in

retailing) Selling, renting or servicing Sound Equipment Jobber Any other classification Manufacturer (State it)I belong to a serviceman's organization Yes No


(If any other, state what it is)

We stock the follow-ing checked items:

O TUBES0 PARTS RECEIVERS BATTERIES, etc. SOUND EQUIP. ELEC. APP'L'S.

Service Mgr. Serviceman

We own the follow-ing instruments:V -T VoltmeterTube CheckerAnalyzerOscillatorSignal GeneratorVolt -Ohm Meter

0 OthersD MANUALS

9 3

neirraffitea killegla:More Dollars Per Man Per Month in the

PAY -ROLL WAR SAVINGS PLAN

TO WIN THIS WAR, moreand more billions are neededand needed fast-AT LEASTA BILLION DOLLARS A

MONTH IN WAR BOND SALESALONE!This means a minimum of 10 percentof the gross pay roll invested in WarBonds in every plant, office, firm, andfactory in the land.Best and quickest way to raise thismoney-and at the same time to "brake"inflation-is by stepping up the Pay -Roll War Savings Plan, having everycompany offer every worker the chanceto buy MORE BONDS.Truly, in this War of Survival,VICTORY BEGINS AT THE PAYWINDOW.If your firm has already installed the

Pay -Roll War Savings Plan, now t taetime -

1. To secure wider employee par-ticipation.

2. To encourage employees to increasethe amount of their allotments forBonds, to an average of at least 10percent of earnings-because"token" payments will not win thiswar any more than "token" resis-tance will keep the enemy fromour shores, our homes.

If your firm has not already installedthe Pay -Roll War Savings Plan, now isthe time to do so. For full details, plussamples of result -getting literature andpromotional helps, write, wire, orphone: War Savings Staff, Section E,Treasury Department, 709 TwelfthStreet NW., Washington, D. C.

U. S. War Savings BondsThis space is a contribution to America's all-out war program by

RADIO SERVICE -DEALERRadio Service -Dealer, November, 1942

NEW DISPLAY FOR NEEDLES

>> Jensen Industries, Inc., 737 NorthMichigan Avenue, Chicago, offer a new,uniquely designed counter needle mer-chandising display which occupies acounter space of 4.1" x 111(", by 1317i"in height. It contains a "Baker's Doz-

en" of Jensen Long -Life PhonographNeedles, each needle being attached toa two color round package which is in-serted in individual compartments. Awindow banner depicting the superiorperformance of Jensen needles is alsoincluded.

CLAROSTAT CONTROL EARNS "A">>>> The inspection routine or qualitycontrol practiced in the Clarostat planthas won the rare recognition of an "A"classification granted by the EasternProcurement District, Army Air Force.This means that Clarostat's own in-spectors, having demonstrated a highdegree of quality control to the satis-faction of the Air Force, are now en-trusted with full responsibility of meet-ing all requirements as established.Duplication of inspection during fabri-cation by Air Corps inspectors can thusbe eliminated, and the latter can nowconfine their activities to general super-vision of the inspection system and thefinal approval and stamping of com-pleted assemblies.

WINDOW TRIM ATTRACTSCUSTOMERS

>>>> First of a series of suggested win-dow trims to utilize display materialto best advantage, the Ken-Rad RadioTube window trim illustrated is beingoffered to dealers as a model handlingof available material. The display setconsists of a large 19" x 24" easeledcard "Selected for Service," three win-dow streamers illustrating the sametheme, one cutout "Ken-Rad on Pa-rade" and two twin -tube cutouts.

Tube cartons and crepe paper trimare added to make a pleasing displayhigh in attention value, yet easy forany service -dealer to construct with aminimum of effort or expense. Forfurther particulars write Ken Rad,Owensboro, Ky.

TO HELP WINTHE WAR

Today, the 36 -years of

skill and experience that

pioneered anddeveloped

the "QUANTITY-plus -

QUALITY" manufacture

of BRACH products, are

directed exclusively to-

ward serving our armed

forces on their road to

Victory.

L. S. BRACH %IFG. CORP.World's Oldest and Largest Manufacturers of Radio Aerial Systems

55-65 DICKERSON STREET NEWARK, N. J.

SaieFuwavoK4"GUARANTEE"

USE STANCORST.ruplt

STANDARD TRANSFORMER CORPORATION

1500 NORTH HALSTED STREET... CHICAGO

Radio Service -Dealer, November, 1942 ,5

VITAL need to enlist approximately100,000 skilled technicians immedi-

ately in the Army Air Forces, SignalCorps and Ordnance Department wasannounced by the War Department onAugust 9.

These specialists are needed now tokeep equipment in operating order. Sogreat is the present emergency that aspecial recruiting campaign has beenlaunched to find men who can step im-mediately into important maintenancejobs.

Opportunities for Promotion

To be eligible, men must be between18 and 44 inclusive, citizens of theU. S. and physically qualified accord-ing to general standards of militaryservice. They will enlist as privates,but non-commissioned officer or techni-cian ratings are often given men doingjobs of this sort Skilled men areneeded, and promotion should be rapidwith commensurate increases in pay.Whereas a private receives $50 amonth, a master sergeant, the highestnon-commissioned grade, receives $138to which certain allowances may beadded. The Army pays all a man'sexpenses-food, clothing, shelter andmedical care.

To make sure that industry's pro-duction program is not upset, all menwho wish to enlist as mechanics andtechnicians now must be cleared bytheir local Selective Service Board be-fore acceptance by the Army.

