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THE AIRCRAFT RADIO SERVICE MAN

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Cathode- Ray Test Equipment - New "Blind Landing" System -60- W. Amplifier L_New Department: "Learn - by -Experimenting" Beginners' Practical Radio Course

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RADIO -CRAFT for OCTOBER. 1937 193 Haw ¿Jijcrt mom a go Joe

NO. NOT SO GOOD BILL, TOM.IVE BEEN TOO BUSY YOU HAVE THE SAME BUT I'M STILL PLAYING MAKING GOOD MONEY Our OF CHANCE TOM. ABOUT THERE'S OJC IN BERLIN WITH RADIO. HAD RADIO LATELY TO"PLAY WITH IT. A YEAR AGO ISHOWED DJ C YOU A THE TENTH FOREIGN UST NIGHT. BOOK FROM IS RADIO STILL NATIONAL RADIO INSTITUTE STATION TONIGHT. RADIOS YOUR HOBBY TOO? YOURE SURE LUCKY, BILL. TELLING ABOUT THE CERTAINLY PUN. I NOTICED YOUR NEW CLOTHES OPPORTUNITIES ANO AND SNAPPY CAR. I THOUGHT FUTURE IN RADIO, AND YOU HAD INHERITED A 110W OTHERS HAD SUC- MILLION. CEEDED THROUGH THEIR HOME TRAINING, WELL I ENROLLED.

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THIN I CAN MAKE OR INSTALL AM) OR YOU CERTA¡ NLY N.R.I TRAINING REAL MONEY MAKE 0000 1'M DOING SWELL IN RADIO. IF BILI SERVILI LOUD MONEY IN ANY ONE .,KNOW RADIO. CERTAINLY PAYS. SCRs/ICING SPEAKER SYSTOLE MARY 'AND I ARE TO BE OF THE MANY MINE NEVER I JUST STARTED SUCCEEDED ,RADIO MARRIED NEXT MONTH, SETS. OTHER NEW ANO SOUNDED BETTER AfEW MONTHS I CAN ,GROWING BRAUOKS RADIO h MORE THAN ,A TOO: AGO ANO IM PLAYTHING. IT'S A WO F RADIO. fIe °OING ALREADY MAKING TO SEND FOR GOOD MONEY BUSINESS AND GROWING OB GET A \ THAT FREE BOOK IN MY SPARE PAST. TAKE MY YIP AND JOB IN A `rt RIGHT NOW/ r TIME. GET INTO RADIO NOW, TOM! BROADCASTING j THANKS' ¡` _ STATION j

OH,TOM, ITS WONDERFUL OUR WORRIES ARE NOW FAST YOU'VE GONE OVER. I'M MAKING GOOD AHEAD IN NAO /O. WE MONEY NOW, AND THERE'S NEVER COULD HAVE A FUTURE AHEAD FOR US GOTTEN MARRIED ON IN 4540/O. e . a e (will train you to WHAT YOU WERE start GETTING BEFORE. a spare time or full time Radio service business Without Capital

Many Radio Experts Make $30, $50, $75 a Week 1. EM YOU want I F. Smith, President to make morn f I. , HERE'S I:. 1, MAKE GOOD'MONEY _, National Radio PROOF made molly opla,rtultille. cur ., IL.r.. , Institute Inm r fu!. Had,., lai, Established business of your . 'l'ltra =ut of cers,, f,nir hurtle: in the United 1914 Mvireates have Radio sets which regal irly require repairs, . vi,ing, new tubes, $3,500 a Year in Own Business etc. Many eta ro old and will s.rm be relitared by new model,. I will train you to sell. install, servies all D'pes of Radio sets start your men completing R. -to Radio service business and build it up on utuney made in spare "After the N. I. Course I be- time while learning. Mall coupon for my 64 -page Iwulr. it's FREE. came Radio Editor of the Buffalo Courier. Later I started a Radio service business of my Gat Ready Now for a Business of Your Own and for Jobs Like These own, nd averaged over $3,500 a year. " -T. J. Broadcasting statists employ engineers, operator:. .tat i,m managers and pay te $7,000 Year. TELAAK, 657 Broadway, Buffalo, N. Y. Share Ume Radio set servicing pays as numb his $'Pmt 37mí a year -full tinte Radier servicing ..í x. jabs t, as muni as $30. Val, $ :. a week. Slimy Stade, experts own and operate their own time or part time Radio sales and ,en in. business,,. Stadio manufacturers Jobber, $10 to $25 a Week in Spare 'Erna and employ testers, inspectors. foremen. :sunnier:, .sen irTnen, Laying Up to 5';.IIIIO a Sear. I "I am making from $10 to $25 a week in spare Radio operalnrs In ships get gomd pay and . t the world besides. Automobile, t''ii a aviation. rommereial Radio. and loud spealirr ,n s infer time while still holding my regular job as a good oplrnunitie: n for the future. Television promise: many Ia.sI Jobs :.nn. Men I trained at h.nm, de ' machinist. I owe my success to N. R. 1."- have good into In all these branches lot Radio, Read their letters in niy 6I -page WM. F. RUI'P. 203 Front St., Conshohocken. Pa. book. Mail the coupon. Many (Make $5. $10. $15 a Week Extra in Spare Time While LearntnP uo `' GET MY FREE LESSON Practically every twit:M mbo:xi musts a I' .,.I .paspare tome senit-en,:u, . Tile ars.h. .tar yo:. or u I wit mending y,.1 Extra a,xlaaey Si eets. They .ho.v '' p on Radio Servicing Tips you hose to edo Haiti° repair Sob. -how' t. .a.h in qu,rk!.y. Throughout your training I send you and i leas that have ern Plans ,."d Mare '.q, 4 time money fur his of renow.. 1 . you apeeial lta,iiu ,nip- I prove n,;l that my training 1. , m .nt for em,dueting experiments and building circuits whir¡, q4' ,s praet nal. money-making infonnatbal. ¡unstrap, ¡moon:tot Muth, Prin..mle'_ >b. 'training gh.es you -S'''''<'''.y that It is easy to understand that practical Radio experience while learn.ng. 'n. ``lO`1`: it Is just what you need .4. YIy to twister Radio. lesson test, "Radio Re- Find Out What Radio Offers You-Mail Coupon Now JLpr o , ceiver Troubles -Their Cause and Slail the coupon now far, icy yr.. 1e,...I and ,,,yl honk - .$i'*' V r nv Bement)" lovers a lung list of Ra- 'Rich ltewaNs Ill Radio.' (loth nee L anyone amt ( t »t r year. old. My (nook point, , Its 1,:nh,:, tLnre l R, dio receiver troubles in iii time ''Y ..sp >' A.C., f ul fun time , pimrtu ices, and 1,,.e coning i O .r,..0..\"- batten, universal. auto. T. It. F., Television; shows my Training Ita,lm alai TeI: -ar .1.-.4.- ' .autel I.etenslyne, all -ware and other vision; tells about my Money a Itacl: Agree:11 et; ,, ., types of sets. A cans .haws you letters from men 1 trained. telling J reference are doing i what . 4eer System you rho they Q`p gives probable cause n:hlio u MAIL, THE COUPON:b and a quirk way to locate and rein - envelope, or paste it on a penny ,_ Úw¡n '4,D 6 4y edy them set trouble:. A special Q 4G section Is devoted to receiver chock. ,_,,OC. ..'s ip. alignment, balancing. neutral- J. E. SMITH. President 5 wv izing and testing. (let rho lesson NATIONAL RADIO INSTITUTE ' Free. No obligation. Just mall Dept. 7KX, Washington. D. C. comsat. /.4'.., ,,,f...-4-,0o° o Get a Lesson and 64 page book 9CPt 9y43 ,44.I MAI LTHIS FREE O Please Say That You Saw !t in RADIO -CRAFT adio- raft Fos The

SERVICE MAN DEALER . RADIOTRICIAN /

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HUGO GERNSBACK, Editor -in -Chief Latest in Test Apparatus for the Service Man 2 I 6 N. H. LESSEM C. P. MASON 4"- Associate Editor Associate Editor "Learn -by- Experimenting" Beginners' Practical Radio Course -Experiment No. I (The "Radio Whistle ") R. D. WASHBURNE, Managing Editor Sol D. Prensky 218

1111111111111111111111111111111111111I I I I I I111111111111111111I I I I I I I I I I I I I I I I I rann 111111111111111111 I I I I I I I I I I I I I I I I I 111111/01111 II 1 1 1 1 1 1 11 mra u ABC of Modern Vibrator Servicing F. E. Wenger 220 CONTENTS - OCT. 1937, ISSUE The Latest Radio Equipment 221 Volume IX Number 4 Modern Servicing Oscilloscopes 222 Business Problems of the Service Man....Jack Grand 223 Editorial: Marconi Hugo Gernsback 197 SHEET: The Radio Month in Review 198 RADIO SERVICE DATA -157 (Fiver Roamio) The "Resonoscope" Electronic Device Detects No. 212 -Crosley Model A -New 224 "Off -Key" Notes 200 Auto Radio Condenser Tester New "Resolution Tester" for Cathode -Ray Tubes 201 Build This "Intermittent Open" Joseph Mosio 225 The "Air- Track" System of "Blind Landing" Speeds Free -Point Testing Charles E. Planck 202 New Instrument G. H. Koch 225 The Aircraft -Radio Service Man N. H. Lessem 202 Correct Playback of Spot Recordings-Part I Guglielmo Marconi -1874 -1937 203 Ralph L. Power 226 New U. S. Coast Guard Aviation Radio 203 Radio Wittiquiz 226 New Tubes for the Radio Experimenter -Part II Operating Notes 227 R. D. Washburne 204 Servicing Questions and Answers 227 New Set Tester Features Low -Ohm Scale 256 B. O. Burlingame 205 Book Reviews

What Size Oscilloscope? G. M. Buchard 205 u10n11111 n1111n11nun 111111 u1111 u nu111111n1110uu111111nu111010nnm11111111n1111111111111111m 111nnu1111u1111u11nu11nun Importance of Modern Test Equipment Glenn H. Browning 206 NOVEMBER RADIO- CRAFT- How to Make "The Seafarer" Loop -Type Boat Radio Set -Part II Raymond P. Adams 208 RADIO Build This "Optimum- Test" Tube Checker VOCATION NUMBER! Milton J. Reiner 209

Business -Like "Silent" Servicing J. P. Kennedy 209 Facts and figures show that radio facilities are rapidly Bigger Service Profits from Better Tools! being expanded into numerous fields. Radio program O. J. Morelock 210 reception and transmission, public address, and electronics put to new uses. The innumerable money- New Circuits in Modern Radio Receivers-No. I all have been F. L. Sprayberry 211 making possibilities of these 3 major fields will be evident who reads the and semi-techni- How Dependable Are Your Meter Readings? -Part I to the radio man technical A. A. Ghirardi 212 cal articles in the forthcoming November issue of RADIO- How to Make a Class AI Push -Pull Negative -Feed- CRAFT- back 60 -W. Amplifier Walter J. Bronson 214 -on the newsstands October I.

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Published by Radcraft Publications, Inc. Publication office: 29 RADIO -CRAFT is published monthly, on the first of the month preced- Worthington Street, Springfield, Mass. Editorial and Advertising ing that of date: subscription price is $2.50 per year in U. S. and Can- Offices: 99 Hudson Street, New York City. Chicago Advertising ada. (In foreign countries, $3.00 a year to cover additional postage.) Office: L. F. McClure, 919 North Michigan Avenue, Chicago, Ill. Entered at the post office at Springfield as second -class matter Western Advertising Office: Loyd B. Chappell, 530 West Sixth St., under the act of March 3, 1879. Los Angeles, Calif. Foreign Agents: Text and illustrations of this magazine are copyright and must not be sondon- Gorringés American News Agency, 9A Green St., Leicester without of the copyright owners. Square, W. C. 2, England. reproduced permission Paris -Messageries Dawson, 4 Rue Faubourg, Poissonniers, France. Melbourne -McGill's Agency, 179 Elizabeth St., Australia. Dunedin -James Johnston, Ltd., New Zealand. Copyright 1937. Radcraft Publications. Inc. 194

RADIO -CRAFT for OCTOBER, 1937 195

MANY OPPORTUNITIES a FOR THE ll -. COYNETRAINED--- ` P4. RADIOMAN are You Ready fora Better Job -More Pay? Don't be an untrained man. Let me show you how to get your start in Radio -a fast growing, live money- making industry. Prepare for jobs as Assembler, Inspector and Tester-Radio Sales or Service and Installation Work -Broadcasting Station Operator -Wire- less Operator on a Ship or Airplane or Sound Work - HUNDREDS OF OPPORTUNITIES for a real future in radio! 12 Weeks of Shop Training We don't teach by book study. We train you on a great outlay of Radio, Television and Sound equipment -on scores of modern Radio Receivers, actual Broadcasting equipment, Television apparatus and Sound Reproduction equipment, Code and Telegraph equipment, etc. You don't need advanced education or previous experience. We give you - RIGHT HERE IN THE COYNE SHOPS - the actual practice and experience you'll need for your start in this great field. And because we cut out all useless theory and only give that which is necessary you get a practical training in 12 weeks. Mail coupon for all facts about my school and training methods. TELEVISION andPUBLIC ADDRESS Television is sure to come as a commercial industry. Rapid progress is now being made in developing this new field. It will offer opportunities to the man who is trained in Radio. Here at Coyne you learn Television principles, and work on actual Television equipment. Public Address Systems offer opportunities to the Trained Radio Man. Here is a great new Radio field which is rapidly expanding. Prepare NOW for these wonderful opportunities! Learn Radio Sound s Work at COYNE on actual Sound Reproduction equipment. Not a home study course. SEND FOR DETAILS OF MY ELECTRIC REFRIGERATION AIR CONDITIONING "PAY AFTER AUTOMOBILE ELECTRICAL WORK Instruction now included at no extra cost. Here is your opportunity to learn these valuable allied lines without extra tuition charge. GRADUATION" PLAN TO Mail the Coupon below and I'll tell you about my "Pay After PART TIME EMPLOYMENT Graduation" Plan which has enabled hundreds of others to get HELP YOU "EARN WHILE LEARNING" Coyne training with very little money. On this plan you can get If you are short of money and need part time employment to help your training first, then take 18 months to complete your small pay for your room and board while monthly tuition payments starting 5 months after you begin training, my Employment Depart- training. Not a home study course. ment will help you get a part time job. Mail the coupon for all details of this "Tuition Payment Plan." GET THE FACTS PRACTICAL WORK Don't let lack of money prevent at COYNE in Chicago A your sending in the Coupon. Mail ACTUAL, PRACTICAL WORK. You build and service radio sets. : the Coupon today and I Will send a: lli k You get training on real Broadcasting equipment. You construct i `7ÍQ h Coyne Book Television Receiving Sets and actually transmit your own Tele- fyuolul otf Fe ABTFREE vision images over our Television equipment. You work on real Sound equipment. You learn Wireless Operating on Actual Code H. C. LEWIS. Pres. Practice apparatus. We don't waste time on useless theory. We give you the practical training you'll need for in I Radio Division, Coyne Electrical School your start Radio 500 S. Paulina Dept. Ill. -in 12 short weeks. If you desire code, this requires additional St., 77-1H, Chicago, time for which there is no extra charge. Dear Mr. Lewis: -Send me your Big Free Radio Book, and all 1 details of your "Pay After Graduation" Plan including valuable Mail Coupon Today for All the Facts instruction in Electric Refrigeration, Air Conditioning and Auto- I mobile Electrical Work. H. C. LEWIS, Pres. RADIO DIVISION Founded 1899 I Name Coyne Electrical School I Address 500 S. Paulina St., Dept. 77 -8H, Chicago, Ill. City State 14rase Sa That Ian Saw It in RADIO -CRAFT 196 RADIO -CRAFT for OCTOBER, 1937-

go' t-e,test ADVANCE SALE EVER GIVEN A RIDER MANUAL

Never has a Rider Manual had the enthusiastic reception invaluable section entitled "How It Works." This separate which Volume VIII enjoys -even before its publication. section meets the current need for special technical infor- Never have the advance orders been so great. This is the mation on the modern radio set -outside as well as whhin result of, FIRST: The tremendous and ever -increasing popu- the actual radio circuit. Motorized tuning -special auto- larity of Rider Manuals. SECOND: Technicians' recogni- matic frequency circuits -these and other mechanical as tion of the thorough planning which has gone into this well as electrical kinks and innovations of the modern set latest volume. For, this is NOT just another volume; must be understood if the serviceman is to work on the RATHER it is so complete and so well laid out that it better sets -which pay the bigger profits. actually represents a great forward stride toward the perfect Manual. Of course, you need all the preceding volumes of Rider Manuals which cover receivers issued between 1920 To deliver the same degree of completeness which has and 1937. Check your Rider Manuals with the list below characterized other Rider Manuals it was necessary to and order any missing volumes when you order your Volume make Volume VIII over 1600 pages. Think of it, over 1600 VIII covering the 1937 -1938 models. pages chock -full of dependable information which will . make the radio serviceman's work easier and more profitable Vol. VIII .$10.00 .. . 1937.38 Vol. IV 7.50... 1933-34 -and at no increase over the price of Volume VII f And Vol. V11.. 10.00...1936 -37 vol. III 7.50... 1932-33 - Vol. VI . 7.50 -.1935.36 Vol. II . 7.50 ... 1931-32 in spite of today's rising costs of publishing, each copy of Vol. V .... 7.50 ... 1934.35 Vol. I .. 7.5 0 ... 1920.31 Volume VIII will be supplemented with an additional

V O L U M E V I I I I N TWO SECTIONS "HOW IT WORKS" MANUAL INDEX A new "plus" service for Rider Volume VIII contains more than 1600 pages of circuit Information Check this easy to follow Indes. Manual user. A separate section en receivers produced by over a hundred different manufacturers. See the tremendous umber of sets which goes with every copy of Volume Auto -radio receivers, hore receivers, inter -communicating systems, and models covered Note, too, VIII and describes the Technical we public address ampliRers, electronic musical instruments, etc., are all that this Indes proves what soy - Features, both mechanical and information on every set is As to the the information "that electrical, that servicemen must covered. completeness of and the models Instantly found." A time saver and know to repair the modern set with represented, we suggest your compering it with any other service o convenience for you. This Indes Automatic Frequency Control sys- now offered. Compare the replacement pans list, the alignment of about 118 pages covers all eight tems and motorised tuning devices. instructions. Compare it for convenience in use, or anything else Rider Manuals and goes with every You will find this section of great value. which would hove a bearing on its value to you. copy of Volume VIII. JOHN Fe RIDER, Publisher, 1440 BROADWAY, NEW YORK PLACE YOUR ORDER TODAY N11111/ti

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adio@ffFOR THE SERVICE MAN. DEALER RADIOTRICIAN "Takes the Resistance out of Radio " 111111111111111mminnueniimiliumei m memi mmununnumeennmunn minim imeeneen murmur nunuuu mmii oninemelemm ineenenem n ueemmnmemnimonnuxuneemeennenummeem enur Editorial Offices: 99 Hudson St., New York, N. Y. HUGO GERNSBACK, Editor Vol. IX, No. 4, October 1937

: 1111111111111111111111111111111! MARCONI An Editorial by HUGO GERNSBACK

c::N JULY 20th, there died in Rome, Guglielmo Marconi motion picture or other inventions usually accredited to him. who may turn out to be the greatest radio figure the Neither Marconi nor Edison were pure research men who world has ever seen. discovered new principles and used them. Marconi . . . wireless . . . radio, all are used Why then Marconi's greatness? It is one thing to discover synonymously and you cannot very well think of wireless an important and record -making discovery, but it is quite or radio without the accomplishments of that indefatigable another thing to find a practical use for it. The two, as a genius who was the first to capture the public's imagination rule, have little relation, and it is usually the man with th3 by an accomplishment, which in the early years of wireless imagination, and the hard -working experimenter who, know- well nigh bordered on the miraculous. ing certain principles, applies them to practical use. If it had 1 Marconi no doubt will go down in history as one of the not been for Marconi, Hertz's discovery might have lain race's great benefactors, as great or greater than any other dormant for decades, but the highly original experiment: benefactor who ever lived. The debt which the world owes and the terrifically hard work coupled with boundless er.- to Marconi is staggering -if you figure only one single result thusiasm which Marconi applied to a well -known principl of his accomplishments -the saving of tens of thousands of gave him the credit which rightfully belongs to him. lives which would have perished in the sea and otherwise, And let no one if it had not been for Marconi. think that it was all easy and that wireless But communication sprang into life overnight. It was always the saving of untold lives is only one of the things hard work in the face of an incredulous world. Indeed, after that the world is indebted for to Marconi. The wireless, his first experiments in Italy were successful, the Italian later the radio age, has brought to life not only a huge government in their shortsightedness would have nothing industry, but has brought all humans closer together, has made rapid to do with Marconi's "contraption" as they termed it. This communication, particularly between fixed and made it necessary for Marconi to go to England and con- mobile stations, a possibility and lately in broadcasting has given tinue his experiments there. Soon his signals had reached the human voice wings such as it never before dreamt across the English channel to France, and from then on of having. wireless communication required no further proofs of its Yet great as Marconi's accomplishments are, he was not practicability. the pure inventor type of man, although his name is frequently linked with the word "inventor." Without trying to But still wireless in those days was very crude and far a detract from Marconi's greatness -there could be nothing from universal. In the meanwhile Marconi surrounded him- further from my mind-Marconi was really not the man self with good technical talent; he also knew where to get who invented wireless or radio. He admitted this freely in needed finances, and finally he availed himself of every new his own lectures. The credit for the original invention belongs invention that came along to make his system more practical. to Heinrich Hertz, who, long before Marconi, investigated While he devised many radio circuits, he did not himself in pure scientific terms the electro-magnetic waves, and discover the fundamental tuning principle, yet he improved indeed to Hertz belongs the honor of being the real Father existing methods of tuning-syntony -as it was then called, of Radio. and soon it became possible to operate many wireless stations Hertz it was who in his laboratory actually transmitted without too much interference from each other. and received wireless signals. By means of a spark coil he But Marconi was not content. He never rested on his let loose into free space wireless waves. For a receiver he laurels. He always was a modest worker who gave credit merely used a small loop of copper wire and observed a small to whom credit was due, and the honors for dreaming about spark which appeared between the two open ends of the trans -Atlantic wireless and the courage to actually start loop every time the key of the transmitter was depressed. experimenting with it in the face of an incredulous world, o These experiments were made by Hertz while Marconi still certainly belong to Marconi. It should not be forgotten that was a boy, but, Hertz was a pure physicist and had little it took a tremendous amount of courage and belief in himself imagination. Marconi, reading of Hertz's experiments, to think that a new and untried system of transmitting promptly started to experiment on his own behalf, and soon electromagnetic waves over almost 2,000 miles of curved he had a wireless transmitter and receiver going on his ocean surface was within the realm of even a remote father's estate in Bologna, Italy. Even Marconi's "coherer" possibility. That took more than courage. It was really a was not his own invention, but Branley's. Others before had supreme heroic gesture, and it is probably for this one out- noted that loose metallic filings in a glass tube became con- standing accomplishment, more than any other, that the ductive to the electric current when exposed near the wave world is paying homage to the dead inventor today. effect of a spark coil or high -power induction coil. In his later years, Marconi again was responsible for As for the elevated aerial used by Marconi, this also was great improvements in radio communication, particularly not an invention of his own as Nikola Tesla had already in the shortwave range and his final researches in the micro- patented a wireless system years before the youthful Mar- wave field which hold great promise, were cut short by his coni began his own experiments. It was Tesla too, who seems untimely death. to be the first to show the use of an elevated conductor for Marconi was truly an international figure, and if there inter -communication purposes without wires. is one man who ever trod the earth, who is entitled to have All of this should not detract anymore from the glory of a monument erected in his honor in every civilized country Marconi's accomplishments than the parallel facts that Edi- on the globe, that man without a shadow of a doubt is the son was not the original inventor of either the electric light, illustrious Marconi.

