ya - worldradiohistory.com€¦ · it stresses the many uses of different types of test equipment;...

a

flab. Ili. lib. I ilb..011". lb.

YA

116' #ik%.t.

Here's the Greatest Book for Service Men!

OFFICIAL RADIO SERVICE HANDIBOOKBy J. T. Bernsley

OFFICIAL

RADIO SERVICEHANDIBOOK

OVER 250 PAGES OFOPERATING NOTES -

Whether it is a fadingjob, lack of sensitivity,noise within the recei,er, aligning a chassis,poor A.V.0 action, orany other trouble that isusually the "bugaboo"of most Service Men,you will find the symp-toms and remedy clearlydescribed' in OFFICIALRADIO SERVICEHANDIBOOK. The ex-act procedure for repair-ing, as well as thecharacteristic trouble inalmost all models of man-ufactured sets, will befound in the section onOPERATING NOTES-over 250 pages of thisdata, the most importantinformation to any radioman in the servicingfield. The material in thissection has been arranged,as well as classified, sothere is no difficulty inimmediately locating thenecessary information.

HERE'S the book .on radio servicing that con-tains everything Service Men must know. The

book, OFFICIAL - RADIO SERVICE HANDI-BOOK, is edited by J. T. Bemsley, foremost radioservice authority. This 1936 service guide is theonly book of its kind-its editorial material is sowell prepared that the technical information can beunderstood by even beginners in radio servicing.Every page contains new material, new illustrations-no reprinted literature.

The OFFICIAL RADIO SERVICE HANDI-BOOK covers thoroughly over 500 radio topics. Ittells you how to analyze the latest commercialreceiver circuits; how to really make money servicingmidget sets; and, how aligning supers can be madeeasy. It stresses the many uses of different typesof test equipment; it gives you short cuts in trou-ble;shooting and repairing; and, contains over 250pages of operating-5notes on 1,000 manufacturedreceivers. So upto-date is the OFFICIAL RADIOSERVICE HANDIBOOK that it explains thoroughlythe features and innovations in the most modern ofreceivers.

OVER I ,000 PAGESOver. 1 0.0 0 Illustrations

Beautiful, Gold -stamped Linden Covet, 6x9 Inches

PARTIAL CONTENTS OF THIS GREAT BOOK!PART I-CIRCUIT THEORY AND ANALYSIS

R.F. Fundamentals; Superheterodyne Receiver Theory; A.V.C. and TuningIndicator Circuits; A.F. Fundamentals; Power Supply Theory and Circuits;Speakers, Reproducers and Pick -Ups; Commercial Receiver Circuits of. All Types;How to Analyze.

PART 2-MODERN SERVICING AND TEST EQUIPMENTFundamentals of Metering and Test Equipment; Standard Servicing Instru-

ments; The Cathode Ray Oscillograph and Associate Instruments; How to BuildEssential Servicing Test Instruments.

PART 3-PRACTICAL SHORT-CUTS 'IN TROUBLE SHOOTING & REPAIRINGLocalizing Trouble by Inspection Methods; Short -Cuts with Test Instruments;

How to Quickly and Properly Perform All Types of Repairs; Unusual ServicingExperiences; Tube Troubles and Characteristics.

PART 4-SPECIALIZED RECEIVER AND INSTALLATION DATAAlt Wave and High Fidelity Receiver Servicing and Installation Data; Auto

Radio Receiver and Installation; Specialized Servicing and Installation (RemoteTuning Controls, Home Recording, Automatic Record Changers, ApartmentHouse Antennae, etc., etc.); Eliminating Noise Interference.

PART 5-MODERNIZATION AND CONVERSION DATAModernizing and Improving Methods for All Types of Receivers; Converting

A.C. Receivers for D.C. Operation and Vice Versa.

PART 6-SOCIAL AND ECONOMIC' PROBLEMS OF THE SERVICE MANImproving Knowledge and Technique; Social Problems-How to Organize,

Listing of Servicemen's Organizationi; The Future of the Servicing Profession.

PART 7-OPERATING NOTES AND PRACTICAL DATA LISTINGSOperating Notes on Over 1,000 Receivers; I.F. Peaks of Approximately. 3,000

Receivers; Voltage Dividers for 300 Receivers; Speaker Field Listing; RadioMathematics and Measurements.

Send remittance of $4.00 in form of check or money order for your copy of theOFFICIAL RADIO -SERVICE HANDIBOOK. Register letter if it contains cashor currency. THE HANDIBOOK" IS SENT TO YOU POSTAGE PREPAID.

RADCRAFT PUBLICATIONS, Inc.99 -SS HUDSON STREET

NEW YORK, N. Y.

SERVICINGWITH

SET ANALYZERSA STUDY OF THE THEORYAND PROPER APPLICATIONOF MODERN SET ANALYZERSAND ASSOCIATED APPARATUS

BY

H. G. McENTEE

RADCRAFT PUBLICATIONS, INC.PUBLISHERS

99 HUDSON STREET NEW YORK, N. Y.

Copyright 1937 by Hugo Gernsback Printed in U.S.A.

Table of Contents

CHAPTER I-INTRODUCTION Page 3Relationship Between Analyzers and Manufac-turers Receiver Specifications-Vacuum Tubes,The Focal Point of Set Analyzing-What Is anAnalyzer?-Limitations of the Analyzer in Re-ceiver Servicing.

CHAPTER 2-FUNDAMENTAL ANALYZER PRIN-CIPLES Page 7

Switches, the Various Types and Their Uses-Meters, the More Commonly Used Types-Ele-mentary Set Analyzer Circuits.

CHAPTER 3-TROUBLE SHOOTING WITH THESET ANALYZER Page 18

Preliminary Checking - Testing Tubes UnderOperating Conditions-Isolating Trouble by theProcess of Elimination-Point-to-Point Testing-Checking Individual Components.

CHAPTER 4-ASSOCIATE TESTING EQUIP-MENT Page 28

The Vacuum Tube Voltmeter-The Test Oscillator-The Output Meter-The Oscilloscope.

CHAPTER 5-COMMERCIAL TESTING EQUIP-MENT Page 32

CHAPTER 6-THE RMA SOCKET NUMBERINGSYSTEM Page 58

SERVICING WITH SET ANALYZERS

CHAPTER 1

Introduction

Year by year, as we progress in radiowe find new equipment and new methodsbeing developed and perfected for testingand servicing. Much of this new equip-ment is forced upon us by the engineeringprogress that is constantly being made inthe field of radio receivers. The set whichis now an open book to the well versedService Man would have been a completemystery to the repairman of not so longago. We have progressed from the timewhen all sets used only one kind of tube,the triode (and not very many of these),to the point where we now use tubes, someof which have as many as nine separateelements in one bulb. We now have overtwo hundred tube types, and more arebeing added each month to this huge list.Only a very few of these may be used in-terchangeably, and most of them are suitedfor but a single purpose. Many of thetubes are able to perform more than oneduty by virtue of their multiple elementconstruction. Thus, the type 6Q7, is theequal of three tubes, since it has a triodeand two diodes in its shell. Many sets aredesigned with several of these multi -func-tion tubes in the line-up.

We find that, as a general rule, radiosets are designed according to their tuberequirements. Hence, we should endeavorto test them and make our analysis fromthe same viewpoint. While it would beasking too much of any Service Man toexpect him to memorize every tube withall its characteristics, it is possible and infact imperitive that the general classifica-tions, such as converters, R.F. amplifiers,audio pentodes, and the like be understood.Also, the Service Man should be thor-oughly familiar with the main arbitraryclassification of all tubes, that is, by fila-ment or heater voltage ratings. Thus wehave the 2 volt line, the 2.5 volt line and

the 6.3 volt line, with several others whichare not found very frequently and are oflittle importance today. An effort shouldbe made to keep all the latest tube dataof each manufacturer on hand, so thatwhen a new tube is encountered, no timewill be lost in searching for its character-istics. When a set is to be analyzed, then,and the proper readings are not obtainedat any one tube socket, an understandingof that tube and its associated circuits willlead to speedy correction of the trouble.

New wrinkles and methods are broughtout from time to time in the line of servic-ing proceedure. The most recent of theseis the so-called "point-to-point" method.While it is not as rapid and is considerablymore involved than employing a completeanalyzer and checking voltages from thesocket by means of a connector plug it is,however, more convenient for those whoare not familiar with circuit design, andtherefore cannot make an accurate deduc-tion when the meter readings are not cor-rect. Also, it is the only method wherebydeep seated or obscure troubles can be lo-cated-and is generally employed by theefficient Service Man as a supplementarymethod of ascertaining the location oftrouble after the analyzer is used. Theequipment employed for "point-to-point"tests is, usually, a multi -calibrated sensitivemeter having various D.C. voltage scales,in addition to an "ohms" scale for resist-ance measurements. Two test prods areemployed, and voltage or resistance meas-urements are taken across various partsof the receiver until the trouble is found.

The new testing equipment has provisionfor limited point-to-point testing built intoit in the form of the 'free reference point"switch system. Former analyzers alwaysmeasured voltages between the tube termi-nals and some common point, such as thetube cathode or ground. By means of the

3

4 SERVICING WITH SET ANALYZERS

new system, however, the reference orcommon point may be shifted, by meansof the proper switches, so that the voltage(and in some cases the resistance) may bemeasured between any two tube terminals,this being done rapidly and right at thetester, without having to break into thereceiver.

Since modern radio receivers are so vast-ly different from those which were con-structed from 1923 to 1926-the precisionand servicing care necessary now is also ofa much higher order. The equipment, asdescribed, is comparable to that of thelaboratory in efficiency, and permits bothrapid and accurate determinations oftrouble.

The circuits used at present are infinitelymore complex than those that were usedeven a few years back. The widespreaduse of multi -function tubes adds to theconfusion also, for in the older sets acertain tube could safely be assumed tobe doing one job only, while at present asingle tube may be employed for three ormore unrelated functions. A descriptionof a relatively simple set will prove thispoint. We will take as our example a setof the so-called A.C.-D.C. classificationwhich has a total of six tubes. This setis of the "all -wave" type so we are greetedat the start with a complex array of coils,thirteen in number, and a switch to selectthe required band. Next in line is amulti -function tube, the 6A7, which is bothoscillator and mixer. This is followed bya 78 tube as the I.F. amplifier, then an-other multi -purpose tube, the 75. This oneperforms three distinct operations. It isthe second detector, the first A.F. ampli-fier, and the generator of A.V.C. voltage.The second A.F. tube is a 43, a pentodeamplifier. The power supply is quite sim-ple in this type of set, since there is nopower transformer. However, this factimmediately leads to more complications,for the designer has used the 25Z5 rectifiertube as a voltage doubler in order to se-cure a higher voltage. The final tube, alsomade necessary by the lack of a powertransformer, is a "ballast" tube, which isnothing more than a resistor enclosed in abulb. So here we have a "simple" set inwhich three of the six tubes perform mul-tiple functions. How is the Service Manto "shoot trouble" in such equipment, anddo the job in such time that he will makea reasonable profit for his pains? The onlypossible answer is through the use of the

latest and most efficient type of analyzingequipment.

While we will not attempt to discuss thetheoretical design of receivers here, it willbe apparent to all that the removal of anytube or tubes from their sockets will dis-turb the voltage distribution to all othertubes in the receiver. In the older types ofreceivers it was almost the invariable cus-tom of designers to include in the powersupply circuit a fairly heavy wire -woundresistor, called the "bleeder", from whichthe various voltages needed for the tubeelements were obtained by means of tans.This stabilized the circuit to a certainextent, since the current through thebleeder was fairly high, so that if a tubewas removed, the overall voltage chancrein the circuit was not very great. Thepresent tendency seems to be to eliminatethe bleeder resistor, and to supply allvoltage needs by means of series resistorsdirectly from the high voltage lead. Thisnewer method of voltage distribution hasthe advantage that each individual tubeelement may be snnnlied with exactly thecorrect voltage, but it also introduces dif-ficulties in measuring these voltages. Whenan analyzer is applied to the tube terminalsupnlied by a series resistor, the currentdrain of the meter in the analyzer causesan additional voltage drop in the resistor,which must always be taken into consid-eration. Where the resistors are of a highvalue, such as those used in the plate cir-cuits of audio amplifiers, the drop is sohigh that the readings are not to be trustedin most cases, and we must turn to othermeans of measuring the functioning ofthat particular circuit. This is one of thelimitations of present analyzers, but as longas it is thoroughly understood, no harmwill be done.

The value of an analyzer depends uponthe fact that nearly every form of troublein a radio set manifests itself in irregularvoltages or currents.

When a Service Man arrives on the iobafter receiving a call, he should first satis-fy himself that the trouble lies in the re-ceiver itself. If the symptoms seem toindicate that tubes are bad, they should betested first; merely because that is theeasiest operation to perform and, usually,indicates the greatest source of trouble.If defective tubes are found, they shouldbe immediately replaced by good ones be-fore any other tests are made.

Plate, screen -grid and control -grid volt-

SERVICING WITH SET ANALYZERS 5

ages should then be measured, and thevalue checked by reference to manufactur-ers' data or tube charts. (The ServiceMan should make it a point to always havesuch information with him for referencepurposes.) If it is found, for instance,that only one tube has no plate voltage,then reference should be made to the cir-cuit diagram, to determine what can pos-sibly cause the lack of voltage on theparticular tube in question. Do not jumpat conclusions; but conduct a systematictest from the tube's plate through everysingle piece of apparatus in that plate cir-cuit, right down to the power unit. Inthis manner the defective piece of appara-tus is bound to be checked.

On the other hand, if, to take anotherinstance, three tubes that should have thesame voltage have none, then the troublelies either in the power unit, or else in apiece of equipment that is common to thosethree tubes ; and the attention of the repairman should be directed accordingly.

Abnormally high plate or screen volt-ages usually mean that the grid bias or"C" supply for the affected tube hasfailed. This is especially noticeable in anytube whose plate supply circuit does notinclude a high resistance. A tube that isresistance coupled to the following tubewill not show this high plate current be-cause the increased current causes a laro-evoltage drop through the resistor. In thiscase, however, other symptoms are readilyapparent, for the resistor will probablyshow signs of overheating.

Often a thorough check of the tubevoltages and currents shows that every-thing is correct. It is then necessary totrace through the set until the defectivestage is found, and to test every piece ofequipment in this stage until the poor unitis isolated.

This general analysis, which will be dis-cussed in detail in another chapter, illus-trates the absolute necessity of a devicewhich will facilitate the measurement oftube voltages and currents and permit thetesting of individual pieces of equipment.These fundamental essentials are to befound in modern analyzers. With moderncompetition in the field, rapid accurate ser-vice is not only desirable but absolutelyessential, if a Service Man is to get alivelihood out of his business. A modernradio set analyzer is the only piece ofequipment that affords the necessary easeand rapidity of operation.

From the above it may seem that all thatone has to do is to plug in his analyzer,manipulate a few buttons, and the trialsand tribulations of the receiver will be laidbare. This is not so. The only thing thatcan be expected of any analyzer is that itshall be a means for conveniently measur-ing the various voltages and currents atany tube socket with the tube connected tothe socket. The interpretation of the read-ings is left to the Service Man himself.However, by proper reference to tubecharts and circuit diagrams, coupled witha little knowledge and common sense, theaverage Service Man can locate trouble in

a relatively short time.There is often confusion in the minds

of some as to just 'what is an analyzer?'In the strictest sense we might say that ananalyzer is an instrument for testing volt-ages and currents at the tube sockets of areceiver. However, common usage has ex-panded the term to include various sup-plementary equipment, so that the modernanalyzer often contains a tube tester, ca-pacity and resistance (and often induct-ance) tester, a service oscillator, and other

economy, since the most expensive part ofthe analyzer, the meter, is used in theother circuits as well. It also makes forcompactness, a feature that the ServiceMan greatly appreciates after lugeing theusual heavy equipment around on his dailycalls.

One of the most desirable advantages ofan analyzer, aside from its primary func-tion, is its ability to test tubes. The cor-rect method of tube testing has long beena question of dispute. In this connection,the Service Man is usually not in a posi-tion to expend large sums of money onelaborate bridges which accurately measuresuch characteristics as mutual conductance(incidentally now, by the recent ruling ofthe I. R. E. "mutual conductance" hasbeen changed to "transconductance", Sm),A.C. plate resistance, amplification con-stant, etc. The Service Man is, usually,only interested, so far as tube checking isconcerned, to know whether the emissionis normal. For a transconductance test,the same instruments are usually employedbut a calculation is necessary. (This willbe explained in a succeeding chapter.) Asan added feature, most analyzers have ar-rangements which permit the use of eachinstrument, independently of the analyzer.This is a very useful device; especially if


tests are to be made on the bench asidefrom regular receiver work.

A small 3.0 to 4.5 volt "C" battery ishoused in most analyzers, in order to per-mit the use of one of the voltmeters as anohmmeter; the scale of the meter is thendirectly calibrated in ohms. This featureis a distinct advantage, where resistor re-placement is necessary. Some manufactur-ers have even gone so far as to includecalibration charts for inductance and ca-pacity measurements on the A.C. milliam-meter scale when such a meter is includedin the analyzer.

It is in the nature of things, that differ-ent manufacturers should include variousincidental refinements which they believevaluable (some of which have already beenmentioned and will be discussed in detaillater) with the result that the Service Manis usually at a loss to determine just whatkind of an analyzer to secure for his pur-pose. Unfortunately, another man's adviceusually does not apply to a particular case,and the Service Man is usually left tochoose for himself. His choice will prob-ably be determined first by the amount ofmoney he has available to spend, and thenby his requirements.

A few of the more costly instrumentsinclude an all -wave test oscillator which isbuilt right in. Most active Service Men,however, prefer to have this instrumentseparate, as it adds considerable weight andbulk to the already unavoidably large ana-lyzer. It goes without saying that it is

absolutely necessary for the Service Manto possess a test oscillator, since the ser-vicing of superheterodynes, which aregreatly in the majority now, demands theuse of such equipment.

There are other pieces of apparatuswhich are often included in the largercommercial set analyzers, and which forthat reason we must mention here. Forexample, when a test oscillator is usedto align a receiver, some sort of metermust be used to note the results of thealigning operations. The human ear is avery poor judge of sound intensity, there-fore some sort of instrument is neededto record accurately the changes in adjust-ments as they are made. The so-called"output meter", which is nothing morethan a low current drain A.C. volt -meterwhich records the output of the set result-ing from the use of a tone modulated testoscillator. In most cases the D.C. meterin the analyzer is used in conjunction witha small copper -oxide rectifier, as this com-bination draws very little current, and ob-viates the necessity of a special meter forthe purpose.

Other supplementary equipment which isused to test receivers, in conjunction withthe analyzer will be described briefly inanother chapter, as it is felt that the Ser-vice Man should have at least a generalunderstanding of equipment such as theV.T. voltmeter, the oscilloscope, the testoscillator and such apparatus.

Ir

CHAPTER 2

Analyzer Fundamentals

The modern analyzer must be designedwith several fundamentals in mind. First,it must be capable of performing everytask that the Service Man will require ofit in his daily rounds. Since it must becarried by hand a great deal of the timeit should be as light and compact as it is

possible to make it, without sacrificing anyof the necessary features. It is usual toprovide a small space in the instrumentcase itself for carrying the associated cableand all the adapters that go with it, aswell as test leads and any other equipmentrequired. It used to be the practice tocarry tools as well in the analyzer case, butthe instruments have so expanded in sizeand complexity that there is now little roomfor such accessories. Indeed, the worryof the designer is to make the apparatussmall enough to be called portable, and yetbe capable of doing everything the presentday Service Man wishes.

The final point to consider is that thecircuits should be made as near foolproofas possible, that is, it should not be pos-sible to ruin any of the apparatus by op-erating the wrong switch. This can becarried only to a certain point, of course,since no matter how perfect the circuitsare worked out, if the user has the volt-meter set to the 10 V. scale, and the meteris inadvertenly connected across a 500 V.supply, some damage is sure to be done.In this connection, low current fuses aresometimes used and are quite effective inpreventing meter damage.

.The SwitchesAnalyzer switches have to perform with-

out failure a multitude of functions. Theymust be very carefully constructed, sinceall action of equipment is dependent uponthem. The contacts must close positivelyand the contact resistance must be verylow, and as nearly uniform as possible.

Fig. 1. Types of switches used in analyzers.These are knife switches.

All the better switches now used haveeither solid or plated contacts of somemetal such as silver.

There are so many kinds of switches usedthat it is an impossibility to describe themall. An attempt will be made to discusssome of the more commonly used types, sothat the reader may become familiar withthe methods used in swtiching.

Diagrams of some of the more widelyused knife switches are shown in Fig. 1.

The abbreviations used are standard andare listed below for convenience.