For a limited period this RecruitingProgram offers trained men an oppor-tunity to choose any one of the threebranches, Air Forces, Signal Corps orOrdnance Department, for which theirexperience and skill qualifies them.These men are expected, after a mini-mum of on-the-job instruction to fa-miliarize them with Army machinesand Army ways, to qualify as mainte-nance experts.

"HELP WANTED"

Jobs to be Filled

The Army Air Forces want men toserve as radio operators and radio me-chanics.

The Signal Corps wants men whoseexperience qualifies -them as telephoneand telegraph cable splicers, telephoneand telegraph installer -repairmen, radiooperators, telegraphic printer oper-ators, telegraphic printer installer -re-pairmen, and telephone and telegraphwire chiefs.

Best in Training and Equipment

While the type of work these menwill do should be familiar to them al-ready, the machines and equipmentused by the Army offer new opportu-nities for valuable experience. Allthree of these branches of the Armyare equipped with the most modern,most highly developed machines anddevices in the world. Some of theequipment is secret. The man who

any of thesejobs will have learned much that willbe helpful in postwar industry.

lobs in the Air Forces

Here is a picture of the type ofwork which technicians in the AirForces perform:

Aircraft Radio Mechanics adjustand repair various types of transmit-ting and receiving _radio equipment asmembers of the Ground Crew.

Aircraft Radio Operators operatetransmitting and receiving radio equip-ment (partly in code), and make ad-justments and minor repairs. Somecan become aerial-- radio operators-part of the Air Crew, with a 50% payincrease.

Jobs In the Signal Corps

The Signal Corps operates theArmy's highly specialized communica-tions system. But it does more thanthat. It furnishes equipment to otherbranches of the Army and it is con-stantly pioneering in its field.

Signal Corps men have the satisfac-tion of knowing that they are fur-nishing Army staffs with the spot newsof battle to guide important and split-second tactical decisions. The list ofjobs given above offers a broad pictureof the type of work the men do. Be-cause much of the equipment is secret,

however, it is impossible to givedetails.

Field Staff of Recruiters

Because of the importance which theArmy attaches to finding these neededspecialists quickly, a special staff of re-cruiters will be at work throughout theUnited States, equipped to answer allquestions. Men who are interestedshould visit their local recruiting sta-tions. Postmasters can direct them tothe nearest station where full informa-tion is available.

Enlistment Plan

All men who apply for enlistmentwill be examined carefully upon theirexperience and qualifications. AirForces men must pass a special intel-ligence test as well as an oral tradetest given by an office of the UnitedStates Employment Service.

The Signal Corps will accept a rec-ognized radio or telegraph license ormembership in either the RMS or RSAfrom applicants who desire to becomeradio operators or mechanics. TheCorps will also approve men who areactively engaged in radio service workor who are graduates of a recognizedradio school.

Once the qualifications of an appli-cant are satisfactorily determined, hewill be given a thorough physical ex-amination. If no disability is discov-ered, he will be sworn in immediatelyas a private in the Army of the UnitedStates.

All recruits will be sent to a Recep-tion Center for the same kind of"processing" which every man receiveswhen he enters the Army. This is amatter of a few days at most. Fromthe Reception Center, Air Forces menwill go to an Air Forces station, SignalCorps men will be sent to the nearestSignal Corps Replacement TrainingCenter and Ordnance men will proceedto the Ordnance Department TrainingCenter.

Here they will begin their real mili-tary training and also learn the main-tenance jobs for which the Army sosorely needs them. By putting theircivilian skills in uniform these men.willfight with the tools they've alwaysworked with.


KAHN HEADS SALESMANAGERS CLUB

>>>> Jerome J. Kahn, President of Stand-ard Transformer Corporation, hasbeen elected Chairman of the SalesManagers Club, Western Group, forthe ensuing year. Mr. Kahn succeedsMr. S. N. Shure of Shure Brothers,who has served for the past twelvemonths. Mr. Shure piloted the clubthrough practically all of the initialpriorities period, and during his ad-ministration the group prospered andexpanded in educating jobbers andmanufacturers on priorities develop-ments. Mr. Kahn will take up the taskfrom this point on and carry on withthe policies which he has helped to es-tablish. For the past several years hehas been one of the most active manu-facturers in the radio replacementparts field. He was a member of theoriginal Priorities Committee of theRadio Parts and Associated Industries,he was Chairman of the Radio VictoryDinner held at the Stevens Hotel lastJune and did an excellent job in mak-ing that affair a huge success.

Mr. Kahn was the original sponsorof the "Keep 'em Playing" campaigndesigned to bring pressure on the prop-er groups in Washington to make anallocation of critical materials for re-placement parts for home receivers. Heis now a member of the Radio Replace-ment Parts Industry Advisory Corn-emittee working with WPB, a directorof the Radio Manufacturers Associa-tion, and Chairman of the RMA Priori-ties Committee.

Paul H. Tartak, President of theOxford Tartak Radio Corporation, waselected Vice -Chairman of the Group,while Miss H. A. Staniland of Quam-Nichols Company and Kenneth C.Prince, Chicago attorney, continue asTreasurer and Secretary respectively.

FIRST AID INDEX>>>> A First Aid Index in handy pocketsize form is being issued by Sylvaniafor servicemen to use with local waremergency volunteer groups. It meas-ures 61/2 x 3 inches folded, and fits intopocket, purse or auto compartment.They are available at 5c each, minimumquantity for imprinting by Sylvania isone hundred.