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! I I I I I I I I I I I I I 1111111 1 1 1 1 111111111 I I I I I I I I I I I I I I I I I I I I I I I I I I 111111

It may be that short -wave apparatus RADIO SETS IN EUROPE,27,719,925J6.t1937 will developed, IN be and generally adopted, GERMANY NEW SETS LICENSED 1936 to facilitate distress calls; but its very GREAT BRITAIN range militates against its being heard 3,145,000 by the nearby relievers -and, in that waste of water around the islands lately visited only by eclipse observers, the most powerful of apparatus would have been none too strong for a call for help. WAR ON "GYP" MIDGET SALES

chute-- Comiulate Genel:,l. I, l',., ... RAIDS were made, simul- CZECHOSLOVAKIA ITALY Nikola Tesla, wizard of high -frequency electricity taneously, last month by and prophet of radio, was honored on his 80th the District Attorney of 622,962 birthday by his native land, Yugoslavia, with the NE HERLANDS stamp reproduced above. (The characters in the New York. on a group of dealers, DENMARK right vertical column spell his name in the charged with selling midget sets to Serbian alphabet.) which well -known nameplates had been SWEDEN attached. A New York law specially prohibits the practice. During the pre- PCL AND RADIO PROVED ceding weeks, the Federal Trade Com- AIR NECESSITY mission also had issued orders to stop Y its use, as well as by imitation of radio set makes. its absence, radio last Ii month again showed A HUNDRED YEARS strikingly its paramount importance in Figures of International Broadcasting Union, Geneva. RADIO? how Europe Licensed 3,000,000 new radio sets last the development of modern travel. OF year. The proportionate growth was greatest in Again a flight was made over the Pole, estimating the period be- countries like Greece, which more than doubled the number. (Spain and U.S.S.R. omitted and some with continual ground communication; tween first conceptions of colonies included in the total.` two great boats (both illustrated at the famous inventions and bottom of page 199) made the first their reduction to practice, a recently - the first practical demonstrations. Tele- trip of what will develop into regular publicized report from Washington vision (},y wire) as a concept preceded commercial transatlantic schedules, with gave the average period as 176 years, radio some years. radio as their safeguard-and a famous and that for radio as 70 years. It is true aviatrice disappeared into the silence. that communication at a distance is a LOWER RATES FOR Amelia Earhart and her navigator, very old idea. (At one time, it was sup- Capt. Noonan, may have met some posed that 2 needles magnetized to- CHEAPER TUBES disaster in which radio could not gether would be "sympathetic" and that SINCE the freight rates on have helped; we do not know. But they one would turn as the other did, at any radio tubes were fixed in did wilfully discard a standard ship set distance. This was disproved by Sir 1934, there has been a which, if they had been living, and Thomas Browne, who showed that the "reduction in the value per pound of known the code, could have brought re- effect could not he obtained, even in the glass tube shipments, while the value l:ef straight to them from the Navy, next room.) It is also true that induc- per pound of metal tubes has also grad- equipped with directional finders operat- tive effects were observed during the ually reduced since their introduction", ing on this frequency. It seems still early 19th Century, but not explained. the R.M.A. announced last month; and doubtful whether any messages were However, the first conception of radio, for that reason it has applied for a re- of actually received from them; and on as such, came with Hertz' experiments; duction in rates on this classification tir July 19 the search was abandoned after and within 10 years, Marconi had made goods. 17 days of feverish excitement. WIND-DRIVEN GENERATOR

Photograph of the northernmost radio station in the world. UPOL, Lat. 90 deg. North. It was established it changes position America's Ladybird No. I shown at the controls exactly at the North Pole but, since it is based on ice drifting in the Arctic Ocean, of her famous "flying laboratory" in which (minus slightly from day to day. Behind the black (to pass the heat rays, and afford best visibility to airplanes) the 500 kc. radio installation, after leaving Miami) station tent with Soviet emblems can be seen aerial masts, wind- driven generator, and other tents she and her navigator Captain Noonan flew into of the party. The station operates on amateur 20- and 40 -meter bands at 1900 and 2130 GMT the great mysterious silence of the unknown. (which is also NM).

198 RADIO -CRAFT for OCTOBER, 1937

I I I I I I I I I I N 11

Radio is now such a vast and diversified art it becomes nec- IN REVIEW essary to make a general survey of important monthly developments. RADIO -CRAFT analyzes these developments and presents a review of those items which interest all. farmed the alarm had worked perfectly. As previously stated in Radio -Craft April 1937, "SOS Robot Threatens Radio Operators "), commercial opera - Ill's have not taken very kindly to the new idea. 4 SOVIET INSTITUTE FOR TELEVISION TELEVISION in the Soviet Union is somewhat behind the stage reached in the United States, Germany and Great Britain, it would seem from an announcement, last month, that its trans- missions are with 120 -line mechanical lens-discs; but with the setting up of an Institute of Television officially, and the dispatch of engineers to study foreign methods, considerable advance can lie expected soon. It is estimated that the Soviet Union has now 3, million receiving sets, typically of the 4 -tube el,,, NN, 01,1100 e 0 The new antenna of WIXKA (Boston) is unique in variety; and 400 amateur transmitters. being used simultaneously for receiving, while broadcasting on ultra -short waves. It is grounded to the Bradford Hotel sign, as a lightning surge protector. MUSICIANS Transpolar flights are now becoming the , r thing. Radio communication, maintained ov e t course, adds greatly to their certimty. Part AGAINST DISCS apparatus being set up in the cab n of the ANT RADIO radio compass loop is ALARM AND PICKUPS -the seen ahead.

WORKS ( Vl'l I l':It "headache ", of FIRST instance in which the kind so common, is DRAMATIC RCA's new automatic ra- promised to the radio dio alarm served an Amer- industry by the ultimatum issued last PROGRAM CAUSES ican vessel in distress occurred last month by the American Federation of ERRORS month when an emergency signal was Musicians that it will strike against the received by the Ensley City from the "indiscriminate" use of phonograph HILE the ingenuity of Sandgate Castle's newly -installed auto- 1 pro' ram directors is of records or transcriptions at broadcast matie alarm. Charles J. Pannill, presi- stations, and also to prohibit its mem- great interest when ap- dent of Radiomarine Corp., was in- bers from furnishing music to he picked plied to current events in a realistic up for broadcast by radio from places manner (:;hakespeare did it on the outside the studios. The deadline for stage), it nevertheless causes much mis- action was set at Aug. 14. The action apprehension from listeners who hear is stated to be the reaction of musicians but a bit of it. Such a program, last to increasing unemployment, and their (Continued on page 247) blaming "canned" music for the condition. RADIO PLAYS IMPORTANT ROLE IN PIONEER TRANS- ATLANTIC FLIGHTS THE two great flying ships "Pan-American Clipper III ", eastbound, and the "Caledonia" of English Imperial Air- ways, westbound-on July 6 crossed the Atlantic simultaneously, preparing the course for commercial 1 -day travel between Europe and America. They passed, midway in flight, and exchanged radio greetings and weather information, while invisible to each other. Right. the "Clipper ", and an operator at the radio equipment; left, the "Caledonia ", and her radio equipment, more fully l 'Imtoe -'1'ho .erold:wu (London) and 51a,,nrs N'irele:s 'Fele :rel,h Co., Ltd. shown.

RADIO -CRAFT for OCTOBER, 1937 199 THE "RESONOSCOPE" NEW ELECTRONIC DEVICE DETECTS "OFF -KEY" NOTES Vocalists and instrumentalists now have available an inexpensive instrument that far outstrips human skill in detecting Singer testing pitch of her voice by observing wave- in a musical form on cathode -ray screen of resonoscope. deviations the pitch of note.

ALLEN B. DuMONT01011110101111llli llllllllllllllllllllllllllllllll0011llllll101111110lllllllllllllllllllllllllllllllllllllllllllllllllll

SOME OF THE USES OF THE N INGENIOUS electronic "robot" used, or any harmonic of same, the NEW "ELECTRONIC is now available which not only waveform will appear to stand still on sounds the Simon -pure tone for the screen. If the note is "flat" or lower MUSIC ROBOT" guidance, but also checks a voice in pitch than the horizontal -sweep (I) Facilitates tuning reed and string or musical instrument and indicates its standard, the waveform will appear to instruments not only for fundamental pitch and its quality! In other words, be moving to the left. if higher in pitch notes but for all octaves. the note under examination is made to or "sharp," it will move to the right. (2) Each instrument in a band may be write its own harmonics on the cathode - The speed with which the waveform tuned to produce new ensemble effects. ray screen, in direct comparison with moves across the screen is a direct in- (3) Singers may actually "see" and the pure note. The eye, far more criti- dication of the extent to which the quickly correct errors in pitch. cally than the most musical of ears, instrument or voice is off -pitch. (4) Broadcast stations use this "robot" determines the musical quality at a to quickly pitch musical groups. glance. OBTAINING FREQUENCY "STANDARDS" (5) Music teachers now may "demon- strate" a student's tone -quality and pitch. OBTAINING HORIZONTAL- AND VERTICAL - Any of the 12 standard frequencies SWEEP FREQUENCIES in this new "robot" may be selected one The "resonoscope," as this new elec- at a time by the turn of the large con- tronic instrument is called, is a develop- trol knob on the front panel. The posi- ment of the Allen B. DuMont Labora- tions are marked C, C *, D, D#, and tories. It comprises a special cathode - so -on. These 12 frequencies represent ray oscilloscope used in conjunction the 12 notes of the chromatic scale. with a standard set of musical frequen- Each setting of the control accom- cies representing the 12 notes of the modates all octaves of the particular chromatic musical scale. These standard note. The middle- octave notes appear as frequencies, produced by 12 electrically - simple waveforms on the cathode -ray driven tuning forks (see Fig. B), are screen. The higher octaves appear as utilized to synchronize a sawtooth oscil- multiple waves, while lower octaves are lator in step with them. The oscillator simply portions of the waves. See Fig. 2. is employed to provide a horizontal- One of the special features of the cir- ,weep frequency for the C.-R. tube. cuit of this oscilloscope is that the hori- Meanwhile, a voltage amplifier is em- zontal -sweep circuit is automatically ployed to pick up the music of any sin- changed in frequency to compensate for gle musical tone by means of a sensi- the change in frequency in going from tive microphone. The amplifier output, one note to another. See Fig. 1. This which constitutes the vertical -sweep fre- allows the sweep circuit to be readily quency, is placed on the vertical plates synchronized at all times by the stand- of the cathode-ray tube. ard frequency of the tuning forks, and These horizontal- and vertical -sweep assures the observer that the number frequencies combine to provide a visual of waveforms on the screen is a direct image of the waveform of the musical indication of the octave to which he or note under observation. See Fig. A. If she is playing or tuning. that musical note is of the same "pitch" The frequencies of the standard Underneath side of resonoscope chassi , showing master tuning forks and driving solenoids. or fregffeney as the standard being (Continued on page 245)

MICROPHONE 0 0

AMPLIFIER ty s; s o f t t t t s ¡ L A 440.00 trTES 91113 CYCLES) D s s r

A' (466.16 CYCLES 329.63 CYCLES E

NOTE OFF -KEY NOTE OFF -KEY NOTE EXACTLY CYCLES CYCLES, F B ( 493.86 349.23 POWER (SLFLAT)v (SLI IN -KEY LINEAR SUPPLY SHARP) C (261.63 CYCLES 369.99 CYCLES Fe /SWEEP Fig. 2. The vocalist (or instrumentalist) provides vertical0 -sweep-circuit frequencies by singing (or playing) into the microphone; which is connected Ce (2rr.le CYCLES 39200 CYCLES, G through an amplifier to the " resonoscope." "Drifting" of the waveform left STANDARD FREQUENCIES or right from a central position indicates. respectively. "flat" or "sharp." CYCLES 415.30 CY,E5) D (293.66 Ge (ELECTRICALLY- DRIVEN Radio-Craft editors have witnessed demonstrations of this amazing device TUNING FORKS) which prove quite definitely that even professional singers and musicians seldom realize when they are off -key. In fact. other tests show. skilled instrument tuners may vary I/3 -cycle from fundamental notes; but this new. Fig. I. Tuning forks determine the horizontal -sweep- circuit frequencies. uncanny. "electronic robot" is precise to about 0.002 per cent!

200 RADIO -CRAFT for OCTOBER, 1937

NEW "RESOLUTION TESTER" FOR CATHODE -RAY TUBES Here is a simplified description of "the initial nucleus of the instrument which the Service Man of the future who intends , to do television work will require." Its complicated pattern , facilitates testing television receiving tubes.

W. E. SH RAGE IIIIIIIIIIIIIIIIIIIIIB 111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111 ONE WHO GLANCES superficially those resembling somehow a number of which, once in a sxsasar:ssmsara. z - over the column -full of patterns, the complex figures asT :ao. Fig. B, shown at right probably while, appear on the screen of their kak 4 4 k: - will not hesitate to assume that "magic box "; especially when voltages sk a - 4 - the summer's heat has caused the edi- having odd frequency relations are ap- tors to go "haywire." Nevertheless plied to the terminals of the oscilloscope. <'ï<}C.:M1::<:sT< :SSs-:::::'r:: : do belong in Radio - But one glance at Figs. A and C, 'krks:ks:kssk52' these illustrations k6k::ka:ki:ka::_::::. s-' . Craft. The patterns concern every pro- showing, respectively, a complicated ísks:aAk::kaai:::::: _::>::::::::::=":: gressive Service Man and amateur who block diagram, and the inside and out- in a few years hence intends to be as side views of an obviously complicated much up to date as he is today with master oscillator, will immediately ex- modern principles of radio. clude the thought that these patterns are the incidental product of work per- "A CIRCUIT FOR STUDYING KINESCOPE formed with a cathode -ray tube. RESOLUTIONS" Mr. C. E. Burnett (of RCA's televi- Those among us who are familiar sion laboratory), the originator of these with the operation of the Service Man's patterns, and the designer of the master cathode-ray oscilloscope will probably oscillator illustrated in Fig. A, calls it: recognize some waveform designs as "a circuit for studying Kinescope resolutions" which makes the issue by no means clearer. However, the same facts, when presented in simplified language resolve themselves into something which, after all is not so very complicated; in fact it is not hard to foresee that a considerably simplified form of this elaborate master- oscillator equipment will, in the near future grace the Serv- ice Man's workbench just as the tube tester and cathode -ray oscilloscope do today!

THE "FLYING SPOT' HAS "STREAMLINE" SHAPE! Now here are the actual reasons for this odd experiment! Television engineers observed that Kinescope (a type of cathode -ray tube designed especially Fig. A. Front and rear ews of the master- oscillator equipment used. (Continued on page 252)

MULTI - r REO. TRIPLER F REQ. T RIPLER POWER OUTPUT MASTER ISOLATION Q AMPLITUDE Q AMPLITUDE AMPLIFIER OSCILLATOR AMPLIFIER VIBRATOR CONTROL CONTROL 493920 -- 493920- 246.960-. 74O,BBO-'. 2222640'- 2222640-

1 S NE NAVES TUNEO ISOLATION MULTI- BLOCKING AMPLIE IE R POWER OUTPI;' A PLIFIER VIBRATOR OSCILLATOR Q AMPLITUDE AMPLIFIER 493920 IQOBO. CONTROL 740,660-- . 70,560-Y 740860--

ISOLATION SAW -TOOTH ISOLATION DISCHARGE AMPLITUDE AMPLIFIER WAVE FROM 60,. CONTROL AMPLIFIER TUBE SUPPLY ISOLATION IQO8O'.. 0OBO-.. LINE AMPLIFIER I. OH I ICON TAL DEFLECTION AMPLI FIER TO HORIZONTAL IoCBO OR DEFLECTING COILS MULTI - FREQUENCY VIBRATOR TRIPLER 'SINE WAVE TO GAIO OF. KINE SCOPE SAW-TOOTH ' 7- WAVE

MULTI- BLOCKING TO VERTICAL VIBRATOR I OSCILLATOR COILS IBO. 30'x. DEFLECTION

NOTE NUMERALS BETWEEN BLOCKS DESIGNATE RATIO OF FREQUENCIES with tester (see Table I). Fig. C. Block diagram of the "resolution tester" showing the various frequency relationships. Fig. B. Patterns obtained RADIO -CRAFT for OCTOBER, 1937 201 "AIR- TRACK" SYSTEM OF BLIND LANDING

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII CHARLES E. PLANCK

THE FAMILIAR "curved beam" any airport. Figure A is an action view radio safe landing system has been of the system shown in Fig. B. (Figure developed by the Washington In- B is a phantom diagram prepared by stitute of Technology to the point where staff artist T. D. Pentz.) it is now ready for commercial use on (Cantfinued on page 248) Fig. A. Note "cross- pointer" (course indicator) meter on instrument board.

OFF COURSE ON COURSE'' 0. TO LEFT A BELOW FLOHT PATH ©- ANO ON FLIGHT PATH ©. RIGW - - Ø. ABOVE FLIGHT PATH © ON

M 'K UN AIRPORT CONTROL TOWER CONTAINING OR EDGE OF FIELD. GIVES PILOT MONITOR BOX SHOWING OPERATION AUDIBLE SIGNAL OF AIR TRACK. OPERATOR IS IN 2 -WAY COMMUNICATION WITH PILOT.

AIR TRACK EQUIPMENT INSTALLED IN TRAILER MOVABLE TO EITHER END OF ANY RUNWAY.

Fig. B. Any deviation of the pane from the slopi.ig "air track" while landing is instantly recorded of the "cross- pointer" meter on instrument board. THE AIRCRAFT -RADIO SERVICE MAN N. H. LESSEM Most radio Service Men fail to realize the MILLIONS of dollars have been spent and are being spent in developing aviation; radio facilities con- excellent business prospects that lie in "pr - stitute one of the major factors in dependable aircraft operation that has received more than its share of financial vate" aviation -per the author's Table I. backing. As a result, intensive work by "flying laboratories" and land crews connected with the larger transport companies has produced discoveries and equipment of great importance. Radio has greatly increased the dependability of commercial air travel, and the basic new developments of the large aviation companies are gradually being adapted to the needs of the private flyer.

THE AIRCRAFT-RADIO SERVICE MAN At left is reproduced a suggestion, by Radio -Craft, that appears in colors on the cover of this month's issue, which portrays only one activity of the aircraft -radio Service Man. (See Table I- "Sources of Revenue for the Aviation -Radio Service Man" -for a more representative visualization of the subject.) We wish to point out at this time that, merely because the number of aviation -radio receivers in use is small compared with the number of home -radio sets, it should not be pre- supposed an excellent living cannot be made servicing aviation -radio equipment. In the first place it is almost a matter { of life and death to maintain the radio equipment in perfect operation; regardless of the cost, within reasonable limits, this apparatus must be kept in perfect shape, and therefore since the servicing demands are relatively limited it becomes evident that this type of radio servicing commands considerably better prices. (Continued on page 230) RADIO -CRAFT for OCTOBER, 1937

1J$ ugiíeYuYo fbiarconí 1874=1937

NEVER before has the lifetime of desert, to ships on remote seas, to avia- a single man been so identified tors flying above the clouds, and into a with a change in the conditions of myriad homes in every city in the land. life on the globe, of which he was the The monument of Guglielmo Marconi, most conspicuous creator, as that of for all time, is the "ether" vibrant about Marconi. Five centuries since the dis- us -even within us -with the messages covery of printing have been required of all humanity. to spread its efficacy over the globe. The Of the man's personality, little need electric light had been known 50 years be said: he was modest, self- effacing in before Edison made it a commercial suc- his work; maintaining the spirit of sci- cess; the steamboat had been demon- entific inquiry until his last moments. strated 250 years before Fulton found The first and most characteristic a backer for his dream. But the mathe- thought in his mind, as triumphs and matical conception of radio waves had honors were showered upon him, was hardly been published before Marconi that he was able to make his genius 1 'hotn- -Wide World via the Marmillen Co no had The late Guglielmo Marconi, "Father of Radio" was born; he was a growing boy, active helpful to others, as other man who died of a heart attack at his Rome estate in the study of science, when they were done upon so wide a scale. His inter- early Tuesday morning July 20th, 1937 at the age first definitely discovered. He was still nationalism was joined with a pride in of 63. The entire world mourns his loss. young in years when he converted their his country, which had initiated modern coni could die, and wireless development possibilities into demonstrable fact. On science with Galileo, and for whom he would inevitably and continuously con- the anniversary of the organization of could speak with a voice that was heard tinue. His work lives on and grows, his company to exploit the invention of and inspired confidence throughout the whether he lives or not. And that means practical "wireless " -40 years to a day inhabited globe. that his work is immortal. His genius -he died. And his invention carried the The Father of Radio has ended his gave the idea to the world; and the fur- news of his passing to discoverers share of the great work. But, as Pupin ther perfecting of his idea needs no seated on the Pole, to nomads in the said, a quarter of a century ago: "Mar- genius."