S.P.S.T.-Single-Pole, Single -Throw.S.P.D.T.-Single-Pole, Double -Throw.D.P.S.T.-Double-Pole, Single -Throw.D.P.D.T.-Double-Pole, Double -Throw.T.P.S.T.-Triple-Pole, Single -Throw.T.P.D.T.-Triple-Pole, Double -Throw.

Knife switches are rarely used in ana-lyzer construction; not because they areinefficient, but because of the great deal ofspace required to house and manipulatethem. The basic principle of switching isthe same, regardless of the mechanical ar-rangement of the swtich.

The type most commonly used in analyz-ers is shown in Fig. 2A; this switch,known as a push-button type, is composedof four blades a, b, c and d. Blades aand c are tied together by a bakelite stripk. When the button S is pushed in, the


Fig. 2. Push buttons operate these switches.They are quite compact.

plug P pushes down blades a and c; sothat blade a makes contact with blade b,and blade c with blade d. When the fingeris released from S, the spring T removesP from the blades, and both circuits areopen. It is seen that this switch is similarin action to the D.P.S.T. knife switch ofFig. 1. This type of switch (sometimescalled a Jack Switch) is very small, rapidof operation and quite fool -proof.

This jack or push-button switch may, bysimple mechanical changes, be made to per-form a variety of purposes. For instance,Fig. 2B shows a push-button switch whichopens one circuit at the same instant thatit closes another. It may sometimes bedesirable to open one circuit a little beforethe second circuit closes ; this can easilybe accomplished by making the contact onblade d of Fig. 2B slightly shorter thanthat on blade a. By having a sufficientnumber of blades, it is possible to switcha multiplicity of circuits simultaneously.

Another type of switch that is widelyused is the so-called rotary type. Severalvariations of this are shown in Fig. 3.The first shown at Fig. 3A is the simpletap switch which, in this case, enables usto connect one lead to any of 5 others.This is not as flexible as is required insome circuits so the scheme at Fig. 3Bis used. Here either side of the circuitmay be connected to any of 5 other leads,enabling a much wider range of use. Asthe switches are shown, it is necessary to

Fig. 3. A few of the simpler types of rotaryswitches. Several arms may be used.

make connection to the arm by means ofa flexible lead. This is very undesirable,as such leads cannot be used for long with-out breaking. Therefore, connection ismade as at Fig. 3C, the end of the armopposite the taps being shaped so that itrubs on a semi -circular plate, the connec-tion to the circuit coming from this plate.

To enable still wider application, theswitches are arranged in "decks", oneswitch and set of taps to a deck. Thesedecks are piled up one above another, sothat all the switches may be operated byone common shaft. This arrangement isused in most present day equipment, as itenables the greatest variety of circuitchanges for the least space.

We have heard it truthfully said thatswitching is one of the most interestingproblems that the layman can find in electri-cal work. It taxes the ingenuity of the mind,without requiring detailed technical knowl-edge. No better examples of switching tech-nique can be given than those employed inthe modern set analyzer. At this time we

Fig. 4. Measuring filament current.

will not enter into a detailed account of thepossible switching arrangements which areobtained with the types of switches de-scribed heretofore; as that will be treatedat the end of this chapter, when we showhow a simple analyzer is to be designed.

Suffice to say that it is possible to designa switch for almost any imaginable circuitarrangement. Some of these will be pre-sented from time to time as the occasionarises.

The Milliammeter

The milliammeter is the basis of virtuallyall measuring equipment used in the setanalyzer and associated equipment. Forthis reason, we will try to detail the actualtheory of operation as much as possible inthe limited space available.

Stated fundamentally, every kind ofelectrical instrument (whether it be a volt-meter, ammeter, wattmeter, etc.) works


Fig. 5. Current passing through any coil ofwire produces a magnetic field.

simply because an electric current is flow-ing through it. As an example, assume thebattery of Fig. 4 to be lighting the tubeconnected to the battery. If it is now de-sired to measure the current passingthrough the filament of the tube, an in-strument called an ammeter is inserted, ineither leg of the line, as shown at A. Nowit does not matter in which leg of theline the meter is inserted ; since it willread the same in either case, because thecurrent coming out of the battery into thefilament must be exactly the same as thecurrent coming out of the filament at theother end, into the battery. Stated in an-other manner, the filament and the meterare connected in series across the batteryterminals. Furthermore, it is a universallaw that the value of the current in a seriescircuit is the same throughout each andevery part of the circuit. Since that is thecase, it does not matter in which leg themeter is inserted; the same amount ofcurrent flows through the instrument. Itshould be particularly noted that, with theinstrument connected as shown in Fig. 4,the current that flows through the filamentmust of necessity flow through the meter.

We come now to the question of whatmakes the meter read. The problem isvery simple when considered in the lightof elementary magnetism. Whenever acurrent flows through a wire a magneticfield is generated. The intensity of thefield is dependent upon the length of thewire and the strength of the current. Thefield flows in a direction as indicated in

Fig. 6. Two fields produce a motion.

Fig. 5.When the wire is placed between the

poles of a magnet, as shown in Fig. 6, aforce will be exerted upon the wire and ifit is free to move, it will do so in thedirection of the arrow. If the wire iswound into the form of a coil, the. fieldwill be as shown in Fig. 7. When sucha coil is placed in the magnetic field, wehave the elements of a moving coil meter,as shown in Fig. 8. Since like poles repeland unlike poles attract one another, thecoil will tend to turn in a direction indi-cated by the arrow. The turning tendencyis opposed by the hair spring, and theamount of turning is directly proportionalto the amount of current flowing in thecoil. The needle is fastened to the coil,and as the latter turns, the needle movesover the scale, which upon proper calibra-tion, will indicate directly the amount ofcurrent flowing.

Now if the meter is connected in the cir-

CURRENT ENTERS

n cl, el, (7), clin (i)

=N. S-7.

V 0 (DUO 01 0CURRENT LEAVES

Fig. 7. Determining field polarity.

cuit shown in Fig. 4, the 2 leads of themoving coil are connected into the circuit.If the meter is rated at 100 milliamperes,and more than this flows in the circuit,the meter will probably be damaged. Itwould seem necessary then to connect ameter of higher range in the circuit. How-ever, it is possible to use the original in-strument by placing a shunt across it.The following paragraphs will describe theconstruction and use of a shunt.

Since the moving coil is of extremely lightconstruction, in order that it may rotateeasily, it must be wound with very finewire. Practically, this means that theamount of current that can safely flowthrough this coil is very small-only a fewthousandths of an ampere. If the safecurrent -carrying capacity of the wire is,for example, ten one -thousandths of oneampere, (10 milliamperes or 10 mills.),how can the meter be safely placed in acircuit in which 2 amperes are flowing?

The meter is safe because not all of the


Fig. 8. The ammeter reads because the movingcoil is twisted in the field of the permanent

magnet, and turns on the axis.

current flowing in the circuit passesthrough the moving coil. As an example,let us assume that we have a meter with amoving coil so designed that, when tenone -thousandths of an ampere flow throughit, the meter reads full-scale. This meansthat under no conditions can more than10/1000 of an ampere safely flow throughthe coil. As the instrument is now, it isa 10 -milliampere meter.

If a resistance which is equal to theresistance of the moving coil is placed inparallel with the moving coil of the meter,then one half the current in the circuit willflow through the moving coil, and theother half through the resistance.

To take an example, the resistance ofour moving coil is, say, one ohm, and itrequires 10/1000 of an ampere through itto give full-scale deflection. We now placea one -ohm resistor in parallel with it, giv-ing the circuit of Fig. 9. If the currentflowing in a circuit in which the meter isnow connected is 10 mills., then 5 mills.will go through the meter, and 5 mills.through the resistance. The currentthrough the meter being now one-half ofwhat it was before the resistance was con-nected, the meter will, of course, only readhalf as much. If the current in the cir-cuit be increased to 20 mills., 10 mills. willgo through the moving coil of the meter,and the other 10 mills. through the re-sistance. The meter will now read full-scale.

It should now be noted that, without theexternal resistance, the actual currentthrough the circuit goes through the mov-ing coil and the meter reads the actualcurrent in the circuit. With the resistance

connected across the moving coil, only onehalf of the current in the circuit will flowthrough the moving coil, and the meterwill read only one-half the actual currentin the entire circuit. To obtain the correctcurrent. then, it is necessary to multiplythe meter reading by the factor 2 .

If, instead of the one -ohm resistor(which resistor is known as a shunt) a/A -ohm resistor was connected in, then onlyone-third of the total line current wouldpass through the moving coil, and the re-maining two-thirds would pass through theshunt. The meter would then read only

of the actual current in the entire cir-cuit ; so that it would be necessary to mul-tiply the meter reading by the factor 3,in order to obtain the actual currentflowing.

The addition of these shunts, then, per-mits the extension of the amount of cur-rent that can be measured by an instru-ment. The same meter whose moving coilcan safely carry but 10 mills., can, with theuse of the proper shunt, be arranged tomeasure several amperes. For conveniencea switch may be provided, to throw in anyone of a number of different shunts ; sothat different ranges on the instrument areavailable. This is shown in Fig. 10. Bysetting the switch on the proper tap, anyone of three ranges can be selected.

If the internal resistance of the meter isknown, then the resistance of the shuntnecessary to extend the range of the in-strument may be calculated from thefollowing formula,

R-r

n-1The symbols are as follows :R-resistance of the shuntr-internal resistance of the metern-the number indicating how many times

the meter range is to be multiplied.The use of this formula may be illus-

MOVING COILRESISTANCE1 OHM: CURRENTFOR FULL SCALE

DEFLECTION10 MILLS

EXTERNALRESISTANCE,

1. OHM

Fig. 9. A shunt alters the meter range.


trated by this example: suppose we have amilliammeter with an internal resistance of.01 -ohm and it has a scale range of 25 ma.The meter is to be made so that it willread up to 100 ma. Our factor, n, is then4. If we substitute these values in theabove equation it becomes,

.01R- -.00333 -ohm.

4-1The purchase of a resistor of this small

value and one that is accurate to about 5%or less is rather a problem. However, itcan be made quite easily. Suppose we takeour 25 ma. meter and put a current ofabout 20 ma. through it. Let us say theexact reading is 22 ma. Then, when wehave applied the correct shunt, the scalereading should be 22/4 or 5.5 ma. It isthen a simple matter to connect a piece oflow resistance wire across the meterterminals until the reading is exactly 5.5,with the same current as was previouslyused. We know then that the resistor isof the required value.

The D.C. Voltmeter

It has been stated that current must flowthrough an electrical measuring instrumentin order that it may function. The volt-meter is no exception to this, and, thoughit is not always understood so, a voltmetermeasures current, as will be shown.

Current flows in an electrical circuitonly because a potential difference exists.If the resistance is constant the amount ofcurrent flowing is directly proportional tothe voltage causing the current flow.Therefore, in a D.C. circuit, if the voltageis doubled, the current also doubles, and

Fig. 10. Modern instruments have several shuntsselected by a switch, with the meter sca e

calibrated in the various ranges.

11

Fig. 11. The resistor limits the current flowingthrough the meter.

so on. This means, then, that if an instru-ment is connected ACROSS (in shunt withthe circuit) the voltage to be measured,and if furthermore, the resistance of theinstrument is constant (as it always is),then the current through the instrumentwill be directly proportional to the voltageacross which the instrument is connected.In the formula of Ohm's Law, I (currentIntensity) equals E (Electromotive forceor voltage) divided by R (resistance).We may write this also E=RI, whichcomes to the same thing.

It is seen that a voltmeter, connectedacross a certain voltage has a current flow-ing through it; for the same reason thatany resistance connected across a voltagehas a current flowing through it. It is thiscurrent flowing through the meter that ac-tuates it; the manner of its operation beingidentical with that of the ammeter dis-cussed above (Fig. 8). Let it be stated atthis time that exactly the same movement("works") is used in the voltmeter as inthe ammeter; the only difference being inthe mode of connection. Let us examinethe mode of connection more closely.

If we assume that we have the samemilliammeter as before, that is, one witha scale reading of 25 ma. and an internalresistance of .01 -ohm, a voltage of .00025will be required to cause full scale read-ing. The formula is E=-IR or,

25E = .01 x - .00025-V.

1000

Such a rediculously small voltage read-ing would be useless to the Service Man,so we must find a means to use the in-strument on higher voltages while stillkeeping the current through the movingcoil below the maximum safe value (25ma.). We can do this by placing a re-sistance in series with the meter as shownin Fig. 11. If we want a voltage range


ia 000 a

O / 25,000 0.5-OHMS MEG.

/OHMS MEG

10.000 15,000OHMS / OHMS

0.4-MEG.

- +VS +25 +100 -CO

7OHMS5,000> +500 0 ;10 -125 4004'500

Fig. 12. Two methods of connecting the multi-pliers to a voltmeter.

of 10 V. and we know the current mustbe 25 ma., Ohms law gives the resistanceas follows:

E 10

R- -400 ohms.I 25

1000

The resistance of the moving coil is toolow to need consideration in this case, sothe series resistor should be 400 ohms.This resistor is usually called a multiplier.

It must be understood that the resist-ance of the meter cannot change, as it is

determined solely by the resistance of thewire on the moving coil. Thus, for a fullscale reading of 10 V. we need a resistanceof 400 ohms, or 40 ohms for every volt ofthe meter scale. It may be said that thevoltmeter has a resistance of 40 ohms pervolt. This is the common method of rat-ing voltmeters.

This method of expression is also use-ful in determining how much additionalresistance must be used to increase therange of voltage reading of the meter. Ifwe wish to raise the same meter to read100 V., it will require a total of 4000 ohms,

Fig. 13. A meter circuit arranged so that bothvoltage and current ranges may be selected sim-

ply by operating the proper switches.

or 3600 ohms more in addition to the firstmultiplier.

A current consumption of 25 ma. issufficient to make the meter useless forreading the voltages ordinarily found inradio sets, since the current drawn by themeter is higher than that in most of thecircuits to be measured. For example, ifthe screen grid of a tube is fed through aseries resistor and the meter is connectedfrom cathode to the screen grid socketprong, the current drawn by the meter willbe many times that drawn by the screen,and the voltage reading will be entirelyerroneous.

In order to obviate this trouble it is com-mon practice to use a meter which has amuch higher ohms -per -volt rating, or inother words, a higher sensitivity. Thecommonly accepted value is a meter of 1

ma. current drain, or one which will re-quire a series resistance of 1000 ohms -per -volt. For a voltage range of 100 V. sucha meter will have a resistance of 100,000ohms.

It is quite possible to use several multi-pliers with a single meter to have theadvantage of several voltage ranges. Twocircuits for accomplishing this are shownin Fig. 12. At A, the multiplier is in theform of a tapped voltage divider. At Bseparate resistors are used f or each range.The first method has the advantage of lowcost and simplicity, while the second hasthe advantage that a burned out resistorwill not make several of the ranges use-less. It is also more flexible in design andconstruction.

A simple circuit is shown at Fig. 13 forthe use of one meter 40 a multi -range volt-meter and milliameter (or ammeter). Anynumber of ranges is possible by the addi-tion of the required resistors and switchtaps.

The A.C. Voltmeter

A study of the operation of the D.C.meter will show us that if the direction ofcurrent flow through the meter is reversed,then the pointer of the meter will moveto the left instead of to the right. Thismeans that, if A.C. is sent through themeter, then during one half of the cyclethe meter will tend to move in one direc-tion and during the other half of the cycleit will tend to move in the opposite direc-tion. The result is that, at 60 cycles (com-mercial power frequencies), the needle doesnot move at all. To be able to read A.C.,


it is necessary to have a device that willmove in the same direction regardless ofthe direction of the current through themeter. This is what the A.C. meter does.

There are numerous types of A.C.meters, but only one of them will be de-scribed, since the A.C. voltmeters used inanalyzers are of this type. This is desig-nated as the Soft -Iron, or Iron -Vane, typeof meter. A sketch showing its internalconstruction is given as Fig. 14.

A small strip of soft iron M, bent intoa cylindrical form, is mounted axially ona spindle S which is free to turn. An-other similar strip F, which is more orless wedge-shaped, and which is largerthan M, is fixed inside a cylindrical coil;this coil C is wound with fine wire andconnected in series with a high resistance,(the multiplier). When current flowsthrough the coil, both iron vanes becomemagnetized. The upper edges of F and Mboth have the same magnetic polarity-forinstance, both "north" poles ; and the loweredges have the same magnetic polarity-both "south" poles. The two upper edgesrepel each other, and so do the two loweredges; with the result that the free vaneM moves. The pointer therefore moveswith it. When the cycle reverses, themagnetic polarity reverses (the upperedges become south poles and the loweredges north poles), but the repulsive forceis still there; consequently the meter movesin one direction only. The multiplier cal-culations for the A.C. meter are exactlythe same as for the D.C. meters describedabove.

While this type of A.C. meter is quiterugged and inexpensive, it is not widelyused in modern equipment because it isnot very sensitive. In other words, it isa type that makes rathQr high current tooperate it.

For this reason, and also as a measureof economy, modern test equipment almostexclusively uses the rectifier type of A.C.meter. This is simply a D.C. milliameter,of the low drain type, connected to a smallcopper oxide rectifier. The circuit isshown at Fig. 15, and is a diagram for anA.C. voltmeter. It will be seen that theusual series resistors should be used, toenable various voltage ranges to be had.

To offset the obvious advantages of lowcurrent drain and the economy of beingable to use the same D.C. meter for allpurposes, the rectifier type has a few dis-advantages as well The rectifier itself is

13

Fig. 14. The "works" of the iron vane meter.

somewhat sensitive to temperature changes,and also its characteristics change withage, with the amount of current throughit, etc. Also the scale of a rectifier typemeter is crowded at the low end as in otherA.C. meters. However some of thesefaults can be sufficiently compensated for,so that a very usable instrument resultsand this type of meter is almost in univer-sal use at the present time.

An Elementary AnalyzerIn developing a simple analyzer, the

reader should bear in mind that the fin-ished product is not suitable for home con -

Fig. 15. Connections of a meter rectifier.

struction ; since no mechanical or electricalconstants will be given. By describingsuch a theoretical analyzer, the authorhopes to accomplish but one purpose : topresent the fundamental principles behindall analyzers. By doing this, thus illus-trating the methods of design, the morecomplicated commercial types will be more

Fig. 16. One type of meter rectifier.


Fig. 17. An amplifier with and without tube.

fully appreciated than if this mode of ap-proach were not used.

Suppose a stage of A.F. amplification,such as that shown at A in Fig. 17, is

to be examined. For a very complete testit would be necessary to know the follow-ing constants :

(1) Filament voltages ;(2) Plate voltage;(3) Grid voltage;(4) Plate current;(5) Grid current.

Let it also be assumed that we wish tomeasure each of these with as few instru-ments as possible. To measure the con-stants listed above, a single meter wouldhave to be inserted at X to measure platecurrent; at Y for grid current, betweenpoints 1 and 2 for plate voltage; between2 and 3 for grid voltage; and between 2and 4 for filament voltage. Let it befurther assumed that we cannot break anyleads in the set to insert these instruments.

If the tube at A of Fig. 17 be removed,then the connections to the socket remainas in B. Suppose now, we take the baseof an old tube and solder leads from theprongs of the tube base to a socket outsidethe set. The set will function exactly thesame, whether a tube is inserted in theoriginal tube socket, or in the one outsidethe set with the tube base plugged intothe original socket, to complete the connec-tions. This is depicted in Fig. 18. It is

Fig. 19. Checking voltage at extension socket.

now possible to break any leads or insertmeters between any two points in the ex-ternal socket and, at the same time, keep atube connected in the circuit. This, itwill be recalled, is a necessary precautionin all tube service work.

Now that we have devised a scheme toget at the tube socket prongs withoutbreaking into the receiver wiring, we areready to tackle the problem of measuringall required operating characteristics of thetube with a single meter. This is simplya problem of switching. A point to beremembered here is that it is standardpractice to measure all grid and plate volt-ages with respect to the negative end ofthe filament or the cathode depending uponwhich type of tube is under test.

The circuit in Fig. 19 shows a simplemeans of switching a single meter so thatit may be used to measure plate, filamentand grid voltages. However several ad-ditions to this circuit are needed. In thefirst place, the filament voltage is almostinvariably much lower than that of theplate. If a range of the meter were usedthat would measure the plate voltage satis-factorily, it would undoubtedly, be too higha scale on the meter to enable an accuratereading to be made of the filament voltage.So we need to add a switch and severalseries multipliers to enable the meter tobe used at the widely different voltages wehave already encountered.The next difficulty we encounter in using

Fig. 18. The use ofan analyzer plug toextend socket leads sothat tests may bemade without disas-sembling the receiver.