The Sylvania First Aid Index bearsthe approval of the Commander -in -Chief of the U. S. Volunteer Life Sav-ing Corps. With the war increasing infury and hitting- closer to home, Ameri-cans by the hundreds of thousands willbe answering the home defense call tobecome Air Raid Wardens and FirstAiders. Servicemen will find this itemgratefully appreciated by the valianthome front war workers.

*New Ohmite catalog-now available,catalog 18 will be rather helpful tousers of rheostats, resistors, "T" padsand attenuators. Special chokes,switches and mountings are describedfor users of radio and electronic equip-ment. Write Ohmite Mfg. Co., 4846Flournoy St., Chicago,

Lafayette has complete stocks-ready for immedi-ate delivery! Nationally known radio, electronic andsound parts and equipment available for all Militarytraining courses. Lafayette parts and equipment are indaily use by technical schools handling Military train-ing courses including Signal Corps Schools. Write forFREE technical advice-our engineers are at your service.INSTRUCTORS-Write Dept. 11K2 at 901 W. JacksonBlvd., Chicago, Ill., for FREE 130 -page general catalogand Instructive Public Address Catalog listing all P. A.Units.

A number of kits in one are provided by our 7 -tubedemonstration kit (illustrated). It can be built instages, each stage inter-connected with tip jacks.When completed, there are2 stages of R. F., a detectorstage, an audio driverstage, a beam power push-pull audio and a powersupply. The circuit dia-gram will suggest manyinteresting uses.

LAFAYETTE RADIO CORP.901 W. Jackson Blvd., Chicago, Ill.

265 Peachtree St., Atlanta, Ga.Camera Fans: Photographic equipment at lowest prices.

Write for FREE PHOTOGRAPHIC CATALOG!

Coming through . . .

Clear .. intelligible . . in the heat and noise of battle Orders are coming through

-Mee MICROPHONESWhile we cannot discuss the actual developments embodied in many of our newmodels, we can say that they have been designed specifically to limit background noisesand to allow speech to come through the bedlam of battle.

ELECTRO-VOICE MFG. CO Inc.1239 SOUTH BEND AVENUE SOUTH BEND, INDIANA

Export Office: 100 YARICK STREET, NEW YORK, N. Y.

ICadio Service -Dealer, November, 1942 27

Ask Your Jobber-He May Have Some

When we engaged in all outproduction for Victory, veryfortunately we had on handa number of G. I. Motors fordomestic uses. We are gladto make these available tothe trade through our regu-lar jobbers as longas they last.

THE GENERAL INDUSTRIES CO.Dept. 17 Elyria, Ohio

P Aeaid4014,

NA_ In servicing P -A and theatre sound installa-Ar tions, don't overlook that wide selection of

sound -system controls offered by Clarostat.The wire -wound T -Pad constant -impedanceseries CIT-58 control here shown is typical.Also L -pads, mixers, faders, constant -im-pedance attenuators, etc. All are included inthe Clarostat COMPLETE line of controls.

16,.. Likewise in servicing radio receivers, don'tforget those Clarostat replacement controls,plug-in tube -type resistors, voltage -droppingpower cords, etc.

* Ask your local Clarostat jobber about theseaids in your servicing. He's well equippedto take care of your usual and unusual needs.

cLAROSTATaytratoli afe6Wre

28

My Log(Continued from page 20)

most call her a demoralizing influ-ence. She don't mean to cause anytrouble, but she does, just becauseshe's the kind of girl Elaine is.(Jerry says I'm getting sweet on her,but that's a lot of bunk) .

Now when we lost Pete and Hectorto the draft boards two weeks agoand I decided to train a gal to taketheir place, I had an idea that a girlcould be taught to follow-up specificinstructions without too muchtrouble. It don't work out that way.Tippy, who does most of my signalchasing, thought the gal would be ofmost help to us if she learned to workunder him. Hank, who makes mostof the actual repairs, had anotheridea. He wanted Elaine to learn the"rudiments of servicing" first-howto solder connections, how to findbroken leads. or how to discernburned out condensers. Jerry, onthe other hand, figured that Elaineshould work out in the front of thestore with him, talking to customers,explaining 'why we'd need a monthto do a job that usually took twohours. Hell, you simply can't getparts now -a -days, but customersdon't give a hang about yourtroubles. They know their set isdead, and they want it fixed pronto-and they don't care how you doit, as long as you do it in a hurry.

Well, this morning I managed toget the pile of finished work off intoone corner and I found Doc Parson'sold Philco half under the bench. Iknew that chassis was around some-where and I'd been looking for it fora week. Kept stalling Doc by tell-ing him we couldn't locate thetrouble, and to some extent, thatwasn't exactly a lie. We couldn'teven find the set. So I put thePhilco up on the bench and let herheat up. In a few seconds I locatedthe trouble. The avc line wasgrounded, but otherwise she wasokay. I put a tag on it "float avcoff ground and replace 3-megger forluck" and shoved it over to Hank'sshelf. Just as I was doing thatElaine walked in, gave me a cheery"Good morning," took off her coatand said, "What'll I do now Boss ?"I figured this was as good a time asany, so I started to explain to herwhat was wrong with Doe's set, andhow the repairs should be made.She's quick, Elaine is, and in a fewminutes she gave me the whole spielas to what should be done, so I lether start in on her own. I still thinkeverything would have been fine if

Jerry hadn't come in just then witha load of chasses that he'd picked up.