New radio "homing device" and inter -cockpit communi- NEW U. S. COAST GUARD cation help U. S. Coast Guard answer distress calls. AVIATION RADIO

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I il l l l l l l l l l l l l l l l l l l l l l l l l l

ONE OF THE NEWEST additions to the radio equip- This equipment resolves itself into 2 major divisions. ment of the U.S. Coast Guard airplanes is the installa- One is the "homing device" or direction -finding loop antenna tion here illustrated of the equipment aboard the which may be rotated, by the radio operator, by remote amphibian "Dolphin" of the Coast Guard base at Floyd control. In emergencies where minutes are precious this Bennet Airport. (Continued on page 234)

RADIO -CRAFT for OCTOBER, 1937 203 NEW TUBES FOR THE RADIO EXPERIMENTER All the tubes described this month, oddly enough, are amplifiers. Filament voltage range is from 2 V. to 25. One of the most interesting developments is the use of suppressor grids, in place of deflector plates, Fig. A. Four of 6 new tubes described in this article are illustrated. in a beam power tube.

PART R. D. WASHBURNE

LAST MONTH we told you about The 6J5 is a new addition to the line The 2 W. A.C. -D.C. receivers are the types 6C8G, 6W5G, 6G5/6H5, of metal receiving tubes. This new tube, thus giving about the same perform- 6T5, 2 -RA -6 and WL-461 tubes. a detector -amplifier triode, has an ex- ance as the small A.C. receivers using This month we add to the list the ceptionally high value of transconduct- a 42 -type output tube with about 220 V. following types: 6V6, 6J5, 6Y6G, 6V6G, ance -2,600 micromhos. The other char- available for plate and bias voltages. 1G5A, and 25L6G. Next month we'll acteristics of the tube are similar to It would be necessary, have using conven- some more tube types to discuss those of the 6C5. Because of the high tional tubes, to increase the cost of the with you but at the moment let us see transconductance of the 6J5, the tube small A.C. receivers considerably to what sort of devices have most re- makes an excellent oscillator for super- make them give appreciably cently better per- been added to the "electronic heterodyne receivers. The high trans - formance than the 2 W. output A.C: family." conductance also gives the tube advan- D.C. receivers. tages for use as the frequency -control The performance of the small A.C. AMPLIFIERS tube in A.F.C. circuits. receivers may be improved in economy 6V6 Unipotential- Cathode Tetrode Characteristics as well as power output by using an Power Amplifier. The 6V6 and 6V6G Heater voltage (A.C. or 6.3 V. output tube similar to the 25B6G or (the latter is described elsewhere in this D.C.) 25L6 at lower voltages and larger cur- article) tubes were designed by one com- Heater current 0.3 -A. rents than would be the case with the pany primarily for use in the output Direct interelectrode 42 -type output tube. stage of auto -radio receivers. Both have capacities` The 6Y6G tube is being introduced similar characteristics, the chief ad- (approx.) -grid -plate 3.4 mmf. to fill the need for an output tube vantages being (1) use of the beam grid- cathode 3.4 mmf. which will give even more output at 135 principle introduced first in the 6L6 plate- cathode 3.6 mmf. V. on the plate and screen -grid than and (2) a relatively low heater drain *With shell connected to cathode. the type 42 with 250 V. on plate and of only 450 milliamperes. Its features As Class A' Amplifier screen -grid. The high mutual conduct- permit high output power to be realized Plate voltage (max.) 250 V. ance of the 6Y6G results in a fairly in the automobile -type radio receiver Control -grid voltage -8 V. low input voltage requirement for full without any appreciable increase in the Plate current 9 ma. power output, and permits some de- drain from the storage battery. In fact, Plate resistance 7,700 ohms generation to be used where desired. some manufacturers of deluxe auto sets Amplification factor 20 See Fig. 1C. are using two 6V6G tubes in push -pull Transconductance 2,600 mmhos. Characteristics in the output stage of their receivers. (Data courtesy RCA Radiotron) Heater voltage (A.C. or (See Fig. 1A.) D.C.) 6.3 V. The 6V6 is similar to the 6F6 in size 6Y6G Heater -Type Tetrode Power Heater current 1.25 A. (and the 6V6G compares with the Amplifier. The usual A.C. radio re- Plate voltage (max.) 135 V. 6F6G and 42 in size and general appear- ceiver operates with fairly high plate Screen -grid voltage ance). voltages. The A.C.-D.C. receivers oper- (max.) 135 V. (Data courtesy Raytheon) ate at considerably lower voltages. The As Class A' Amplifier recent introduction of 2 tubes, the Plate voltage 135 V. 25B6G and 25L6, for A.C.-D.C. receiv- Screen -grid voltage 135 V. 6J5 Detector and Amplifier Triode. ers has made possible receivers giving Control -grid bias -13.5 V. Except for its higher transconductance approximately 2 W. output at about the Transconductance 7,000 mmhos. this tube is similar to the type 6C5 tube. same cost as the previous A.C. -D.C. re- No- signal plate current 58 ma. More detailed data follow. See Fig. 1B. ceivers which gave about 0.9 -W. output. (Continued on. page 240)

p3 p3 24 4 GI. 0 G 4 G G1 4s G H© 4 ©G HP3 5 5 3 H F t 2 ::: ... ::: 0 2 p p p... 0 ` 2'::C O 2 ::: O © H H . 7 7 8 _ 0 8 H © e H O " H 6V6 KQ ": 6J5 K d 6Y6GO Kd 6V6G K d iG5Gß © 25L6 Fig. I. The tube symbols .and socket connections of tke entire group of 6 new tubes are given á 204 RADIO -CRAFT for OCTOBER, 1937

NEW SET TESTER FEATURES LOW -OHM SCALE This instrument will measure resistance as low as 0.0I -ohm and with comparatively little current drain. It also has other interesting features you should know about.

B. O. COMPACT, businesslike set -tester with a clean, "pro- high- accuracy, solid forged steel magnet, and real sapphire fessional" appearance has been designed to meet the bearings is critically designed, adequately to meet the severe modern requirements of fast, convenient, accurate demands of portable service and the maintenance of high test procedure on all types of radio receivers, P.A. accuracy over a long period of time. A high ratio of normal and theatre amplifiers, television receivers and industrial to overload capacity is provided to minimize the possibilities vacuum -tube devices. of accidental damage in this very sensitive instrument. The new 5- in.- square meter with long- scale, dead -beat, Sensitivity: 1,000 ohms /volt. Any of the 20 ranges is chosen with an indexed selector MECS .001-A..DC WM50 1.5V. switch. A "zero- ohms" adjuster is provided. Ranges: 0/7/ 0 VMA T 0 4 R..) 1.400v (350V (1413V 7MA 35.E 140%A 231/EG5 =MECS w6- 140/350/1,400 V., D.C.; 0/7/140/350/1,400 V., A.C.; L. output -meter ranges; and, 0/200/2,000/20,000 ohms. 30 AS,,,EG MESG5 r40 CTS 110 MEG¡-11Hk OMIS 0116 OMIS IMPORTANCE OF THE LOW -OHM RANGE 0 s- MP M` ó.m°5- 2.S-.l C 300 C.34 The 200 -ohm range of the ohmmeter is of especial interest l 'oMOF- OHMS OHMS OHMS OHMS 300 to the Service Man and electrical trouble shooter as many 1 1 1 1 4 4 4 e ern difficulties are experienced in circuits of such low resistance 3.0000HM5 not to ordinary types of ohm- *FROOHMSppf that the problem will yield OSHM *l.Jt meters wherein the low end of the scale is badly cramped. 3000-' 2.000 ` OlA OHMS OHMS One -half of the scale of this instrument is used to read ww ]` 0.22 FG from 0 to 3.5 ohms, with the first division reading 0.1 -ohm. al 4> [ f0,460 /", OJJ' OHMS It is very easy to read resistance values to an accuracy of 01 NEG t 1`"'J 11771. large and clear. It is recom- 1006=öl9 0.01 -ohm as the divisions are ns~ mended that resistance values over 10 ohms be read on the 244) Fig. I. Circuit diagram of the new tester illustrated above. (Continued on page

WHAT SIZE OSCILLOSCOPE? What with 3 sizes of cathode -ray tubes being used in oscillo- o scopes, the question is -which one to choose? The facts

1 -INCH TUBE are in this article. VISIBILITY FACTOR - - -- 8.35 EFFECTIVE AREA1k - - -- .525g.iw. PATTERN HEIGHT * - - -- G. M. BUCI-IARD IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIli: 11111: I: IIIIIIIiiI11111: 111111111111111111111111111111111111111111111111111111111 :1:1 ( AF LINES) DOTTED SCILLOSCOPE equipment for with the exception of power supply the service work has now become fair- 3 sizes of oscilloscopes are almost iden- ly well standardized into 3 distinct tical in construction insofar as features sizes. These are -(1) oscilloscopes hav- 1, 2, 3 and 4 are concerned. ing tubes with 1 -in. screen; and large - It is true that a certain amount of O size equipment with tubes of (2) 2 -in., economy in power supply is possible or (3) 3 -in. screen size. when the oscilloscope is designed for Similarity. It is well at this point to the 1 -in. tube (as compared to 3 -in. 2 -INCH TUBE consider the actual construction of the tube), however it can readily be seen VISIBILITY FACTOR -- -33.2 instrument and lay aside for the mo- that this economy is of a minor order EFFECTIVE AREA * - -- 2.075o .ias ment the matter of tube size. (Continued on page 243) PATTERN HEIGHT-A - -- 1.44 INS. Regardless of tube size the complete (ìF DOTTED LINES) oscilloscope contains at least the following elements: (1) Vertical amplifier, (2) Horizontal amplifier, (3) Lin- ear time sweep, (4) Spot and focus con - trols, (5) Adequate power supply. Now notice that regardless of tube 3 -INCH TUBE size the oscilloscope VISIBILITY FACTOR - -- 74.656 instrument must EFFECTIVE AREA 4.666so.INs have the above 5 PATTERN HEIGHT 2.16bä. features. In fact, f RADIO -CRAFT for OCTOBER, 1937 205 ,665 NEON - VOLTAGE EYE' LEAKAGE IMPORTANCE OF VISOR MODERN TEST RANGE EQUIPMENT In this pithy article Mr. Browning (remember? POWER -the famous "Browning- Drake" receiver ?) FACTOR relegates "screwdriver and plier" radio repair men to the discard, and shows WHY CAPACITY ON-OFF modern test equipment and procedure are ANALYZER (A CONDENSER ON-OFF essential. UNDER TEST - - ; POWER j GLENN H. BROWNING Fig. A. A typical condenser analyzer using a bridge -balance circuit.

IN THE SERVICE industry, as well as in many other more than comparable with the cost of the equipment- lines of engineering, there has been great advancement provided the the volume of business is sufficient. in the tools employed. It was only some 10 years ago that In a recent radio service class the writer, as a part of the the cathode -ray oscilloscope was more or less a luxury examination, asked each member of the class what equip- and only to be found in the exceptionally- equipped laboratory. ment he deemed absolutely essential for the servicing of Today, however, many wide -awake Service Men employ this modern radio receivers. Naturally, a good volt -ohmmeter of method of analysis which, in many cases, saves time and is wide range was the first selection. The second selection was capable of rendering a real service in the precise analysis almost a toss -up between an all -wave signal generator and of receiver performance. a tube tester. The next choice was a device for testing A few years ago, most Service Men had little more than accurately the condition of condensers. The writer certainly a speaking acquaintance wiih vacuum -tube voltmeters, but agrees that no modern service work can be done without the in recent years this apparatus has become an almost every- aid of the first 3 pieces of equipment. Consequently, we will day piece of test equipment. New types of testing apparatus pass on to other, more specified equipment. are appearing on the market almost every month, with the result that some of the less -informed are in a quandary as USES OF THE CONDENSER ANALYZER to what pieces of service equipment (1) are most valuable It is generally agreed that condensers cause as many from the standpoint of customer satisfaction and what pieces service calls as any other single component part entering of equipment (2) are capable of producing real income from into the radio set, though resistors will run a close second. the standpoint of time saved. Consequently, a good condenser analyzer will save the It is not within the scope of this article to go into a de- Service Man a great deal of time and trouble. Many make tailed analysis regarding the uses of all the various pieces the practice of testing all the condensers in the radio receiver cf equipment which the modern Service Man could employ to determine their condition, for as most work is guaranteed, to advantage if his finances were ample. However, it is the this may save a return call at the expense of the Service Man. purpose of this article to discuss some of the complexities of Paper condensers of small capacity have a somewhat modern radio receivers and the test equipment best adapted prevalent fault of becoming open- circuited, though actual to render customer service at reasonable cost, and to point breakdowns are far from unknown. Electrolytic condensers, out various types of apparatus which will produce a return on the other hand, either fail or increase in power factor to such an extent that their filtering efficiency is impaired. KC. OFF CENTER FREQUENCY Intermittent reception in the radio receiver, which is the -15 -10 -5 0 +.5.+10+15 general bugaboo, is usually due to paper or electrolytic condensers becoming intermittently open. 16 0 RESPONCE A bridge analyzer, such as the one manufactured by the OF SET Tobe Deutschmann Corp., is a typical condenser analyzer WHEN which gives a rather complete analysis of the condition of the TUNED condensers, for not only does it check the leakage of elec- TO trolytic and paper condensers at operating voltages ranging CENTER 14 50 550, also measures FREOUENCY from to but their power factors and (SYMMET- capacity by means of a suitable bridge network. Intermittent RICAL condensers may readily be determined by obtaining a bridge RESPONCE) balance and manipulating leads, whereupon an intermittent condenser will cause the electron -ray tube or "eye ", used as a null indicator, to give a definite indication of such defect. Practically every Service Man will find such a device for obtaining the complete characteristics of condensers a time saver and a financial asset to his business.

USES OF THE FREE POINT TESTER Free point testers (which permit making tests of any two I? tube elements) are many times a great convenience, especially where work is being done at the customer's residence, which t is, by the way, not recommended as general procedure when any major troubles are involved. Even in the shop, however, -15-10 -5 0 +5+10+15 HORIZONTAL DEFLECTING FREQ. VARIATION OF SIGNAL GEN. the free point tester in many cases will weed out defective VOLTAGE KC. OFF CENTER FREQUENCY tubes which no tube tester is able to definitely indicate. By means of free point testers, plate, cathode, and other Fig. I. Analysis of resonance curves of a set obtained on an oscilloscope. currents may be measured and, consequently, biases cal-

206 RADIO-C RAFT for OCTOBER, 1937 t

culated on resistance- coupled amplifier tubes, etc. When free point testers are used in conjunction with the radio - frequency amplifier or intermediate- frequency amplifier, BALANCE BALANCE CONTROL VOLTAGE erroneous indications may result due to the fact that the SELECTOR capacity introduced in the cord leading from the tube socket to the free point tester may start spurious oscillations in ZERO tuned circuits and thus the currents at which the tubes SET actually operate will differ markedly from the normal values. RANGE In receivers having automatic volume control it is some- SELECTOR times essential to measure the bias on the various R.F. and InIls. I.F. tubes which are being controlled. Poor quality in a radio receiver will often result from some part of the automatic volume control circuit being inoperative. The writer PRESS FOR 10 VOLTS has known of cases where the automatic bias, although ob- A.C. tained satisfactorily in the diode detector tube (when measured across the timing condenser) was not delivered to an I.F. amplifier tube, causing faulty operation of the Fig. B. Representative type of infiniteresistance, bridge- circuit voltmeter. receiver. or 3 megohms in series with the drycell. When used on A.C., USES OF THE INFINITE -RESISTANCE D.C. VOLTMETER it should have a sufficiently high resistance so that it may Recently there has been introduced on the market by the be placed across oscillator circuits without stopping oscilla- Hickok Company an infiniteresistance D.C. voltmeter which tion. It should have an input capacity at least as low as 25 seems to answer a long -felt need, for by its means the D.C. mmf., and preferably much lower. bias on any tube can be readily determined without intro- It would be very advantageous if a reasonably-priced ducing resistance in the circuit which would materially vary vacuum -tube voltmeter could be built for the Service Man the bias and thus the operating conditions. which would be sufficiently sensitive so that by placing the The potentiometer -type infinite-resistance voltmeter oper- prod near to but not touching the oscillatory circuit in a ates on a well -known principle of obtaining a balance be- superheterodyne, a reasonable meter reading could be ob- tween two voltages, one the voltage developed in the appa- tained. By means of this instrument the oscillations could ratus itself, and the other the unknown voltage. After the be checked in a superheterodyne without de- tuning the cir- 2 voltages have been adjusted so as to be equal (this adjust- cuit to any appreciable extent. ment is made by means of a balancing system), the un- Many times it is difficult to determine the trouble in a known voltage is measured by actually placing a voltmeter superheterodyne where the oscillatory circuit has either across the balancing voltage developed in the apparatus itself. developed a high- resistance connection or has been shorted, This may sound somewhat complicated but in actual prac- causing the oscillations to cease. Of course by carefully tice it is very simple, for the leads to the voltmeter are checking the circuits with a volt -ohmmeter (using the low - placed across the unknown D.C. voltage and a knob is ad- ohm scale) the resistance of the oscillator coil can usually justed until a meter reads zero, whereupon a button is be detected on the broadcast and some of the short -wave pressed which throws the voltmeter into the circuit and the bands on an all -wave superheterodyne. However, when a unknown voltage is read directly from this meter. The A.V.C. short occurs in the very -high frequency oscillator coils, this voltages may thus be measured (on each tube controlled) condition is difficult to detect since the normal resistance of with various inputs from the signal generator. The actual these coils is extremely low. Superheterodynes which use a bias on resistance- coupled amplifiers may be determined 6A7, 6A8, etc., sometimes refuse to oscillate in specific with accuracy. A faulty bias resistance, of course, may cause regions of the bands, causing the receiver to "go dead" distortion. It may be necessary to unsolder one end of this throughout these regions. Tube tests do not in general in- resistor to measure its value accurately with a volt -ohm- dicate that the tube is defective. However, replacing the meter since an electrolytic condenser is usually connected in faulty tube with another usually remedies the trouble. For parallel which will have some leakage, and this leakage may these reasons a quick method of checking oscillations through be sufficient to give incorrect resistance values. By means all bands is certainly a time saver. of a very high -resistance voltmeter these biases may be measured directly. Of course it probably will be necessary USES OF THE CATHODE -RAY OSCILLOSCOPE to disconnect the condensers for test purposes anyway, so The cathode -ray oscilloscope, especially one of those con- that the above argument for a high- resistance voltmeter as taining a frequency -modulated signal generator as an in- a time -saving device does not always hold true. tegral part of the apparatus, is desirable if the clientele served by the Service Man is of a very high -grade type that USES OF THE VACUUM -TUBE VOLTMETER is willing to pay for meticulous alignment of their high - In receivers embodying automatic frequency control, it fidelity receivers. This applies particularly to sets having is almost essential to have an infinite -resistance voltmeter or band -pass I.F. transformers. Of course the cathode-ray a vacuum-tube voltmeter which will measure D.C. voltages, oscilloscope can be, and is, used as a very handy tool around as well as A.C., in order to align the tuned circuit of the the service laboratory and the ownership of such an instru- discriminator with sufficient accuracy. This adjustment in ment places the Service Man in a favorable position as most receivers is extremely critical and it is necessary, after regards customer acceptance. aligning the I.F. amplifier by means of a signal generator y and an output meter, to accurately set the tuned circuit USES OF THE SIGNAL GENERATOR which is an input into the diode plates. This circuit should There are many customers who could be very readily sold be so adjusted that the voltage appearing across the 2 the idea of having their high -priced sets checked frequently resistors connected in the cathode circuits of the diodes will for alignment, quality, etc. Checking for quality throughout be equal; otherwise the A.F.C. discriminator circuit will not the receiver and loudspeaker requires elaborate equipment. function as it should. In fact, an automatic recording device has only recently been While we are on the subject of vacuum -tube voltmeters, placed on the market. This device puts into the radio re- it might be pointed out that there are good, bad, and in- ceiver a signal which is modulated at various audio fre- different types on the market, and a considerable amount of quencies, and records automatically on a chart the sound discrimination should be exercised by the Service Man in pressure delivered from the loudspeaker at these audio purchasing this equipment. The Service Man can readily frequencies. Undoubtedly future signal generators designed check up to see whether a vacuum -tube voltmeter is suitable and manufactured for the Service Man will have their signal for general work by the following procedure: If the vacuum modulated not only by a fixed 400-cycle note, but will be tube voltmeter measures both D.C. and A.C., it should be able so designed that the carrier from the signal generator may to measure the voltage of, for instance, an ordinary drycell, be modulated by various frequencies over the complete and give the correct value (1.5 V.) with a resistance of 2 (Continued on page 253)

RADIO -CRAFT for OCTOBER, 1937 207 II.,., HOW TO MAKE "THE SEAFARER" LOOP -TYPE BOAT RADIO SET

Part I described the construction of this ma- rine direction- finder and broadcast set. Here

PERMANENT- MAGNET are the loop details and operating data. DYNAMIC REPRODUCER PART II RAYMOND P. ADAMS Fig. A. The Boat Radio Set and (inset) relationship of loop to scale.