Fig. 18. The use of an analyzer plug to extend socket leads.


the simplified circuit of Fig. 19 is that thegrid voltage will cause the meter to readbackwards, which is not of much help tothe busy Service Man. Therefore a switchmust be added to reverse the polarity ofthe meter so that it may be used withoutchanging any of the external connections.Fig. 20 shows this addition, which is usuallya simple DPDT toggle switch in most com-mercial instruments. Since it is locatednext to the meter in all circuits it may beoperated to change the polarity of the meterno matter to what use or on what scale themeter is being used. This reversal of themeter connections may be accomplished au-tomatically in the rotary switch by the cir-cuit of Fig. 21. However, the DPDTswitch is usually included as this feature isuseful in other connections as well.

We still have no provision to measureany of the current operating of the tube.To measure any current value, it is neces-sary to break a lead, so that the meter maybe inserted in series with the circuit of thatparticular lead. This may be accomplishedby the addition of more contacts on therotary switch and connections as shown indotted lines on Fig. 22. It will be necessaryto close the break at points X and Y whenthe meter is not in use for current readingson that element. An easier method is tohave a single push button switch for eachcircuit in which it is desired to read cur-rent. This method is shown in Fig. 23.

Many commercial analyzers use push but-tons to select the various meter ranges, bothfor voltage and current measurements. Thecircuit for voltage change by push buttonsis shown at A of Fig. 24, while B showsthe same system as applied to currentchanges.

Free Reference Point Testing

The latest and most widely used style ofswitching from one tube element to anotheris the "free reference point" system. It will

Fig. 20. Polarity reversing switch.

16

Fig. 21. Rotary switch to shift meter leads.

be remembered that we said all testing wasto be done from the negative leg of thefilament or from the cathode. These tubeelements serving as the reference point forall voltage measurements. In the freereference point system, we can use any tubeelement as the reference point rather thanbeing forced to use the filament or cathode.This is accomplished as shown in Fig. 25,by the use of 2 rotary switches. The switchpoints are numbered according to the stand-ard RMA numbering system. This num-bering system, by the way, has been madenecessary by the wide variety of tubes nowused. As an example, the type 76 tube hasthe control grid connected to the No. 3prong, while the 36 tube has the screengrid connected to the corresponding term-inal on its base. Therefore we cannot al-ways call the No. 3 terminal the controlgrid, or any other element, and a universalnumbering system became necessary.

If we wish to measure the voltage be-tween the grid and plate of our 4 prong

TOi

PLUG

L L

F. VOLTS I

-1_G. VoLis

1-1"

CURRENTVOLTAGE

MUST BE OPENY I TO READ CURRENT,

-CLOSED AT ALLOTHER TIMES.CURRENT SHUNTS

P. VOLTS

tJ

P. CURRENT

MULTIPLIERS

Fig. 22. Current reading leads are dotted.


TO PLUG

PUSH FORG CURRENT

PUSH TO MEASUREP CURRENT

.umm41=M%

5-11111W4.=UV INSULATED

INSULATED

Fig. 23. Reading current by push switches.

tube, we need only turn the selector switchesto the proper positions and the connectionis easily made. This sort of measurementwould have been impossible with the circuitof Fig. 22.

The completed circuit of the simpleanalyzer for 4 prong triodes is shown inFig. 26. If the fundamentals underlyingthe selection of this circuit are clearly un-derstood, it will be a comparatively simplematter for the builder to figure out thecircuit for an analyzer incorporating anynumber of ranges and for any tubes re-quired. In this circuit, provision is madefor external use of the meter with any ofthe voltage or current ranges available, andfor A.C. or D.C. measurements on the tubeterminals.

A few words as to the action of thevarious switches may be of help to the pros-pective instrument builder.

We have discarded the rotary switch ideaof Fig. 22 entirely, and have used push but-ton switches wherever possible. This makesfor the utmost flexibility throughout, muchmore so than the scheme of Fig. 21, for ex-ample. The free reference point selectors,SW1 and SW2 enable voltage measurement

Fig. 25. Free reference point switching.

between any 2 base prongs. When theseswitches are on the "EXT" contact points,the voltmeter is connected to the externalvoltage terminals. For any voltage meas-urements the toggle switch, SW10 must beon the voltage side. Also the meter willnot read unless one of the voltage rangeswitches is depressed. These are SW7,SW8, and SW9.

For any current measurements, whetherinternal or external through the terminals,EXT CURRENT, SW10 must be in theleft position. As a measure of meter pro-tection, the highest range current shunt,R1 is always in the circuit until SW'll orSW12 are depressed, each of the latterbeing of lower range. When making a cur-rent measurement, try the circuit first with-out depressing SWII or SW12. If thereading is too low on the meter to be ofvalue, then one of the switches may beoperated to lower the range.

The current buttons for reading plate andgrid current are connected exactly as inFig. 24 and should be operated one at atime.

Although the meter is marked as amilliameter, it is to he understood that itwill have several scales, and may be cali-brated and read directly in milliamperes or

volts.Provision is made

in" the meter circuitfor reversing andfor change fromD.C. to A.C. read-ings. Although A.C.current readings arevery seldom made,and many metersare not providedwith the correctscales for this use,the rectifier is usu-ally placed in the

PRESS

- READf

100 MA.SHUNT

50 MA. 10 MA.SHUNT) (SHUNT

PRESS TOREAD LOWER

RANGE

Ark METER WILL NOT READ UNLESS ) METER WILL READ 100 MA. UNLESS AW BUTTON IS PUSHED. BUTTON IS PUSHED.

Fig. 24. Voltage and current ranges may be shifted by push switches.


TOPLUG G

F+PUSH FORG CURRENT

/Wag

PUSH FORP CURRENTSW4

'IMr`Sw 3

EXT. CURRENT

F+SEL. SW

F-+ F+ GjP

F --40 EXT.EXT T EXT.

VOLTS

VOLTAGE RANGESSEL. SW .2

R1

CURRENT RANGES

R2 jc(Sw

R3 \SW 12

R5 RE,

SW.7SW8 t SW 9-

CURRENT

+-MA

SW.10TOGGLESWITCH

YOHMS ADJUST,

4.6/

4"NVVR7,

SW.5PUSHRECT.

A.0 FOR A.0

VOLTAGE

APUSH FORREV.SW.6

Fig. 26. An analyzer for checking 4 prong tubes only. It may easily be expanded.

circuit as shown. The voltage droppingresistors for the A.C. voltage rangesshould always be placed between the recti-fier and the external circuit. In this way,the current through the rectifier will al-ways be kept to a very low value, a mostdesirable feature.

It should be noted that although allswitches in this circuit except three areshown as push button types, they may be

of the locking variety, so that when thebutton is depressed, a slight twist willcause it to stay operated.

To expand this circuit for use with tubesof any number of prongs or elements, it issimply necessary to add current measuringbuttons and extra points on the selectorswitches. Also of course, the plug connect-ing cable, and analyzer socket must be cap-able of accommodating the required tubes.

CHAPTER 3

Use of the AnalyzerAlthough this is a book on the technique

and use of the set analyzer, we shouldspend a little time on consideration of thefactors which can make the use of theanalyzer a great deal more profitable andenjoyable.

Firstly, we must recognize that radioset trouble can come from several sourceswhich may be grouped into two headings,those inside the receiver and those outside.A surprising number of "defective" re-ceivers are so only because of some outsidesource of interference, which has no con-nection with the set.

A great deal can often be learned fromthe owner of the set as to what happenedwhen it ceased to function. Certain funda-mental questions may be asked, the an-swers to which will often give a lead asto just where to look for the trouble, andthus much time is saved and the job ismade more profitable in the long run.

Some points upon which to question theowner are as follows :

1-Does the receiver work at all?

2-Did it stop playing suddenly or hasit been getting worse for some time?

3-Does any time element enter into thetrouble? In other words, will theset work for a certain length of time,before going bad?

4-Does it make any queer noise beforeit stops working?

These and many others can be asked de-pending upon the circumstances, and ingeneral, the answers will be of materialhelp. In most cases the customer is onlytoo glad to help and those few isolatedcases where the opposite is the case mustsimply be taken as they come.

If the receiver is workable but an in-terferring noise is heard, remove the an-tenna and ground leads and short theterminals to see if the sound is comingin over the aerial. If the sound disap-pears or is greatly reduced it is in allprobability outside the receiver.

Other than natural fading, almost alltrouble from the outside is in the form ofnoise, so that it is quite a simple task toexonerate the receiver and set about trac-ing down the trouble in house wiring andother likely causes.

If it is quite apparent that the troubleis in the receiver, it may be either of twotypes, mechanical or electrical. The firsttype is usually quite easy to locate, al-though unfortunately, not always so easyto repair. Broken or worn out dials, poorinsulation on wiring, bent or broken shaftsand such faults come in this category.The analyzer is of little use in such casesand the finding and fixing of the troubleis dependent upon the mechanical abilityof the Service Man.

A list of the electrical troubles encoun-tered in receiver would be of little use tothe Service Man and in addition, it wouldlead to considerable confusion. However,the methods to be used for various trou-bles are the same for most any make ofreceiver so that an analysis of the moregeneral methods of testing will be mosthelpful.

The first angle of attack on a faultyreceiver is through the tubes. One methodof proving whether or not the troublecomes from this source is to substitute acomplete new set of tested tubes for thosethat are in the set. This is not very prac-tical however, since to carry a completeset of all the hundreds of tubes now onthe open market, to say nothing of carry-ing several of each type for sets using

18


more than one, is obviously ridiculous.Furthermore such a substitution would notshow just which tube was bad, if morethan one of the originals was at fault. Ifthe receiver itself is at fault, then theService Man will still not know for surewhether any of the tubes are useless.Another disadvantage of the substitutionmethod is that one never knows just whatis the matter with any particular tube thatis supposedly defective. And as a finalargument, it is quite possible for one ormore of the replacement tubes to go bad,which would, to say the least, be extremelymisleading.

So we come to the generally acceptedmethod, that of testing the tubes them-selves, and right on the job. This willresult in finding out for sure just which,if any, of the tubes are poor, whether anyof them are doubtful or apt to go badsoon, and exactly what is the matter witheach bad tube, a valuable point when oneis confronted by a sceptical set owner whohas to foot the bills

Having decided that an actual test ofthe tubes is required, we come now to theproblem of what tests are needed andhow they are to be made. Several areneeded, the most important as far as theService Man is concerned being the testsof emission and that of transconductance(or mutual conductance). Also, it is quiteusual nowadays to test a tube thoroughlyfor shorts between any and all elements.In addition, a "gas test" is sometimes used.

The emission test is one of the simplestand consists of connecting the plate andthe various grids together and applying avoltage as shown in Fig. 1. A plate cur-rent will flow and if the tube is in goodcondition this will have a certain valuewhich will be much higher than when thetube has been used for some time. A tableis usually prepared showing the correctvalues of emission for various types oftubes, and if one is tested and has a con-siderably lower value it is rejected. A tubewhich is just on the border line will prob-ably work quite well in most cases, butwill probably go bad in a relatively shorttime. Although the circuit in Fig. 1 isshown with batteries, it is quite possibleand in fact more practical to use unrecti-fied A.C. for all the required voltages,when this type of test is used in a regulartube tester. The tube itself acts as a

19

Fig. 1. A simple set-up for tube emission tests.

rectifier and plate current flows in theregular way.

The emission test is of some value butit is not sufficient to really show the worthof a tube, for the reason that even if theemission of a tube is quite normal, it is

possible that the grid or some other ele-ment is bent or displaced so that properaction is not possible. It is necessarytherefore to make a transconductance test.

Any tube will function in a radio setbecause the signal voltage on the gridcauses the plate current to increase anddecrease alternately. The greater this in-crease or decrease for a given signal volt-age, the louder the signal. The amount ofincrease or decrease of plate current, pervolt of increase or decrease of grid volt-age, is called the Transconductance of thetube, and is measured in MHOS (ormicromhos, as explained below).

Transconductance is therefore a measureof the "goodness" of a tube. Stated inanother way,

Change in plate current- transconductance

Change in grid voltage

To measure transconductance then, allthat need be done is to apply the normalgrid, filament and plate voltages to a tube,and then change the grid voltage by acertain known amount. The plate currentwill change, in response to this change ingrid voltage. This change in plate current,divided by the change in grid voltage, givesthe transconductance.

For example, suppose a tube be con-nected as shown in Fig. 2, with the switchS on tap 1; and that, at this position, thetube has 3 volts (negative) on the grid,


F.g. 2. Arrangement for transconductance test.An A.C. supply may be used for the heater.

and a plate current of 15 milliamperesflows. The switch is then thrown on tap2; which places 6 volts (negative) on thegrid. The plate current consequently dropsto. say, 5 milliamperes. We know, now,that a 3 -volt change in grid voltage causesa 10 -milliampere change in plate current.The transconductance is then

.01

3- .00333 mhos

The use of such small numbers as .00333is rather unwieldly ; so that, in practice,the micromho is used as the unit. Onemicromho is one millionth of a mho. Toobtain micromhos from mhos, then, multi-ply the fraction by 1,000,000. Performingthis operation in the case above, we get.00333 (mho) X1,000,000=3,330 microm-hos.

Most analyzers have provision for thetransconductance test, but few if any allowfor the emission test. The necessary volt-age for the grid shift is obtained from asmall battery which is also used for con-tinuity tests as will be explained later. Ofcourse, the other voltages must be ob-tained from a receiver, which makes thi:method of testing inapplicable in manycases where the receiver is not in workingcondition when the tubes are to be tested.For this reason, it is usually desirable tocarry a tube tester which will run fromthe A.C. line and thus have its own powersupply independent of the receiver. An-other reason for this is that the voltagesin receivers vary widely even on tubes ofthe same type which may however be usedfor different purposes. This makes it im-possible to draw up a table which willdefine what is a bad tube and what is agood one since the test conditions changewithin such wide limits, and the busy Ser-

vice Man has no time to stop for calcula-tions. About the only use, then, that atransconductance test made with a set Ana-lyzer will be is that it will show up atube that is totally unworkable. Becauseof this limited use, many manufacturersof the latest test equipment are leavingthis feature out of their new models, asthey feel that it is not of enough value tooffset the added expense and circuit com-plication.

Although never found in an instrumentthat may be called solely an analyzer, theshort test and the gas test are includedhere in the interests of completeness, asthey should be understood by the ServiceMan.

The short test may be made by a simplecircuit as shown in Fig. 3. The twoswitches are connected so that each prongof the tube socket has a tap on eachswitch, similar to the arrangement usedin free reference point testing. A neontube which draws very little current maybe connected in series with a voltage sourcebetween any two elements. A short willcause the tube to light. Also a leakagebetween elements will cause a light al-though of less intensity.

The gas test is required because a smallamount of gas in the tube will sometimescause the plate current to rise when thetransconductance test is made and foolthe Service Man into believing that thetube is a good one. It is made simply byapplying to the elements a voltage suffi-ciently high to cause the gas to ionize,when it may be seen as a blue glow. Thevoltage must be variable, as the same valuecannot be applied to all tubes. For exam-ple, a type 6A3 tube must be tested at a

Fig. 3. A simple tube short tester. Contacts areneeded for each tube element.


much higher voltage than a type 30. Inall cases, however, the test voltage willbe somewhat higher than that at whichthe tube normally is operated.

In most cases, the Service Man will findit sufficient to make an operating emissiontest of the tube in question. If the variouselement voltages are correct, and it isfound that the plate current is quite nearthat specified by the maker, the tube maybe quite safely assumed to be normal.

After the tubes have been found to begood and any poor ones replaced, theService Man is ready to proceed with thebalance of the tests on the receiver. Thejob now is to localize the trouble to assmall a portion of the set as possible. Theset may be considered to be divided intocertain sections which we may designateas : the R.F. section (including the I.F.circuits if the set is a superhet) ; the A.F.section; and the power supply. We canbegin by localizing the trouble in one ofthese sections, which will make it mucheasier to track the fault to its exactlocation.

The experienced trouble shooter knowsfrom his past work that certain troublesreoccur in certain sets, so that when hehas found in which section of the receiverthe fault lies, he can quickly spot theactual defect and remedy it.

With a certain amount of experience,troubles in the audio end of the set canbe separated from those in the radio -fre-quency end by a few simple tests. Forinstance, if the detector or any of theaudio tubes is tapped with the fingers amusical sound, not unlike that of a clearbell, will be heard from the loud speaker.If this occurs, then-as a first approxima-tion-the audio part of the set can be as-sumed to be normal ; if not, then this partof the set should be suspected and testedthoroughly.

For the moment, let us assume that theaudio -frequency end is normal. If the setuses a grid condenser -and -leak detector,then placing the finger on the grid con-denser will usually result in a loud whistle.If this does not happen, then the detectorshould be suspected and also tested.

If everything seems normal so far, thenthe radio -frequency part of the set shouldbe given a finger test. If the forefingeris slightly moistened, and the grid connec-tion of each tube tapped, a dull thudshould be heard before and after each tap.

Fig. 4. A common set-up of an amplifier.

21

If tapping the grid of a certain tube doesnot produce any sound then that tubeshould be suspected. This latter test canalso be used, with the some results, in theaudio end of the set.

The above mentioned finger -grid testsare based on the assumption that the gridprongs are easily accessible.. This is notalways so ; with the result that a set ana-lyzer must be resorted to in order tolocalize and locate the trouble.

Remove the first R.F. tube from thesocket, and plug it into the analyzer. Putthe plug of the analyzer in the same socketof the set from which the tube was re-moved. By manipulating the properswitches and buttons, measure the filamentvoltage, plate voltage, plate current andgrid bias. Compare these values withwhat the manufacturer says they shouldbe. (If you do not know what the manu-facturer's specifications are, then comparethe results of the tube measurements witha tube chart.) In any case, they shouldcheck very closely. This process shouldbe repeated for every tube in the radioset. If a grid leak and grid condenser areused, very little, or no grid -voltage read-ing will be obtained in the detector stage.

The greatest of care must be taken toproperly interpret the readings of the ana-lyzer, and these readings depend upon thedesign of the receiver, and upon what typeof circuit is being tested. This is extreme-ly important and emphasizes the fact thatthe Service Man should have a knowledgeof the receiver under test and just whattypes of circuits are used in it. If thisis not obtainable and no information of anykind can be found on the set, the circuitshould be traced out before trying to ana-lyze it, since otherwise there can be no


Fig. 5. Here the coupling medium is resistive.

certainty of just what any particular read-ing may mean.

Some of the more common methods oftube coupling will be discussed, so thatwe can see just what effect they haveupon the analyzer readings obtained.

Fig. 4 shows an amplifier stage, inwhich the input circuit is resistive and theoutput circuit is inductive. This circuitwould commonly be used in A.F. workbetween two stages. A voltmeter connect-ed between the cathode and the controlgrid -should theoretically measure the gridvoltage. However, as we have alreadyseen, any meter of this type draws current,so this current must also flow throughthe resistor R2. This current causes avoltage drop which is so large that themeter will probably hardly move at all.The Service Man would then be led tobelieve that there was no voltage on thegrid, which is not so. A tube which isoperating as a Class A audio amplifier hassufficient negative voltage on the grid topractically preclude any flow of grid cur-rent through the leak. Thus the full volt-age will be applied to the grid. Whenthe voltmeter is connected in however the

Fig. 6. An inductively coupled amplifier.

circuit is upset and the proper voltagecannot possibly be measured at the grid.

A typical example will show how largethis error can be, A type 76 tube has acathode resistor of 2700 ohms, R2, toobtain a bias of about 13.5 V. Supposewe choose the 10 V. scale of a 1000 ohms -per -volt meter to measure the grid voltage.If we attempt to measure the voltage fromgrid to cathode, we will simply be measur-ing the drop in the cathode resistor whichserves as the grid bias. Since the gridleak is of 0.5-meg., the total resistance inthe circuit will be 512,700 ohms, includingthe resistance of the meter. The gridbias voltage is 13.5 V., so the current flow-ing in the circuit may be shown by thesimple equation :

E 13.51- - -.000024-A.

R 512,700

The combined drop across the grid leakand the cathode resistor is shown by :

E = RI = 502,700 x .000024 = 12.06 V.

This leaves 1.4 V. to be read by the meter,which is obviously highly misleading.

When it is known that the input circuitis composed of a resistance load, eithershort this resistance or measure the gridvoltage across the cathode resistor (orother source) which produces the voltage.The latter method naturally gives no as-surance that the voltage is actually reach-ing the grid, so that this point must becarefully checked, and the Service Manshould assure himself that the grid tocathode or filament circuit is intact.

The same precautions should be observedwhen measuring the voltage in the platecircuit. Many receivers nowadays, in factthe majority, have detector and audio tubeswith a resistive plate load. Although theplate voltage is higher than the grid volt-age, the same conditions are to be foundand it is impossible to read the exactvoltage at the plate of the tube with anydegree of accuracy. In the case of acircuit similar to Fig. 5, where both gridand plate circuits include a resistive load,the precautions must be doubly observed.This situation is mainly encountered inresistance coupled A.F. amplifiers.