I helped my pard lay the new busi-ness down in neat piles and then weboth loaded Liz up with the finishedjobs in order to make more room.Hank came in about then and he gotthe job tickets all sorted out forJerry while I tallied the prices tomake sure we hadn't gone "over theceiling" anywhere. And, as we threehad plenty to keep us occupied, wejust forgot that Elaine was hard atwork in the shop. She'd still besoldering things, I guess, if Tippyhadn't come in just then. I sort ofnoticed that he went into the shopwithout paying any attention to him,and I was just coming back for an-other load of sets to pile into Lizwhen a roar burst forth that had toomany decibles behind it for comfort.I barged into the back, and there wasTip, ashen around the lips and shak-ing at the knees. He was incoherent,to say the least, for his first roargave out all he had . . . and over onthe other side of the bench wasElaine, holding on to the solderingiron, waving it in front of her asthough she were one of the ThreeMuskateers, fighting a duel for herlife.

"What happened ?", I asked, butTippy couldn't answer. He justpointed to the chassis on the bench,and to the galaxy of parts that hadspilled out of it. I knew at a glancethen what happened. Elaine hadstarted to work on Doe's set with thesoldering iron. She knew what pointshad to be touched with the iron, butshe didn't care much about the otherpoints that shouldn't have been.Consequence-more parts had beenunsoldered and had fallen out of theset than the average small-time job-ber carries in stock. Well, from nowon Elaine will work out front, awayfrom the bench. And I'm going tohave to sound -proof the shop becausethe noise that Hank makes everytime he finds another part to solderinto Doe's set ain't fit for a niceyoung lady's ears.

SYLANIA GETS "E"

>> Rear Admiral Charles W. Fisher, Di-rector of Shore Establishments, U. S.N. presented the Army -Navy "E" Bur-gee to the Emporium, Pa. employeesand plant of the Sylvania ElectricProducts, Inc., on November 5th.

Sylvania's president, B. G. Erskinereceived the plant flag from AdmiralFisher; an employee accepted the token"E" pin on behalf of all employeesfrom Colonel W. S. Diener, Command-ing Officer, Central Office PennsylvaniaDistrict, Internal Security Board.


Technical Service

PortfolioRESISTORS & VOLUME

CONTROLS

(Continued from page 19)

generated. If the battery voltage is100 and R1 is adjusted to equal Rx,then 50 volts d -c will appear acrossthis noise voltage resulting from theRx. When switch S1 is on point b,50 volts d -c passing through Rx willbe impressed on the input circuit ofthe amplifier. When S2, in the out-put circuit, is connected to the out-put voltmeter, an indication will beobtained proportional to the noisevoltage being applied to the inputcircuit. This indication is noted andS1 is switched to point a. R2 is con-nected across a signal source, usuallya 1000 -cycle audio oscillator, and iscalibrated. When R2 is so adjustedthat the indication obtained with theswitch S1 on point a is the same asthat with the switch on point b, thenthe audio signal voltage is consideredequivalent to the noise voltage in theresistor. Thus, with 50 volts acrossRx, if the noise is 100 microvolts,the rating is 2 microvolts per volt.

In this circuit, all controls otherthan the resistor under test are wire-wound and are free from noise fromcauses which affect composition re-sistors. Other methods are available.Low noise levels are very difficult tomeasure because of inherent noise inthe test apparatus.

MICA CAPACITORS NEEDED BYUNCLE SAM

>>>> It is no military secret that planesand tanks, desperately needed by ourarmed forces, are being held up at pro-duction centers for want of radio equip-ment, which equipment in turn cannotbe completed because of the mica ca-pacitor shortage. The main bottleneckin radio production is mica capacitors.

Responding to the appeal of our Gov-ernment, the Aerovox Corporation ofNew Bedford, Mass., with its mica pro-duction capacity already stepped upseveral dozen fold over pre-war levels,has sent out an urgent appeal to job-bers asking them to make existing micacapacitor stock available to Uncle Sam.Special inventory forms have been pro-vided so that jobbers can simply, quick-ly and explicitly tabulate their avail-able stock and send the information tothe Army -Navy Communications Pro-duction Expediting Agency, PentagonBuilding, Arlington, Va.

'ilL.822hT2, BY GUARDIANSERVE ALL FRONTS!

* Yuletide joys of '42 will not include the many elec-trical gifts which brought us cheer, and ease, and com-fort in other years. Relays by Guardian have marchedon from peacetime industry to the firing lines of war.Doing war jobs in many ways ... in planes ... in tanks... in communications ... in bomb releases and guncontrols. Wartime jobs which Guardian anticipated andplanned long before "Pearl Harbor".

But, while thinking, building, and engineering thefools of war today, Guardian again is looking aheadto peacetime applications of Relays, Solenoids, Elec-trical Controls of all kinds. Write. Our wartime experi-ence can help you build better products for the future.

Controls for Any Purposeranging from 150 watts to1000 craps ... from tinyrelays weighing less thanan ounce .. to big, rug-

ged two -pounders.

GUARDIAN ELECTRIC,637 WEST WALNUT STREET CHICAGO. ILLINOIS

A COMPLETE LINE OF RELAYS SERVING AMERICAN WAR INDUSTRY

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!

ccjust what the Signal Corps Ordered"-and to prove it, signal corps men areusing these 3 specially selected "Vaco"

drivers every day.Thousands of sets of the numbers shown below are already in use, per-forming an important task and helping signal corps trainees to do faster,better work.

"Vaco" Drivers are preferred be-cause they fit the hand properlyand have shock -proof, break -proof, chip -proof Amberyl han-dles and narrow straight bits.