LOOP-ANTENNA building is a matter of trial and turns and load it up to high- frequency resonance with the error. We have used a very small one for general broad- trimmer at zero setting by means of fixed capacities bridged cast-one which works very well. Some builders may across it. Build a loop for the selected short-wave band or prefer to experiment somewhat before deciding upon bands -or, if you prefer, add antenna coils for these bands definite jobs for service -but we shall describe the construc- and a chassis binding post to which an antenna may be tion of the one shown in Figs. A, 1 and 2, with the comment connected. that it will do a very good job as a direction finder. (Continued on page 240)

LOOP CONSTRUCTION DETAILS Secure 2 ordinary embroidery SHIPS COMPASS hoops, one about 8 ins. and SIGNAL one about 7% ins. in dia. To the larger, securely affix a phone MAXIMUM plug. Around the entire rim of the smaller one, drill a series SIGNAL) of size SHIP'S COURSE - No. 27 holes s -in. apart. Insert small, round matches "EXACTLY NORTH; POINT OF in these holes, with MIN. SIG . - an inch or so of each match protruding 10 °EAST MINIMUM 180° OF NORTH. SIGNAL outwardly, and then stagger -wind about 50 ft. of No. 24 SHIPS THIS GIVES STATION PONTER BEARING WHEN MAGNET D.S.C. wire around the COURSE IC-VARIATION CORRECTIONS loop- working back and forth be- ARE MADE. (EDDY, PROTRACTOR SCALE tween CHART AS USED POSITIONED the sticks (as shown in Fig. 2) and in one direction ON S INDIVIDUAL BRDAD BE AFFIXED TO BY EACH LOOP AT BASE until the winding is completed. Cut off the ends of the MARINER. DRAW sloE) matches so LINE THROUGH that the smaller loop will fit tightly into the STATION AT 10° larger, tie the 2 hoops securely together, connect the leads (VARIATION COR- RECTION) FROM ".---,4A1(IM to the phone plug. TRUE NORTH, UM See that the jack on the lift cover (described in Part I of PROJECT SAME .-" SIGNAL this article) is connected to the input SEAWARD AND control -grid -ground GET LINE OF POS- binding posts. Plug in the loop and ITION. TWO TRUE tune in a signal some- STATION BEARINGS where around 1,400 kc. using the tuning dial control. WILL GIVE A-FIX' Vary WHERE THE LINES 1 the setting of the auxiliary loop trimmer and note whether CROSS. SHIPS POINTER or not resonance for the R.F. circuit is obtained and where COURSE ON RECEIVER CABINET it is obtained. If not enough capacity is had to tune the Fig. I. Details of how the direction -finding loop antenna operates. loop circuit to resonance with the signal, add wire to the loop itself until a "hit" is made with the trimmer set for MATCH STICKS INNER approximately minimum setting. If too much capacity is FOR WINDING - LOOP. 6 TD8INS. indicated -then reduce the number of turns until a proper SUPPORTS OUTSIDE DIA. OUTER LOOP= 65/8 TO 8 VnIS condition obtains. OUTSIDE DIA. Now tune to a 550 kc. signal. MAT:- EMBROIDERY Nearly maximum trimmer HOLES DRILLED RINGS APPROX. -IN. capacity should be required for resonance WITH 01A here. If the tuning 78" DRILL WIDE Y8-IN. THICK. will NOT go up to resonance AND SPACED /2-IN.I -your trimmer is too small, AROUND and a larger capacity will be required. Much depends, of RIMS. course, upon loopsize and number of turns. BROADCAST BAND APPROX. 50 FT. N2.24 D.S.C. WIRE STAGGER-WOUND BE- OBTAINING DIRECTIONAL OPERATION TWEEN MATCH STICKS AND 5 RUNNING AROUND LOOP Y2-IN. With the loop built and found tunable to broadcast band CIRCUMFERENCE *C. limits, tape it securely together and give it a couple coats FOR LONG-WAVE BAND LOOP of protective lacquer. Try it out on weak signals. ADD TURNS TO MEET REQUIRE - APPROXAPPROX. MENTS,ORSWITCH-IN PARAL- LOOP When pointed directly at such signals-that is, endwise- LEL CAPACITY. (SEE SPACING the broadcast signal will come in at maximum level. With TEXT.) the loop broadside to the signals, the signal level should be PHONE PLUG FIXED noticeably less, at times inaudible and unreadable on the SECURELY TO OUTER 6E5 "eye ". Even on strong locals -loop turning should afford RING IN ANY NVEN- LEAD TO LEAD TO IENT MANNER a definite point of maximum Z_ PLUG and minimum reading on the PLUG tuning "eye" -with the point of minimum pick -up being the COLLAR SLIDING OVER more easily and accurately defined. PLUG SHANK AND BEARING 360° PRO- Build a loop for the long -wave band- making it somewhat TRACTOR SCALE larger in size and of such inductance that with available I WHEN LOOP WINDING IS trimmer capacity input resonance with the detector circuit SCALE COMPLETED. DOPE WINDING, TAPE is obtained. Sometimes it is good policy-and easy construc- LOOP TIGHTLY, AND PAINT WITH LACQUER.` tion-to simply work out a job with a minimum number of Fig. 2. Detailed specifications on the construction of the loop. 208 RADIO -CRAFT for OCTOBER, 1937

BUILD THIS "OPTIMUM TEST" TUBE CHECKER Service Men -A pioneer in the design and construction of radio test equipment tells you how to make an ultra- modern tube, resistance and capacity tester at low cost. MILTON ;11111

THE MOST important instrument for the radio dealer and one of the most important for the Service Man is a Tube Tester. The design and con- Fig. A. The 'optimum -test' tube checker. struction details of an improved type will be described and illustrated, incidentally, the same components are TABLE I utilized to make several types of tests FEATURES OF THE other than those of tubes. "OPTIMUM-TEST" TUBE CHECKER This tube tester (which incidentally is commercially available (I) Accuracy (circuit error is held to as the Depend- optimum value). able model 306 instrument) has finally passed (2) Protection against obsolescence. with flying colors all require- (3) Ability to test all tubes (emission ments for an "optimum" (best all - test; and improved type of hot around) test unit that would quickly interelement short and leakage and accurately test all the present -day tests). tubes; and in addition provide for forth- (4) Optimum- qualify parts. coming types! The same unit also (5) Simplicity of operation. makes resistance and capacity (6) Low cost ($18). tests!! Ohmmeter ranges The general appearance of the com- (7) (low -ohms: pleted 0 /10,000 ohms; high -ohms scale: device, in a counter -type case, 0/I meg.). is shown in Fig. A (underside, Fig. B) ; (8) Capacity -meter ranges (0.001 -mf. the wiring diagram is given Fig. B. Underside view of the tube checker. in Fig. 1. to 10 mf.). (Continued on page 242)

"Let the customer see you work, but don't let him hear you!" is the advice BUSINESS -LIKE of Mr. J. P. Kennedy, who introduced himself to RADIO -CRAFT readers in "SILENT" SERVICING September 1931 as a business -getting Service Man. mBIBIInNBInWnIBnnBnmuuBBBnIIIBmnuununllllnlmonifiIIBIBBWimilmommili BIBIBNIImmmmmfNWUnnuumnmmmnumnuuumurinumlunnnu unminnmmminmBJ. P. KENNEDY BACK WHEN the daily papers car- MODERN "SILENT SERVICING" TECHNIQUE Now instrument lied radio circuits and you could manufacturers have buy all the parts As circuits became more complex, and eliminated the last psychological bar- at a "dime store," test instruments rier to good service whistles, howls, snaps, and buzzes dis- were designed to probe fees. With an closed many the mysteries of automatic volume con- oscilloscope and frequency modulator or of the ordinary faults of "wobbulator ", a radio receiver. Several million people trol, band expansion circuits, dual I.F. a good signal generator, channels and phase inversion and a multirange volt- ohm- milliam- became extremely clever in analyzing systems, meter, radio by customers still recalled every circuit of a receiver may trouble ear -and repairing their old famil- be analyzed radio sets with a screwdriver. iarity with the noises emanating without a sound emanating Service from from the loudspeaker! These instru- Men found it hard to command "respect - the speaker and protested against rea- ments, :ILIt" service fees. plus a good tube tester, will sonable service fees. (Cost inned on pale 251)

Oscilloscope wobbulator. Sgn.,l generator. 20,000-oh m s olt meter. Ti_be checker. RADIO -CRAFT for OCTOBER, 1937 209 BIGGER SERVICE PROFITS FROM BETTER TOOLS! .... Locating and correcting radio receiver faults in the minimum ...... amount of time results in proportionately increased profits. The author describes in detail the manner in which proper servicing technique and tools make this result possible. O. J. MORELOCK ninon.rnmiuffiuniiiii. mounnnnuuuunuulnonlunuunuluulu nuwwfio mumiunmmnnlnnm mmmommmmnumamR Aer IN THE RADIO repair business, irre- on through the receiver by connecting spective of the individual or com- under the chassis to the socket grid pany, the profits accrued or the terminals. Location of a defective stage salaries paid depend on the number or one supplying incorrect gain calls of sets correctly repaired that leave the for a further examination of the tube service bench for delivery each day. and component parts in the circuit sur- Salaries and profits are a direct in- rounding that tube. terest in any business, especially in serv- (2) Free- Reference Analysis. The ice work and, therefore, an increase in other general method, involves analyzer Fig. A. A high -grade set analyzer designed against of receivers is vital to any or "point -to- point" ( "free point ") meas- obsolescence. Note the replaceable selector block. turnover Beilt-in current jacks automatically place the in- radio repair man. Of course, in attempt- urement. Voltages and currents at each strument in series with any tube element. The excep- ing to increase the turnover, no change tube socket followed by resistance read- tional usefulness of the arriee- connected meter is or discussed by Mr. Morelock in detail. in quality of repair work is suggested, ings where incorrect potentials as this must be kept of the first class in currents appear, will segregate the order to continue a satisfactory busi- defective part. There are other methods ness. From the standpoint of turnover, employed by some Service Men or or- what factors govern the Service Man's ganizations, but these are, in general, ability to accomplish an increase? modifications of these two procedures There are, generally speaking, 2 fac- and may be classed under one or the tors: (1) a simplified procedure for other. locating the trouble and correcting it There is no argument more strongly in the minimum elapsed time; and, in favor of the Service Man than the (2) the use of simplified and accurate use of simple, direct -reading, compact service tools of known quality and de- service instruments. A multiplicity of pendability. gadgets on test units is not only condu- cive to confusion but often causes in- 2 SERVICING PROCEDURES correct interpretation of readings, and As to procedure in locating trouble considerable delay. Many such "gadget 2 methods appear best from the stand- units" appear spasmodically on the point of quick results, preference being market to attract attention in advertise- entirely open to argument in each case. ments, but if purchased are usually (1) Stage Analysis. The first of these found to be confusing or of no value. is the locating of the defective stage The money used in construction of test by making use of an oscillator and a units should be concentrated on the vacuum -tube voltmeter or, possibly an basic needs for accuracy, dependability output meter. This procedure calls for through all kinds of weather and work- measurement of "gain" (amplification), ing conditions, durability and avoidance working through the receiver stage by of obsolescence instead of on useless stage, from antenna to speaker. This controls and devices. What then should can be carried out with an oscillator and Service Men look for in each test in- a vacuum -tube voltmeter, of low- input- strument needed for direct receiver making connections to Fig. B. The two/. rn iavion method of testing tube , capacity design, analysis? used in this specially- designed tube tester, is recom- the grid caps of the tubes all the way mended by R.M.A. as the most economical, flexible and carried (Continued on page 228) and but method of testing tubes. through to the 1st-detector

frequency control discriminator by means of a Fig. 2. Circuit for measuring automatic Fig. I. Circuit for measuring gain -per -stage in radio equipment vacuum -tube voltmeter. conventional vacuum -tube voltmeter. voltages with a conventional for OCTOBER, 1937 210 RADIO -CRAFT NEW CIRCUITS IN MODERN RADIO RECEIVERS The details of the modern radio receiver COUPLING cir- 1Y DE b 05C. 6A 8 G e cuits that make them "different" from previous designs are illustrated and described by a well -known technician. Watch for this department as an exclusive feature in forthcoming issues of RADIO - CRAFT.

F. L. S PRAYB ER RY IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII No. (I) Improved Transrectification. Zenith Chassis No. 5521. Zenith has used the circuit of Fig. lA in many late models to improve 1st- detector action at high signal levels where the A.V.C. tends to bias the converter tube near cut -off. A lead is brought from the control -grid end of the oscilla- for coil to the converter signal -grid lead, around which it is wrapped thus coupling the oscillator signal into the signal control-grid. On high bias values where the signal control - grid is near the cut -off point, the oscillator shifts the control - grid's operating point closer to TUNING INDICATOR the region on the grid- 1a+sw2) voltage- plate- current curve which produces detection. SENSITIVITY SWITCH (2) Separate Discriminator 2nd -Detector Circuit. HIGH AV.0 Fairbanks -Morse 12A Chassis. As per Fig. 1B, .. the last I.F. primary is coupled to 2 secondaries, and each in turn is connected to diodes. One actuates the A.F.C. discriminator while the other acts as a conventional detector. The benefit of this arrangement lies in the resulting circuit simplification. (3) Self -Inverter Circuit. Philco Models 38 -4, 38 -5 Code 121. Philco has found a practical way around using a phase- inverter tube which adds no gain to the amplifier. The result is shown in Fig. 1C. To one screen -grid is added a small load resistor (57) and a signal -coupling capacity to the control -grid of the other TUAUDIO ,ILJ 6Q7G push -pull tube. Operating as an amplifier, but having no SECTION 7 gain the 110 / screen -grid duplicates the control -grid voltage of HIGH MC. MME the tube in which (TO GRID - they both are, in reverse phase, and feeds RETURNS (-3V. (59) -. this voltage to the control -grid of the other tube. OF6J7 BIAS) In this way, a signal is fed to only one grid of the push- b 6A8) (87) pull tube and this tube feeds the other push -pull tube; thus, the need for an extra phase -inverter is eliminated. (4) Tuning- Indicator Sensitivity Adjustment. General Electric Models E -91 and E -95. The General Elec- tric models E -91 and E -95, Fig. 1D, have 2 A.V.C. levels, ( HIGH -V. SEC.) one high level for the R.F. amplifier and a lower level for 19 OH MS the converter and I.F. amplifier. For the 2 high- frequency bands, where DX of low signal intensity is most likely, the colorama tuning sensitivity is fixed at maximum by the 2 connected lugs at the bottom of band switch Sw.2. For the broadcast band, where much higher signal intensities are available, as a rule switch Sw.4 provides a choice of lowering the colorama sensitivity corresponding to the lower level A.V.C. supplied to the converter and 1st I.F. tubes, or using it on maximum as usual. This provides more selective tuning, TC 55 while the A.V.C. voltages DET. 61-16 N. 0.25í+1F. are undisturbed. 55 J M F. (5) Novel A.V.C. Signal Delay. ^aF Philco Model 38 -3. One diode plate of the 6Q7G 2nd -de- R.FC. NOISE-LIM- tector audio amplifier ITER -DIODE TO -1st (Fig. 1E) is used without bias SIGNAL AUDIO for signal rectification, while the other diode is used to 111 LEAD SYSTEM supply 2 separate A.V.C. TO voltages. It is biased through a OLORAMA 0.33- meg.- 0.1 -mf. filter at -3 V. by the drop across the TUNING SIGNAL LOAD 19 -ohm (section) power resistor (87). This also biases all CONTROL DIVIDER foregoing signal control -grids for proper tube operation and A.V.C. R34 the R.F. and I.F. suppressor -grids for better tube efficiency. i Q R22/ rR21 (Continued on page 235) Fig. I. Heavy lines in circuits are those discussed in text. RADIO -CRAFT for OCTOBER, 1937 211 (a)- SELF-HEATING ERRORS DEPENDABLE (A)- FREQUENCY ERRORS HOW INACCURACIES INHERENT IN (r)- WAVEFORM ERRORS THE INSTRUMENT ARE YOUR ITSELF (dl MECHANICAL ERRORS 1 (e) CALIBRATION ERRORS METER READINGS? (f)- BENT POINTER INACCURACIES WHICH HAVE DEVEL- (gl- "ZERO" SHIFT OPED IN INSTRU- Rare indeed is the Service Man who realizes POSSIBLE MENT THROUGH ITS (h) - SPRING ERRORS ERRORS USE & HANDLING just hole, why. and to what extent his service WHICH MAY IL) - BEARING FRICTION OCCUR IN i MEASURE IjI- ELECTRICAL TROUBLES meter readings may be inaccurate -and MENTS (k)MAGNET WEAKENED WITH ELECTRIC- how much it really matters! This article ex- AL INDICATING INACCURACIES INSTRUMENTS III- UNBALANCING DUE TO WAY plains, simply and expertly, the entire subject INSTRUMENT IS (m)- STRAY MAGNETIC FIELDS USED, OR CON- of meter accuracy. The author's published DITIONS UNDER (,I- EXTERNAL TEMP. ERRORS WHICH MEASURE- (0)- INSTRUMENT ALTERS works include his well -known "Radio Physics MENTS ARE CIRCUIT CONDITIONS MADE ,p) QUANTITY UNDER MEASURE- Course," "Modern Radio Servicing," etc. MENT FLUCTUATING INACCURACIES Iqr- POINTER POSITION READ IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII PART DUE TO INACCURATELY ALFRED A. GHIRARDI OBSERVATIONAL Irl- POINTER DEFLECTION ERRORS FLUCTUATION praise, for by working out clever designs, careful selection of materials, and taking advantage of every technical ad- Fig. I. Breakdown chart of the various causes of errors in test meters. vance and possible manufacturing economy, they have suc- available HOW ACCURATE is the voltage reading you just took ceeded in making really fine, rugged, instruments on that receiver? How accurate are the meters you to the Service Man at reasonable cost. are using in your service work, anyway? But the Service Man should realize that these instruments Are you one of those trusting Service Men who are not perfect -no manufacturer claims them to be! Prac- is fairly new or expensive, tical construction difficulties make absolutely precise instru- think that just because a meter to readings that are 100 per cent accurate at any ments unobtainable. A knowledge of the errors likely it will give used to point on the scale? Or, on the other hand, are you one of occur, the origin of these errors, and the means the suspicious but disillusioned type who has tried to check make them negligible (or as small as possible) is of value in test instruments, only to in enabling one to use electrical instruments intelligently the accuracy of the meters his working find that no two readings agree exactly? In either case, you and obtain the best results from them under (in common with most radio Service Men) are the victim conditions. of an incomplete, or inaccurate knowledge of electrical infor, WHAT CAUSES THE ERRORS? strument construction and operating characteristics, that errors do electrical instrument design Now that we are reconciled to the fact anyone closely associated with made with electrical instruments, let and manufacture is well aware that errors exist in all instru- exist in measurements the entire sub- us see what they are and what may cause them. ments, and will admit it freely. Fortunately, inaccuracies have been grouped and is fairly simple interesting. All of the common ject of meter accuracy -and quick reference in a convenient chart in Fig. 1. we can clear up, in this series of articles, some of arranged for Perhaps 4 main sources of inaccuracy: (1) the more troublesome difficulties. Notice that there are those which are inherent in the instrument itself due to its and which may be present even NO METER IS 100 PER CENT ACCURATE design and construction, e firmly in your mind: in brand new instruments; (2) those which have developed First of all, get thi. fundamental fact usage, rough type electrical indicating instruments are in the instrument as a result of its constant no commercial which occur because of the par- guaranteed to read 100 per cent correctly at every point handling, etc.; (3) those instru- ticular way the instrument is used, or the conditions under on the scale -only very expensive laboratory -type those which perfection. which the measurement is made; and, (4) ments approach such of the pointer position by you cannot, and should not, expect the occur through inaccurate reading That means that each of these is further broken readings you take on your servicing meters to be 100 per the observer. In the chart, that's down into its contributing causes. cent accurate. They really don't have to be -but briefly, you should know is, how Let us review these contributing causes of error another part of our story. What they may be present and large the errors are, what their origin is, how you can so that we may understand why the what effects they have on the readings. minimize them, and whether they will seriously affect Itself measurements. (1) Inaccuracies Inherent in the Instrument usefulness of your due to self -heating. Most instru- The accuracy, sensitivity, and reliability of an electrical (A) Temperature errors of the ments contain sources of heat, such as moving coils of fine instrument are determined by its design, the quality resistors, rectifiers, etc., the care taken in its construction, the wire, springs, shunts, multiplier materials used in it, flow. This heat tends to cause a accuracy with which it has been assembled and calibrated through which the currents handled since rise in the temperature of the various parts of the instrument at the factory, and how roughly it has been resistance of these parts, a to make meters that can be priced within -resulting in a change in the made. In order in the current flowing, and a change in the reach of the average user, accuracy has to be sacrificed consequent change the deflection of the pointer. ( "Carbon" resistors have a somewhat. resistance value.) for from less than a dollar up to negative coefficient and hence -decrease in Meters can be purchased the error which may result depends upon the several hundred dollars. Naturally, the more one pays for Naturally, upon used in value of the current or voltage under measurement and an instrument, the better the quality of materials is kept in the circuit. accuracy and care exercised in its work- the length of time that the instrument it and the more the currents involved in the measurements manship and calibration. The general run of meters used Fortunately, since in radio service work are fairly small and the instru- in present -day high -grade servicing instruments represent made time, this accuracy and ments are kept in the circuit only for a very short a good common -sense compromise between problem. sufficient accuracy (around 98 per cent source of error is not a very great price -they provide the shunts and multiplier resistors of resistance for D.C. instruments and 95 per cent for rectifier type A.C. By making of measurements materials which have a very low temperature coefficient instruments) for the general run of servicing change due to heating is are priced within the limits of the Service resistance, their resistance to be made, and increase in resistance of the copper movable Man's pocketbook. Their manufacturers deserve unstinted minimized. The RADIO -CRAFT for OCTOBER, 1937 212