Another combination is shown in Fig.6, where both grid and plate loads areinductive. The inductances may be either


air core as in R.F. coupling transformers,or iron core as in A.F. units. In theformer case, the resistance seldom is over100 ohms, while even the resistance ofaudio transformers is usually below 5000ohms, and so in both cases the resistancemay be neglected and a fairly accuratereading will be obtained at the tubeelement.

The only other possible coupling com-bination is shown at Fig. 7, and is thatwhere the plate load is resistive while aninductance appears in the grid circuit. Itwill be quite apparent which of the fore-going precautions must be followed in thiscase.

Of course, it is possible for the ServiceMan to make allowances for the low read-ings obtained when working on a tubewith a resistive load. In fact, many ofthe manufacturers have presented withtheir service data, voltages charts takenwith a 1000 ohms -per -volt meter, as thisvalue is more or less standard. This is agreat help to the Service Man, since he isprimarily interested in what voltage read-ings will be obtained under practical work-ing conditions, and not in the theoreticalvalues. Here again, a precaution mustbe given. Some of the newer serviceequipment is built around measuring in-struments which have a sensitivity of 2000ohms -per -volt or even higher. Althoughthese new meters are a move in the riohtdirection, the Service Man who owns oneshould use care when he is following amanufacturer's data sheet, to be sure whattype of meter was used to measure thevoltages given.

Let us suppose that, during the courseof our tube measurements, it is found thatthe plate voltage is nearly normal, whilethe plate current is either too low or toohigh (either plate current condition mayresult), and there is no grid bias. Assumethe circuit is similar to that shown inFig. 4. The fact that plate voltage existsindicates that the grid -bias resistor R2(which is in the plate return circuit to"B-") is not open. It may be shorted;the condenser Cl may be shorted; or thetube's input circuit may be open.

Short-circuited condensers are not un-common ; so that the first place to lookfor the trouble is in the condenser. Thisshould be removed from the circuit andtested. (Methods of testing condensersand coils are given near the close of thischapter.) If the condenser is shorted,

Fig. 7. Combination coupling system.

23

then its removal should restore normalbias to the tube. If this does not restorethe bias then Cl is not shorted. Theinput device to the tube's grid whether itbe a resistance (as R1) a choke, or thesecondary of a transformer, should thenbe tested for an open. Finally the grid -bias resistor should be tested for a short.

In many circuits a single grid -bias re-sistor is used for several tubes. If this(corresponding to R2) is shorted thennone of the tubes getting their bias fromthe same resistor will have grid voltage.

In testing a piece of apparatus, it shouldbe completely isolated from the circuitelectrically before any tests are made.

Suppose our analyzer shows no platevoltage on a tube. Our next procedure isto test for voltage between points 1 and 4(see Fig. 4). If voltage is present be-tween these points, then-obviously-theplate coupling device (choke or primary ofA.F. transformer) is open and should bereplaced. If no voltage exists between 1and 4, then the condenser C2 should beremoved ; if its removal restores voltageto the tube, then C2 should be replacedwith a good condenser. If the removal ofC2 does not restore plate voltage, then thegrid -bias resistor R2 should be tested foran open, since the plate current of the tubepasses through this resistor. If this re-sistor also proves to be good, then thetrouble lies somewhere in the power unit.

The circuit of a conventional powersupply is shown in Fig. 8. All power con-nections to the tubes are shown but thevarious coils and other circuit elementshave been omitted for the sake of clarity.Assuming that the circuit is of the T.R.F.type, tubes VI and V2 are the R.F. am-plifiers, V3 is a bias type detector, V4 isan A.F. amplifier, and V5 is the outputA.F. amplifier. Grid bias for tubes VI


Fig. S. The power supply circuits of a typical T.R.F. receiver showing essentials only.

and V2 is obtained by the drop throughresistor R1 in the cathode leads of thesetubes. In addition, R2 is a variable con-trol used to vary the volume. It doesthis by changing the grid bias on the R.F.tubes, so the grid bias should always bemeasured with this control in the sameposition. It is standard practice to makeall measurements with the volume controlon full and the antenna and ground postsshorted, unless otherwise specifically stated.

With zero voltage on the plate of a tube(assume the one we are measuring is V2)then it is obvious that V1 should also havezero plate voltage. In other words, ifseveral tubes obtain their plate voltagesfrom the same point in the power supply,and one of these tubes has no plate voltage,then the others cannot have any (that is,if the coils, resistors and condensers inthe set are good). We have now localizedour trouble down to the power unit.

The next test is across the bleeder re-sistor, R3, where the full voltage of thepower supply should be available. Thisvoltage will be more or less independentof R3, although it will be a little higherif R3 is open. If no voltage is foundacross R3 all the elements of the filtersystem will have to be tested starting atR3 and working back to the rectifier tube,V6.

If Cl, C2 or C3 is shorted, very littleor no voltage will be obtained anywhere.If this condition is found, then the filtercondenser should be tested first, since ashorted filter condenser is about the onlypiece of apparatus that can be bad andaffect the voltage on all the tubes. An-other indication of a shorted filter con-denser is the white heat of the plates ofthe rectifier tubes. With Cl shorted, therectifier plates become white-hot, with no

voltage on the bleeder resistance. WithC2 shorted, both the rectifier plates andLl become very hot, and there is no volt-age on the bleeder. With C3 shorted, therectifier tube, V6, becomes very hot, withno voltage on the bleeder.

With the filter unit testing normal, andthe voltages on the bleeder still low orzero, the voltages on the plates of therectifier tube should be measured. Byproceeding in this manner, defective ap-paratus is bound to be found.

The problem of trouble shooting finallyresolves itself down to the testing of indi-vidual units. For this purpose the analyzeris indispensible. Fortunately there are onlythree properties used in radio sets, namely,inductance, capacity and resistance: andthey are supplied, respectively, by coils,condensers and resistors. We will takethese up in their order.

The Continuity Tesler

Now most analyzers have, as an integralpart of the device, a continuity tester orohmmeter. This is nothing more or less inits essentials than a voltmeter V connectedin series with a small battery, as shownin Fig. 9. With terminals 1 and 2 shorted,the voltmeter reads the battery voltage ;which is the same as the full-scale deflec-tion of the meter. If a resistance R isinserted between terminals 1 and 2, thevoltmeter reads less than the battery volt-age, because of the drop in voltage causedby current passing through R. The moreresistance between points 1 and 2, the lessthe voltmeter reads. This makes it possi-ble to mark or calibrate the scale of thevoltmeter directly in ohms, so that, whena resistor is connected to points 1 and 2,the meter reads a certain figure which is


the value of the resistance in ohms so con-'

nected.

Since this continuity tester or ohmmeteris one of the most important pieces ofapparatus for the Service Man, we shouldperhaps devote a little more space to adescription of the more usual types. Inthe circuit of Fig. 9, when the batterystarts to run down, the meter cannot bemade to read full scale. For this reasona variable resistor is usually included inthe instrument (as in Fig. 10) so that afull scale reading will be easy to obtain.When used only for continuity, this is notso important, but it is absolutely necessary,when the apparatus is used as an ohm-meter, because full scale in this case meanszero resistance. In practice, the test leadsare shorted, and the resistor adjusted untilthe needle reads exactly full scale. Theapparatus is then ready for use.

The higher the voltage of the battery,the higher the resistance must be to com-pensate for it and the higher the ohmmeterwill read on its scale. This circuit canand should be incorporated in the simpletest set shown on page 17, since as hasbeen mentioned before, it will be foundthe most used of any of the associatedequipment in the analyzer. The dottedlines connected to the terminals markedY Z are for this purpose. To use theohmmeter, simply plug into the XY term-inals, and make sure that SW10 is on theVoltage side.

Another type of ohmmeter that is be-coming increasingly popular is the so-called shunt circuit shown in Fig. 11. Thistype is especially good for measuringvoltages below about 300 ohms or so, andthis is just where the series type of ohm-meter circuit is of least use. The shuntcircuit can be read to about ,A ohm withquite good accuracy. This low range ac-curacy is of great importance when testingR.F. and I.F. coils.

It will be seen that the meter reads full

lig. 9. Measuring resistance with a voltmeter.

scale at all times until a resistance is con-nected to the test leads. Since these aredirectly across the meter, the less resist-ance there is in the external circuit, thefarther the meter pointer will move tothe left or zero end of the scale. Withzero resistance, there will be a direct shortacross the meter, consequently it cannotread at all and the pointer will be all theway to the left. If this circuit is incor-porated in an analyzer, a switch should beprovided to open the battery circuit whenthe instrument is not in use, otherwise thebattery will have a very short life.

Point to Point Testing

This type of testing simply means theuse of the ohmmeter to trace out indivdualcomponents of a circuit, and to find thoseat fault. This method of attack is anecessity when the Service Man has nodata on a certain set at hand, and has noknowledge of the circuit or the operatingvoltages. It then becomes necessary totrace out the circuit from point to point.Many Service Men prefer this method toany other.

Coil Testing

If a certain coil is suspected, it shouldbe tested first with the high resistance cir-cuit of Fig. 10. The reading to be obtainedwith a good coil depends upon the type.As has been mentioned before, most R.F.coils have a resistance below 100 ohms,and when we get to the high frequencycoils of the all -wave receivers, the resist-ance is often less than an ohm! A testof such a unit would show such little re-sistance that it might be suspected thatthe coil was shorted. However, most R.F.or I.F. coils have at least a few ohmsresistance, and can be tested quite accur-ately on the shunt type of ohmmeter. Atany rate, the test will show if the coil isopen or not.

Iron core coils of the type now quite

Fig. 10. The usual simple ohmmeter circuit.


Fig. 11. The low range shunt ohmmeter hook-up.

widely used for I.F. and R.F. purposes,as a rule have a lower resistance than thecorresponding air core units. However,iron core coils as used for A.F. work andpower supply equipment have, in mostcases, a reasonable resistance and may beeasily tested. Some of the exceptions arefilament windings, voice coils of speakersand their associated transformer windings,and the primary windings of some of thelarger power transformers. In these andsimilar cases, it is necessary to resort tothe shunt type of ohmmeter, if anythingother than a simple continuity reading isdesired. All coils should also be testedfor shorts to ground and shorts betweenthe windings if there are more than one.Most iron cores are grounded to the :_aas-sis and a short to the core would thereforemake the coil useless.

Most of the service notes now availablehave the resistance of the various coilsmarked right on the diagram or in accom-panying tables. When this is not so, andthere is some doubt as to the correct value,it is sometimes possible to test a similarunit on another set of the same type tofind an approximate resistance value.

Needless to say, great care should beexercised when testing coils or any othercomponent of a receiver, to be certain thatnone of the other circuit elements areaffecting the test. For example, if twocoils are connected in parallel, one of thesemay be open, yet a continuity test willshow it to be OK since the current willflow through the other coil. Naturallythe best proceedure is to remove all com-ponents from the circuit before testingthem, but this is entirely impractical tothe busy Service Man. In many cases itwill be quite obvious from the circuit that

. a coil may be tested while still connected,while in others it will be quite sufficient todisconnect one end of it from the circuit.

As a rule when a coil is defective, it iseither open or has a dead short. One of

the few exceptions is that of A.F. trans-formers, which sometimes develop a partialopen. This is usually easy to observe onthe ohmmeter, as the pointer will jumpback and forth over the scale. Such aunit will always be noisy in service.

Condenser Tests

A good condenser under test should dotwo things: (1) it should not allow D.C.(direct current) to pass through it ; and -(2) it should therefore accumulate andhold a charge, when its rated D.C. voltageis applied. When a condenser is leaky itallows D.C. to pass; so that, to test for aleak in a condenser, all that is necessary isto connect the terminals of the condenserto the ohmmeter. The needle of the ohm-meter should move a little (with the flowof current into the condenser to charge it,if its capacity is large) ; and then returnto its normal position and stay there. Ifit does not return to its normal position,but stays somewhere on the scale, the con-denser is leaky and should be discarded.

It is perfectly possible for a condenserto test O.K. on the small voltage used inthe ohmmeter, but break down completelywhen normal voltage is applied. To com-pletely test a condenser, the rated D.C.voltage should be applied for a few mo-ments, and then removed. The condensershould be allowed to stand charged forseveral minutes, and then discharged. If aspark occurs during discharge, the con-denser is good; if there is a weak spark ornone at all, the condenser is defective.

The above statement applies only to con-densers of large capacity; about V4. to IAmf. and over. For the smaller sizes, thecontinuity test described above is suffi-cient; it being merely sufficient to deter-mine whether or not the condenser isshorted.

It is perfectly possible for a condenserto be open, even though it is a rare occur-rence; an open condenser is one whichpasses neither D.C. nor A.C. This is dueusually to broken or unsoldered leads fromthe condenser plates to its terminals. Tolocate an open in a condenser of smallcapacity, without taking it apart, is prac-tically impossible. In the larger sizes, anopen may be easily found by connectingthe condenser to the ohmmeter of theanalyzer. If the needle of the meter doesnot move and return to its original posi-


tion, then the condenser is probably open.It is very useful to be able to measure

condenser capacity. Some analyzers, whichuse a high -resistance A.C. meter (which isnothing more than a sensitive D.C. meterwith a copper -oxide rectifier in series) arecalibrated in microfarads; to enable theuser to measure capacities from about 0.25to 15 microfarads, with an A.C. line -volt-age of 115 volts at 60 cycles.

Testing ResistorsTesting resistors really involves only the

measurement of the value of the resistance.If the result of the measurement is within10% of the rated value of the resistance,then it may be assumed to be good. If itis far from the 10% tolerance, then itshould be discarded. For all practical pur-poses, resistors may be measured with theohmmeter included in the analyzer.

CHAPTER 4

Associate Test EquipmentThere are several supplementary pieces

of equipment, some of which are containedin the more expensive analyzers with whichthe Service Man should be acquainted.Even if they are not in his analyzer, theyshould be included in his equipment, asthe day of the "single -meter Service Man"is at an end, and the present-day expertmust have all the very latest equipment todo a good job and do it in a space oftime that will allow him to compete profit-ably with others.

The V.T. Voltmeter

The vacuum tube voltmeter is an instru-ment that will measure voltages and yettake no appreciable current from the cir-cuit under test. It will be rememberedthat the usual voltmeter, even the so-calledsensitive 1000 ohms -per -volt variety takes agood deal of current to operate it, so muchso that it is of little use when measuringvoltages in, for example, the grid circuitof a resistance coupled amplifier. TheV.T. voltmeter will do this without dis-turbing the operating voltages and cur-rents of the circuit in any way. This is

fig. 1. A simple V.T. voltmeter. Almost anytype of tube may be used.

because it is entirely a voltage -operated in-strument, while the meter requires power(even though it may be only a tiny frac-tion of a watt).

Naturally we cannot get this action with-out getting power from somewhere, so asource of power in the form of batteriesor the usual rectifier system is needed.

A circuit of a simple V.T. voltmeter isshown in Fig. 1. It will be seen that theinput from the test prods is connectedacross the grid and cathode circuit of avacuum tube. The bias of the tube isadjusted by means of the potentiometer,R2, to any desired value as read on themeter, M. The test leads are then con-nected to the voltage to be measured whichwill cause a change in the reading of meterM. Resistor R2 is then adjusted to bringthe meter M back to its original reading.The difference between the readings ofmeter V, as originally set and at the newsetting of R2 will be the actual voltage atthe input. The actual range of voltagethat can be read depends upon the con-stants in the circuit, such as R2, batteryC, and the plate voltage battery, B.

It should be noted that as the battery Cis connected in Fig. 1, it is necessary toconnect the positive of the voltage undertest to test lead number 1. When thepotentiometer is originally set, the meterM will drop in reading, and the positivevoltage on the grid of the tube will tendto neutralize the bias supplied from bat-tery C, thus causing the meter to increasein reading. Further operation of R2 willnow again raise the bias on the grid andbring M back to the original reading.

When reading D.C., the condenser Clshould always be shorted by SW2. Whenreading A.C., however, SW2 may be open,and it should always be so when measur-ing the A.C. component where D.C. isalso present. Such a case would be the

28


Fig. 2. A dual range service oscillator. This is a simple type of limited use.

measurement of the A.C. at the plate ofa tube where the plate voltage would alsobe found.

SW1 is used simply to open the circuitof battery C so that the battery will notrun down when the apparatus is not inuse. This switch should be ganged withwhatever switch is used to turn the ap-paratus on and used mainly asa protection to meter M. Of course, meterV should be chosen to correspond with thevoltage of battery C.

The tube need not be a type 56 as shown,since almost any type will do. A pentode,such as the 77, 57, or 6J7, with all thegrids tied together will give even greatersensitivity than the 56.

These V.T. voltmeters are made in manydifferent forms and with many circuits,but all work on the orinciple that a vacuumtube is very sensitive to changes in gridvoltage, and since no power is taken bythe grid in this sort of service, there isabsolutely no drain upon the equipmentunder test, as there would be in the caseof an ordinary voltmeter, as described inprevious chapters.

The Test Oscillator

When a radio receiver is to be lined up,that is, when the various tuned circuits areto be tuned to resonance. it is necessarythat a signal be supplied to the receiver.It is quite possible to use the incomingsignal from a broadcast station in somecases, but this is never entirely satisfac-tory. In the case of a TRF receiver, abroadcast signal may be used with fairresults, if a local station is chosen. Adistant station is out of the question due

29

to the fading usually experienced. Whenwe have a superhet that is badly out ofadjustment, or one that has just been builtand never tried, it is virtually impossibleto get the proper alignment through theuse of a broadcast signal, since the I.F.amplifier is running at a frequency muchdifferent from the tuning frequency of theset.

The Service Man should always have athand a service oscillator or signal genera-tor as it is sometimes known. A circuitof such an instrument is shown in Fig. 2.This is a very simple type that is to beused with battery power supply and canthus be carried in a compact shielded casefor portable work. A single type 30 tubeis used, and by the use of SW1, the out-put frequency may be made to cover boththe broadcast and the I.F. bands. Thereare 2 output posts, other than the groundpost, the maximum which is used for alarge signal output, and the minimum,which gives a variable signal through theuse of resistor RI. Operation of SW3changes the value of grid leak and causesan audio tone to be emitted with the R.F.This is necessary when it is desired touse an output meter.

It must be emphasized that the circuitshown is that of a very simple unit. Mosttest oscillators now in use, both batteryand power line operated types, have pro-vision for servicing all -wave receivers.This means that they must cover wavebands from about 150 kc. all the way toaround 20 mc. without any skips. It isquite common to have a separate tube forthe production of A.F. modulation of theoutput signal, since better frequency


SPEAKER

CONNECT HERE,OR HERE

VOICECOIL

I °

SPEAKER

VOICECOIL

CONNECT HERE,

B+OR HERE

Fig. 3. Connection of output meter. The A.C. voltage at the voice coil is low.

stability, and greater flexibility may behad in this manner.

Some of large test analyzers include anoscillator in the same container, while inother cases it is used as a separate unit.At any rate, the use of such an instrumentis very necessary today.

The Output MeterThe use of a service oscillator enables

the Service Man to align a receiver to peakoperation. However, it is necessary to usesome form of indicator to tell when thebest adjustment has been reached. Theear is notoriously poor when it comes tojudging the volume of sound coming froma receiver, so trust must be placed in anoutput meter. This is simply an A.C.voltmeter of the rectifier type, as describedin Chap. 2. It is usually connected toreceiver as shown in Fig. 3. It is bestconnected somewhere in the plate circuitof the output tube, as the A.F. voltage ishighest here. It is quite possible to con-nect the meter across the voice coil of thespeaker as shown. Whenever the meter isconnected to the plate circuit, a condensershould always be in the circuit as thisprevents the D.C. in the circuit from en-tering the rectifier, where it would surelydo damage. It is safest to connect such acondenser in the meter circuit whenever itis to be used for output measurements, nomatter where the meter is to be connected.

It is necessary to have several voltageranges for this use, since the voltage maychange as much 100 V. or more duringadj ustments.

It is interesting to note that in setsequipped with any sort of tuning indica-tor, be it a "magic eye", a tuning meter,a "shadowgraph", or any other, there isno need for the use of an output meter.The tuning indicator on the receiver willserve perfectly in this capacity.

The Oscilloscope

This piece of apparatus is one of themost complicated that the Service Man canuse, and it also is about the most widelyuseful. While it is absolutely impossibleto go into the theory of the oscilloscopein the limited space at our disposal, wecan point out some of the uses of thisinvaluable instrument.

So far as the Service Man is concerned,the foremost use is that of providing agraphic and clear picture of the resultsof any alignment attempts made upon thereceiver. If the results are not what theyshould be, the picture on the screen ofthe oscilloscope immediately shows this,and shows just what results any furtheradjustments have.