Other famous "Vaco" Driversspecially suited for radio workinclude G2 Grip -point Screw -holding and Spin -hex nut drivers.

JOBBERS: Order your "Vaco" signal corpsDrivers immediately , . carry high priorityrating.

Cl1H2m3AWG0. WashingitzzINBOlvdis.VAC® PRODUCTS CO.


TUBE SUBSTITUTION CHART3rd REVISION COPYRIGHT 1942

COWAN PUB. CORP.

DiscontinuedType Replace With Changes

DiscontinuedType Replace With Changes

00A 30 Use 2 -volt filament supply 6N7G 6N7 None023 .. .... OZ4 Use adapter or changesocket 6P5G 6P5GT/G, 76

6F7Socket, see text July RSDSocket (see text June RSD)01A 30 Use 2 -volt filament supply 6Q606GG 6T7G None01AA 30 Use 2 -volt filament supply 6Q7MG 6T7G None1A1 Resistor See text June RSD 6T5 6U5/6G5 None, see text Aug. RSD1A1/5E1 .. Resistor See text June RSD 6T7G/6Q6G. 6T7G NoneIA5G 1A5GT/G None 6U5 6U5/6G5 None, see text Aug. RSD1A7G 1A7GT None 6V6G 6V6GT/G None, see text Aug. RSD1B1 Resistor See text June RSD 6V6GX 6V6GT/G Only differ. is ceramic base1B4 32 Bulb is larger 6V7G 85 Socket (see text June RSD)IB4P 32 Bulb is larger 6W5G 6X5GT/G See text June RSD1B4P/951 . 32 Bulb is larger 6X5 6X5GT/G None1B7G 1B7GT None 6Y5 6X5GT/G Socket (see text June RSD)1C1 Resistor See text June RSD 6Y7G 79 Socket (see text June RSD)1C5G 1C5GT/G None 6Z3 1-V None1D1 Resistor See text June RSD 6Z4 6Z4/84 None1D7G 1C7G Requires higher filament 6Z5 6X5GT/G Socket (see text June RSD)current 6Z5/12Z5 6X5GT/G Socket (see text June RSD)1E1 Resistor See text June RSD 6Z6MG See text July RSD1E2 Resistor See text June RSD 6Z7G 6N7 See text June RSDIE5GP

IESGT1E7GIF1IF7GH1F7GVIGI

NoneResistorIF7G1F7GResistor

See text June RSDSee text June RSDSee text June RSDNoneNoneSee text June RSD

7A7LM7B5LT7B6LM7B8LM7C5LT7G7WD11

7A77B57B67B87C57G7/1232No replacement (obsolete)

None, see text July RSDNoneNoneNone, see text Aug. RSDNone, see text Aug. RSDNone1G4G 1G4GT/G None WD12 No replacement (obsolete)1G5GT/G 1F5G, 33 See text June RSD WX12 No replacement (obsolete) .1G6G

1H5G1G6GT/GIH5GT None 12A

12A56J5GTNone Socket, fil. voltage

See text June RSD1J1 Resistor See text June RSD 12A8G 12A8GTNoneNone

1J5G1K1.

1L1INI

1F4, 1F5GResistor

ResistorResistor

Socket (see text June RSD)See text June RSDSee text June RSD

12B712J7G12K7G12K8GT

14A7/12A712J7GT12K7GT12K8

NoneNoneNone, see text Oct. RSD1N5G

1P1IP5G1Q1

1N5GTResistor1P5GTResistor

None

See text June RSD

I2Q7G12SA7G12SK7G12Z5

12Q7GT12SA7GT/G12SK7GT/G6Z5

NoneNoneNoneNone1Q5G

1RIG1S1GITIG1U11W11Z12A3H2A7S

1Q5GT/GResistorResistorResistorResistorResistorResistor2A32A7

NoneSee text June RSDSee text June RSDSee text June RSDSee text June RSDSee text June RSDSee text June RSDSee text June and Aug.See text June RSD

14A414A714B614B814C514E614 E714F714N7

7A414A7/12B77B67B87C57E67E77F77N7

Fil. voltageNoneFil. voltageFil. voltageFil. voltageFil. voltageFil. voltageFil. voltageFil. voltage2B6 6B5 See text June RSD 15 No equivalent See text June RSD2B7 6B7 See text June RSD 24 24A None2B7S 6B7 See text June RSD 24S 24A Socket (see text June RSD)2E5 6E5 See text June RSD 25A6 25A6GT/G None2G5

2S/4S2Z22Z2/G843Q5G5W45W4G5Y3G5Z4G5Z4MG6A46A4/LA6A5G6A6X6A7S6A8MG6AB56AB6G

6U5/6G56116

3Q5GT/G5W4GT/G5W4GT/GSY3GT/G5Z45Z447, 6F647, 6F66A3, 2A36A66A76A8GT, 6A86AB5/6N56B5

See text June RSDSee text June RSDSee text June RSDSee text June RSDNoneNoneNoneNoneNoneNoneSee text June and Aug.See text June and Aug.See text June and Aug.6A6X has ceramic baseSee text June and Aug.None, see text Aug. RSDNone, see text Aug. RSDSocket (see text June RSD)

25A6G25A7G25AC5G25B525136G25138GT25DSGT25 L625L6G25N6G25S25Z5MG25Z6G27S3135A5LT35L6G35S/51S

25A6GT/G2SA7GT/G25AC5GT/G6B543I2BSGTNo equivalent25L6GT/G25L6GT/G6B51B5/25S25Z525Z6GT/G27No equivalent35A535L6GT/G35