coil is compensated -for by using a control- spring material which produces a restraining spring that weakens just the right amount with change of temperature so as to offset the effect of the resistance increase of the movable coil. By employing these refinements in design, the actual error due to self -heating in commercial instruments is kept so low IF THE POINTER STRIKES DONT BRING THE BENT THE STOP BUT STRAIGHTEN THE that it is negligible. AT THE END OF POINTER BACKTO ZERO SCALE AND POINTER ITSELF - (B) and (C) Frequency and waveform errors. Errors due BENDS'- BY ADJ THE ZERO'SCRE CAREFULLY. to variation of frequency (A.C. measurements), seldom PIVOT TOP BEARING bother the Service Man, because these errors are negligible .-' PIVOT AND - for the frequencies of the A.C. circuits he has occasion to make measurements on. The same is true of waveform variation, which is, to a certain extent, analogous to variation of CONTROL frequency. MOVABLE I (D) Mechanical colt SPRING' l' m errors. The quality of the control springs E WOUND ON 0 used in an electrical instrument has a very important bear- ALUMINUM { U`' ing on its permanency and accuracy. The springs are such FRAME important items in the LOWER meter, that the rigid inspection they L BEARING undergo before the meter leaves the factory of any reliable O AND PIVOT manufacturer makes them almost certain to be in perfect condition. What may happen to them later will be CROSS PIECE discussed. ZERO" / .... Another mechanical error may be caused by friction in ADJUST- / the jeweled MERE ) y bearings. This trouble also, has been reduced SCREW to insignificant Í proportions by proper inspection at the fac- O POIÑTER tories. However, as we shall see presently, rough handling, --o or excessive wear may cause this trouble later. ....---.°e (E) Calibration errors. The scales for very inexpensive IF THE POINTER I5 NOT instruments AT THE CORRECT "ZERO" are engraved or printed all in one batch, on - -".--<:: TO START BRING IT ... the assumption of a MOVABLE COUNTER - particular deflection law for a given WITH,ALLREADINGS EXACTLY TO ZERO BY BALANC_ WILL BE IN ERROR CAREFULLY COIL type instrument; generally the - ADJUSTING ING WEIGNTS individual instruments are THE -ZERO" ADJ. SCREW. ` then adjusted by trial to make their deflections fit the scales as closely as possible. Naturally, such meters do not give STRAY A.C. MAGNETIC STRAY D.C. accurate FIELD FROM POWER MAGNETIC readings; but since the sale price is so low, the TRANS. OF RECEIVER UNDER O FIELD OF DYNAMIC cost of individually calibrating each instrument would be .j TEST. SPEAKER METER METER - f---- - prohibitive, and there is no other alternative. y For the better grade instruments, it is common practice to calibrate x the scale of each instrument individually. It is not cilstzi v necessary, of course, to determine every scale d. division by RECEIVER _ t test, especially - on direct -current instruments with nearly SPEAKER uniform scales. It is usually considered sufficient to check :.t STRAY A.C. MAGNETIC FIELDS DO A STRAY D.C. MAGNETIC FIELD WILL only a few points on the scale of a D.C. instru- NOT AFFECT THE READING OF A PER- AFFECT THE READINGS OFTHE METER ment by actual test. The intermediate points are filled -in, MANENT- MAGNETMOVABLE COIL TYPE IF IT IS POWERFUL ENOUGH AND D.C. OR sometimes by hand, preferably by a mechanical method. Of RECTIFIER -TYPE A.C. METER. NEAR ENOUGH TO THE METER. course, if the shunts, multiplier resistors, or condensers used in the instrument are not accurate in value, this will affect © O the accuracy of the entire instrument. Any subsequent . changes in these values due to `raging" of the resistors, con- . 1 densers, control -springs or magnets, will also affect the accuracy. (Scales, even, are preferably of metal, for per- manence.) (2) Inaccuracies Developed Through Use and Handling of the Instrument DISCONNECT IT FROM A good electrical instrument is as fine and delicate a piece BEFORE USING YOUR OR MOUNTING IT ON ALL CIRCUITS AND TILT SERVICING INSTRUMENT A VERTICAL TEST IT IN SEVERAL POSITIONS of mechanism as a fine jeweled watch. It should be handled INA TILTED POSITION PANEL LIKE THIS: TO SEE IF POINTER with just as much care LIKE THIS. STANDS EXACTLY AT as such a watch, if its original ZERO. accuracy is to be maintained; for many things may happen to it at any time, impairing its accuracy and reliability. Such a simple thing as a bump, or a fall, always possible 1 with lo e 0 0 5 lo o to o s ro portable instruments, may have serious consequences. With permanently -installed instruments, a knock or a blow, continual vibration, effect of powerful nearby magnetic fields, overloads or other disturbances -any of these may affect (a) (b) (C) (d) (e) instruments to such an extent as to make their readings - TAPERED MODIFIED MODIFIED KNIFE- "KNIFE- - KNIFE- unreliable. "SPADE- (F) Bent pointer and overload. If too great a voltage is wPOIN0TER POINTER POINTER POINTER POINTER applied across the meter terminals (or stated in another way, too much current is allowed to flow through the meter coil), OBSERVER O OBSERVER the pointer may strike against the end /!, VF stop with sufficient LINE / violence to bend it. See Fig. 2A. If this occurs, never bring r.\I LIFE LINE SIGHT the pointer back to zero by means of the zero -adjusting SIGHT \; . SIGHT screw, for this will not bring the indications into even approximate agreement with the scale markings. It will bring S the moving coil into an initial position far different o 0 b 0 5 from which occupied that it when the initial calibration was OBSERVED '.--POINTER OBSERVED ~POINTER (OBSERVED POINTER made. See Fig. 2B. The correct thing to do is to straighten POSITION POSITION POSITION) the pointer itself, in order to bring it back to zero. (Fig. 2C.) POINTER POINTER POINTER Errors due to bent pointers are quickly detected (in most "CORRECT" "INCORRECT" "INCORRECT" instruments) by a lack of parallelism between the pointer (LOW READING) (HIGH READING) (Continued on page 236) Fig. 2. Illustrations detailing the points discussed in the text. RADIO -CRAFT for OCTOBER, 1937 213 HOW TO MAKE A CLASS Al PUSH -PULL NEGATIVE -FEEDBACK 60 -W. AMPLIFIER Unlike previous types of negative- feedback amplifiers described in RADIO -CRAFT this new unit incorporates 3 stages utilizing this circuitarrangement. New tubes are featured. WALTER J. BRONSON

I I I I I I I I l I I I I I I I I I I I I I I I I I I I l l I I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I I II I II I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 10.111111 I I I I I I I l l l l the 60 -W. push -pull negative- feedback amplifier. Fig. A. Appearance of of Radio -Craft magazine.) Let us now see how these requirements are met. CIRCUIT DETAILS First, a portion of the signal is fed back from the control -grids of the 6F6 push -pull A -prime stage to the cathode of the 6C8 push -pull voltage amplifier tube V2. (See Fig. 1.) This tube is the driver stage in push -pull combination to the 6F6 grids. Second, feedback is accomplished in the following stage 4 by taking part of the signal from the control -grids of the 6L6s through C13 and C14 including R15 and R16 which are connected to the grid- returns of the 6F6 input transformer Tl. It is well to mention at this point that TI is especially designed where feedback was a prime factor in the design of the amplifier. The secondary is constructed with 2 separate windings making this an ideal component for this particular type of audio work.Although,this transformer can be used for the more straightforward audio systems by simply making a jumper connection from one secondary section to the other. Third, negative feedback is again fed through a resistance - the plates of the 6L6s to the negative wiring and small parts. capacity network from Fig. B. Under chassis view of the amplifier showing grid- returns of the same stage. This not only compensates in the "B" voltage supply regulation, amplifier to be for certain deficiencies HE BEAM -TUBE high- fidelity dual but also aids in the correction of 3rd-harmonic distortion of 3 well -worked out stages of nega- ff described incorporates the 6L6s. tive feedback. ON CONSTRUCTION due to incorrect plate and screen -grid NOTES Distortion, In constructing the amplifier and power supply for this voltage regulation, is a very serious condition -particularly, the feed- system, care should be exercised in closely following in high -power amplifiers that incorporate negative imperative, however, if designed feedback original layout of components. It is backs. Proper methods and carefully- used in conjunction with this ampli- power supplies will correct this preamplifiers are to be systems with well -designed should be perfectly shielded. Although ample off all possible troubles generally encoun- fier, that they fault and ward is available at the 2 primary stages driving the inter - in type of audio amplifier design. (A more de- gain tered this stage driving tubes. tailed discussion of feedback amplifiers in general covering wiring the system is incor- will not be taken up in To simplify construction and their operation and construction into separate units, that is, all audio parts and tubes this article, since much has been published in previous issues porated

,4 . iC13 .02-MF. 600V. BOTTOM c3, a1- 500- 200- VIEW OF 6C8 G MF 6CBG 1 ßlMF / 6F .G'6 pNf) OHM SOCKET 6L6GS 60oV T2 50.060 ' 600V l - 0HM5,1W. LINE 'R11, 1r R3 10.000 0.15- OHMS MEG. RIO 1 W. 500 R5 DIMS, x 1W. Ri .R4. /15 x 0.15' OHMS MEG. ^ t.w. 300V OHMS R6 4 w DIMS C BIAS WR 1011, C16.0.1- o 6F6 -05, O.SMF, MF., 600V. C1B.05- C4, la SOY. R2. / R20, 275V. 3.000 MF, R17 2W 6001. -15,000 kC14:02.MF RIB- OHMS. 1.W. RB/ OHMS, 1 600V 10.000 OHMS. (EACH) (OPTIONAL) 2W 2,500 CIO R22.500 OHMS, 10 W. .020W 2W. L R6 T MF,SOV_ 014145 VOL CONTROL G. s.r 0MM5 sw. 50.000 arrangement. amplifier. The tubes are hooked up In class A -prime Fig. I. Schematic diagram of the 60 -W. push -pull negative -feedback l RADIO -CRAFT for OCTOBER, 1937 214

are on one chassis; and power transformers, including their filter systems and rectifier tubes, are on a separate chassis. The dimensions of foundation chassis are as follows, 9 x 14 x 1% ins. deep; 3/32 -in. -thick aluminum is used. This material was selected for the foundations to minimize weight and for its inherent qualities in the effect of shielding all possible stray hums from audio components and wiring.

TUBE SEQUENCE The 6C8s. The primary input stages are comprised of two 6C8Gs, V1 and V2. These tubes are classified as double triodes with the exception of having a separate cathode for each triode section of the tube. Due to the development of S this new tube, voltage amplifier circuits are greatly simplified, and especially suited where push -pull operation throughout the entire audio system is desired. In the arrangement on the schematic diagram, the reader will note that 1 tube is equivalent to 2 tubes in a straightforward class A push - pull arrangement. Improvement in quality reproduction of the 2 input stages is obtained by employing separate bias resistors and filter Fig. C. Appearance of the heavduty networks to each individual cathode. power supply of th; Tube V1 is shown in the schematic diagram with an open - circuited input: this increases the possibilities of varied types of input couplings and multiple mixer stages. By having a throw -over switch special detector combinations of the phase- inverter type can easily be directly coupled to the input of this amplifier. Simplification of volume control is procured by using a dual 0.25 -meg. volume control having an audio taper operating in tandem. The location of this control is in the control -grid circuit of the following 6C8 which is V2. The 6F6s. Driver voltage for the 6F6 control -grids is accomplished by utilizing the 2 plates of V2 connected at the interstage transformer in push -pull class A. Ample driving power is obtained at this point when the 6C8 plates are operated at approximately 275 V. The grid -returns of the 6F6s operated in class A -prime are taken out with a lead to the negative return of the power transformer P.T.2 having the proper dropping resistor to ground. Bias voltage for the two 6F6s should be approximately 28 V. negative. Fig. D. Under chassis view of the power supply showing wiring. However, it is best recommended to use a semi -variable resistor at this point for obtaining "C" -bias in cases where "B" -POWER SOURCE the bias voltages are apt to be abnormal; this also simplifies A glance the adjustments at the schematic diagram, Fig. 2, will reveal and insures correct tube operation. an unusual method in securing plate V3 and V4 6F6s are triode- connected and screen -;rid voltages (plate and screen for all tubes. Two heavy -duty power transformers are grid tied together at socket). For V3 and V4, "B" voltage effectively put to use, each is 300 from mid -tap of driver transformer transformer having its own to ground. This individual rectifier and "B" filter networks insuring against voltage is taken from a 300 -V. point at the P.T.2 power possible current over -loading supply. These tubes when the operation of the are operated at strictly class A -prime amplifier is susceptible to long hours driving the control -grids of the final of grueling work. stage. Rectifier tubes consist of an 83 for plate rectification The 6L6. This output stage utilizes 6L6s of operated in class P.T.1 supplying plate voltage and current only to the 6L6 A- prime. Negative "C" -bias voltage for the 6L6 stage is plates. approximately 36 V. for both tubes. A semi -variable resistor It is not necessary to use a high- current -delivering recti -' similar to the one used in the 6F6 stage is also employed fying tube for P.T.2 at this point for correcting since only the plates of the smaller bias voltage and simplifying tubes including screen -grid supply for 6L6s adjustments. Supply voltage for the is being drawn screen -grids of the from this source; a 5Z3 affords ample output. The total 6L6s is secured from a 300 -V. point of the P.T.2 power current drain from this power supply supply. Supplying the plates of is approximately 125 the 6L6s is "B" voltage, ma. Transformer P.T.2 is rated at 200 ma., therefore, "B" taken directly from P.T.1, having exactly 405 V. D.C. from voltage and filament supply for mid -tap of output transformer a large -size radio tuner can to ground. Unit P.T.1 is be easily drawn from this source. Due to the fact that the "B" solely the power supply including filament supply for the voltage supply is taken from P.T.2 6L6 plates and filament. supplying the input (Continued one page 251) rOV. (BOTTOM VIEW)SOCKET R27 405V. CH .1 pTl 7. NOTE2 sV' C26. 10.000 J (.000-011m BMF. OHMS, NOTE 1 CCH.g " í000011M 5Z3) R23 600V. C21, 5V R24 BMF, 50w FIELD COIL 831 COIL 16 MF 1c . - 600V '600V. R25 R22 33DV. 4 / c. _e R21 330v C23/ C24 C25 / MF. R26 7 8 7 MF 0.1-6166. tr, 600V. 0.15-MEG. V8 600V. I W. (UNUSED) I. / (EACH) V7 0.1 -MEG. 15,000 NOTES 1AND2. BREAKW"H 16MF 1500 MS, . (EACH) 200V., OHMS, +\ JUMRER ON EITHER FLUG. IF (IMUSEO) o Il` 4. 25 W. SOW 5 - VLUGIN SPEAKER FIELOISUSED. CHASSIS C27 T (SEMI-VAR.1 R28. 6.3V.' P29 C28 100OHM5.25W I- 16 ME (SEMI -VAR.I LSW 200V' I 110V,-

Fig. 2. Schematic diagram of the heavy -duty power supply. Actually there are 2 separate supplies, each with its own filter network. RADIO -CRAFT for OCTOBER, 1937 215 LATEST TEST APPARATUS FOR THE SERVICE MAN Fig. A. The "Cyclops" 9 -in. volt- ohmmeter in use. A is no It is furnished in a portable case VOLT -OHMMETER (0.1 -volt) on all bands. (There "CYCLOPS" high -output tap.) A with overall dimensions of 711a x 8112 x INS. IN DIAMETER! uncontrollable, is IS 9 uni- selector switch provides 400 -cycle 21/2 ins. Its total carrying weight THE AVERAGE shop Service Man R.F., unmodulated 514 lbs. See illustration at Fig. C. internally- modulated (1384) with his array of tools, hot soldering R.F., externally- modulated R.F., and iron, test equipment, etc., spread before 400 -cycle push -pull sinusoidal audio him and with test prods in his hands voltage for amplifier tests that is ad- HIGH -SPEED FUSES probing at certain voltage sources, must justable 0 -1.2 V. The rotor -inductor PROTECT IN NEW in METERS crane his neck and squint his eyes switching is done by making all coil PRACTICAL WAY order to get a reading on his small volt- contacts direct to the oscillating circuit. ohmmeter; and while he does this one entire R.F. SIMPLE METHOD of protecting To exclude strays, the -made volt -ohm- of the prods very often slips and he in a separate, copper- A commercial or home circuit is enclosed is suggested by a lab - loses contact. Follows "cuss words", etc. shielded box. Power supply and module- milliammeters All this fuss and bother can be elim- shielded, oratory that has long specialized on this for circuits are independently merely of the sub- 4 mated, according to the manufacturer power chassis, power supply subject. It consists and the of a double-pole selector switch of the new 9 -inch "Cyclops" Volt -Ohm- cord, and R.F. units are completely stitution meter shown in Fig. A. It has a scale -section filters, for the commonly used single -pole type; isolated by shielded, multi with special 9neter -type which is more than 61/z ins. long, The outer interlocking case is uni- in conjunction enabling accurate readings from a dis- welded in a rich, dark fuses. and finished to various tance of 3 or 4 ft. green baked crystalac trimmed with The one pole is connected because of its special The shunts as in the original hook -up and Furthermore, etched silver designation plates. various construction, only a 4 -in. hole is re- is one 76 oscillator, the other arm is connected to tube complement of a limited range. Usually, quired for mounting. It has a good one 6X5 rectifier, and one 6N7 modu- meter fuses "business -like" appearance, which will the range from 1 /100- to 14-A. can be lator. 4 types of impress most set owners. Its main job, (The Clough- Brendle Co.) split up most effectively by however, which it does very nicely, is to fuses: the 1 /100 -, the 1/32 -, the 1/a- and afford quick, accurate meter indications, ENGLISH- READING COMPACT the 14 -A. ratings. This covers the range which is the easily readable. In this sense it is a VIBRATOR CHECKER from 1 ma. to 100 ma. real time saver and will be appreciated commonly -used scale. See Fig. 1. KNOWN AS the model 4100, this using the method described and in every service shop. checks By (1303) newly-developed instrument illustrated in Fig. 1, the Service Man all types of auto or 6-V. household vi- used in checking are can speed up the time brators, regardless of whether they by quick insertion of the test prod. If, AN R.F. SIGNAL half -wave, full -wave, synchronous, non- potential is AN ACCURACY of by accident, a damaging GENERATOR WITH synchronous, etc., and regardless contacted it merely means the blowing OF 1/2% what the prong arrangement might be. fuses, thereby the of inexpensive meter AS the model 110, this A universal adapter takes care of saving the cost of replacing expensive KNOWNreading, silver -finish diel may be latter. shunts and delicate meter movements. of the direct -read- (1385) estimated to 1/a of 1 per cent. See Fig. The meter used is "weak" or B. Its accuracy is claimed to be 1/2 of 1 ing type, indicating "good", and its frequency range is 100 "bad" vibrators. It tests for shorts, per cent low MUTUAL-CONDUCTANCE kc. to 31 mc. sticking contacts, unsteady output, -TEST METER starting. Only 2 TUBE AND MULTI The radio- frequency output is con- output and poor TESTER not only tests through vernier con- switches and a meter compensator need THIS TUBE tinuously variable of all tubes but also indicates volts, ohms, 4 -step ladder attenuation be "wiggled ", affording simplicity trol and a nlilliamlperes, output, mnicrofarads, ca- from minimum to 100,000 microvolts operation. See dia. Fig. 3 (pg. 217).

1.00o( 0.25. METER ) METER FUSE51 + MEG. 750 A MEG el . 500V 0-25 MEG. 250v. 0.15- ' MEG. t00V' p080 50v._ 40.000 Ic0.C.1 I `- ==1r OMMS 1MÁ

5.000 A.C. MerA I OMMS ..f 5V f1SÉ TAP SWITCH 1 A.l: aC D '6L.

The simple but very practical method of Fig. C. This new vibrator checker tests all types of Fig. I. on protecting expensive volt- ohm -milliammeters utilizes auto or 6 V. household vibrators. Can be used fuses. shop, or carried around. a 2 -deck switch and fast -acting "meter" counter, in the service deck carries the fuses. but 51/2 lbs. Extra Fig. B. This signal generator has 0.5% accuracy. Weighs above description of device. -addressed. stamped envelope. Kindly give (number) in Name and address of any manufacturer will be sent on receipt of self RADIO -CRAFT for OCTOBER, 1937 216

Work's more profitable when the Service Man uses the radio equipment described on these pages. Extended ranges feature some of the test instruments here illustrated; others bid for attention via other advantages. In several instances schematic circuits have been made available to the technician so that he may determine for himself the relative merits of the respective instruments. 4 I I I ::1111111111111111II I I I111111111111111111IIf 1111i11111I1I111111111111111111:f IIIIIIIIIIIIIIIIIIII1l111111111111i1111111111111111111111111111111911111111111111111111D1111111111111011111111111111111111

parity, leakage and deribelr! dial, before delivery to the customer. As a tube tester it has a dual -reading To get the maximum benefit from scale, one marked POOR and RE- Automatic Tuning, the setting of each PLACE and the other graduated in individual station must be exactly on micro -ohms of mutual conductance. See its correct frequency. If this setting -up Fig. D. New mutual . tester. Fig. D. is attempted simply by tuning-in a conducfa -ce tube In addition to the quantities listed broadcast station, it will be found that above it also indicates the amount of probably no two people will tune the hum in filter systems and checks the radio set to the same point, when inductance of chokes with or without listening to the same station. To pre- the D.C. component of current. vent this possibility, this new signal The A.C. voltmeter is accurate on generator and "station setter" was de- all commercial and audio frequencies. veloped to guarantee 100% accuracy on The ohmmeter uses no batteries, oper- every station. ates from the built -in power pack. A few of the many features of the The meter used is a d'Arsonval type, 1938 model 077 signal generator or scale length ever 4 ins., with etched Station Setter are: dial easily readable, owing to color Operates from A.C. outlet; covers grouping of ranges. The sanie scale highest and lowest frequencies (115 kc. is used for reading A.C. and D.C. volts, to 37 mc.), in fundamentals, not har- and it is uniform. No copper -oxide monics; generous overlap of bands: rectifiers are used anywhere in the cir- combined on -off and modulation switch; cuit; all rectification is accomplished by new knife-edge pointer for accurate vacuum -tube circuits. readings; 3 output connections; ex- Fig. E. Signal generator or "station setter ". The unit is contained in a compact ceptionally high R.F. output; full at- case through careful arrangement of tenuation on all bands controllable in the component parts. Case is rubbed steps or continuously; 400 -cycle audio

walnut, operating panel is etched signal provided; equipped with 6 ft . chromium finish. All necessary leads cable and plug having extra outlet are furnished. Instrument is the model built -in; unaffected by line-voltagt AC -51X. variations. (Hickok Electrical Inst. Co.) (1306)

SIGNAL GENERATOR AC -DC MULTIMETER FOR OR "STATION SETTER" FOR RADIO, P.A. AND AMATEUR PHILCOS 1938 -LINE RADIO SETS USE AN A.C.-OPERATED signal genera - T11 A.C.-D.C. MULTIMETER de- tor-a precision- built, laboratory - scribed below has been primarily de- type instrument -has been especially signed to cover all the ranges required developed to meet the needs of those in modern radio servicing. Its adapt- Service Men who may be called upon to ability to P.A. and amateur transmit- service the new line of Philco "Cone - ting needs is due to an additional high - Centric Automatic Tuning" radio re- voltage range (2,500 V. A.C. and D.C.) ceiver models. See Fig. E. It is essen- accessible through a separate set of tial that these radio sets be properly twin tip -jacks. An individually -cali- set -up to the stations on printed the (Continued on paye 246) Fig. F. A universal A.C.-D.C. multimeter.

0.10725 MEG -z. 1wú°s 400MA 9.800 01045 -L i6 PAD tST 100 MV .4 o 0 0 0 0 0 00 o 0 i 15.000 4 .LOrE 9.90D OHM5 Em DC o o 0 0 0 0 o O 21.74 / OHMS) 00 o- I II3at 9500...'5 50 OHMS 4.SVT eF -DC = 166.66" 10V. 50V 250V. 1.000V 1 AMP SOMA i = 2500 2594M OHM5 C-WW,A / /

`A C. . 5.000 - 1.5- l f 10MA LOW OHMS 9.500 '(0.2. 6)75 - 01.445 OHMS t \ t-1 00 M5 MEG. MEG Ç 0 OHMS j 7 ILt11111 1.5 I 0.5- 40 t '10.000 MEGS A OHM OHMS OHMS O L. RECTIFIER 40.000 -® tt\ TEST + 01445 -2500V} A. E. ADAPTERS

Fig. 1. Schematic circuit of the A.C. -D.C. meter illustrated in Fig. F. Fig. 3 Schematic circuit of vibrator tester shown in Fig. C. RADIO -CRAFT for OCTOBER, 1937 217 "LEARN -BY- EXPERIMENTING" BEGINNERS' PRACTICAL RADIO COURSE

EXPERIMENT NO. AUDIBLE TONE GENERATOR

( "RADIO WHISTLE ")

Here is an entirely new way of learning radio! You learn basic principles while building useful radio units!