There has recently been placed upon themarket a small oscilloscope tube whichmay be operated from voltages of a valuesuch as found in most radio receivers.This is quite an advance, since in thepast the voltages were usually over 1,000V., thus necessitating very expensive powersupply equipment. The new small tubecosts only about % what the older andlarger ones do, and this fact, together withthe lowered cost of the power supply, hasbrought the cost of a complete oscilloscopewithin the reach of most Service Men,something that certainly could not be saidof the larger equipment. While the screenof the new tube is only 1 in. in diameter,this is entirely adequate for any needs ofthe average Service Man, the larger tubesbeing needed only in laboratory and re-search work. Furthermore, the small sizeof this equipment makes it quite practicalto carry the oscilloscope on Service callswhere it might be needed, something thatwould be very impractical with the largerequipment.

Besides its use in aligning receivers, theoscilloscope has many other uses that are


of great benefit to the Service Man. Forexample, it may be used for distortion andphase shift measurements in amplifiers,calibration of oscillators, voltage measure-ments, all kinds of transmitter tests, andmany others.

When using the oscilloscope for align-ment purposes, it is necessary to use withit a "frequency modulated" oscillator. Thisis merely a modification of the usual testoscillator, and many of the latter have theFrequency modulation feature built in sothat it may be used when required. Suchequipment "wobbles" or shifts the fre-quency of the oscillator back and forthabout 10 kc. from the main frequency. Inother words, the frequency shifts a totalof about 20 kc. A circuit for an instru-

ment having this and other features willbe found in the commercial equipment sec-tion, as will a companion oscilloscope unit,using the new small -size tube.

Other Equipment

There are, of course, other pieces ofequipment that the Service Man will needfor certain jobs, but they are not includedin the Analyzer, are not usually used withit, and thus cannot be considered withinthe scope of this book. Such apparatus asthe Resistance Bridge, Beat frequency os-cillators, both R.F. and A.F., and the likecome under this heading. The serious Ser-vice Man will be able to find considerableliterature on such instruments, both inmagazines and specialized books.

CHAPTER 5

Commercial Test Equipment

RCA Frequency Modulated Oscillator

Fig. 1. The RCA No. 150 Frequency Modulated All -Wave Oscillator.

The equipment illustrated in Fig. 1 isknown as a frequency modulated oscillator.It will supply an R.F. output of about 0.25V. over the range of 90 to 32,000 kc.,this range being covered in 6 bands. Ap-proximately 30% A.F. modulation at 400cycles is available.

The frequency modulation feature isused in conjunction with an oscilloscopefor alignment work. The sweep widthmay be varied between ±-20 kc. at max-imum and ±0.5 kc. at minimum. Thisfrequency modulation is accomplished with-out the use of any moving parts, since itis entirely electronic in nature. A syn-chronizing voltage for the oscilloscope issupplied by the instrument.

Complete control of the output is possi-

ble. The various coils are aligned bymeans of air trimmers which assures perm-anent calibration. The power supply isself-contained and the instrument requiresabout 30 W. The weight is 17 lbs.

The companion unit, a complete minia-ture oscilloscope, is illustrated in Fig. 4.This uses the new 1" cathode ray tubeand the associated circuits include a linearsweep, synchronizing control, and verticaland horizontal amplifiers.

While these two units are designed tobe used together, either may be used sep-arately. The oscilloscope used alone willoperate as a sensitive A.C. voltmeter, andmay be used to check phase shift anddistortion in amplifiers, modulation intransmitters, A.F. wave form and so on.

32

SW

EE

PV

OLT

AG

EG

EN

ER

AT

OR

6C6

PIL

OT

LIG

HT

6.3V

.X

V2

X

FR

EQ

UE

NC

YC

ON

TR

OL I

IlI

II

0.1

-ME

kw..w

agiW

L%

tW

ME

I8

ME

G.

C_*

1 cn

1C

rLM

Er

MB

__ 4

onF

OR

40

IC

YC

LES

ON

LY25

,000

''O

HM

S

A-

FO

R 2

5C

YC

LES

ON

LY

.035

-

ME

.035

-

W.E

S5

0.1-

ME

5Q00

0O

HM

S

640

OH

MS

60C

YC

LES

ME

G.

39,0

0cO

HM

S

X V

3 X

.05

-M

E

5,60

0O

HM

S

\.01-

1110,

000

ME

x V

5 X

OH

MS

7M.,

,0.

1-27

0.,

9-29

EO

HM

S.y

rM

ME

II'4

MP

,

. 01)

0.1-

270

ME

GM

ME

/VA

RIA

BLE

OS

C. A

ND

MIX

ER

6A7

0.1

-M

E

.001

-

(426

i113

5#

5a 2

5-M

FM

E'--

--"

I, c

sy .

/910

OH

MS

_,

,yc0

AE

Ic1

60 C

YC

LES

,

.

RE

CT

8o -

Iuu

c0R

25E

-

7)iA

4

ON

LY

VI

X

6.3V

.

10m

i

MS

T

47,0

00O

HM

S

4400

111

OH

MS1

4-50

iMra

_E6,

800

A E

lk-

15

OH

MS

330

MM

E 4

SO

MM

E56

,000

OH

MS

6,80

0O

HM

S

440

OH

MS

ME

120

OH

MS

12 M

E

.007

ME

20 ME

ti 0.1-

ME

G.

X V

4 x

-

MM

E

I1

_,'

91F

IF7

XE

D,

R.F

.O.

- A

UD

IO-0

50

SY

NC

R 0.1

-

ME

0.1-

14..

C.W

27,0

00O

HM

S

-1I

II N

IO.A

*

5-45

M14

S3

-AM

PI,

FR

EQ

.

r-

4

NO

TE

'A"

SE

GM

EN

TN

EX

T T

O P

AN

EL

\R

AN

GE

K.C

.

SW

ITC

HP

OS

ITIO

NIN

K.C

.S

W.1

90-3

254r

2,50

0-7,

000

2.32

5-1.

000

5-7.

000-

14,5

003,

1000

-2,5

00 6

-145

00-3

2,00

0

MM

iI

0-0

0-0-

036

0 M

ME

ti

MM

E4-

25

4-V

25M

M-I

FI

00n0

,20

,000

OH

MS

1--

-1 / II

i

I_.

+,,,

I10

,000

I1,

200

10"

L_O

HM

SI

'OH

MS

OH

MS

Jy.

007-

110.

47JI

IM

EG

.

IM

ME

150

7 I

L

270

MM

E5-

45M

ME

I

am -

82 M

MF

.-

00b1

V-

47 M

M

0 00

0 0

\-

FOT

O 0

.

0 0

0-2/

P

SW

2

'660

0000

0

HO

-0

non

*Mt

312

Fig

. 2.

Circ

uit o

fth

e ap

para

tus

show

n in

Fig

. 1.

The

re a

re n

o m

ovin

g pa

rts,

the

freq

uenc

y m

odul

atio

n be

ing

acco

mpl

ishe

d el

ectr

ical

ly.

CO


0.1 -ME.

VERT.

G NOFF

0.1 -ME

913

SYNCHRONIZINGA P H

OFF

BLUE&YELLOW

3,5001 MEG.

MME

820 OHMSYNCHRONIZINGTRANSFORMER

I YELLOW G25-MEG.

GREENBLUE

2,700'OHMS

10,000

10.000OHMS

8.200OHMS

'820 .01- .035-MME. ME ME. ME. ME OHMS

20 OHMS

2014 CHOKE1.000 OHMS

100VROTA

BRN

WAt 2.70080 OHMS-

BROWN& BLACK

BLACK& RED

&IA,RED

& BLACK

2.SV.9 BLACKYELLMZ,

7 110V. A.0

ANODEDEE.

Ng I /PLATE G RID

*0 (46

P OP®PLATE

DEF.LOWER

cAmE4 , \ HEATERHEATER yi ANODE

913 1922

By itself the oscillator may be used asan A.F. or R.F. all -wave instrument, theA.F. and R.F. outputs being had eitherseparately or combined.

When used together for the alignmentand observation of tuning on a receiver,

the combined apparatus will provide anactual picture of the adjustments beingmade on the receiver. Such use is almosta necessity if correct operation of a multi-tude superhet set is to be had. The so-called "flat top" tuning curve is easy tosecure by this method.

Fig. 4. At top ofpage, the RCA No.151 Oscilloscope. Thisapparatus is illustrat-ed in Fig. 4 at right.A movable shield isprovided over thecathode ray tube endto cut off light. Con-trols are provided forcentering the beam,for focus and intensi-ty, fine and coarsefrequency sweep, syn-chronization, and on -off and gain controlsfor each amplifier.The power supply iscompletely self-con-tained and the appa-ratus weights 14% lbs.


LO. RES.

0-1MA.40

OHMS

0+0

0.26-MEG.

13

-- 0.5-MEG:

LL

12 °e --x`

2.3411 0.135-

OHMS10

40_1 MEG.

90. 5 - 0.149-24

OHMS 81 7 161,200OHMS,

MEG.

1.5V-

Fig. 5. The circuit of the Ranger Examiner Model 735 D.C. test meter. The small size makesthis very handy, as it may be tucked in a pocket or in the service kit.

RANGER EXAMINER MODEL 735 D.C. VOLT-

OHM.MILLIAMMETER

This compact instrument will be foundof great utility to the Service Man. Itwill probably be used not so much as amain test unit as it will an auxiliaryportable job which can be tucked in acorner of the tool kit or even in a largepocket.

It may be used for such purposes as :Check voltages, such as plate, grid,

screen, suppressor, battery, D.C. filament,drop across resistors, chokes, connections,field coils, etc.

Check current such as: plate, grid,

Vg. 6. Appearance of the tiny unit, the circuitof which is shown above. A 2 -inch meter is used.

screen, bleeder, total rectifier, electrolyticcondenser leakage, etc.

Check resistance and continuity such as :pure resistive circuit, chokes, coils, con-denser leakage, shorted connections, opens,etc.

The meter has scales to read to 750 V.,100,000 ohms, and 150 Ma. The meter hasa 0-1 ma. movement, thus giving a sensitiv-ity of 1000 ohms -per -volts.

An ohms adjustment is provided, andthe necessary 1.5 V. battery is included inthe case.

READRITE 720-730A SET ANALYZER

These instruments are complete resist-ance and voltage continuity testers in com-pact form. They may be used on radioreceivers, P.A. systems and for othersimilar work.

Although the set contains two meters,there is only a single pair of jack connec-tions for measurement of voltage, current,or resistance. Therefore, once the testleads have been plugged into the jacksthey need not be changed when shiftingmeter ranges or when testing from a re-ceiver socket.

One meter is used for the A.C. voltagereadings only and this does away with thecomplicated rectifier and switching circuitsordinarily needed for changing from A.C.to D.C. The other meter takes care of theD.C. voltage, D.C. current, and the ohmsreadings.

A simple arrangement of jack switchesis employed to connect the milliammetercircuit into any of the leads from the tubesocket for measuring element current. The


Fig. 7. The ReadriteModel No. 730A SetAnalyzer. Althoughthis is a compactunit, space is pro-vided for carrying theplug with its cord andadapters. The doublerow of jacks enablesthe user to connectthe meter to any ofthe tube circuits.

Fig. 8, below. Thediagram of the aboveunit. This makes itquite clear how thejacks are used foranalyzing purposes.Note the connectionsto the meter.

SOCKET

TO PLUG

I

GREEN^GRAY"'

A,B.0 D

-0

BLUE

WHITE

-0YELLOW

-0SOCKET

EGND T -C 7 6

I BLACK

7 P-0

4

BROWN

4 -RED

-o -0 -02

-03

S

3 4

0.149-MEG.(#7304 ONLY)

BATTERY CONNECTEDHERE WILL BREAKTHE

#720A.103OHMS

#730A-.67OHMS

#720A=1,2'75OHMS

#730A- 7.14OHMS

150OHMS

12

FF13

#7204 40,5001 OHMS

#730A: 0.135-o a MEG.

1.250OHMS

110 720A-45,000.3 OHMS

100 104 #730k 0.15-MEG.6,000

OHMS 9 0,5 7204,90.000OHMS

TJ 730A.0.3-MEG._WM&

BATTERYJACKS

0+


test leads from the meter circuit are sim-ply inserted into the proper jacks, andwith the selector switch set on the properscale, the current is quickly read.

OPERATION OF READRITE MODEL720A -730A

The operation of the 720A -730A is verysimple. Connect the pair of 31 cords whichare furnished with the testers to the jacksmarked "positive" and "negative". Theselector switch is set on the desired posi-tion for the voltage or current to be meas-ured and the free ends of the 31 cord areconnected across the voltage source. Re-member that to measure voltage, connectthe free ends of the 31 cord across thevoltage source, and to measure currentconnect the free end.in series with one sideof the circuit. To measure continuitiesand resistance connect the battery of theproper range as shown in the continuityand resistance chart across the battery-and the battery + jacks, observing thepolarity. Have the 31 cords plugged intothe postive and negative jacks, the selectorswitch set on the proper position as shownin continuity chart. Connect the free endsof the 31 cord across the continuity or re-sistance to be checked. To test Condens-ers use 60 cycle A.C. instead of batteries.

Furnished with the Model 720A -730Ais an eight conductor cable, one single wirethat has an alligator clip, the control gridwire, and five adapters.

Connect the 720A -730A to the radio setby removing the tube in the stage whichis to be tested, place the tube in the propersocket on the Models 720A -730A. If thetube is other than a 7 prong place theproper adapter on the plug and insert plugin the radio set socket vacated by thetube.

Now turn the radio set on. Allow thetube to reach normal operating tempera-ture and proceed to analyze the circuit,first by measuring the filament voltage bysetting the selector switch on the properposition either 10 or 25 volts, dependingupon the filament voltage of the tube. Ifthe filament voltage is below 10 set theselector switch on 10 volts A.C. Be surethe type 31 cords are connected to thejacks marked positive and negative andthe battery is not connected to the jacksmarked battery- and battery+. The fila-ment connections on a 4 base tube are No.1 and No. 4. As it is desired to placethe voltmeter across the filament, the free

ends of the 31 cord would be placed injacks No. 1 and No. 4.

After the filament voltage is determinedthe next voltage to be measured wouldbe the plate. Always be sure to refer tothe tube base chart to determine the re-spective number for the different elementsof the tube. In a 4 tube socket of the201-A type the plate voltage would bemeasured from plate to filament. The voltmeter would be connected from the jack(black) No. 1 to the jack (black) No. 2-No. 2 being the plate connection in thistype tube. As No. 3 is the grid connec-tion and grid is generally negative, it willbe necessary to reverse the procedure hereand connect the No. 31 cord, which is inthe negative jack to the jack (black) No.3, and the No. 31 cord which is in thepositive jack to jack (black) No. 1.

By using this method the voltage be-tween any two elements in the tube maybe checked. However, bear in mind thatvoltage is generally measured from thecathode and in filament type tubes theheater is considered as the cathode.

The black lead wire, which has the al-ligator clip, is connected to chassis orground. Voltages can then be measuredthrough the cable connections from theradio chassis or ground to any element ofthe tube. Bear in mind that the jackmarked positive should be connected to themost positive portion of the voltage whichyou are measuring. The jack marked nega-tive should be connected to the most nega-tive portion of the voltage which you aremeasuring. Do not forget to set the se-lector switch on the proper position forthe voltages or current you are measuring.

To measure plate current it will -be nec-essary to set the selector switch on theproper D.C. milliampere position, and asthe No. 2 socket contact is the plate con-tact, it will be necessary to plug the 31cords which are connected to the jacksmarked positive and negative to the redand black jack No. 2. Connect same sothat the meter will read forward.

READRITE TUBE TESTER-MODEL 430

Illustrated on next page are a front viewand the circuit of this new tube tester.There are two meters in the instrument,one of which is shadow type used to readthe line voltage, which must of course beset to a certain valixe every time the ap-paratus is used. The other meter is a


Triplett with a 0-8 ma. movement, and isequipped with an "English Reading" scale,so that tubes may be instantly classifiedas "good" or "bad".

The scales of the instrument are so fig-ured that a tube will show "had" on themeter scale if the tube has depreciatedmore than 35%. So that the meter mayhave a direct reading scale, it is necessaryto have a load in the circuit, and a loadcontrol used as a voltage divider is in-cluded, the settings for various tubes beingfound from the large chart carried in thecover.

The short testing circuit is very positivesince the main meter is used as a shortindicator. The A.G. from the power trans-former is rectified by a copper -oxide unitand is then applied to the tube elementsby means of the tube selector switch. Leak-ages in excess of a half a million ohmsmay be detected, which value is far beyond

CAP 3

1-1,000OHMS

6,500OHMS IY\AMI-

13

12

10

5

TC

45001.1M5

4

4

2,600OHMS

6OHMS

LINEMETER

PILOTLIGHT

CIO

30V.

*3

5 OFF4 3 2 1 TC

'10V.

-A

2.5a3°

6.3co --1 7.1

1.5OFF

25

30OHMS

15OHMS

1,000OHMS

10.2 hMP

145OHMS

QUALITYTEST

Fig. 9, top, Readrite tube tester. The circuit is shown in Fig. 10 directly above,


the sensitivity needed for this service.Since the elements are numbered accordingto the RMA standards it is a simple mat-ter to find which is shorted, if the metergives an indication.

Complete facilities are afforded for thechecking of all tubes with more than one

plate, such as the 19, 6A6, and all the dualrectifier types.

A pilot light is used in the form ofindirect illumination of the line voltagemeter so that there is always a positiveindication when the apparatus is turnedon.

RANGER EXAMINER MODEL 740 VOLT-OHM-MILLIAMMETER

The instrument illustrated below is ofthe universal type and may be used oneither A.C. or D.C. The ranges coveredare as follows :

0-10 50-250-500-1,000 A.C. or D.C. volts;0-10-50-250 D.C. Ma.; 0-300 and 0-250,000ohms, with provision for extension of thisrange to 2.5 meg. The meter is of the400 micro -amperetype, and is shunt-ed to produce asensitivity of 1,000ohms -per -volt onthe D.C. ranges.Through the use ofa special compen-sating circuit thesame sensitivity isavailable on theA.C. scales. A cop-per -oxide rectifieris used. A 1.5 V.battery is includedin the instrumentfor the ohms scales,and should haveexceptionally longlife, as the currentis only 2.5 ma. onthe low ohms scaleand 400 micro -A.on the high scale.The usual ohms ad-justed is provided.The switching isgreatly simplifiedthrough the use ofpanel jacks inwhich the test leadsare plugged, forthe various meteruses. Also a smalltoggle switch isprovided to changefrom A.C. to D.C.measurements.

A novelty is provided in the form ofa case with a small compartment for car-rying the required test leads and withroom also for a few small tools. Testleads and alligator clips are furnished.

TRIUMPH MODEL 77 OSCILLOGRAPH-

WOBBULATOR

Since it is necessary to use a frequencymodulated oscillator when aligning a re -

MODEL 740 VOLT OHM-MILLfAMMEFER

Fig. 11. The Ranger Model 740 Meter. Note the leads compartment.


siTNOEf MPL

Fig. 12, right. TRI-UMPH MODEL 420TUBE TESTER. Thisinstrument is of thetype mainly used forcounter display test,since it is laid outwith a sloping paneland may be had withan illuminated signto fasten on the top.It is of the loaded cir-cuit type, that is, aload switch must beset before the tube istested. A neon bulbis used as a short in-dicator. The line volt-age is observed on thesingle meter, and aline voltage regulatorwhich operates toshift taps on the pri-mary of the powertransformer, is usedto obtain the correctreading before test-ing.

0Fig. 13, below showsthe schematic circuit.

MEG.

990


6"1/1 11.)61f0.1- 1 10ME. MEG. ME

0.1- 1

ME MEG.Fa#

.2,200OHMS VI

X X

6A6o4

10 ME

0.1 -ME

0 25-

0.25-MEG. GI -

ME

25.0002 OHMS

MEG.

0.1- \---`ME

.-0.1-MEL_AAAAmi.- 2 MEG.

I 2i,0060.1- je OHMS

OHMS

120'OHMS

50.000OHM

50,000OHMS

55.000OHMS

18,200 L-0.OHMS

10,000OHMS

913TUBE

__E1 . V4,

MEG' I 2MEG. `MEG.

A/

4 2 MEG.

250OHMS

0.25-4 MEG,

2.5MEG

885 .0025-01- o35- ME 750

M ME0.25- N* MFME \101-

V2 200\ I\ I7 T

r\Yrtri-

5250MME

O1- 25000I M F. OHMS

6A7

swig,4*

01§Afi

Imo."750 OHMSMME

5000 t,OHMS 'mE

110V. AC.

0

V3

MEG.2.5

MEG

W2

MEG.

o. .6ME

4=Mr.

1111111M111WATII(20000 .000(20,000 5000

-OHMS OHMS OHMS OHMS

76'

(.01-REME.ME

25,000OHMSR.F.