NoneNoneNoneFil. voltage-SocketSocket (see text June RSD)Fil. volt., see text Oct. RSD).None, see text Oct. RSDNoneNoneSocket-Fil. voltageNoneNoneSee text Oct. RCD.Socket (see text June RSD)

NoneNoneSocket (see text June RSD)6AC5G 6AC5GT/G None 39/44 7B7, 78 Socket, see text July RSD6AC6G 6B5 See text June RSD 45A 45 None, see text Aug. RSD6AE5G 6AE5GT/G None 46A1 Resistor See text June RSD6AE5GT 6AE5GT/G None, see text July RSD 46B1 Resistor See text June RSD6AF6GT 6N5 See text June RSD 48 No equivalent6B6G 75/65Q7 Socket (see text June RSD) 49 No equivalent6B7S 6B7, 6B7G See text June RSD 50Y6G SOY6GT/G None6138GT 6B7, 6B7G Socket 51 35 None6C5G 6C5GT/G None see text July RSD 55 85 Filament voltage6C5MG 6C5GT/G None 55S 85 Socket-Fil. voltage6C7 85 Socket (see text June RSD) 56S 56 See text June RSD6D7 Socket (see text June RSD) 57S 57 See text June RSD6E6 o replacement

58S 58 See text June RSD6E76F5MG6F7S6G561156H6G6H6MG6J5G6J5GX6J7MG6E6G6K6MG

6K76F5/6F5G/6F5GTNone6U5/6G56U5/6G56H6GT/G6H6GT/G6J5GT/G, 6C56J5C.6J7GT, 6K7G6K6GT/G6K6GT/G

Socket (see text June RSD)Socket, see text July RSD

None, see text Aug. RSDNone, see text Aug. RSDNoneNoneSee text July and Aug.Only differ. is ceramic baseNoneNone, see text Aug. RSDNone, see text Aug. RSD

70A7GT ...70L6GT75S7989117L7GT117M7GT117Z6G117Z6GC182B/482B183/483

70L7GT25L6GT75No equivalentNo equivalent117L7/M7GT117L7/M7GT117Z6GT/G117Z6GT/GNo equivalentNo equivalent

See text June and Oct.Fil. voltageSocketSee text June RSDSee text June and Aug.NoneNoneNoneNoneSee text June RSDSee text June RSD6E7MG

6L6GX6K7GT, 6K7G6L6G See text July RSD

Only differ. is ceramic base485950

No equivalentNo equivalent See text June RSD

6N5 6AB5/6N5 None, see text Aug. RSD 1232 7G7/1232 None6N6 6B5 Socket (see text June RSD) 1852 6AC7/1852 None, see text Aug. RSD6N6MG 6B5 Socket (see text June RSD) 1853 6AB7/I853 None


Something new has been added to this space -saver oil -filled high -voltage capacitor. Notethe two terminals-spaced on the steppedterminal post. This means the can of thishandy inverted -screw -mounting capacitor is

now insulated or "floating." No longer is

an insulator washer required when non -grounded mounting on a metal chassis is de-sired. 600 to 1500 v. D.C.W. .5 to 4

mfd. Ask your Aerovox jobber for new"Victory" catalog.

EROvoxCoRPORAvoN

NEW BEDFORD, MASS., U. S. A.In Canada: AEROVOX CANADA LTD., Hamilton, Ont.

EXPORT: 100 Varick St., N.Y., Cable 'ARIAS'

'NEW CATALOGOF SOUND AMPLIFYING SYSTEMSAUDIOGRAPH Sound Systems represent thelatest in Public Address equipment-a com-plete line plus pre -tested accessories.

NEW LOWER PRICESOutstanding quality and performance atprices that help you meet any competition.

WRITE FOR YOUR FREE COPY

R AE FIRST NAME IN SOUNDMod, latlasts4s-illoesq at Pennsylvania Ave., Plymouth, MO.

Radio Service -Dealer,

COLOR CODE RESISTOR CARD

>>>> Sylvania announces a Color CodeResistor card for radio technicians is-sued as a help in Wartime radio serv-icing.

In handy pocket size form, the Syl-vania Color Code Resistor Card shouldprove to be a valuable aid in circuit re-vision work. It clearly shows the A, B,C, and D color denotations of a resistor,explains the resistor color code andgives examples. On the reverse side ofthe card is Ohm's Law, one of the basicradio circuit formulas. Its definitionand explanation is a helpful referencefor radio men.

COLOR CODE CHART-RMA STANDARD

AXIAL TYPE LEADS ADIAL TYRELEADS

A B C DBlackHrovm

'535'InoUOremBluePurple

BlankBrown

Green 5

PurpleGtny

°

Orange 000Yellow 0000Green 00000Blue 000000Purple 0000000

ry00000000

e.iRe 000500000

No Color ±20Silver clog

Gold ±

Resistor Colo Code. The A color of a resiotor denotes the first sig-nificant figure. Om B for the tecond signifies t figure end the Cficolor indimtes the number of didiers after the first two significant

gures. The D color denote, the tolerance value of the resistor.E ample:

Band A (Axial TYPO or Body (Radial Type) Ited,810v1 8 =I

Type) or ET' 1=00101 1100) =oneValue of Resmtor -= 2500000ms

Servicemen are running into an in-creasing number of circuit revisions,and technical as this onegive servicemen a lift in the very toughjob of keeping America's Radio work-ing with a limited amount of materials.