CONDUCTED BY Fig. B. The audible tone generator for work. Fig. A. The parts needed for Experiment No. code SOL D. PRENSKY

IT IS THE AIM of these Experiments to show fundamental their training by poor grounding in the basic principles of principles of Radio in their practical applications, with their field. the additional thought in mind of using commercially - In a recent talk, Mr. J. K. Whitteker, Chief Instructor at available parts, selected and adapted, so that they will R.C.A. Institutes, said, "Opportunities for Service Men and serve as general -purpose construction material. In this way, other radio workers are increasing considerably as a large much of the apparatus used in one Experiment may be used number of those in the field drop out because of their in- again and again for other Experiments, thus keeping the adequate training in the fundamentals of the science of cost of the apparatus within reasonable limits. radio." It therefore is a matter of first importance to beginners VOCATIONAL POSSIBILITIES and experienced men alike to bend every effort to master As radio develops, the need for well -trained men becomes fundamental principles. These Experiments will go far to much greater. The lack of proper training has become all answer that purpose if the reader actually performs them, the more pronounced with the many new developments like and in addition, consults a standard text book on principles automatic frequency control and the like. Many, who are of radio* for explanations of the many topics and terms sincere in their desire to follow new developments, find encountered in the Experiments. It is to be emphasized that themselves badly handicapped by the fact that no amount any explanations given here in the course of the Experi- of practical experience can make up for the gap left in ment, are not to be regarded as complete, but simply as guides to the principles involved. Saggeslions for Texte The material to be covered by these Experiments will be "Radio Physics Course" by A. A. Chirardi -very comprehensive in the presented in a sequence of individual Experiments, each of fundamentals and quite a large book. which will be a unit in itself, and will assume no previous "Elementary Principles of Radio" by Burns -a much smaller book than above. knowledge of radio to any extent, except that which can be "Principles of Radio" by Henney -a general text. obtained directly from a text book. Generous use will be "Practical Radio Communication" by Nilson and Hornung -a good made of pictorial aids in the beginning. The wood chassis reference book. in the first Experiment, which can be any cigar box, will be "How to Become a Radio Service Man" by Louis Martin -a Radio -Craft Red Book for those interested in service work and a good start to get an found very convenient at first, before it is replaced by work idea of what is to be done. and how. with a metal chassis in later Experiments.

TYPE 30 TYPE TUBE. PH T, T. v PHONES TRANSFORMER TRANSFORMER 0 i C. STMENT CONDENSER Pi 1G o R SEC. RHEOSTAT

"B-A+

Cp SEC. K. KEY R, RHEOSTAT BATTERY +1%2 +3 +4%2

Fig. 2. The wiring diagram in section A is for the convenience of those who cannot easily follow the schematic diagram in section B.

218 RADIO -CRAFT for OCTOBER, 1937

GENERAL TUBE P PRINCIPLES -THE VACUUM p G Since practically all radio work centers about the vacuum IV tube, it is necessary that we start with a simple picture of SEC how this exceedingly versatile device works. O J. O ` I,Y/IVlV/ ..il+. C- C A radio tube (or "vacuum tube ") is inherently an amplifier PH. (IRON T PHONES COREI TRANSFORMER or booster device which can increase the strength of any TOO (BOTTOM VIEW) viEw TUBE SOCKET given signal (radio program, static, dots and dashes, etc.), G T. TYPE which is passed through it properly. It can also easily be modified to produce its own signal, which can be translated BE by headphones into sound, as will be seen in this experiment. :;: F F S-, (TOO VIEW) However, no matter to what use the tube is put, its funda- KEY OR SWiT CH -f mental operation is the same, and it will be exceedingly Aw)STO- Á helpful, therefore, to carefully consider this basic operation. HA DR / R- 1 The vacuum tube, used in radio, is shown (see Fig. 1B IABLE RESISTOR and C) to consist of 3 elements, which are labeled according --4Y2 CARBON 41/2V. ''_h 11 1 13 i - s4h to physical as follows: 11111 ELEMENT 3ORYCELLS their appearance t CONNECTED IN tIATL Filament -a thin wire which is heated by an electric i` .ZINCELEMENT INSERIES OR C - - O .A -C- BATTERY current (from a battery or other source) to a point where it gives off small particles of electricity called electrons, GRID GRID which (when in motion) constitute an electric current. ;I n Plate-a small sheet of metal which is connected externally FILAMENT 11 to the positive side of a battery (or other source of electric FILAMENT ^ current) and thus made to attract the electrons from the ' 'i iil i¡i? filament, which have a negative charge. The similarity of this electric attraction to the well -known magnetic attrac- , . i tion between magnets is shown in Fig. 1D and E. Here it is seen that when a magnet is presented to another 11W, '. magnet suspended by a string, the first magnet when held fl PLATE O '-r. 'C' 11 PLATE in one position will cause the suspended one to be attracted to it (since then, the "unlike poles" [North -South, North - STRING .- South] face each other). When the first magnet, however, P G MAGNET is turned over so that it is reversed, right to left, it will be ATTRACTION found to repel the suspended magnet (since now the `like poles" [North- North, South -South] are facing each other). /r' ).a)\ Grid -a mesh or open lattice -work of wire (placed be- Ja tween filament the and plate) with spaces between the wire, ..f..\ F+ i \ F- through which the electrons must travel on their path to LATE GRID ` O MAGNET SUPPLY } SUPPLY the plate. When this grid is connected to the positive side STRING

of a battery, or other source of electrical supply, it will I MAGNET increase the flow of electrons since, being positive, will it I I t REPULSION also attract the negative electrons because of their "opposite charge." However, the same grid, if connected to the negative side of an electrical source, will now repel the negative elec- ..I r` - FILAMENT trons back to the filament, since "like charges of electricity - SUPPLY fJ - © + I II I repel each other." In this case the number of electrons avail MAGNET able to flow to the plate becomes smaller. Thus, as shown in Fig. 1B, when the grid is positive, the C, ADJUSTMENT CONO. TYPE 30 .01-MF, t'T al number of electrons flowing to the plate becomes TUBE,V CONDENSER greater, since the grid is now helping the current (electrons). f 5,000- When the grid is negative (see Fig. 1C), the total number l OHM cf electrons flowing to the plate becomes less, since the grid RESISTOR now retards the flow of current (electrons) to plate. G the R In this manner, the grid acts as a "control valve" or (RHEOSTAT(RHEÓSTAT "trigger" so that a small change in the electrical charge of IN the grid controls a large change in the flow of electrons j I\AV\A (which is the current) to the plate. T The vacuum tube, in operation, consists of 3 complete PRl.sï Cf il 7I2WATT. f (fi electrical paths, each a completely closed "loop ", called 110V. LAMP MAGNETIC shown dotted in Fig. 1F. circuits, as O ;MS SEC' -A' firm- LOUD SPEAKER (A) The filament loop is fed by the "A" battery or other / form of (low or filament) voltage supply which heats the rZ ~ t K, KEY filament, causing it to give off electrons. 110V.,A..oa O.C. B+ 410, (B) The grid loop (input circuit) contains the signal --INTERNATIONAL OR CONTINENTAL CODE ^- A PUNCTUATION: which is to be amplified. The electric charge (or available .- N .... 1. 0-- -- energy) from a battery which is applied to this circuit is B O - 2--- PERIOD C P - called the "C" (low, to medium, grid) voltage. - - - - 3-- - INTERROGATION (C) The plate loop (output circuit) contains the signal, D - Q - -- 4 - 5 which has been amplified. The voltage supplied to this circuit E R - -- is called the "B" (high or plate) voltage and the positive F- 5 6- BREAK side of it is connected to the plate to furnish "plate voltage." G - - T - 7 U 8 -- -- The tube operates in the following manner: The input H.. - - - WAIT I V 9 - signal, by means of the electric charge it gives to the grid, ---- is able to control the large stream of electrons which travel J - - - W -- - 10 ENDOFMESSAGE- from the filament to the positive plate. By means of such a K-- X - - --- "trigger action" the tube acts as an amplifier. L Y - - - © EÑD OF TRANSMISSION M - Z The tube and the other radio parts which will be used in - - -- the first Experiment are shown in photographic form in Hg. I. A, Symbols of parts used in this experiment; If and C, The action of (Continued on page 232) he grid in a radio tube; D and E, Illustrating attraction and repulsion; F. Fundamental circuits of a radio tube; G, S text; H, The code.

RADIO -CRAFT for OCTOBER. 1937 219 ABC OF MODERN VIBRATOR Y SERVICING Fundamental theory concerning the operation of the interrupter -type and synchronous - type vibrators, and the construction of suitable test units, are discussed. .f

F. E. WENGER Fig. A. New modern test tester des4:ed to all types of vibrators. 11111111111111111111111111111111111I I I n 111111111111111111111111111111111111111011111111111111111111111111111111111111111111111111111101111111111111 AUTOMOBILE -RADIO servicing today, can be greatly After we have A.C. in the secondary, this is rectified the speeded up by the use of a Vibrator Tester. Before same as A.C. is rectified in the conventional A.C. power pack. describing the testing of vibrators, I believe it is well Filtering is substantially the same as that for home-type to take the "mystery" out of the operation of vibra- radio receivers and is designed for the frequency of the tors. Successful servicing of auto -radio sets is entirely de- vibrator. pendent upon the Service Man's understanding of the fundamentals of vibrators and their associated circuits. SYNCHRONOUS -TYPE VIBRATOR Vibrators should be called automatic switches whose time Figure 1B shows the synchronous -type vibrator. Note that constants are governed largely by the mechanical construc- the current in the primary takes the same path as it did tion of the vibrator or switch. in the interrupter -type vibrator. However, the reflected voltage in the secondary is rectified somewhat differently, INTERRUPTER -TYPE VIBRATOR inasmuch as it does not use a tube, but uses the same reed Figure IA shows the interrupter -type vibrator connected in to interrupt the current in the primary and to pass current full -wave circuit. only in one direction. Current from the "A" battery flows through the center -tap During the first part of the cycle one -half of the secondary of the transformer in the lead marked "A HOT," and with is delivering current to the reed, and during the second half the reed in the upper position, the current flows with the of the cycle, the other half of the secondary is delivering arrows. The reed remains momentarily in the upper position current to the reed. Thus, we have accomplished the purpose until ti-e electromagnet draws the reed to the lower position of rectification and passing current in one direction only, and current is interrupted through the upper section and without the use of a tube. The center -tap of the secondary starts flowing in the lower section of the transformer. The in this instance becomes "B± ". The 2 reeds can be elec- contact with the reed is made momentarily until the electro- trically insulated from each other as is necessary in some magnet again returns the reed to the top position. (The radio sets where the negative return is below (less than) electromagnet is not shown in the circuit as this can be ground potential. However, the reed works in synchronism either a series or a shunt type coil.) It is easily seen how with the primary, hence, we have self-rectification. the speed of the reed and the dwell of the contacts will pro- By the foregoing description and a study of the action of duce pulsating D.C. voltage in the primary of the trans- the vibrator and a study of the circuits, it will be noted 0 former. This pulsating current is reflected as A.C. voltage that the transformer and filter systems are separate parts of on the secondary. The transformer ratio is generally 40 -to -1. the vibrator proper and should be tested and analyzed the Thus, we have an alternating voltage in the secondary of the same as similar circuits are in conventional home -radio sets. transformer 40 times that of the battery. (Continued on page 247)

O © fB o fj .A HOT - FULL-WAVE INTERRUPTER-

t PULSATING «ecess D.C. f "B +' TO ÌIiI.icj FILTER [[[ VIBRATOR REED

5 AC. "_ .yyrr cecictczáz=etc` ---.B+" TO A liiR[[Stf - «t-` FILTER 1 ar a T«Qi c A lB ) etc 624, 842o1or. l REED - f r__wetitIOdQ(al QQQ[iI`' ({ I il(tZL. B¡[fad `1`zizc.. . . Fig. I. Section A shows the interrupter -type vibra- r[ QT tor working "full- wave.' The pulsating D.C. in the 5.000 .(Í. .. primary is transformed into A.C. in the secondary OAMS i at a voltage 40 times greater than that in the B1F. .0I-MF primary. A rectifier tube is then required to 2.000V SOOV. B the wlnlehronous -type (CCM) obtain D.C. Section shows vibrator, also working "full- wave." Here, however, O through the _CAUe.9S00oMMS the A.C. in the secondary is rectified t_ medium of contacts on the vibrator reed. A separate rig. 2. Schematic circuit of the vibrator tester illustrated in Fig. A. rectifier tube is not required. 1937 220 RADIO -CRAFT for OCTOBER, This department brings to you each month the newest developments in electronic, radio and public- address equipment. Aggressive tech- THE LATEST nicians use this department to keep posted on + the newer and better ways of doing things. RADIO EQUIPMENT

ULTRA -MODERN DESK -SET 3 -IN, INTERPHONE t INTERPHONE (1286) CRYSTAL SPEAKER -MIKE (The Webster Company) (1290) 4 FOR THE BUSY business man (The Brush Development Co.) there is now available a combina- ALTHOUGH somewhat greater tion desk set and wire-type inter- amplification is required, the 's office communication system. The new crystal-type speaker -mike here desk set incorporates 4 nested ash- illustrated affords a greater fre- trays, 2 fountain -pen funnels, and quency response range than is avail- The newest in office intercommunicat - troughs for pens, erasers, pencils ing units includes, in this all -bakelite able from the ordinary run of mag- and clips. Like this desk equipment apparatus, 2 pen -wells and 4 ashtrays. netic and dynamic transducers de- (1286) the A.C.-D.C. "Amplicall" inter- signed for interphone service. phone is made of molded black bake- As a microphone, its output level lite. Both 2 and -way multiple- station is approximately -40 db. (0 ref. systems are available in apparatus equals 1 V. per dyne per sq. cm.) having the same general appearance. and it is worked directly into the control -grid of the first tube with a grid resistor of 1 meg. When IMPROVED TUBE SOCKETS switching the unit to loudspeaker (1287) position, it is not necessary to use an output transformer between the last stage and the speaker. It is MADE PARTLY of isolantite common practice to shunt -feed the A cleverly- designed socket that will last these new sockets feature in tube plate through a typical Compact audio rack -panel. (1291) appeal to the radio man is here illus- load resistor; and to couple the trated. The isolantite on addition a prong -grip that extends top rotates speaker to the plate by means a a metal baseplate to any desired posi- the whole length of the tube prong. of 0.05 -mf. condenser (to tion in order to facilitate wiring. (1287) The face of the socket is electrically shunt a a- "dead " -no metal extends through meg. resistor across the speaker). !r. Still another feature is the design hich permits rotation, of the .ilantite body to any one of C. posi- RACK -PANEL tions on a metal holder, to facilitate wiring. An isolantite stand -off pillar COORDINATED SOUND is provided; except for the octal SYSTEM (1291) socket which is supplied with 2 metal pillars. (Wholesale Radio Service Co., Inc.) Handset has crystal microphone and SCHOOLS, offices, factories, magnetic earphone. (1292) churches, community centers, NEW BULLET -SHAPE etc., will be particularly interested MICROPHONE (1288) in the self-contained sound system here illustrated. It permits personal calling, mass announcements and the THE NEWEST in bullet -shape dy- rebroadcasting of radio programs or namic microphones features the phonograph records. All components -e of a built -on volume control. are carefully coordinated with each other. Includes The response characteristic is said an all -wave radio receiver. A dynamic microphone in a bullets to be from 20 to 9,000 cycles. Par- shape housing; a volume control is ticularly recommended for use with built -on. Frequency response, 20 to 9,000 cycles, it is said. (1288) a "guitar" amplifier. The bakelite case is available in black, Chines,- MICROPHONE HANDSET red or ivory. FOR TRANSCEIVERS, ETC. (1292) filament rheostat. 1293) FAST -ACTION ARTISTIC A.C. ( INTERPHONE (1289) IMPROVEMENTS in earphones and (United Sound Engineering Co.) microphones have been combined in n new handset for communicating IN THE "personal call -phone" sys- systems, radiophone equipment, tem illustrated an earphone pro- monitoring set -ups, etc. vides comparative privacy; raising Earphone is modernistic type. the earphone from its rest makes 2,000 ohms D.C. resistance (for conversation confidential by bring- plate circuit of a type 56, 76, etc.). ing the remote party's voice over Microphone is a crystal unit that the earphone instead of the loud- peaks at 3,500 cycles for improved e The earphone supplied in addition o speaker. A busy signal is provided. speech intelligibility. Damping pre- the loudspeaker affords, in this u - Every station is a master. The finish vents blasting in close -talking. usually fine- appearing interphone, t e is black with aluminum trim. (Continued en page 23x) Pulpit -type velocity facility of privacy. (1289) mile. (1294)

Crystal "inter phone" transducer has good fidelity. ( 1290) An aircraft radio receiver that obtains 4 -tube efficiency with only 2 tcbes. (1295)

RADIO -CRAFT for OCTOBER, 1937 221 e MODERN SERVICING OSCILLOSCOPES Increase in oscilloscope sales prove that they are becoming more and more popular as regular servicing instruments. Outlined in this article are the features of some of the latest commercial units.

IIIII1111111111111111111881I1. II IIII81181111I1III8 8 8 1 8111111181 1I1. 111111111111118111111I I8I IBII I I IIIIII1111I111111111111111111111111I IIIIIIII IIIIII811IIIIIIII IIIIBIIIII8111IIIIIIII

CATHODE -RAY of 125 -950 mmf. (it is calibrated with "ANALYZER" IS NEWEST SERVICE the special shielded coaxial cable [GI TOOL which connects the instrument to the INSTRUMENT contains the fol- receiver being tested), and is used to align R.F. of THISlowing sections: a 2 -in. oscilloscope the antenna and stages (cathode -ray tube and its power sup- both home- and car -radio sets. This ply), separate amplifiers for the hori- feature enables the engineer to correct- zontal and vertical deflecting plates, an ly align car-radio receivers which re- electronic "wobbler" (frequency modu- quire a variety of accurate "dummy antenna" values for best results. Fixed lator) of improved design, a linear - condensers of 0.1- and 0.5 -mf. are in- Fig. A sweep circuit, and a group of variable and fixed alignment capacities. cluded for I.F. alignment. Spare switch An all -wave signal generator, either positions are available should other external or built -in, is a necessity when values be needed. using any cathode -ray equipment for The coaxial cable is connected to the radio receiver alignment. In order to control -grid of an I.F. tube or to the prevent obsolescence of modern equip- antenna of the receiver (H) (the cor- ment which the engineer might already rect alignment capacity being used), own, this instrument was designed to and the "high" side of the diode -load operate with an external signal genera- resistor of the receiver 2nd -detector is tor. connected to the vertical amplifier (I), All the sections of the block diagram as shown. The horizontal amplifier (J) (Fig. 1) enclosed by the dotted lines is internally connected to a source of are contained in the single attractive 60 -cycle voltage. metal case shown in Fig. A. The controls A few of the many applications in which this model 96 instrument will have been divided into 4 groups -(1) Horizontal, (2) Vertical, (3) Linear save the service engineer time and Sweep, and (4) Alignment Capacities - trouble are: aligning R.F. or I.F. stages so that the analyzer is easily operated of home- and car -radio sets, adjusting and the necessary adjustments may be low- frequency padders without the quickly made. necessity of rocking the receiver gang The fixed oscillator (A, in Fig. 1) condenser, aligning A.F.C. circuits (vir- Fig. 8 which operates at a frequency of 800 tually impossible any other way), and kc., is frequency modulated ± 15 kc. correctly aligning "flat- topped" high - by the "wobbler" (B), thus producing fidelity circuits. Hum and distortion may a bandwidth of 30 kc. be easily located and corrected when This frequency -modulated wave is using the linear sweep (K). mixed with the unmodulated output of the signal generator (C) in the frequency changer (D), the output of COMPACT FOUNDATION which has a contact bandwidth (30 kc.) OSCILLOSCOPE USES I -INCH C.-R. regardless of the signal- generator fre- TUBE quency. The signal generator must be ITH PROPER external addition, adjusted to a frequency which is either W this basic oscilloscope offers facili- 800 kc. higher or lower than that de- ties for the study and adjustment of sired. For example, to align a receiver numerous circuit problems. It may be at 1,000 kc. the generator must be set adapted for R.F. and I.F. alignment, for either 1,800 kc. (1,000 + 800) or resistor, condenser, vibrator and many 200 kc. (1,000 - 800) . other tests. See Fig. B. 441 The output of the frequency changer The oscilloscope incorporates an RCA is fed into the attenuator (E) which in type 913 cathode -ray tube with 1 -in. Fig. C turn feeds into the alignment capacities fluorescent screen; has vertical and (F). The variable capacity has a range horizontal deflector -plate terminals on the front panel, as well as controls for intensity, focus, and sweep amplitude; incorporates a built -in 60 -cycle sweep circuit. The instrument is housed in a metal case with black "electro- enamel" finish and measures only 57/s x 7% x 4% ins. deep. The front panel of this model 840 Ranger Examiner is finished in silver and black. READRITE METER WORKS Fig. I. Block diagram of the oscilloscope illustrated on 234) Fig. D in Fig. A showing circuit sequence. (Continued page t 222 RADIO -CRAFT for OCTOBER. 1937

BUSINESS PROBLEMS OF THE SERVICE MAN The problems confronting a Service Man just branching out "on his own" are many and oft - times unforeseen. This series of articles treat of these problems in a thorough -going, practical and personal manner. Don't miss them! 4 Conducted by JACK GRAND