OUTPUT

MF )

50.000- OHMS

10 10.000ME OHMS

V6

Fig. 14.14. Circuit of the combined oscillograph-wobbulator. The 76 tube is the wobbler oscillator.

strument is of great use to the ServiceMan since a frequency modulator is in-cluded in the unit. The apparatus may beused with any external all -wave oscillatorand is entirely electronic in nature, withno moving parts. There are terminalsprovided for R.F. input from the oscilla-tor, and output terminals for the frequencymodulated output to the receiver undertest. The necessary synchronizing connec-tions to the cathode-ray tube sweep circuitis made within the unit. The modulatedoscillator or wobbulator is fixed at a fre-quency of 840 kc. and is wobbled plus orminus 15 kc. Thus the desired frequencyfor receiver alignment purposes may beobtained by adding or subtracting this 840kc. with the frequency provided by theexternal all -wave oscillator. As an ex-ample, to secure 456 kc. for aligning areceiver I.F. stage, the external oscillatormay be set at either 1296 kc. or 384 kc.

The oscilloscope circuits may be usedseparately if desired. All the usual con-trols are provided. Either horizontal or

vertical amplifier may be used or may becut out and each has its own amplitudecontrol. Beam centering controls are pro-vided, although as a rule the beam will befound correctly centered.

A wide range of sweep frequencies arehad through the use of the coarse and finecontrols. The use of the locking controlis a great help in steadying the image onthe screen. In practice, the locking con-trol should never be advanced more thanenough to steady the image.

Considering all the apparatus included,the case is very compact, measuring 1334x 10 x 83/4 ins. deep. The weight forshipping is 16 lbs.

TRIPLETT MODEL 1250 V.T. VOLTMETER

The measurement of low Alternatingand Direct current voltages has becomeincreasingly important in servicing themodern radio sets, as well as in manyother applications. The ideal Voltmeterfor measurement in any circuit is one


which requires minimum current for itsoperation. Such voltmeters operatingunder nil current condition are now avail-able for the first time in a practical in-strument of unquestioned accuracy. TheTriplett Vacuum Tube Voltmeter is aninstrument of comparative high torque anddoes not depend for its super sensitivityon high resistance, as does the ordinarytype of instrument which consumes cur-rent in its operation. All current to oper-ate the Triplett Vacuum Tube Voltmeteris cancelled out by the unique nil method.It is necessary in a Vacuum Tube Volt-meter to have an instrument that is notdifficult to use and one in which the cali-brations are not subject to change in thetube value. Tube characteristics willchange and cause calibration changes whichupset the circut and brings about an un-certainty as to accuracy of the ordinaryinstrument. The cut-off adjustment is verycritical, which will vary somewhat withdifferent tubes. This characteristic alsoaffects the calibration even when the tubeis operated at low emission. The rangesof the conventional Vacuum Tube Volt-meter are limited, and if a meter shunt isused the saturation point of the tube issoon reached. The scales of the averageVacuum Tube Voltmeter are not linear,but are quite distorted, especially on rangeswhich cause the tube to work on a char-acteristic other than applies to the currentsquared scale. To overcome these de-ficiencies in calibrations which are de-pendent on the particular tube to whichthe circuit used in the Vacuum Tube Volt-meter of the conventional type is calibrat-ed, the Model 1250 Bridge Type VacuumTube Voltmeter has been developed.

The Model 1250 employs an entirely newcircuit of the Bridge Type in which thesecond tube is used along with a sensitiveGalvanometer to balance out the currentin the circuit, thereby making a calibra-tion adjustment each time a reading istaken. In this way the input voltage ofthe first tube is under definite control,regardless of what the characteristics maybe of the particular tube used in thatcircuit.

The type 76 vacuum tube forms thefourth arm of a Wheatstone Bridge alongwith two 6000 ohm and one 40,000 ohmresistor for the other arms. The resist-ance of the tube is controlled by the10,000 ohm variable rheostat which in thisway sets the bridge in balance and thus

eliminates tube calibration. When a signalis applied to the prods of the input leadsthe grid of the 6C6 tube goes positive up-setting the normal plate and cathode cur-rent of this tube and in turn upsetting thebalance of the Bridge. A bucking outvoltage can be applied to the Plate Cathodeof the 6C6 tube by Control No. 1. Whenthis equals the input voltage the currentthrough the 6C6 tube will be normal andthe Bridge will be in balance. Since thebucking out voltage is equal to the inputvoltage when the bridge is balanced, theD.C. Voltmeter placed in this circuit willgive a measurement of the input voltage.Any other type of the so-called "Slideback" method of balancing out the currentleads to inaccuracy and difficulty in ob-taining zero adjustment compared withthe bridge type used exclusively in theTriplett Vacuum Tube Voltmeter whichpermits adjustment to a very fine degreeby the galvanometer method.

The conventional Vacuum Tube Volt-meter using an input voltage divider bringsabout a decided disadvantage in the dis-crimination of frequencies. In additionthe voltage divider draws current from

source of voltage which is being meas-ured. It is important that the currentdraw be kept to a minimum since a draincauses a large error, depending upon thecircuit measured. The balancing outmethod in the Triplett Vacuum Tube Volt-meter makes unnecessary the use of aninput voltage divider and, therefore, thecircuit is undisturbed in relation to thefrequencies, and the amount of currentdrawn can in no way upset the circuit.

The Model 1250 Bridge Type instrumentassures accuracy in a Vacuum Tube Volt-meter which is entirely independent oftube error. Elimination of calibration andother errors in this newly developed cir-cuit is an outstanding feature that everyuser will appreciate.

TRIPLETT MODEL 1260 A.F. OSCILLATOR

The purpose of an Audio Frequency Os-cillator is to furnish an audible frequencyto test Audio Amplifiers, speakers, P.A.systems, etc. The circuit used in the model1260 is the familiar feed -back systemwhich has the ability to generate a purenote, is very stable and can be made withan accuracy of frequency far beyond theneeds of the service shop or Laboratory.This type of audio oscillator is generally

D C

., A

.G.

6C6_

\*0

.1 -

ME

0.1-

MF

LM

EG

.

mad V1

766,

000

OH

MS a V

2

OH

MS

40,0

00O

HM

S

10,0

00O

HM

S

40,0

00O

HM

S

7.50

0O

HM

S

SO

RA

NG

ES

WIT

CH

2,20

0O

HM

S

40,0

00O

HM

S

5M

EG

.X

0.1

-D

.4.0

-0-1

MA

0.1-

ME

G.

M E

GA

LV.

2.5V

.

'7

GR

OU

ND

CLI

P

SW

ITC

H C

ON

TR

OLL

ED

BY

RH

EO

ST

AT

CO

N-

TR

OL

IR

135V

. 135

V6.

5V.

.000

,6.

5V (2_(

)

P

V3

-r1.

16

6M

EM

E

-\-t

eigf

ft.f

110V

.X

rAP

PR

OX

I MA

TE

VA

LUE

FO

RA

.C.

CA

LIB

RA

TIO

N O

NLY

Fig.

15.

The

bri

dge

-typ

e ci

rcui

t use

d he

re a

ssur

es p

erfe

ct c

alib

ratio

n.T

he 7

6 -t

ube

is p

art o

f th

e br

idge

.T

his

is a

n ad

vanc

ed "

slid

e -b

ack"

V. T

. vol

tmet

er


mikrb.2 ii0.2=i NOTE SW. CONTROL -ME SMES ED BY RHEOSTAT R1

Fig. 16. Circuit of the Triplett Model 1260 A.F. Oscillator.

constructed on the same principle as radiofrequency oscillators except that large in-ductances are used which are generallyof the iron core type to improve the Qfactor.

The Triplett Audio Oscillator makes useof the negative characteristics of the 6C6Oscillator tube, as shown in Figure No. 1.This tube feeds the oscillation through a100,000 Ohm Potentiometer to the grid ofthe 76 amplifier tube. In order that thewave form may be as pure as possible theoscillator tube operates with low ampli-tude and the wave is amplified in such amanner that the power taken off does notupset the frequency. The frequencies fur-nished are 100, 250, 500, 1000. 2000, 3000,4000, 5000, 7500 and 10,000. As shown inFigure No. 2, the values are obtaned byplacing different capacities across the chokein the screen circuit of the 6C6 tube. Theselector switch is used for this purposeand to change from the iron core chokefor the first three frequencies to the aircore type for the last seven frequencies.

After the oscillations are amplified theyare passed to the universal Output Trans-former with secondary impedances of15,500 and 5000 ohms. The secondary im-pedances are connected to a switch andjacks. Two jacks are used for the output.The various secondary impedances are con-nected across these output jacks. The15,500 and 5000 ohm impedances are de-

signed to match the input of variousamplifying systems.

The power is furnished by an A.C. linesupply fed to the power transformerthrough the "OFF -ON" switch which isoperated by the gain control. The highvoltage of the transformer is rectified byan 84 full -wave tube and this current isfiltered by a conventional brute forcefilter.

The modulation is the tuned choke typeusing 30 henries and 275 millihenries chokesand nine condensers. The chokes aretuned by connecting the condensers acrossthe chokes with the control marked"FREQUENCY SELECTOR". This con-trol is marked with the fundamental fre-quencies availatle.

Operating Instructions

1-Connect tester to A.C. line of suitablevoltage and frequency.

2-Connect tester to audio amplifier usingthe two jacks marked "OUTPUT".The connections to the amplifier willvary with the make of the amplifieror P.A. system. However, on P.A.systems this will generally be made tothe phonograph pick-up jacks or themicrophone terminals. On radios whichhave connections for phonograph pick-up the Oscillator will connect to thephonograph jacks. When phonographjacks are not available, use the high


impedance setting of the impedanceswitch and connect jacks across theaudio grid input. In like manner eachaudio stage may be connected.

3-Set "OUTPUT IMPEDANCE" switchmarked 15, 500 and 5,000 ohms toproper impedance for the input of theamplifier.

4-Turn the Oscillator ON by rotatinggain control from OFF position to theright.

5-Turn the set audio amplifier volumecontrol ON.

6-Turn the set audio amplifier powerswitch ON.

7-After allowing the tubes to warm up,select the frequency desired by rotatingthe "FREQUENCY SELECTOR" tothe desired frequency.

8-Attentuate the signal to the proper levelby adjusting the gain control. Alwayshave the amplifier control on full.

9-While oral indications may be used, itis best to use visual means for indica-tion of the amplifier output.

Fidelity Curves1-Fidelity curves

should be runon all high fidel-ity Audio Am-plifiers. Thiscan be done bestwith the Trip-lett Audio Oscil-lator in conjunc-tion with Trip.lett Output me-ter.

2-Adjust AudioOscillator, as be-fore.

3-Connect outputto voice coil ofamplifier speak-er.

4-Set "FRE-QUENCY SE-LECTOR"switch to 1000cycles.

5-Adjust gain con-trol so that thespeaker does notoverload.

6-Adjust output to a point of about two-thirds of full scale. It may be neces-sary to rotate the gain control untilthis is accomplished. However, use theproper meter scale and the one whichdoes not permit the Amplifier to over-load.

7-Plot the reading on graph paper.

8-Rotate the frequency control to all thefrequency positions marked on panel,plotting each reading of the output onthe graph paper.

9-When the last frequency is plotted thecurve can be drawn and the character-istics of the Amplifier noted.

In making this test do not move thegain control.

TRIPLETT MODEL 1200-C METER

The Triplett Model 1200-C Volt-Ohm-Milliammeter has been designed for sim-plicity of operation, extreme accuracy-both D.C. and A.C., assurance againstabsolescence and a maximum of safety.

Fig. 17. Appearance of the Triplett Model 1260 A.F. Oscillator.


A most unique and practical arrangementis the separate A.C. and D.C. instrumentscombined in a single Bakelite case andfastened to the panel on two strong hinges.The purpose of this exclusive type ofmounting is to give an accurate readingangle at any position the tester may beplaced, thereby avoiding parallax, one ofthe most common errors in meter reading.Often the variations of readings due toparallax is greater than the difference be-tween precision and non -precision instru-ments. By pulling forward on the knob attop of meter case the Bakelite case housingthe two meters can be instantly tilted toany desired reading position, which willplace the meter scale in direct vision withthe operator's eyes.

The instrument scale readings are -0-10-50-250-500-1000 volts, both A.C. and D.C.The D.C. meter is used also for measuring0-.25-1-10-50-250 milliamperes and resist-ances-on a low ohm scale from .5 to 500ohms with approximately 13 ohms centerscale and on 1500 ohms, 1.5 and 7.5 meg-ohms scales with approximately 240, 24,000and 120,000 ohms center of scale. Allmeter readings are obtainable by settingthe selector switch to the proper position,marked to correspond with the scalenumerals. The zero setting for ohms

Fig. 18. Triplett Model 1200-C Volt-Ohm-Milliatneter.

readings is accomplished by adjusting themeter needle to full scale by using a smallscrew driver to turn any one of the threerheostats. The shafts of these rheostatshave slotted heads projecting through thepanel and marked "Ohms Adjustment".There is an individual rheostat adjustmentfor each of the megohm scale readingsmaking it unnecessary to readjust eachtime the scale is changed. A single rheo-stat controls the zero adjustment for theLOW OHMS and 1500 ohm scales as thecurrent consumed is the same, and onesetting serves for both adjustments.

Two jacks are used for the measure-ment of A.C. and D.C. volts, D.C. milliam-peres -1500, ohms 1.5 and 7.5 megohms.A third jack is used for the measurementof output voltages when the meter is usedin conjunction with an oscillator, and an-other jack is used when measurements aremade in the low ohms scale. No. 32 cordswith prods and tips are used in conjunctionwith these jacks. The output jack has acondenser in series with the meter move-ment to prevent the application of D.C.current to the A.C. output meter.

TRIPLETT MODELS 1231.1232 OSCILLATORS

An oscillator properly used is an aid toradio servicemen in the finding of radio

set troubles. Thereis no need to limitthe oscillator to asingle functionsuch as required inaligning tuning cir-cuits of a radio re-ceiver, as it hasmany useful appli-cations not com-monly known toservicemen or ifknown, not general-ly used.

An oscillator canhe used for nearlyall tests encounteredby the radio ser-viceman, includinglocating and isolat-ing actual defects;testing tubes in areceiver under ac-tual operating con-ditions. To appre-ciate and learn theusefulness of an

till1

1111

1411

1111

1122

.5V

./4,

500

OH

MS

65O

HM

S20

(:)

OH

MS

NO

TE

:X

. CA

LI B

RA

TIO

NR

ES

IST

OR

,A

PP

RO

XIM

AT

EV

ALU

E

20,2

00O

HM

S

25,0

00O

HM

S

19

18\\

17 .

14

90,0

00O

HM

S-

22,0

00O

HM

S

200

MIC

RO

AM

PS

450

OH

-/2

03

\ 4 5 6 7

810

z 2.

5M

EG

.

-1.2

5M

EG

.

1M

EG

.

ME

G.

50,0

00O

HM

S

10,5

00O

HM

S7,

800

OH

MS

1,60

0O

HM

SI

X3,

000

X4.

8X

7.8r

X 1

.512

0 kX

.393

OH

MS

OH

MS

OH

MS

OH

MS

OH

MS

OH

MS

WW

1*W

MA

,'

40 OH

MS

PE

R V

OLT

25M

A o LOW

OH

MS

O

A.0

-D.C

.v.

-0.

MA

.

0+ OU

T-

PU

T

5 ME

o

Fig.

19.

Cir

cuit

of th

e T

ripl

ett m

odel

120

0-C

test

er.

Not

e th

at2

met

ers

are

empl

oyed

, alth

ough

bot

h ar

e sh

own

here

as

one

unit.


X- APPROXIMATE VALUE

Q_Q.0 0 A -.) Q_OS)

--aQ,900 B

--jQ100 C-t00000j

ISM D

00/00 E - 0 0_0_0

US&

OS US)

OS 0 0 0

FVOQUO

1_

50,000OHMS)

-VVVW1-

soMME

\11

AUDIOSIGNAL

01 -ME

0.1 -MET /76'76

--- 850OHMS

300MMF

V2

450 utsj_OHMS MOD

--':o ,

Q psMOD

F.01 -ME

NOTE:COILS INDIVID-UALLY SHIELD-ED

530MMF

-08

-

E.

F

X 50MME

2MF

300V

1_

mE OFF

MF,,,ma_.00

u'110V. A.C.

850OHMS 1

AMAN

84

V3

300V,CT.

6 3V400 MA.

c, 6.3V.;800 MA.

300 MMF

2ME

400V

MIN.

O

MAX.

L50 OHMS GN D.,

Fig. 20. Circuit of Triplett Model 1232 Signal Generator. The line input is well filtered.

oscillator the radio set circuit should bestudied in order to understand how to feedthe oscillator signal into various parts ofthe circuit. Radio engineers mutually agreeupon one point of tube testing, i.e., thebest method of testing a radio tube for itsworth is under actual operating conditionssuch as the tube is subjected to in theradio circuit, accomplished by an oscillatorproperly applied to the radio circuit.

Most tube testing apparatus which ser-vicemen use comprises the so-called statictest. It is commonly known that a tubewhich may test perfectly under a so-calledstatic test will not perform under actualdynamic conditions. It is, therefore, highlydesirable when a radio set is brought tothe bench for repair not only to align thecircuit, but also "Testing of Tubes" bymeans of the oscillator. To use the out-

put meter properly, connect the oscillatorto the aerial and ground of the radio re-ceiver, adjust the attenuator so that thereis minimum signal voltage appearing acrossthe loud speaker coil. Connect the meterbetween the plate of the output tube andchassis. This signal voltage shows up asan audible whistle, or when using theoutput meter, as a deflection of the meterneedle.

All tubes should be in their respectivesockets and the voltage characteristics ofthe radio receiver carefully checked pre-viously to see that the proper operatingvoltages are being applied to the tubes.

In testing tubes by the oscillator methodthe A.C. signal is actually applied to thegrid of the tube. Proceed by connectingthe oscillator to the radio receiver and havethe output meter connected as above. The

signal is then atten-uated to a minimumvalue with all thereceiver tubes inplace. The logicalplace to begin a testis with the firststage. This may bethe R. F. stage or itmay be the firstoscillator detectorstage.

Secure a newtube of known per-formance ha v ingthe same character-istics as the one re-moved from thecircuit. Substitutethe new tube for thetube which is in theset and note on theoutput meter theincrease or decreaseof amplification incomparison withthe original tube inthe radio set.

A decrease in theoutput meter reading indicates the tubeshould be replaced. A reading of the samemagnitude would indicate the tube is per-forming satisfactorily. Proceed throughthe entire receiver stage by stage using thesame method.

Since the rectifier tube does not am-plify and is essentially a diode rectifyingdevice, we are primarily interested in theamount of current this tube will put outat the proper voltage for actuating theradio receiver.

After testing all the stages of the radioset it is logical to test the rectifier tubeby the oscillator method, although ourpreliminary check may have shown thistube to be putting out the proper voltageand the proper current. However, we cansubstitute a new rectifier tube for the onewhich is in the set and note if there is anyincrease in the indication of output meter.

The 1231 contains two type '30 tubesattached to the underside of the panel,which are accessible by removing the fourscrews holding the panel in the corners.The case also contains beneath the panela 72 volt battery and 3 ordinary flashlightcells. The 1232 contains a power pack and2-76, 1-84 tubes.


Fig. 21. Triplett Model 1232 Signal Generator. The Model 1231 is similarin appearance, but has set of batteries in the case.

The tubes and batteries should be re-placed when tests show they have depre-ciated approximately 35%. The powerpack is self contained in the 1232.

To connect the oscillator for use, con-nect the GND and MAX. jacks to theproper position in the radio set.

DEPENDABLE EQUIPMENT

Master Multitester Model 410

This instrument is shown on page 50. AllD.C. measurements are made at a sensi-tivity of 2,000 ohms -per -volt, while A.C.readings are at 1,800 ohms -per -volt. Anelectronic rectifier is used for the A.C.readings. The apparatus is capable ofmeasuring inductance, capacity and powerin decibels, as well as the more usual volts,ohms, and milliamperes. Below at left onthe same page is the Model 503, which,when used with a multimeter, provides acomplete set tester. It will accommodateall present tubes, and has full provision forthose with more elements which may bebrought in the future.

The unit at the lower right is the Model409 meter, which is quite similar to the410, except that it is in a more compact


Fug. 22. Dependable Model 410 Multitester.

case and has no facilities for measuringcapacity, inductance or power levels.

Both the 409 and the 410 feature a largefan -type meter which has a 0-500 micro-ampere movement. Both use the electronicrectifier, which does away with the dis-advantages of the more usual copper oxidetype.

Fig. 23. The Dependable Model 503 Analyzer.

meters, both of whichtroled from one shaftThe apparatus may heimum of switch setting, yet affords veryfine results.