Resistor cards are available throughSylvania jobbers or can be secured bywriting directly to Sylvania News, Em-porium, Pa.

*WALSCO GETS TREASURY FLAG

>>>> The "Star Spangled Banner" is be-ing sung every pay day by the em-ployees of the Walter L. Schott Com-pany, makers of Waisco Products, 9306Santa Monica Boulevard, Beverly Hills,California, in honor of the "Bulls Eye"flag now waving over their plant. Itwas awarded to them by the U. S.Treasury Department because all em-ployees are buying War Bonds throughthe Payroll Allotment Plan.

FORTUNE KILLED IN CRASH

>>>> J. Douglas Fortune, Industrial SalesEngineer of Thordarson Electric Mfg.Co., was fatally injured while pilotinga plane near Chicago on Saturday, Oc-tober 17th. Mr. Fortune was inter-nationally known for his developmentwork in radio and electronic equipment;was a regular contributor to manyleading radio publications and authored"Amateur Radio" a book widely readby Amateur Radio operators. Mr. For-tune's untimely death is a great loss tothe radio industry which he so faith-fully served.

November, 1942

Old Man Centralabreminds you to always "specifyCentralab" when ordering parts.

r24\ FIXEDRESISTORS

CERAMICCAPACITORS

VOLUMECONTROLS

WAVE CHANGESWITCHES

TOGGLESWITCHES

CentralabDIVISION OF GLOBE UNION INC.

MILWAUKEE, WIS.

RELAYSRESISTORS

RHEOSTATSThe oldest and most completeline for use in commercial,police, fire department and gov-ernment radio and signal work.Proven dependability and con-servative ratings. You are notexperimenting when you installWard Leonard items . . . youknow they are right.

WARD LEONARDRADIO SPECIALTIES

WARD LEONARD ELECTRIC COMPANY46 South St., Mount Vernon, N. Y.

Please send me Circular 507 covering Relays,Resistors and Rheostats.

Name

Street

City and State

Call Signal

31

AttentionTube Distributors

We will pay list less 50% for the follow-ing tube types, of standard manufacture,individually cartoned. We cannot supplypriority rating. Would consider buyingyour complete stocks at slightly betterdiscount. WIRE us collect if you canfurnish over 100 tubes, WRITE us if youhave less than 100 for sale. Depositwired or mailed with each of our orders,balance COD.

165/25S2A32A4C5U4G5V4C5Y3G or CT5Z361356C66H6 G or GT

6J5 C or CT6K7 C or CT6L6 C or CT6SC7 or CT6SQ7 C or GT304570L7CT76802051

W. R. BURTT308 Orpheum Bldg. Wichita, Kansas

Production DesignerWant competent man capable of super-vising drafting or layout job, able torecommend modification of a completedesign to facilitate production by mod-ern methods. Man with experience inmanufacture of light equipment of astructural nature for limited produc-tion ; requires broad experience withknowledge of relative merits of allwell-known production methods suchas bending, forming, drawing, punch-ing and forging.Man of these talents not now in 100%war work will be highly compensatedwith unusual opportunity and perma-nency in important war assignmentwith large manufacturer located inBoston.Give complete particulars for interviewin Chicago. Applications held strictlyconfidential.Write Box A-lj Radio Service Dealer

Instruments Wanted!The Signal Corps, Aircraft Radio

Laboratory, Wright Field, Dayton,Ohio, has need of or can place incritical war industries meters and testequipment for training purposes.

Write stating type, condition ofequipment, and price desired to

Director, Aircraft RadioLaboratory,

Wright Field, Dayton, Ohio

We have available a supply ofRCA Victor service notes for 1938,1939, and 1940. If you would likea set-over 200 pages of detailedservice data-send 45c in cash tocover postage and handling.

"BRAND EX"-a guide to eeneealedservIse data en "private breed" setscan be had for 25e per espy. It totress -Indexed for Broad -name, Menu -facturers outlet, Identification marks,its. Hurry before the supply Is ex-hausted. Onto they aro gone therewon't be any more.

RADIO SERVICEMEN OF AMERICA, Inc.RSA Press & Supply Service

414 Dickens Ave., Chicago, Illinois

RSAman in Far East Writes-

"Radio servicing here in Bombayand Ceylon is `very different.' We findreceivers of all makes, from A to Z;American, British, Australian andJapanese. The American brands areeasiest to service because the manu-facturers gave consideration to theservicing factors while Continentalmakes show no standardization and onthese we have no manuals from whichto gain help. It's a tedious task ! InCeylon there are but few dealers andeach repairs his own sets. There areno up-to-date servicing organizationsand the average so-called Manager orRadio Engineer in charge of dealers'shops don't know the difference be-tween a rectifier and detector valve."Signed, Sam Shroff, Ceylon, India.(This letter, dated Dec. 2, 1941, wasmailed before the Jap's attack on PearlHarbor and attempt to conquer India.)

*Fraenckel To G -E Electronics Dept.-V. H.Fraenckel will have charge of the co-ordination of commercial engineeringof all product lines of the GeneralElectric Radio, Television and Elec-tronics Department, according to a re-cent announcement by Dr. W. R. G.Baker, Vice -President. G. F. Metcalf,formerly in charge of this work, hasentered the U. S. Army with the rankof Lieutenant Colonel, Signal Corps.Mr. Fraenckel will report to G. W.Henyan, Manager of the Transmitterand Tube Divisions of the Department.