I I I I I I I I I I I I 1 1 1 1 1 1 1 111111111111 1 l l l l l 1111111111111111111111111111111111111111111I111111111111111111111111111111111111 1 111111111111111111111111111 ti 1111 ti LL IS SERVICE BENCH OF SUCCESSFUL SERVICE MAN not gold that glitters," "knock -out" at elec- The service bench illustrated above is that of a successful Service Man, nor is every idea a howling trical refrigeration F. C. Weckman, of Pittsburgh, Pa., who started on a small scale and gradually success! We humans expanded until now he occupies a total floor space of 6,500 sq. ft. have a and radio servicing, The Picture shows a very small portion of the 6,500 sq. ft. of floor space, great weakness, we get an while Mr. Holtz which is used for auto -radio installation and service. quite a bit of which ie idea and build up in sent in by dealers who do not install or service their radio sets. On the it our imagina- considered himself extreme left is a display board which speaks for itself. This board partially tions until it is beyond reasonable at- a "cracker-jack" as hides from view the tube shelves. The analyzer shown at left of the bench tainment. Data is collected from all an electrical con- is the new Triplett 4-unit case made up of (I) point -to -point tester. (2) tubs sources. We argue the possibilities of tractor. Mr. Holtz (Continued on pago 246) the idea from all angles trying to con- also stressed his popularity and large After you have formed your opinion, vince anyone who will listen that the acquaintance in his home town. He felt put it down on paper, and see how it idea is fundamentally sound. that better opportunities presented compares with the following (illus- Should anyone disagree, then in our themselves in the North -West than trated) analysis. opinion, they just don't get the right here in the East. First-neither has had any business slant. Criticism, even if sound, is dis- The seed was there and the idea grew. experience. regarded because of the extreme en- They decided on a partnership and pro- Mr. Holtz has not been in his home thusiasm on our part. ceeded to make plans accordingly. town for 12 years, and is depending It is just too bad -in fact, brutal - No sooner said than done. They went upon friends and acquaintances that he what a pencil and a piece of paper will to the superintendent, presented their has not seen for years. do. Putting an idea on paper allows case and tendered their resignations. I learned that neither one knew how scrutiny and study. It is surprising how The superintendent had known these many electrical contractors were in things change when imagination is men for a long time and thought well that town, nor could they inform me as eliminated. of them. He offered his good wishes to the number of radio service shops When two or more men get together, and at the same time, in a spirit of located there. They did not know the invariably, discussions arise. Qualifica- friendship, offered them the following type or number of industries in the tions and abilities are discussed, oppor- proposition. vicinity nor did they know whether the tunities and the success of various en- If Mr. Jerod and Mr. Holtz would homes were in congested or scattered terprises are the topics of conversations. take care of the refrigeration plant in areas. They made no effort to determine Ofttimes the desire for a business the chain branch of that city he would the competitive conditions. career and a partnership is the out- secure for them space in the basement From this point on, lack of business come. of that store, rent free. They could experience becomes noticeable. The type of discussion just described also put a sign in one corner of the By studying the sketch (Fig. 1) of was instrumental in the creation of an window. The only stipulation being the store and the space allocated to idea whereby a partnership arrange- that one of them had to be on duty all these men, it became apparent that in ment was created. The "idea" which the time. To this Mr. Jerod and Mr. order for a customer to get to the serv- these two men built up in their imagina- Holtz agreed. ice department they would have to go tion will be our topic for discussion this The picture described is beautiful - through the store, downstairs and to month. prospects looked bright. Combining the rear. True, the space is large, but The names used are, of course, fic- refrigeration and radio servicing with not readily accessible. titious. We shall call these men Mr. electrical contracting as an all -year- Although a sign is permitted in the Jerod and Mr. Holtz. 'round business was a master stroke- window, no merchandise could be dis- Mr. Jerod, a young, unmarried man, and on top of it all -rent free! played, therefore, possible sales of is employed by a large chain organiza- In summation-the following points (Continued on page 246) tion at a fair salary as a refrigeration are outstanding: engineer. During his spare time he had (1) Mr. Jerod is a good man on radio taken a resident course in radio serv- and refrigeration service. O icing and had graduated. Upon com- (2) Mr. Holtz is a good electrician. © pleting the course, he continued work- (3) Both men are good workers, they WINDOWS ]. ing for the chain, and after working are congenial and have worked to- MAIN hours, he would study and experiment gether for a number of years. FLOOR further on radio subjects and servicing. (4) A place of business has been (Q= LOCATION Mr. Holtz, middle -aged and married, provided -rent free. OF SIGN) is employed by the same chain organiza- Mr. (5) Jerod has a circle of friends IÌItlIÚ9{' tion as an electrician. He had been with and acquaintances as prospective cus- ENTRANCE iii£dF this concern for 12 years. Previous to tomers. this time his home had been in one of (6) The combined financial resources the north -western states. are over $1,000. BASEMENT ALLSOTTED FOR Again I repeat -the picture is good. SERVICE DENT. THE PROBLEM Now let us analyze their problem. As mentioned in the beginning of the text with reference to group conversa- ANALYZING THE PROBLEM tions, these two men had ideas in com- What in your opinion are the possi mon. They both wanted to go into busi- bilities of success for Mr. Jerod and Fig. I. The rent -free space offered as "fair exchang ness for themselves. Mr. Jerod was a Mr. Holtz? for one man's full -time services.

RADIO -CRAFT for OCTOBER. 1937 223 Radio Service Data Sheet 212

CROSLEY MODEL A -I57 (FIVER ROAMIO) AUTO RADIO 5 -Tube Superheterodyne; Automatic Volume Control; Direct Tuning

The Fiver Roamio direct -tuning, auto- radio superheterodyne. The power supply and speaker are self -contained, the latter being mounted on the left side of the housing.

Y ~ The Crosley Model A -157 auto -radio set is a single unit, 5 -tube superheterodyne receiver, incorporating A.V.C. and many advanced features in circuit design. The power supply unit is an integral part of the i;;L:Ì receiver chassie ame uses a primary -type vibrator. IWJ Tubes ana Voltage Limits. The following table gives the functions of the tubes used, together with the voltage readings between the tube to socket contacts and the receiver chassis. Voltage readings taken with a. 1,000 ohms/volt, 500 in (DS N -V. voltmeter (except filaments) with receiver ° a. operating condition and no signal input. o , 3 TUBE SOCKET VOLTAGE READINGS o Tube Function H P S Su K Ca G.. 4.2 ó2a á 6A8G Osc: Mod. 6.0 220 90 - 0 90 4) Y a > 6Z7G I.F. Amplifier 6.0 220 90 0 0 - - cn03 \^ Wv 6Q7G Diode Det. & A.F. Amp. 6.0 110 - - 0 éa=ÑfR _\ LL Output 6.0 200 220 0 - - s3 - , 6R5G Rectifier 6.0 220 - ffffL - - - - Power Output approx. 4 W. Battery Drain approx. 5.7 A. at 6 V.

Connect the output meter to 3 and 4 of the 6K6G output tube socket. Be sure the meter is protected from D.C. by connecting a condenser (0.1 -mf. or larger-not electrolytic) in series with one of the leads. 1. Tuning I.F. Amplifier to 455 kc. oc n (a) Connect the output of the signal generator through n 0.02 -mf.. ^s or larger. condenser to the top cap of the 6A8G Osc: Mod. tube, leaving the tube's control -grid clip in place. Connect the lead from the z ground $ a signal generator to the receiver chassis frame. Keep the generator leads as far as possible from the control -grid lends of the other screen -grid tubes. 1- (b) Adjust the station selector so that the rotor plates of the tuning condenser are completely disengaged and turn volume control to max. QVylyttQy I (c) Set the signal generator to 455 kc. -. (d) Adjust both trimmers located on the 2nd I.F. transformer for maximum output. (e) Adjust both trimmers located on the 1st I.F. transformer for maximum output. (f) Repeat operations (d) and (e) for more accurate adjustments. In order to prevent A.V.C. action always use the lowest signal generator output that will give a reasonable output meter reading. 2. Aligning R.F. Amplifier. (a) Connect the output lead from the signal generator through a 250 mmf. condenser to the "ANT." connection of the receiver. (b) Set the signal generator to 1,400 kc. o (c) Adjust the station selector to 140 on the dial. (d) Adjust the trimmer on the "OSC." section of the tuning condenser W for maximum output. o (e) Adjust the trimmer on the "ANT." section of the tuning condenser LL I for maximum output. rD ly to (f) Readjust the station selector for maximum output. Do not readjust w x Ñ the OSC. trimmer. for more accurate adjustment. i (g) Repeat operation (e) IL U O ana 3. Adjusting Antenna Compensating Condenser. Ó- (a) Set the signal generator to 600 kc. (b) Tune in a 600 kc. signal with the station selector for maximum output. (e) Adjust the antenna compensating condenser, Cl. (d) Repeat operations (b) and (c) alternately until no further improvement can be obtained. (e) Set the signal generator to 1,400 kc. again. (f) Tune -in the 1,400 ke. signal with the station selector for maximum output. (g) Readjust the trimmer on the "ANT." section of the tuning condenser for maximum output. It will be necessary to adjust the antenna compensating condenser to has been installed in the car. e.i the car antenna after the receiver (a) After the installation is complete, tune -in a WEAK station between 55 and 65 on the dial. (b) Adjust the antenna compensating condenser for maximum volume in the speaker.

for OCTOBER, 1937 224 RADIO -CRAFT

BUILD THIS "INTERMITTENT OPEN" CONDENSER TESTER A factory -type "breakdown -test oscillator" is described.

JOSEPH MOSTO Fig A. Appearance of the "intermittent open' condenser tester.

NE OF THE MOST difficult condenser troubles to immediately, and in others it may be necessary to allow the detect is the problem of open, or "intermittent open" condenser to "cook" for 5 or 10 minutes. If such a weak O paper condensers. To detect these conditions quickly contact is present it is certain that the heavy R.F. current, and efficiently a special type of tester has been designed and which passes through the condenser, will produce the de- is in use in a well -known condenser factory. Service Men sired permanent open and thereby the faulty condensers can may wish toduplicate it. See Fig. A. be eliminated. See Fig. 1 for schematic circuit. The tester consists of a push -pull oscillator circuit that will deliver approximately 8 watts of R.F. power. This HOW TO USE THE INTERMITTENT -OPEN current is sufficient to tend to break down any intermittent CONDENSER TESTER contact between the condenser terminal, or wire, and the The circuit is so arranged that the condenser under test condenser foil. In some cases this break -down will occur is placed in a series resonant circuit with the variable condenser of the tester. By varying the capacity of the variable VIITLR CH .1 C.70MMF CV V.T. 45 MA. condenser, with the 1500V. 350 200 (650v CV, test condenser in the circuit at (snow) MMF. l 15061A terminals TEST, resonance is indicated by maximum glow L SEC.) u L2 i of the pilot light, V. Also, it is possible to have a capacity / \ o indicator by calibrating the variable condenser with standard o condensers of known capacitance. Intermittent -open con- °o can be detected by flicker of the light; and C3. densers the pilot 2TURN5 no -glow indicates a completely -open condition. á00v. C2,D1.MF (ucv) In construction of the tester, it may be necessary to / 800V 45 adjust the coupling of the coils in the resonant circuit to CI.00SMF. I R.FC.. 150MA.. glow light, however, x obtain maximum of the pilot after a - 400V 110V A.C. few trials this condition can be obtained satisfactorily. Use

Fig. I. 5d nef;. circuit of the condenser tester s`,ow.., ab_e. (Continued on page 241)

NEW INSTRUMENT SPEEDS FREE -POINT TESTING A new device permits breaking various tube circuits to obtain current instead of voltage measurements.

H. KOCH IlfRlllfflfffllftlffllfllRRRiRfRffllflffllllilfllRRRRRRRi fRRRRRRRRRffiRRii

NEW INSTRUMENT has made it possible to quickly Fig A. The new instrument which facilitates free -point testing. Its "series- and conveniently make the very important current circuit" jacks permit current readings of any circuit. A measurements and point -to -point voltage and resistance tests through the cord-and -plug method of analysis. Also, it eliminates the confusion caused by the great number of i tube types now in use, in new and old receivers. Through the use of machined cards (see Fig. A), placed over the jack switches, covering the internal connections and designations of all types of tubes, the operator has an ideal set -up for making a complete analysis without interruption of his trend of thought. Tube manufacturers can arrange the elements in any sequence they see fit for it is no longer necessary to refer to a complicated chart or to try to remember the connections or numerology of the various elements. This instrument, which has been given the name of "Anal -O- Scope," when used with any volt -ohm- milliammeter is a practical and convenient device for taking current readings. Due to the complexity of the present -day receiver with its complicated and high -value resistance networks. the current method of analysis is becoming a very practical Fig. I. Schematic diagram of the instrument illustrated above. Note the (Continued on page 249) "series- circuit" jacks for insertion of a current -reading meter.

RADIO -CRAFT for OCTOBER, 1937 225 CORRECT PLAYBACK OF SPOT RECORDINGS

Proper playback of spot recordings is equally if not more important than the actual recording. Here are some inter-

PROPER ANGLE OF esting facts. r NEEDLE WHEN PLAYING BACK ACETATES

RALPH L. POW ERIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIPA RT I r.....,.. O Y E, 30 TO 32 DEG. the ordinary playback pickup totally the record space, or lands between the fails to reproduce many of the recorded grooves when there is any appreciable WHEN LESS THAN 30 DEG. frequencies! side pressure. Naturally, the remedy is The average playback set -up is en- to use an arm the greatest longest possi- tirely unsuitable for use on instan- ble length, together with a frictionless G TRAILING -SHOED PLAYBACK NEEDLE taneous recordings, for the following pivot bearing. reasons: Further examination discloses that a Fig. I. A, Adjustments of the phono pickup; B and great number of pieces of equipment C, Proper playback angle of needle and head. (1) Excessive head weight results in excessive needle pressure (which causes used to playback instantaneous records not only fail to reproduce for the listen- tearing of the groove bottom and sides) ; NUMEROUS articles have been er the frequencies and quality recorded written in the matter of exact (2) Too -short an arm results in ex- on the discs, but very often the modu- recording procedure for the mak- cessive side -wall pressure at the ex- lated groove in a single playing is not ing or cutting of instantaneous records treme end of the are in the swing of only seriously deteriorated but in many on both aluminum and the so- called the arm across the record. cases completely ruined. acetates. But articles covering the sub- While not so serieus on cellulose- ject of correct playback have been rare. coated material, its most aggravated ACETATE RECORDS VS. form shows up on aluminum, where COMMERCIAL PRESSINGS WAX, ACETATE AND ALUMINUM there is of necessity, a very shallow It must be borne in mind that there is RECORDINGS groove together with a soft, pliable a vast difference between acetate rec- Close examination of recordings on playback needle which quickly wears ords and commercial pressings. wax, acetates and aluminum show that its point out of the groove and onto (Continued on page 244)

FREE -A I -year subscription to RADIO -CRAFT to vorit each person who submits a WITTIQUIZ that in the opinion of the Editors is suitable for publication in RADIO -CRAFT. Read the following WITTIQUIZZES; can you spot the RADIO correct answers? Now send in YOUR idea of one or more good WITTIQUIZZES based on some term used in radio, and win an award. (Contest rules appear on page 235.)

WITTIQUIZ IIIIIIIIIIIIHIIIIII IIIIII IIIIIIII I I IIIIII IIII IIIIII I IIIIIIIII IIIIIIII IIIIIIIII I IIIIIIIIIIIIIIIIIIIIIIIIIIIW 'IIIIIII IIIIIIIIIIIIII IIIIIIIIII IIIIII li

(10) Did you ever know that ampere - (a) A grid, cut on the diagonal. (b) point of amplification versus percentage hour is- A direct component of the grid voltage. curves. (d) The amplification factor of (a) A popular radio program. (b) A (c) A neutral voltage on the grid of a a power tube. quantity of electricity. (c) A fractional tube. (d) An intermediate component of (17) Most radio fans know that a part of an hour. (d) A particular kind the grid voltage. voltage divider is- of time. (e) An astronomical expres- (14) A haywire hookup necessarily (a) An official appointed by the sion of distance. (f) The speed of an must be- F.C.C. to see that radio voltages are electric current. (a) A circuit wired carelessly. (b) A evenly divided among licensed broad- (.11) Radio- frequency currents travel cross -connected radio network program. cast stations. (b) A voltage- measuring along the surface of a wire because - (c) A farm -type radio set. (d) A radio instrument. (c) An electrical mathe- (a) The shortest distance between 2 set connected by means of wire from a matician. (d) A resistor provided with points is a straight line. (b) 2nR is the bale of hay. contacts for obtaining desired voltages circumference of a conductor. (c) Cen- (15) Volume control. Are you when a voltage exists across the entire trifugal force drives it there. (d) "Skin - thoroughly familiar with these words? resistor. (e) A resistor which generates effect" is characteristic of high -fre- Would you say that they referred to- various voltages. quency currents in a solid conductor. (a) A device for reducing signal in- (e) Skip- distance effects arise at high - tensity. (b) A dietician. (e) A weak (18) It is now definitely established frequencies. radio tube. (d) A low-loss potenti- that the Luxemburg Effect is: (12) You may not know offhand, but ometer. (a) The peculiar property of micro- l E. M. F. means - (16) If you overheard a conversa- waves hastening the "souring" of a (a) Equipment Manufacturers Fra- tion in which you caught only the particular cheese. (b) Cross- modula- ternity. (b) Electromagnetic force. (c) words power factor would you know tion of radio waves in the ether. (e) A Electrical motor friction. (d) Electro- this was a reference to- frequency drift of the transmitter due motive force. (e) Electrical microfarad. (a) An electricity generating sta- to a high cheese content in the casein (13) Did it ever occur to you that tion. (b) The ratio of true to apparent insulating parts. grid bias is- power. (c) The nomograph crossover (Continued on page 235)

226 RADIO -CRAFT for OCTOBER, 1937 l

OPERATING NOTES SERVICING QUESTIONS ANALYSES of & ANSWERS Service Men may write, requesting answers to specific service questions. Address inquiries to Service Editor. For questions answered by mail, RADIO RECEIVER SYMPTOMS a service fee of 25c per question is made. Only questions of wide interest can be published. 1111111111111111IIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIII11111111111111111111111111111111111111111111111111111IIIIIIIIIII I1111:1IIIIIIIIIIIIIIIIIIIIIIIII111111111IIIIIIIIIIIiIIli11I1lI1II1111IIIIlI11 IIII1111IIIIII IIIIII1111IIIIIIIIIII IIIIIIII II IIIIIIII II I I IIIIIIII IIIII IIIIIB I IIIII I III I I Illlllllll I

Pilot 114, 115. When the complaint of fading, justment must be made with the permanent Note: An effort is being ade to maintain 48- intermittent reception or oscillator drift is re- magnet in place, although the latter may be hour service on mail inquiries. from Service Men, ceived on these models, determine whether the turned down in order to gain access to the ad- addressed to "Servicing Questions & Answers." fading exists on all bands or only over the low - justing screws. It should be remembered that Let us help you on that rush job. frequency portion of the broadcast band. the keeper bar must not be removed until after Since an inter -station noise suppressor stage the magnet has been returned to its position P.A. FADER is employed, a shift or frequency drift of cnly across the pole- pieces. (26) D..1. Fink, Long Beach, L. I. 4 or 5 kc. will produce an inoperative condition BERTRAM M. FREED (Q.) What is meant by a "fader" as applied when the silencing stage is switched on and to a P.A. system? How is same used and why? being used. Reception can again be obtained by Majestic 130. Fading on these models is usually (A.) A fader system that is usually associated re- tuning to the carrier. An intermittent oscilla- traced to the grid- return bypass condenser,. with P.A. work is a means of regulating the tor plate coupling condenser, a 0.01 -mf. unit These condensers are in small metal cans located intensity of the input signals (voice or music) (see Fig. 1E), has been found at fault in this under the gang condenser shield. See Fig. 1A. by the operator of the system in order to permit case. This condenser connects between the type a mixing of voices, or phonograph recordings, 76 oscillator tube plate, and the arm contact of Majestic 90. Fading on these models is caused or both. the rear section of the wave -band switch. Upon by cathode bypass condensers in the R.F. and A series of potentiometers, connected to the replacement mount the unit firmly to remove detector stages. Another complaint on this model various inputs, is so arranged that, by rotating the possibility of vibration and consequently is inability to get stations on portion of dial the controls, mixing is accomplished. microphonics. caused by shorted gang condensers. BURNED -OUT AUDIO RCA Victor RAE -79, RE-81. Although these Majestic 70. Weak and distorted reception on two models use entirely different chassis. they the Majestic 70, which clears up when putting TRANSFORMER are both radio -phonograph combinations wherein the aerial on the grid of the 2nd or 3rd R.F., (27) H. C. Johnson, Springfield, Mass. the phonograph pickup is employed for home but gets weak and distorted when putting the (Q.) I have a Silver -Marshall model 730 and radio recording as well as record reproduc- aerial back to the aerial post, is caused by an "Round- the -World 4," battery operated. In the tion. "open" in the volume control. See Fig. 113. schematic circuit of this receiver a No. 255 After some period of use, in every case where blot/tic Isxnweri Silver -Marshall unit is used in the 1st audio the home recorded records are produced, it will stage. and a potential between 45 V. and 135 V. be found that not only will record reproduction Philco 54 A.C.-D.C. Distortion. Check wire - L specified. I am using a "B" a :imil:atur in become weak and distorted but that home or wound resistor on rear -right of chassis. The low- place of the "B" batteries. On the 90 -V. tap of radio recordings cannot be made with the same er portion of this unit develops high resistance the "B" eliminator I get a vol::,. e reading of volume and clarity as before. Since an additional (contact), and gives the type 75 tube triode - 135 at the plate Prong of the UX 222 socket. weight is placed upon the phonograph pickup grid an incorrect bias. Remedy -clean the In an effort to improve reception, I stepped up when producing home recorded records, the terminals and wire thoroughly, and resolder or the voltage regulator on the "B" eliminator, and pickup device is subjected to a good deal of replace unit. Distortion can aLso be caused by as a result burned -out the primary side of the strain, inasmuch as it is not especially manu- gradual increase in volume control resistance, No. 255 transformer. I replaced it with a factured for this purpose. and generates an due to wear. which changes the diode load. See straight audio transformer having a ratio of unusual amount of heat when used for any Fig. 1C. 3 -to -1 and it works, but not very satisfactorily. length of time. This causes the wax with which Please advise me how I can correct this trouble. the pickup coil is impregnated, to melt and run RCA Model R-10. When noise, similar to a (A.) The reason that the voltage reading on down between the pole pieces and armature. and noisy tube or loose connection, is encountered on the plate of the type 222 R.F. tube seems to be upon the rubber damping blocks. Of course. this model, it may be caused by the metal excessive is primarily due to a minimum drain this action does not take place until several grommet through which passes the control - of your set; in other words. the 'B" eliminator months of operation when the loss in phono grid wire to the 1st- detector being loosely fastened was designed to supply more plate current - output becomes markedly apparent. to chassis. A minute potential, which shorts inter- approximátely from 60 to 100 Ma. The only method of effecting a repair is that mittently to chassis, due to mechanical vibration. Therefore, you can readily understand why, of dismantling the entire pickup unit, being is developed in this small metal loop. This results with very little plate current being drawn by sure to place a keeper across the magnet before in a varying voltage being superimposed on the (Continued on page 254) its removal and noting its polarity in relation signal voltage going to the control -grid of the to the pole- pieces. The armature and pole- pieces tube. As there is a great deal of ampliflcati.1 should be carefully cleaned so as to be entirely present, the noise resulting is very objectionable. MICROPHONE INPUT TUBE free from the impregnating compound. In some See Fig 1D. OF AMPLIFIER instances, it is necessary to replace the rubber ALEX PLAKAPIs dampers, which have become well "soaked," so to speak, before satisfactory operation can be Wet Electrolytic Condensers. It has been called obtained. These rubber dampers may be made to our attention that occasionally, the electrolyte !:o. from the rubber of an ordinary baby bottle from wet electrolytic condensers will leak out jlPICKUP nipple. of the container, run down the side and harden. After all have been cleaned POTEN- parts and the leaving an unpleasant deposit. This is entirely i' TIOMETERS rubber dampers installed, the pickup should be natural due to the chemical action in condensers re- assembled, the magnet remagnetized, if possi- of this type. Fig. 926. Fader -mixer for P.A. systems. ble, and the armature adjusted so that it is In the manufacture of these condensers. sev- equi- distant between the pole-pieces. This ad- (Continued on page 249)

MF. SHORT T- ANT. O X I TT TT ` ` w (REPLACE THIS L I (g)- RESISTOR) SILVER - 0.25-MEG. MARSHALL TO GRID B GRID -W .04 MF. CONTROL N4.225 UNIT 04 MF 64 OF 2NO. RETURN (DEFECTIVE) .- 6+ -B +'. (DEF CTIVEI -c_.- OPENS HERE ??? RF OS C. Fig. Q27. Open resistor in S -M model 730 set. 24 76 J_ 1 METAL 1sT-

1.- MET WIRE - WOUND I RESISTOR + O05C. 7

REAR OF el WAVEBANDiTL4J) .01-MF J O FRONT OF CHASSIS CHASSIS ..--- SWITCH (FAULTY CONDENSER) Fig. I. notes Operating on: A, Majestic 130; B, Maje tic 70; C, Philco 54; D, RCA R -I0; E, Pilot 11415, Fig. 928. Defective electrolytic' in RCA 417 -M.