The instrument is housed in a GoldenOak case with a panel finished in antiquebronze. A leather handle which lies flat

SUPREME MODEL530 OSCILLOSCOPE

This unusual in-strument uses a 2"tube, a radical de-parture from all theother popular pricedunits which haverecently beenbrought out. Thismodel has no linearsweep, but has pro-vision for 60 -cyclesweep. A verticalamplifier is avail-able, and may becut out if not need-ed. Another featureis the return sweepeliminator, which isvery useful whenusing the 60 -cyclesweep frequency.The spot may bepositioned by meansof two potentio-are separately con -through the panel.used with the min -

Fig. 24. Dependable Model 409 Multimeter.


SW.

- 1AMP

I

V1

45,0005T4 OHMS

C6.3V

z6.3V.

0.1-MF-

0.22Y1 ME

PILOTLIGHT

z

10160 910MEG.

OHMS

4ME

045-MEG./

0.15-MEG.

37,000OHMS

0.75-MEG.

40,000OHMS

0.5-MEG.

0.5-MEG.

75.000OHMS

'`'0.13-MEG.

50,000OHMS

27000OHMS

z V2 z

`.0022 ME

2 ME

I4

4ME

3'7 24-XHMEG.

V3

0.33-MEG.

6J7 T

0.5- MEG.

1'

Y

0.25- 7ME

a 5-MEG.

0 HOR-EXT.

GND.

© VERT.

_=-C) GND.

Fig. 25. Circuit of the Supreme Model 530 Oscilloscope. A new 2 -inch tube is used.

when not in use is fastened to the top.All the parts are selected for the longest

possible life, an example of this being theresistors, which are of the Bakelite encasedtype throughout. The power line is fusedon both sides with special quick -actingfuses for perfect protection. A pilot lampis on the panel and gives a sure indicationwhen the equipment is turned on.

The apparatus may be used for a greatvariety of tests. It is especially welladapted to making modulation percentagetests on transmitting equipment. It isalso useful in studying A.F. waveforms.It may be used for either single or doubleimage alignment of radio receivers, whenused in conjunction with a signal generatorwhich has a means of frequency modula-tion.

The special cathode ray tube which isused in this instrument is a new develop-ment, and is of the glass type, similar tothe larger 3" tubes. It has a screen areaof 3.14'sq. ins., which is about 4 times that

of the 1" tube. The tube is thoroughlyprotected by a magnetic shield in the case.

SUPREME MODEL 535 OSCILLOSCOPE

This instrument has all the features ofthe unit described on page 51. In addi-tion, it has a wide range linear sweep.This includes a coarse and a fine frequencycontrol, the total range being from 15 to30,000 cycles and over.

Besides the vertical amplifier, as usedin the Model 530, a horizontal amplifier isalso included.

Means are provided for synchronizationof the sweep voltage so that the imagemay be quickly "locked in".

The sensitivity of the vertical amplifieris about 0.7 V. per inch, while that of thehorizontal amplifier is 0.8 V. per inch.

Metal tubes are used for the amplifiersto afford perfect shielding, and each am-plifier has a separate ground pin jack.


VER.INPUT

OFF ON

0.2-ME

VERT.GAIN

0.5:7MEG.

.0022-

V1

'6J7

35,000OHMS

0.1 -ME

885 EXT. SYN4--)-2.

V2X X10,000OHMS

4ME.

(910OHMS

_V

xx I

/ I

35,000OHMS

4MF

0.2 -ME

0.5-MEG.

HOP.INPUT

`SYNC.SEL.3,000INT. 60 OHMCYCLES SYNC.

EXT. CONTROL200 OHMS

FINE FREQ. -0.82-5 MEG. MEG.

.0026- 1200.25 -ME .027 -ME ME MMF.y

irLIIIIILV'is6N1(6Vii61/16-V

v7/7,7v7v7(0.1-MF 0068 -ME. '550MME-4,

V`%/ N/V V V VVRANGE SELECTORvy vvvv vy

MME0.1 MEG.

V4

60CYCLES

6J 7Y

VHOP.GAIN

EXT.SWEEP v

910OHMS

lon,<"

0.2 -ME35.000 I1400 VOHMS 7

24XH

It

3.7

(MEGAA

22,000OHMS

62,000OHMS

23000OHMS

1,000OHMS

0.2-MEG.

0.13-MEG.

I I-

50.000OHMSFOCUS

40,000OHMS

180.-MMF

20,000OHMS

z

V3

0.5-MEG.

/ 200MME

/

25 k___ /10 5,000 0.1-/2'

MF ME. OHMS NiF.25V. INTENSITY

.0 2-MEG

INT.

`L.

_Y

4ME

-3.700 OHMSV5

.0022 ME' r INTSWEEP

0.5-MEG. +117t

V6,3vVX XzzketkPILOTLIGHT6.3V.

117V. 0.10psw.

2.55116.3Y. 5V

Fig. 26. Supreme Model 535 Oscilloscope with linear sweep circuit.

SUPREME MODEL 550 DELUXE RADIO

TESTER

One of the outstanding features of thisnew tester is the use of a radically new typeof meter. Previous meters on test equip-ment needed so many scales that the read-ings were often difficult to interpret. Theohms scale in particular led to confusion,since it is so crowded at one end.

The so-called quadrimeter used on thistester has a double scale arrangementwhereby one meter movement is made toserve for two separate sets of scales. Sincethe ohmmeter scale is one of the most con-fusing due to it's non -linearity, this scale isplaced separately from the others. All thescales are very long and easily read.

The panel of the apparttus is of etchedantique bronze and the case is of Golden


Oak. The latter has an easily removablecover, and there is room in the case tocarry all the necessary test leads and otherconnections.

Complete facilities are provided for test-ing tubes by the use of the grid shift test.This, of course, entails the use of powerfrom the receiver being checked. All typesof tubes including triodes and multigridtubes may be checked in this manner (aswas described in Chapter 3).

Resistance readings up to 200,000 ohmsare made by the use of a 4.5 V. batterycontained in the case. When higher rangesare required, use is made of a small built-inpower pack, and readings may be made allthe way up to 20 megs.

Electrostatic capacity leakage tests areeasily made, and it is not necessary to ob-serve polarity when connecting the con-denser to the circuit.

The use of the copper -oxide meter recti-fier circuit allows the use of the instrumentfor conducting output tests and for A.C.measurements. A.C. measurements aremade on the same scales as the D.C. meas-urements, thus greatly simplifying the read-ings.

This apparatus is very useful for testing

in other fields than radio receivers. Sincevoltages up to 1,400 V. may be read, theequipment will be very useful to the trans-mitter engineer and the P.A. or theatresound system Service Man. Special con-nection leads are made for the latter use.

The d.b. readings run from -10 to +46,and capacity ranges from .002 to 14 mfd.Currents may be read up to 14 A., in D.C.only.

CLOUGH-BRENGLE VACUUM TUBEVOLTMETER

This apparatus has been designed to havethe widest possible range and yet alwayswork on the linear part of the tube charac-teristic. There are three scale ranges, 0-1.2V., 0-10 V., and 0-100 V. The circuit issuch that both the square law and peakmethods of measurements are applied incarefully chosen ranges.

Normally the equipment is used with thetube placed in clips inside the cabinet. Thismakes it very conveniently portable. Underthese conditions of operation, the input cir-cuit consists of 300 mmf. in parallel with10 megs. However, if a lower input im-pedance is desired, or if it is desired to elim-inate excessively long leads between the

Fig. 27. The new Supreme Model 550 Set Analyzer. A special "quadrimeter" is used.

14 A

MP

.02

OH

MS

TE

ST

LEA

DS

0-30

0O

HM

S

2

ELE

CT

RO

LYT

IC

0-1

MA

118.

5O

HM

S

1(O

HM

Sja

?'

14A

MP

) D

.CV

.!D

EC

DC

MA

AC

V.

OH

MS

NE

ON

LA

MP

.01

-0.1

-M

E -

11

ELE

CT

RO

-S

TA

TIC

CO

'M

E

--A

AA

AA

{-60

0 O

HM

S

ELE

CT

RO

LYT

ICT

O A

NA

LYZ

ER

PLU

G A

ND

CA

BLE

450

TC

.8

76

5.4

32

350

AA

1_1

_2.

000

OF

F20

,000

0.2

-ME

G. 2

.ME

G. 2

0ME

G.

..- ,...

OH

4.5V

. BA

TT

ER

Y26

,000

OH

MS

7_M

S_

0.32

11

. M E

L'

OH

MS

-B

AT

TE

RY

6,70

0O

HM

S

0.50

1 -

ME

VO

LTS

28°,

000

10.2

1-P

0.35

-(0

.7-

ME

G.

ME

G.

ME

G.

.045

8 0.

0185

- .0

085-

.004

8- 6

0197

MP

ME

. M

E M

E M

R.

735

140

350

700

1400

x2,3

48 e

7,06

722

3.99

8O

HM

S O

HM

SO

HM

S

O+

10+

20+

3044

0

TO

PC

AP

10,0

00O

HM

SM

I

7,50

0O

HM

S2W

.-'

17,5

00

RE

V. A 1

AM

PF

US

E

)P

LO

T L

IGH

T

Fig

. 28.

Dia

gram

atic

vie

w o

f the

Sup

rem

e M

odel

550

Del

uxe

Set T

este

r.A

sel

f-co

ntai

ned

pow

er s

uppl

y al

low

s ve

ry h

igh

resi

stan

ces

to b

e re

ad, a

nd m

akes

poss

ible

com

plet

e co

nden

ser

test

s.T

he r

ows

of d

ots

repr

esen

t dec

ks o

n th

e se

lect

or s

witc

hes.


O

O

GND

10MEGS

VON ..v. 20%

-

L

1116F5

SW.4

V1

.05 -ME

RED

.005MF

I

-

BLACKGREENS/

PLUG(BOTTOM

VIEW)

SW.1

r --

RECT.5Z4

r I ME400v

-JCHOKE 40 ME

25V.-,

4 MF 100450V OHM+ (EA.) + POTc ZEROININ ADJ.

V2RI

: 110V.PILOT LIGHT

LI6.3

A.C.V.

x X

L.H R.H.

200 1.OHMPOT onPEAK 100BIAS OHMS.ADJ. 'kW

sagir,

0.5 -ME

200V.

0.1-M EGWt 101

17000OHMS

IOW.±27.,

SOCKET(TOP

ZIADEA

ALTS SW.

MA.

7

cI

SW.2 IOMSONt 21.000

V2W. +21.-H8%

0.19 MEG 1W,+27.89.

0 1-MEG.

1W±107.

Fig. 29. Clough-Brengle Vacuum Tube Voltmeter with tube -type test prod.

tube input and the circuit under measure-ment, the tube prod may be removed fromthe cabinet and connected in close prox-imity to the circuit under test. The inputimpedance directly into the grid of the tubeis 8 mmf. when used in this manner itis imperative that there be a closed circuitfrom tube cap to return, with no seriescondenser.

CLOUGH-BRENGLE MODEL 105OSCILLOSCOPE

The now highly popular 913 cathode raytube is used in this equipment. The tubeis provided with a shield which may beused when the instrument is in operationunder rather strong light. The screenshield is simply pulled out from the panel.

All the controls are carefully groupedso that those which apply to one circuitelement are close together. Thus all thecontrols for the cathode ray tube itself arein a row along the bottom of the panel.

Amplifiers for both vertical and horizon-tal plates are provided, as is a wide rangelinear sweep system. Full synchronizationis also a feature.

WESTON MODEL 772 ANALYZER

This tester is the first to use a super-sensitive 50 -microampere meter movementas a basis of all measurements. This re-markable meter enables measurements to bemade at a sensitivity of 20,000 ohms -per-volt. Many other advantages accrue fromthe use of this meter. For example, the

Fig. 30. Appearance of unit above.

ohmmeter ranges extend up to 30,000,000ohms, yet there is no need for a high voltagepower supply for this range, the necessary15 V. battery being contained in the cabinet.The lowest ohms scale is 0-3,000 and allohms readings are made from a single scale.

Fig. 31. Clough-Brengle Midget Oscilloscope.


D.C. VOLTSOHMS, M.A.

+©

+@1MA

100 MICRO

+ 0

15,000OHMS

(; o

ACVOE55

O

MCOUTPUT

METER

DECKNEAREST

PANEL

10V50V

250V.

1000V o

250 MAP

50 MA,.

10 MA.R x10,000

---.----.----OHMS.

40.000OHMS

7.500

0.2-MEG."0.'75-MEG

132OHMS

236.5OHMS)

1.048OHMS

26,313OHMS

A.C.VOLTSONLY

0.15MEG.

MEG.

4MEG.

15MEG.

BLK

123.3OHMS

OHMS

'gms

21aOHMS

226,780OHMS

NORMALD.C.

VOLTS

GREEN

18.15OHMS

OHMS

=. 1.5V

1t.V.

RED

Rx 1,000

Rx 10R

1,900OHMS

2,368'OHMS

236.5OHMS

Fig. 32. Weston Model 772 high sensitivity analyzer.

Both A.C. and D.C. voltage readings upto 1,000 V. may be made, the A.C. readingsbeing at 1,000 ohms -per -volt, while theD.C. readings are at 20,000 ohms -per -volt.Current readings up to 250 Ma. are possible.There are two high sensitivity current

Fig. 33. Front view of the Weston 772.

scales, 1 Ma., and100 microamperes,these being reachedby separate jackson the panel as aprotection to themeter.

Output meterjacks are provided,and these differfrom the A.C. jacksby the addition of aseries condenser,which is usuallyneeded for thispurpose.

This instrumentcomes complete in acovered case whichhas a large pocketfor carrying thetest leads which arealso supplied.

The panel is fin-ished in black en-amel with chro-mium and red trim,and the meter is ofthe bakelite casedtype.

The appearance of the WESTONMODEL 669 VACUUM TUBE VOLT-METER may be seen in Fig. 35. The cir-cuit is shown in Fig. 34. There are onlytwo tubes used, one of which is the powersupply rectifier. The power line connec-tion cord is of the double fused type forpositive protection against shorts. The ap-paratus is directly calibrated in 6 rangesup to 16 V. These readings may be easilymultiplied by factors of 10 and 50 by meansof a simple voltage divider system. Theinput capacity is only 4 mmf. and the gridcap of the tube projects through the panelso that it is an inch or more from anygrounded surface.

The accuracy is within 3% from 40 cyclesto 50 mc. Accuracy on the very low rangesis assured by the use of a neon tube acrossthe power supply which tends to hold thegrid and plate voltages steady regardlessof line fluctuations. A simple control isprovided to compensate for ageing of thetype 78 measuring tube or for use when anew tube is to be inserted.

The WESTON MODEL 692 TESTOSCILLATOR is pictured in Fig. 36. Thisunit is particularly notable for it's very

careful and com-plete shielding.Triple shielding isused and this cutsthe external field toa negligible amount.

The power sup-ply is obtained froma 221/2 V. "B" bat-tery and a 41/2 V."A" battery. Bothof these are entirelyself-contained a n dwell shielded. Aseparate tube isused for R.F. andA.F. oscillation andthe A.F. tube maybe cut out or itsoutput may be sep-arately used at will.A connection is pro-vided for use of ex-ternal A.F. modulation. Also, for use whenaligning receivers wtih a cathode ray oscil-loscope, a jack is provided for the use ofan external frequency modulator or wob-bler.

The maximum R.F. output is 0.2 V., andthis may be cut down to about 1 microvoltby the use of the R.F. attenuator. TheA.F. output is 1 V. at 400 cycles.

A plug-in coil system is employed, thisallowing complete freedom from inter -


Fig. 34. Weston Model 669 V.ampere instrument,

57

T. Voltmeter. The meter is a 100 -micro -not 100 ma., as shown above.

action between coils of the various bands.The coils are carried in a handy holder, andplug into a cast aluminum compartment.The guaranteed accuracy over the entirefrequency band is 1%. The various bandscovered run as follows : 100 to 250 kc.;250 to 550 kc.; 535 to 1,600 kc.; 1.5 to 4mc.; 4 to 10 mc.; and 10 to 22mc.

The apparatus is supplied complete withall tubes and batteries, and a carrying casemay be had if desired.

Fig. 35. Weston Model 669 V.T. Voltmeter. Fig. 36. Weston Model 692 'rest Oscillator.


TUBE TYPES

and Base Diagram Numbers

Tube Base Tube Base Tube Base Tube Base

01A 4-D 5V4G 5-L 6L7G 7-T 35/51 5-E1AI 4-A 5W4 5-T 6N6G 7-W 35S/51S 5-EIA4 4-K 5X4G 5-Q 6N7 8-B 36 5-E1A4T 4-K 5Y3G 5-T 6N7G 8-B 37 5-A1A6 6-L 5Y4G 5-Q 6P7G 7-U 38 5-FIBI 4-A 5Z3 4-C 6Q7 7-V 39/44 5-F1B4 4-K 5Z4 5-L 6Q7G 7-V 40 4-D1B4T 4-K 6 4-A 6R7 7-V 41 6-B1B5/25S 6-M 6A3 4-D 6R7G, 6S7G 7-R 42 6-B1C1 4-A 6A4/LA 5-B 6T7G 7-V 43 6-B106IC7G1D1

6-L

7-Z

4-A

6A5G6A66A7, 6A7S

6-T7-B

7-C

6Q7G6V66V6G5-C7-R

7 -AC

7 -AC

45

4646A1

4-D

5-71D5G 5-R 6A8 8-A 6V7G 7-V 46B1 5-7ID5GT1D7G

5-R

7-Z

6A8G6B4G

8-A5-S

6X56X5G

6-S6-S

4748

5-B

6-A1E1

1E5G4-A5-R

6B56B7, 6B7S

6-D

7-D6Y56Y7G6-18-B

4950

5-C4-D

IE5GT 5-R 6B8 8-E 6Z5 6-K 53 7-B1E7G 8-C 6B8G 7 4-A 55, 55S 6-GIFI 4-A 6C5 6-Q 8 4-A 56, 56S 5-A1F4 5-K 6C5G

66- Q 9

4 -A 56AS 5-A1F5G1F6

6-X6-W

6C66C7

6-F7-G

1012A

4-D

4-D57, 57S57AS

6-F

6-F1F7GIGI1G5G

7 -AD

4-A6-X

6C8G6D66D7

8-G6-F

7-H

12A512A71223

7-F7-K

4-G

58, 58S58AS596-F

6-F

7-A1H4GSH6G

5-S

7 -AA

6D8G6E5

8-A67-RB

15 5-F6-B

71A75, 75S

4-D

6G1J6G1K1

7 -AB

4-A

6E66E7 7-H

1198

206-C4-D

7677

5-A6-F

HUG 4-T 6F5 5-M 22 4-K 78 6-F1T1G 4-T 6F5G 5-M 24A, 24S 5-E 79 6-HIV 4-G 6F6 7-S 25A6 7-S 80 4-C1Y1 4-A 6F6G 7-S 25A6G 7-S 81 4-B1Z1 4-A 6F7, 6F7S 7-E 25B6G 7-S 82 4-C2 4-A 6G5 6-R 25L6 7 -AC 83 4-C2A3 4-D 6H6 7-Q 25L6G 7 -AC 83V 4-L2A5 6-B 6H6G 7-0 25S 6-M 84 5-D2A6 6-G 6J5G 6-Q 25Z5 6-E 85 6-G2A7, 2A7S 7-C 657 7-R 25Z6 7-Q F5AS 6-G2B7, 2B7S2E5

7-D6-R

6J7G6K5G

7-R

5-U25Z6G26

7-Q4-D

19

V996-F

4-E2S/45 5-D 6K6G 7-S 27, 27S 5 -A X99 4-D2Z2/G84 4-B 6K7G, 6K7 7-R 30 4-D 182B/482E 4-D3 4-A 6L5G 6-Q 31 4-D 183/483 4-D4 4-A 6L6 7 -AC 32 4-K 210T 4-D5 4-A 6L6G 7 -AC 33 5-K 485 5-A5U4G 5-T 6L7 7-T 34 4-M 864 4-D


aaTAIDIC EXULEITHE. ONE MAN IN 1000 W440 CANSERVICE MODERN RADIO. REC.-EIV.G.RS

RADIO SERVICE WORK_NOW OFFERS GREAT -ESTOPPORTUNITIES SINCERADIO BEGAN

Radical changes have takenplace in radio receiver designduring the past year. Cir-cuits and construction are verydifferent from the receiverswith which the radio service in-dustry has had its greatest ex-

perience. Even more sensationaldevelopments with further compli-cations are coming next season. Whowill service these receivers? Certainlynot the "old timer" who knows noth-ing about modern receivers! Re can'tdo it. That is why, right now, thereis an urgent demand for reliable ser-vice men with up-to-the-minute knowl-edge of modern radio receivers. Suchmen can step out and earn up to $3an hour doing nothing but pleasantservice work in the better homesaround town.