A native of Illinois, Mr. Fraenckelattended L'Ecole Polytechnique fromwhich he received the equivalent of aMaster's degree in Science in 1925.Later he took graduate work in physicsat the University of Chicago and theUniversity of Michigan, where he wasa member of the staff of the PhysicsDepartment and the Department ofEngineering Research respectively.

He was employed by the GeneralElectric Company in October, 1937,working in the Vacuum Tube Engi-neering Department. In October 1939he was transferred to the ResearchLaboratory where he was engaged inresearch on electronics and televisionproblems until his recent appointment.

*Multiple Station InterComm- The W-105is an interesting new low-cost com-municating system for office and in-dustrial application announced by Rau-land. Warehouses, service stations,small factories, wholesale distributors;professional and business offices willfind this system saves time and moneyfar beyond its cost.

This system consists of a Master, orcentral control unit, the only amplifierin the entire system. Up to five Re-

mote, or outlying sub -stations can beused. The Master or central unit cancall and converse with any one of thefive Remote stations as selected.

A new and special feature of thissystem is that the Master unit can calland "listen -in" or converse with allfive Remote stations at one time. Thisis done by means of the sixth, or "all"position on the selector switch. Furtherparticulars, write "Rauland," care ofRADIO SERVICE -DEALER, 132 W. 43 St.,New York City.

100% In Bond Buying Plans-Allied RadioChicago, Illinois, distributor of radioand electronic equipment, is proudlydisplaying a huge MinuteMan flag,symbolic of a 100% voluntary enroll-ment by its employees in the PayrollSavings Plan for the purchase of WarBonds.

Under this plan, sponsored by theU. S. Treasury, regular deductions aremade from each paycheck, and WarBonds are delivered to employees assoon as sufficient credits have accumu-lated.

Two days after A. D. Davis, Presi-dent, had appe'aled for cooperation withthe plan, all departments reported a100% enthusiastic response.

Hutchins Enters Service-Ever sincePearl Harbor/ Henry Hutchins, Gener-al Sales Manager of National Unionhas felt the urge to return to the NavalService to do his bit. He did it, and isnow Lieutenant Commander Hutchins,U. S. Naval Reserve on active duty.When this war is over he will be backwith National Union again.

N -U Announces Volume Control-The new"Say - a - Shaft" Control introduces anew development in replacement con-trol design by utilizing the shaft fromthe defective control. Not only doesthis "Say -a -Shaft" for vital war ma-terial requirements, but for the service -dealer it guarantees that the shaft willbe of correct diameter and length andthat the knob will fit the control per-fectly. No cutting, filing or specialknob is necessary regardless ofwhether the knob requires a flat, splitknurl or other special shaft -end.

Every control has a switch-comescompletely assembled so that the switchmechanism is inoperative. However asimple operation places the switch inaction when necessary. The new Na-tional Union controls are available atN -U jobbers in various resistance val-ues, tapers and taps to satisfactorilyhandle about 95% of usual replace-ments encountered in radio servicework.


TRIPLETTege INSTRUMENTS

THESE PHOTOGRAPHIC REPRODUCTIONS ARE THREE-QUARTER SIZE

MODEL 437 -JP

Maximum Service in Minimum Space

TRIPLETT Ogg- INSTRUMENTS

Precision performance by new thin instrument withstandard Triplett movement housed in either metalor molded case. No projecting base; wider shroudto strengthen face; simplified zero adjustment;balanced bridge support; metal bridges at bothends; doubly supported core. For "Precision inlimited space" write for Triplett Thin Line Bulletin.

MODEL 372

SIMPLEINSTALLATION

DIAGRAMS

Model 437 - J P Model 372

The Triplett Combat LineNew Answers to specialized needs of War: Produc-tion Speed-up and Standardization; Performanceunder the Stress and Vibrations of Combat Service.Model 437 J P -A rectangular line of meters to meetdimensions shown (see diagram). Wide-open scale formaximum readability. Complete coverage AC -DCVoltmeters, Ammeters and Wattmeters. Magnetic orstatic shielding provided on order. Molded PlasticCase for maximum protection in high voltage circuits.Pivots, Jewels and other component parts designed tomeet severe vibration requirements.Model 372-Frequency Meter-"All-American make"Vibrating Reed Frequency Meter. Maximum readabil-ity by grouping of Reeds. Range -Frequency -Voltageto meet specific requirements. Protected against ex-cessive panel vibration. In standard 3 inch mountingor on special order in any cataloged Triplett Case.

A WORD ABOUT DELIVERIESNaturally deliveries are subject to necessary priorityregulations. We urge prompt filing of orders for deliv-ery as may be consistent with America's War effort.

TRIPLETT ELECTRICAL INSTRUMENT CO.BLUFFTON, OHIO

Wtt%

The sa-rne-Raytheon.

-radiotobes

that gave570t1

top qualityperforrnance

are no -w givingunfailing

-periorovance

-with the:oal Corpsdespite

field

conditionsana theyrg

of everycliniate.

llaytheonsare now..on

2,0100-day

-watchesin

the junglesaoa in the Arctic--auty

that imeans

freedomto the -w

'TheyWAIStllot

faitand they

do not fail, lataraoto thousands °G

Antericans

workingto raake

it so --1110IIIIVSS

CO 1A10E,

RAYTHEON

PRODUCTION

CORPORAIION

Netcton,IVIass

Newyork ChicagoLos Angeles

Atlanta

DEVOTED TO RESEARCH AND THE MANUFACTURE OF TUBES FOR THE NEW ERA OF ELECTRONICS

sf,rvice dealer

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