No Past Experience NeededPast experience actually counts forlittle at this time, because the swiftchanges in receiver construction havemade knowledge of old equipmentpractically useless. Even though youmay not know one tube from anothertoday . . , still, you can take E.T.A.training and make more money servic-ing modern radios than many of the"old timers" are making. E.T,A,graduates are doing it every day.Many of them are making more moneyas E.T.A. Certified Radio Techniciansthan they ever made in their livesbe f oie !

Be An R. T. A. Man and You'll Bethe One Man in 1000

E.T.A. training will equip you to givefast, complete service to any radioreceiver built. The jobs that puzzleand sometimes baffle the usual serviceman will be simple as "A.B.C." toyou . , when you become an E.T.A,Certified Radio Technician. It is verypossible that you will be the onlyservice man in your locality able toquickly diagnose and quickly repairthe new types of radio receivers. Bethe one man in 1000! You can.

Radio TrainingAssociation of America

4525 Ravenswood AvenueCHICAGO, ILLINOIS

Important and far-reachingdevelopments in Radio createsudden demand for speciallyequipped and specially train-ed Radio Service Men.

THIS CIRCUIT ANALYZERAND POINT-TO-POINTRESISTANCE TESTER,INCLUDED IFIalEEOF EXTRA CHAR GE

FOUR- LARGE KITSPRACTICEEQUIPMENT

IT'S JUST AS SIMPL-E AS THISOF COURSE

I CANFIX IT!-

. ...

-1

I MADE 518 at)I0 -DAYTHERE'S NOBODYELSE IN TOWNWho CAN FIXTHESE NEW -SETS

R.T.A. Membership ValuableWith your course of training, and as long afterward as you mayneed help, you always have available, without extra cost.valuable consultation service on any problem that may arise inyour radio service work or on any of the newer developmentsthat may appear in new radio receivers from time to time.

To Help You Make Money QuicklyR.T.A. supplies you with an excellent and reliable Circuit Testerand Point -to -Point Resistance Checker as is illustrated above --one of the handiest pieces of portable service equipment. Itquickly helps you locate trouble in any type of radio receiver,old or new.

SEND COUPON ist=i1A. G. Mohaupt, EngineerRadio Training Ass'n. of AmericaDept. RSA -77, 4525 Ravenswood Ave., Chicago, Ill.Dear Mr. Mohaupt: Please send me your free book of factsabout radio opportunities and bow I can make big moneyquickly. Also tell me how I can obtain your Circuit Analyzerand four big experimental outfits.Name

AddressCity State


5-7

6-X

TUBE AND BASE DIAGRAMS

(Viewed From Bottom of Base-RMA Numbering System)

6-A

7-A

6-B

7 -AA

6-C 6-D

7 -AB 7 -AC

6-E

7 -AD

Above and on page 60 are shown the bases of the latest types of tubes at the time this bookwas written. Others will doubtless soon follow.


Here Are the Other TitlesIN THE

RADIO -CRAFT LIBRARY SERIESPRESENTED on this page are the other books

in the RADIO -CRAFT LIBRARY SERIES-the most complete and authentic set of volumestreating individually important divisions of radio,refrigeration and air conditioning. Each bookhas been written for the purpose of giving youthe opportunity to specialize in one or more of thepopular branches of the subjects mentioned. The

Book No. 2

And How They WorkWith Complete Technical Data onAll Standard and Many Special

TubesBy ROBERT HERTZBERG

Book No. 3THE SUPERHETERODYNE BOOK

All About SuperheterodynesHow They Work, How to Build and

How to Service ThemBy CLYDE FITCH

Book No. 5HOW TO BECOME A RADIO

SERVICE MANHow to Get Started and How toMake Money in Radio Servicing

By LOUIS MARTIN

Book No. 6BRINGING ELECTRIC SETS

U P -TO -DATEWith Pentodes, Multi-Mus, DynamicSpeakers-Complete Information onHow to Modernize A.C., D.C., and

Battery -Operated ReceiversBy CLIFFORD E. DENTON

Book No. 8RADIO QUESTIONS and ANSWERSA Selection of the Most Importantof 5,000 Questions Submitted byRadio Men During the Course of

One YearBy R. D. WASHBURNE

material in these books is very helpful ... you 11find them valuable in your work ... and show youhow to increase your earning power.

The authors of these books are well-known toall . . . they are authorities on the subjects onwhich they have written. This is the first timethat you are enabled to build a library of uniformtechnical books by such popular writers.

Here Are the Titles -Book No. 9

AUTOMOBILE RADIO ANDSERVICING

A Complete Treatise on the Sub-ject Covering All Phases from In-

stalling to Servicing andMaintenance

By LOUIS MARTIN

Book No. 10

HOME RECORDING AND ALLABOUT IT

A Complete Treatise on Instanta-neous Recordings, Microphones, Re-corders, Amplifiers, Commercial

Machines, Servicing, etc.By GEORGE J. SALIBA

look No. 12

PUBLIC ADDRESS INSTALLATIONAND SERVICE

Modern Methods of Servicing andInstalling Public Address Equipment

By JOSEPH T. BERNSLEY

Book No. 13ABC OF AIR CONDITIONING

An Accurate Simplified, TechnicalReview of the Fundamentals of thisLatest Branch of Engineering, In-

cluding Servicing Data onPresent-day Units

By PAUL D. HARRIGAN

Book No. 14

POCKET RADIO GUIDEHandy Reference Book for RadioMen - Set Construction Articles -Audio Amplifier Circuits - UsefulRadio Formulas and Data-HandyShort Cuts - Index to Important

Articles Printed inRADIO -CRAFT Magazine

By N. H. LESSEM

Book No. 15

ABC OF REFRIGERATIONA Compendium of the Principles ofRefrigerating for Service Men witha Detailed Listing of Defects andHow to Overcome Them, with Hints

on Setting Up a Service ShopBy TRAFTON MASON

Book No. 16

PRACTICAL RADIO CIRCUITSA Comprehensive Guide to AllTypes of Radio Circuits for the Ser-

vice Man, Constructor andExperimenter

By DAVID BELLARE

ALL BOOKS UNIFORMThe books in the RADIO -CRAFTLIBRARY SERIES are all uni-form ... size 6 x 9 inches. Eachvolume contains an average of50 to 150 illustrations. The booksare printed on an excellentgrade of book paper.

RADCRAFT PUBLICATIONS, INC. 99 HUDSON ST. NEW YORK, N. Y

CLIP COUPON-AND MAIL TODAY !11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111114

= RADCRAFT PUBLICATIONS, INC., 99 Hudson St., New York, N. Y.E I have circled below the numbers of books in the RADIO -CRAFT LIBRARY SERIES, which == you are to send me POSTAGE PREPAID. My remittance of $ is enclosed at the == cost of fifty cents for each book.= The amount of my remittance is (Stamps, checks or money orders accepted.) El-

= Circle numbers wanted: 2 3 5 6 8 9 10 12 13 14 15 16 === Name Address =...

City State SS= Send remittance by check, stamps or money order; register letter if you send cash or stamps. =MilliillillifillillilillifillillIMiliiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiIHMIUM=1111111111111117


7-8

7-1-1

7-U

8-C

7-C

7-K

7-V

8-E

7-1)

7-0

7-W

8-0

7-E

7-R

7-F

7.5

7-Z 8-A

7-G

7-7

8-B

SYMBOLS: F-Filament; H-Plate; K-Cathode; G-Control Grid; Gs-Screen Grid;Ga-Anode Grid; Go-Oscillator Grid; Mod-ulator Grid; T-Target Plate; Su-Suppres-sor Grid; Dp-Diode Plate; Nc-No Con-nection; Hc-Heater Center; Top Cap;XS - External Shield; S - Metal Shell;

-> Locating Pin.

"G" tubes and those with similar characteristics.

Type Description Similar to: Type Description Similar to:1C7G Pentagrid Converter 106 6F6G Power Output Pentode 421D5G Super Tetrode Amplifier 1A4 6H6G Double Diode 6H611D5GT Super Tetrode Amplifier 1A4 615G Triode Amplifier *1D7G Pentagrid Converter 1A6 6J7G Amplifier and Detector 771E5G Screen Grid R -F Amplifier.... 1B4 6K5G High Mu Triode Amplifier1E5GT Screen Grid R -F Amplifier.... 1B4 6K6G Power Pentode 411E7G Output Double Pentode 6K7G Super Control Pentode 781F5G Power Output Pentode 1F4 6L5G Triode Amplifier 6C5G§1F7G Double Diode Pentode 1F6 6L6G Power Amplifier 6L61G5G Power Output Pentode 6L7G Heptode Mixer 6L771H4G Amplifier and Detector 30 6N6G Power Output Amplifier 6B51H6G Double Diode Triode 1B5/25S 6N7G Class B Power Amplifier 6A61J6G Class B Twin Amplifier 19$ 6P7G Pentode Triode 6F71R1G Battery Receiver Ballast 1Y1 6Q7G Double Diode High Mu Triode 6Q7t1T1G Battery Receiver Ballast 6R7G Double Diode Med. Mu Triode 6R7t5U4G Full Wave Rectifier 5Z3 6S7G Super Control Pentode 6D615V4G Full Wave Rectifier 83V 6T7G Double Diode High Mu Triode.. 6Q7G§5X4G Full Wave Rectifier 5Z3 6U7G Super Control Pentode 6D65Y3G Full Wave Rectifier 80 6V6G Power Amplifier5Y4G Full Wave Rectifier 80 6V7G Double Diode High Mu Triode 856A5G Power Output Triode 6A31 6X5G Full Wave Rectifier 846A8G Pentagrid Converter 6A7 6Y7G Double Triode Amplifier 796B4G Triode Power Amplifier 6A3 25A6G Power Pentode 436B8G Double Diode Pentode 6B7 25B6G Power Amplifier 4316C5G Triode Amplifier 6C51 25L6G Power Amplifier6C8G Double Triode Amplifier 25Z6G High Vacuum Rectifier and6D8G Pentagrid Converter 6A7§ Voltage Doubler 25Z56F5G High Mu Triode Amplifier.... 6F5t

* New Characteristics.$ Except filament current (240 Ma.).

§ Similar but not identical in characteristics.I Similar except for capacitances.

All tube data courtesy Hygrade Sylvania Corp.


COMMON FORMULASOhms Law

Calculation of voltage, current andresistance.

EI = -

R

I is the current in amperes ;E is the potential in volts ;R is the resistance in ohms.

The formula may also be written intwo other forms :

E = IR and R = -

Inductive Reactance of a CoilThis comes in handy when working

out the value of choke coils and thelike.

Reactance in ohms = 2tfL 7C = 3.14f = frequency in cycles;I, = inductance in henries.

The capacitive reactance of a con-denser may be figured from :

Reactance =106

277f C

= 3.14 ;f = frequency in cycles;C = capacity in mf.

Resistance CalculationsResistances in parallel may be fig-

ured from this formula :

RI X R2R=

RI + R2R = the total of all the resistances ;R1 and R2 = the individual resist-ances.

For a series connection, it is simplynecessary to add up the values;

R= R1 + R2 ± R3 + R4

Calculating the Wavelength andFrequency

A simple formula for this is of greatuse to the Service Man. It is :

2. = 1,885 V LC= wavelength in meters ;

L = inductance in microhenries ;C = capacity in mf.

The formula for calculation of fre-quency is :

f=106

217V LC= 3.14;

f = frequency in cycles;I = inductance in henries;C = capacity in mf.

A.C. Circuits CalculationsOhms law may be used in this work

as follows :E E

E = IZ I=-Z = -Z

E = potential in volts ;I = current in amperes ;Z = impedance of circuit in ohms.

The impedance may be found from :Z= VR2 + (XL Xc)2

Z = impedance in ohms ;R = resistance in ohms ;XL=reactance of inductance in ohms ;Xc=reactance of capacity in ohms.

Use of the DecibelThe decibels equal to a certain

power ratio is 10 times the logarithmof that ratio.

P2N = 10 Logio

P1N = decibels ;

P2= power ratio.

P1When voltage or current are being

considered, the constant 20 is used inplace of 10.


J. E. SMITH, PresidentNational Radio Institute

Established 1914The man who has directedthe home study training ofmore men for the RadioIndustry than any other

man in America

Oleizetit_124crof

Earned $50First Month

in Spare Time"I knew noth-ing aboutRadio. Afterfour lessons I

vegan servicing Radios,earning $50 the first month.Last winter I made as highas $100 a month in sparetime."- G. F. WALTON.808 West Olney Road,Norfolk, Va.

OwnBusiness

Pays$300

a Month

"I now havemy own Radiobusiness which shows threehundred dollars a monthprofit - thanks again toNational Radio." FRANKT. REESE, 39 N. FeltonSt., Philadelphia, Penna.

GET FREE LESSONon Radio Servicing TipsHere's proof that N. R. I.Training is practical,money -making information,that it is easy to under-stand-that it is just whatyou need to master Radio.The sample lesson text."Radio Receiver Troubles-Their Cause an -a. Reme-dy," covers a long list ofRadio receiver troubles inA. C., D. C., battery,universal, auto, T.R.F.,superheterodyne, all -waveand other types of sets.Get this lesson Free. MailCoupon.

I WILL TRAIN YOUTO START A SPARE TIME OR FULL TIME

RADIO SERVICE BUSINESS

WITHOUT CAPITALDo you want to make more money?

The world-wide use of Radio hasmade many opportunities for you tohave a spare time or full time Radioservice business of your own. Threeout of every four homes in theUnited States have Radio sets whichregularly require repairs, servicing.new tubes, etc. Many sets are oldand will soon be replaced by newmodels. I will train you at home inyour spare time to sell, install, ser-vice, all types of Radio sets-to startyour own Radio business and buildit up on money you make in yourspare time while learning. Mail cou-pon for my 64 -page book. It's Free-it shows what I have done for others.

Many Make $5, $10. $15 a WeekExtra In Spare Time

While LearningPractically every neighborhood

needs a good spare time serviceman.The day you enroll I start sendingyou Extra Money Job Sheets. Theyshow you how to do Radio repairjobs that you can cash in on quickly.Throughout your training I send plansand ideas that have made good sparetime money for hundreds of fellows.I send special equipment which givesyou practical experience-shows youhow to conduct experiments andbuild circuits which illustrate im-portant Radio principles.

There's A Real Future in Radiofor Well Trained Men

Radio already gives good jobs tomore than 300,000 people. And in1936, Radio enjoyed one of its mostprosperous years. More than $500,-000,000 worth of sets, tubes andparts were sold-an increase of morethan 60% over 1935. Over a millionAuto Radios were sold, a big in-crease over 1935. 24,000,000 homesnow have one or more Radio sets,and more than 4,000,000 autos areRadio equipped. Every year mil-lions of these sets go out of date andare replaced with newer models.More millions need servicing, new

tubes, repairs, etc. A few hundred$30, $50, $75 a week jobs havegrown to thousands in 20 years. AndRadio is still a new industry-grow-ing fast!

Get Ready Now for Your Own RadioBusiness and for Jobs Like These

Broadcasting stations employ en-gineers, operators, station managersand pay up to $5,000 a year. Sparetime Radio set servicing pays asmuch as $200 to $500 a year-fulltime servicing jobs pay as much as$30, $50,, $75 a week. Many RadioExperts own their own full or parttime Radio businesses. Radio manu-facturers and jobbers employ testers,inspectors, foremen, engineers, ser-vicemen, paying up to $6,000 a year.Radio operators on ships get goodpay and see the world. Automobile,police, aviation, commercial Radio,and loud speaker systems offer goodopportunities now and for the future.Television promises many good jobssoon. Men I trained have good jobsin these branches of Radio.

Find Out What Radio Offers YouGet My 64 Page Book Free Now

Act Today. Mail the coupon nowfor my Free Lesson and my book,"Rich Rewards in Radio." Both arefree to anyone over 16 years old. Mybook describes Radio's spare timeand full time opportunities and thosecoming in Television; tells about myTraining in Radio and Television;shows you actual letters from menI have trained, telling what they aredoing and earning, tells about myMoney -Back Agreement. Find outwhat Radio offers YOU! MAIL THECOUPONin an en-velope,or pasteit on apennypostcard-NOWI

J. E. SMITH, President, Dept. 7JA1.National Radio Institute, Washington, D. C.

RICH REWARDS

IN RADIO

Akt,

GOOD FOR BOTH SAMPLEEL EBSOSOOK.

FREEJ. E. SMITH. President, National Radio InstituteDent. 7JA1, Washington, D. C.

Dear Mr. Smith: Without obligation, send me the Sample Lessonand your hook about spare time and full time Radio opportunities,and how I can train at home in spare time. (Please write plainly.)

Name Age

Address

City State 14X1

Which of These

OFFICIAL RADIO SERVICE MANUALSDo You Need to Complete Your Files?

There's perhaps one or more of these great service manualswhich you might need to complete your set. Collectively theyrepresent the largest collection of service data ever compiled.Evidence of their importance to Radio men is shown by thefact that over 80,000 OFFICIAL RADIO SERVICEMANUALS have been sold during the past few years. Usethe coupon below to order your Manuals.

1,200 Pages1936 OFFICIAL RADIO. SERVICE MANUAL9 x 12 Inches Over 2,500 Illustrations Looseleaf Binder, Hard Covers

LIST PRICE $7.00

1935 OFFICIAL RADIO SERVICE MANUALOver 1,000 Pages 9x12 Inches Over 3,000 Illustrations Flexible, Looseleaf, Leatherette Cover

LIST PRICE $7.00

1934 OFFICIAL RADIO SERVICE MANUALOver 400 Pages 9x12 Inches Over 2.000 Illustrations Flexible, Looseleaf, Leatherette Cover

LIST PRICE $3.50

1933 OFFICIAL RADIO SERVICE MANUALOver 700 Pages 9x12 Inches Over 2,000 Illustrations Flexible, Looseleaf, Leatherette Cover

LIST PRICE $5.00

1932 OFFICIAL RADIO SERVICE MANUALOver 1,000 Pages 9x12 Inches Over 2,000 Illustrations Flexible, Looseleaf. Leatherette Cover

LIST PRICE $5.00

1931 OFFICIAL RADIO SERVICE MANUAL630 Pages (Including Supplements) 9x12 Inches Over 1,500 Illustrations

Flexible, Looseleaf, Leatherette Cover

(Including Supplements)LIST PRICE $4.50

For Car -Radio Servicing - Get TheseOFFICIAL AUTO -RADIO SERVICE MANUALS

1935 MANUALOver 240 Pages 9x12 Inches Over 500 Illustrations

Flexible. Looseleaf, Leatherette Cover

LIST PRICE $2.50

1933 MANUALOver 240 Pages 9x12 Inches Over 500 Illustration.,

Flexible, Looseleaf, Leatherette Cover

LIST PRICE $2.50

Send remittance for any. OFFICIAL RADIO SERVICE MANUAL in form of check ormoney order. Register letter if it contains cash or currency. ALL MANUALS ARE SENTPOSTAGE PREPAID.

RADCRAFT PUBLICATIONS, Inc.99 -SS HUDSON STREET NEW YORK, N. Y.

Let these eminent Radio Authors guide yothrough your radio service work 1

The importance of Radio Service Men can beap-preciated when it is realized that of the 56,200,000radio sets in the world, over one-half of thatnumber are in use in this country. Approximately22,500,000 must be serviced, and the Radio Serv-ice Men are the only ones that can do this big job.

RADIO -CRAFT is published exclusively forService men. It is edited with the view to givethe Service Man the latest and most valuableservice information obtainable. It is the maga-zine to read if you want to be successful in radioservice work.

The list of contributors shown at the right repre-sents the finest array of authorities on radio serv-icing on the staff of any publication. Thesewriters are continually working for your benefit.

Get a copy of the current issue of RADIO -CRAFTfrom your newsdealer today-read it from coverto cover. Then judge for yourself if it is not thefinest servicing magazine published today. Onceyou have read your first issue, you'll never let amonth pass without getting the next issue.

We will send you RADIO -CRAFT for One Yearat the Special Rate of $2.00. (Foreign $2.50.)This is a saving of 1/3 over the regular newsstandrate. Send remittance in form of check, stampsor money order to

Editors ofRADIO -CRAFT

HUGO GERNSBACKEditor -in -Chief

R. D. WASHBURNEManaging Editor

N. H. LESSEMAssociate Editor

C. P. MASONAssociate Editor

Contributors toRADIO -CRAFT

M. M. BRISBIN

KENDALL CLOUGH

A. A. GHIRARDI

GLENN H. BROWNING

CHARLES SICURANZA

SAMUEL C. MILBOURNE

F. L. SPRAYBERRY

ARTHUR H. LYNCH

A. C. SHANEY

BERTRAM M. FREED

J. B. CARTER

CLIFFORD E. DENTON

MILTON REINER

FRANK J. LESTER

J. T. BERNSLEY

RADIO -CRAFT MAGAZINE99 -SS HUDSON STREET NEW YORK, N. Y.

ya - worldradiohistory.com€¦ · it stresses the many uses of different types of test equipment;...

Documents