RADIO -CRAFT for OCTOBER, 1937 227 228 RADIO -CRAFT for OCTOBER, 1937

BIGGER SERVICE PROFITS FROM BETTER TOOLS (Coutin ucd franc pagc 210) IN ANALYZERS 2 years. This in itself is an enviable record for any piece of equipment and should point out the )CV 112(. of this type are and probably advisability of purchasing an analyzer de- always will be the most important dollar unit only on volts, ohms and milliamperes, earners of the radio service business. These pendent and mechanically independent of all tube base devices when fundamentally built depend on the connections. basic units of the radio industry, namely---votis. For accurate service work, current readings ohms and amperes. An analyzer should be built are indispensable and should always accompany a incorporating a around high -grade meter point- to-point properly- treated magnet, sapphire jewels and analyses to protect all parts in receivers from overload. may exces- the hardest pivots obtainable. Poor treatment Tubes draw sive currents under conditions not directly of magnet steels may cause a drop of 10 per cent or more in an instrument sensitivity after obvious such as incorrect grid bias potentials, and these in turn may cause excessive currents a period of weeks or months; soft jewels will to be drawn through or soon wear sloppy and cause errors when the output transformers other parts that may not stand the overload. analyzer is used in different positions such as Where well -regulated power supplies are in- at 45 deg. angles or when mounted upright in corporated in the receiver, these overloads may a test panel; and blunt pivots result in bad be overlooked without a direct-current measure- friction. Any one of these defects may not just ment being made directly at plate; make the meter inaccurate but may render it the excessive current often causes a transformer failure to entirely useless and or more spent on the $1 $2 occur a week or two after delivery of the receiver. instrument can be entered in the "well assigned cost" column. A photograph of the selector block detachable from an analyzer with built jacks Since all voltmeters are adjusted milli -or micro- -in current which automatically put series ammeters with accurate series resistors and, there- the instrument in with any of the is shown in fore, the accuracy of voltmeter is directly tube electrodes, a Fig. A. Plate control -grid dependent upon the construction and tolerance currents, currents, screen -grid currents, diode A.V.C. and A.F.C. of the resister used. No voltmeter can ever be currents can all be measured quickly and effec- better than the grade of resistance unit in- with corporated with the instrument. Accordingly, tively such a device. manganin- wire-wound spools or other types of high -grade precision resistors are vital if any IN TUBE CHECKERS reasonable accuracy is expected from the device. In tubo testers the method of standard measure- Commercial carbon resistors will function all ment. the flexibility of circuit, the construction right in receivers where 10 per cent tolerances of the instrument and the grade of other parts are sufficiently accurate for general receiver used are primarily important. operation, but in voltmeters they add con- With the large number of tubes on the market siderably to the overall tolerance in the form of today the total emission method of measurement inaccurate adjustment and differences in resist- as worked out by the sub- committee on tube ance with temperature and humidity. These testers of the Radio Manufacturers Association resistors are commonly made up of carbon par- has proved to be the most economical, most ticles held together with a binder of glue, or flexible and best method of testing tubes both some similar substance which is in itself hygro- for the Service Man and the dealer. scopic, attracting and holding moisture under There was always argument with regard to suet weather conditions. This substance will also mutual conductance versus emission readings and, expand and contract. changing the position of in general, mutual conductance readings are best the carbon particles in contact and, therefore, it where they can be measured accurately. To make is very difficult to expect any sustained accuracy correct measurements, however, requires most for meter work on resistors of this type. For a definitely a patch -cord system of jacks and plugs few cents more per resistor, 'Ai -per cent -adjusted to handle the multitude of tubes encountered precision resistors can be used with the instru- today. Potentials directly proportional to the ments and maintain the basic meter accuracy ratings as released by the R.C.A. License Bureau over each of the voltage scales. must be applied to each of the electrodes and Rectifiers for A.C. ranges should always be this in turn requires several instruments for the of the full -wave type if uniform results on electrode potentials in addition to a direct-reading various waveforms and frequencies are expected. mutual conductance meter. Testers such as this These units depend upon the current density are available on the market and are continually used in the discs for accuracy over wide tem- sold to certain organizations and to some of the perature and humidity limits, and therefore, larger service concerns, but at prices in the where 1 milliampere or lower sensitivities are order of $300 or $400, and in general, the margin used, the discs should be as small as possible. of profit on tubes handled by the Service Man In addition, all of these full-wave meter recti- will not warrant an expenditure of this amount. fiers come under the Weston Instrument Com- Furthermore, in testing a large number of tubes pany patents and a great deal of research has patch cords are rather complicated to handle and been done by this company on the method of the average Service Man or dealer could not construction of the discs for meter work. take the time to set up each tube base for test High sensitivities in analyzers are becoming while the customer waited. This R.M.A. circuit more important daily due to the high impedance as mentioned above, with maximum flexibility and resistance circuits used in many of the of switching for the tube bases incorporated in modern receivers. Analyzers of 20,000 ohms /volt a tester of high grade construction, is the best type have been placed on the market by the answer for the tube tester problem as far as Weston Company and these analyzers have a Service Men are concerned. A typical tester of great many advantages over the former 1,000 this calibre is illustrated in Fig. B. ohms /volt types. Not only are high -sensitivity Accurate measurement of transformer poten- voltage ranges available for accurate direct - tial is vital as read directly on the teeter instru- reading measurements of plate, screen -grid and ment; coupled with a method of line voltage con- control -grid voltages with minimum instrument trol that will afford good regulation and complete drain, but current readings down to 0.5- micro- adjustment all the way from the lowest to the ampere can easily be measured with these new highest line voltages encountered. Sockets that instruments. The current readings thus obtain- do not grip the tube too tightly and thus wear able are just as important as the high -sensitivity out easily should be used, this requirement being voltage ranges in measuring detector diode cur- very different from that found in the average rents, oscillator grid currents, high -mu triode radio set where tubes must be gripped tightly plate currents, and output pentode distortion and inserted only 3 or 4 times during the life- grid currents. The Service Man in purchasing time of the receiver. A single tube tester con- his equipment should not afford to overlook these tact may have to outwear 100,000 tube pins extended advantages in the advancement of the inserted during the life of the tube checker and radio instrument art. this requires special design. Current readings are as vital as they ever were in servicing the modern receivers. Analyzers IN VACUUM -TUBE VOLTMETERS with attached cord and plug, and built -in sockets These are baiea II y rain iu- frequency and audio- are, however, not obsolescence -proof and it is frequency tubes, and should in general be so highly advisable to purchase an analyzer with a considered, except where actual A.V.C. direct - detachable selector block. Instruments of this current potentials are to be measured. A vacuum - kind have been on the market 4 years with no tube voltmeter is the type of R.F. voltmeter change whatsoever in the analyzer proper; a needed for gain -per -stage measurements right .small skirted adapter unit being the only at the control-grids of the tubes, audio measure- purchase required to carry through a complete ments across grid windings and bypass conden- gamut of octal tubes announced during the last (Continued on pago 230) Please Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT fo- OCTOBER, 1937 229 EVERYTHING IN RADIO atliweseakos FOR DEALERS SERVICEMEN SOUNDMEN AMATEURS EXPERIMENTERS : filpfe Q. ritt, .40*

32 TESTED AND APPROVED KITS! Rodio Builders- here's un assortment of kits 65 GREAT NEW KNIGHT RADIOS! ranging from a 1 Tube set to a 14 Tube All Wave Superhel for purse Automatic Tuning, powerful performance und rich -kits every and purpose! Write for Free Pans 26 MODERN PIA, SYSTEMS! tone are the features of the new KNIGHT Radios. Lists -for any kit in KNIGHT "Integrated" Sound Systems Models for every taste described any radio publication. and purse, from 5 to 16 . from 8 to 60 watt s -portable, permo- tubes, for AC, AC -DC, 6 Volt, 32 Volt, Battery and nent and mobile -for 110 Volt, 6 Volt Auto operation. Beautiful Console, Chairside, and Universal operation: Also -new Phono -radio, Table and Chassis models -at un- 2 -Way, Selective and Superselective beatably low prices. See all 65 models in your KNIGHT Intercom Systems. 1938 ALLIED Cotalog!

MORE THAN 12,000 RADIO PARTS! Listing more than 12,000 exact duplicate and replacement parts, the 1938 ALLIED Catalog 26 LATEST AMATEUR RECEIVERS! offers a tremendous assortment for repairing See the most complete line of Amateur receivers or building any radio circuit. This great book in Radio- beginning page 114 on of your 1938 enables you to spot the port you want - 68 NEWEST TEST INSTRUMENTS! ALLIED Radio's Catalog! leading makes-National, conveniently, quickly,eaoctly! Radio's most extensive line of test in- Hollicrafters, RCA, Sargent, Hammerlend, etc. Also struments-new 2" Cathode Ray Os- latest RCA, Utah, cilloscope, Oscillogrophs, Ana- and -Star All Trans- lyzers, Tube -Checkers, Set -Tes- mitters; books, ters, Signal Generators, Meters, parts, tools. Every- etc. Also, new Build -Your -Own thing from a grid Kill and 20,000 ohms -per- to a 1( cap KW volt equipment. X- milled

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PARTS KITS AMATEUR GEAR

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WRITE FOR ALLIED'S NEW 1938 CATALOG - RADIO'S LEADING SUPPLY GUIDE! Send for this great book today -164 big pages packed with Everything in Radio! Thousands of parts, dozens of radio sets, kits, Public Address Systems, Test Instruments, Amateur Receivers, books, tools, etc. -at prices that will save you money on every purchase. See the separate P.A, Amateur, Service and Radio Set sections -see the revised, extended v ports sections -see 1938's latest radio developments -all in your 1938 ALLIED Catalog! It's new, complete, and different from any other radio book ever published -a book written by and for radio men. Every page has been planned to make your radio buying easier and more profitable. Write for your FREE copy now -it's radio's easy -to-read, easy -to -shop, easy -to- order -from catalog! EVERYTHING IN RADIO - AT LOWEST PRICES! ALLIED carries in regular stock all leading radio lines at lowest prices. We can obtain for you special or "hard -to -get' equipment on short notice -our central location under one great roof means faster service for you. Consolidate your purchases -fill all your radio Allied Radio Corp., 2 needs from one single dependable source -ALLIED-Radió s Leading Supply House! Dept. -K8, 833 W. Jackson Blvd., Chicago, Ill.

your , i'aLdny i ALLIED RADIO Need MC -Had S 1.oa,ImK SUN.], CORPORATION .,,L!r,. N:., 833 WEST JACKSON BLVD., CHICAGO, ILL. Please Say That You Saw It in RADIO-t lRAFT 230 RADIO -CRAFT for OCTOBER, 1937

BIGGER SERVICE PROFITS FROM BETTER TOOLS CINAUDAGRAPH I trill tic m d frort Pap,' 22B) sers, R.F. potentials in superheterodyne oscillator filtered so that signals will not feed back circuits, in trap circuit adjustments and in through the line into the receiver under test thus response -curve measurements. making it impossible to attenuate the signal in Copper -oxide rectifier instruments cannot be the receiver to a point where it later can be used to advantage on R.F. resonant circuits be- aligned. In any event shielding must be com- cause of frequency limitations and due to the pletely incorporated so that alignment below the fact that any loading of these circuits tends A.V.C. level on all receivers can be carried out to pull them out of resonance. The direct inser- in case it is difficult or impractical to eliminate tion of a vacuum tube is about the only other A.V.C. action during the alignment procedure. )11,---\ method of measuring the potentials across these Input impedance must be as high as possible circuits. In this regard, a well -designed volt- and should be limited only by the measuring meter should have a minimum input capacity, tube itself, as this impedance will load the cir- connections being made directly to the tube with cuit under measurement. Stability of readings is no voltage divider or selector switch being used essential as devices, especially line-operated in the circuit. Such component parts will shift types, will fluctuate with line voltage potentials the capacity a few micro- microfarads each time and cause incorrect meter readings unless some a new section of the voltage divider or a new form of regulation is used. Without regulation position on the rotary switch is used, thus on the lower ranges the instrument pointer will shifting the resonant frequency of the circuit vibrate with small line potential surges and make on which the measurement is being made. This it extremely difficult to obtain any kind of a will, of course, cause a direct error in the read- reading. ings as the voltage thus read will differ on each The vacuum -tube voltmeter will be sold con- range. tinually in parallel with the oscilloscope as there CIINAUDAGRAH are definite advantages in each type of instru- Magic Magnet Speakers IN OSCILLATORS ment. For service work the vacuum -tube volt- Accuracy of calibration, frequency stability meter with its direct readings in vats is much -extensively utilized by all leading radio re- and shielding should be looked -for. Accuracy of easier to understand and simpler to operate ceiver and P. A. equipment manufacturers -are frequency calibration is important in alignment and, in general, will handle all the measurements available in a complete range of sises from 51/2 work both at intermediate frequencies where required of the Service Man. The A.V.C. or any to IB inches. to meet your every radio require. it is vital and on the various wave bands where direct -current potentials cannot be read on the specific alignment points are mentioned by the oscilloscope, as, an axis shift only will result ment. manufacturer. No oscillator regardless of how and in turn, actual gain -per -stage readings in If you demand utmost dependability and fidel- well it is calibrated will maintain sustained ac- volts cannot be taken. Furthermore, the resist- ity of reproduction from your equipment -in- curacy without good coil construction and air - ance- coupled amplifiers used in oscilloscopes are sist on Cinaudagraph P. M. speakers. Carried dielectric condensers. Trimmer or compression - notoriously poor on radio frequencies, some of type waveform ; in stock by all progressive distributors. Free de- padders have very poor humidity coefficients them completely distorting the direct and are, in general, the very parts that cause connection to the tube plates appears to be the scriptive literature on request. drift in alignment of receivers. They, therefore. only answer where R.F. measurements are con- should be eliminated in oscillator construction cerned. Sensitivity, however, directly at the and air condensers used throughout. Carefully - plates is not sufficient for many operations and constructed coils, preferably on molded bakelite here again vacuum -tube voltmeters can be built forms, should be used to assist in maintaining with much higher sensitivities. good accuracy. The Service Man should expect The oscilloscope will. however, be used where CINAUDAGRAPH individual calibration of each oscillator that he an image of the waveform is required but this CORPORATION purchases if such a unit is worthy at all of in general, is not a definite requirement for maintaining any kind of a frequency tolerance Service Men in regular repair work. In any Speaker Division Stamford, Conn. throughout its useful life. event, the operator should be quite familiar Battery operation has several advantages with the oscilloscope before attempting to make coupled with some disadvantages, but allows a large number of measurements with it. very complete shielding as the Energy source is Two circuits showing methods of measuring completely enclosed within the shielded ease. A.C. automatic frequency control discriminator voltage, operation can be used but must be very carefully at tl gain per stage, appear in Figs- I. and 2.

THE AIRCRAFT -RADIO SERVICE MAN

I Con t ill otri jrunr page 20:0 EQUIPMENT REQUIRING SERVICE within the range of equipment that must be kept in top -notch condition, regardless of (rea- The itinerant flyer may have in his plane only sonable) expense, by competent radio Service Men. the simplest of radio equipment- perhaps only receiver and not an aviation weather broadcast TABLE I even a transmitter. On the other hand, his SOURCES OF REVENUE FOR THE AVIATION - equipment may be so comprehensive as to in- RADIO SERVICE MAN clude a beacon receiver, aviation weather re- ( I ) Servicing existing radio receiving ceiver, and a so-called auxiliary beacon receiver capable of all -wave reception and thus permitting and transmitting equipment, including the reception of broadcast programs; and, a direc- power supplies and antenna systems. tional -loop antenna that in conjunction with one (2) Modernizing existing radio equip- or another receiving sets Permits taking cross- ment to include additional services, such bearings from either beacons or broadcast - as pilot -to- copilot (or passenger) com- 6oöv. station signals. This receiving equipment plus a munication system, directional -loop anten- 2 for both code and tele- I- or -way transmitter na, extended frequency range, etc. ELECTRC)LYTICS phone operation may comprise the more inclu- (3) Locating and minimizing or eliminat- Your choice of either metal -can or card- sive radio set -up. in ignition interference. board -case general- utility electrolytic'. The Department of Commerce reports that Compact. Fit anywhere. Inexpensive. Sale of replacement components. there are approximately 1,000 private and public (4 **600 v. D.C. working. Provide extra safety landing fields (soon, many more -including (5 Sale of new transmitting and re- margin. Use them to meet high surge emergency landing fields dot the land) ; ceiving equipment. voltages. -will and approximately 4,750 privately- operated (6) Custom construction of radio trans Metal -can type inverted -screw mounted. airplanes. Since all the commercial airplanes have milting and receiving equipment. Cardboard type has Adjustimount univer- their own radio service crews it is unlikely that sal metal flanges. the average aviation -radio Service Man will have 15th Anniversary Edition. much opportunity to make repairs to the radio TRANSMITTER AND New CATALOG. new equipment of such installations -except, perhaps, NEW items. Ask your jobber-or write us in a case of extreme emergency. ADDRESS di rect. PUBLIC MANUAL Spare does not permit the lengthy discussion Not only radio amateurs and public address r- that would be necessary to completely analyze men (to whom it is dedicated) but anyone at all the faults and remedial measures connected with interested in radio will welcome this excellently- private- aviation radio servicing -books have been prepared manual. It is chock -full of theory. dia- written on this subject alone-suffice it to say grams and practical data on transmitters and that antenna and counterpoise systems, battery - P.A. Some of its chapter headings are: R.F. and generator-operated radio transmitters and Circuits ; Audio Circuits ; High- Fidelity Audio receivers and their respective types of current - Circuits; Controlled- Carrier Modulation ; Plate - CORPORATION ; ; the more modern Supply Design ; Typical Rectifier Circuits Power 70 supply systems and even in Wr'v m,pm SI. Brooklyn. N. Y. installations, private communication systems be- Supply Filters, and others. The book is avail- tween pilot and co -pilot or passenger, all come able from United Transformer Co. for 25c. Please Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT for OCTOBER, 1937 231 AUDIO BEAT nu. OSCILLATOR Based on Developments of H. J. BERNARD INCORPORATING the original developments of H. J. BERNARD, managing editor of "Radio World," this Audio ltrat Frequency Oscillator, our AUDIO- METER, combines stability with enormity of output voltage. Direct -reading in audio frequencies, 0- 10.000 cycles, and also direct reading in output volts, 0-2 volts. Other beat frequency oscillators cost twice as much or more, yet provide only % 'o!t output Or less. The audio beat frequency oscillator heretofore t.is been restricted largely to laboratory use. duo t.. prohibitive prices. However. we mecialise in 1.tdueing prerision equipment at a price servicemen afford. So for the first timo servieemon am check the fidelity of audio amplifiers in ro- relvers, of toddle address systems. of speakers and other acoustic deviir,. Also. hre.m e of the high output, dead amplifiers can he tracked right down to their offending short or open. The ACDIOMI l-TElt is provided with dial scale - . niches in diaueter (extraordinary slat.), 8-1 'rnier dial and costly planetary drive, also cl ose- ` eallbrated scale. so that evenn tha tower..san .ire gaeneies for tuning musical instrtmelds nit br read exactly. Our instruments, expertly designed, carefully manufactured, are sold only by us. the The instrument is equipped with an adjuster. manufacturer, only to you, the consumer. Our no- middleman policy SAVES 101' crated frequencies a always right- Wink( 1'1' T(1 of any mmerrlal Irequeney (93. /u. l,ti rs e..) and also on dr. 190 -130 V.1. with five tubes an d test end s. S hip, ht N ILs. Nil prig, 914.4,1 INFINITE IMPEDANCE A -C and D -C VOLTMETER N1'INITE resistance voltmeter.; enable JCST to show what an astonishing in- very accurate d -c measurements of cir- strument this is, we have a 0 -500 cuits in which hardly any current flows, microammeter of d'Arsonval movement. such as diode loads and a -v -c supplies. Moreover, the meter has nearly five Infinite impedance volt -meters permit inches of spread clear across-enormous a -c measurements of tuned circuits or visibility. Then there are six scales, any other networks. Here is a remarkable 0- 1.5- 5 -15 -50 -150 volts, a.c. or d.c. answer to the serviceman's crying need for The INFINOMETEIt such an instrument. Not only does the IN- has a bucking cir- FINOMETER draw nbsolutrl!r no current in cuit for zero meter reading, two input making d -c measurements, but it is also a tip jacks, and a six- position range vaetium tube voltmeter that duplicates the switch. It works on any frequency a.c., same feat on a.c., measuring voltage of any frequency. Despite this double service-meas- also 30 urement of both a.c. and d.c. without loading sling. wt. 10 lbs. Complete $ .40 -the price is les, than half that of most with three tubes, low - cu rrent- drawing instruments that measure capacity test prod cable, ,mly d.c. net price

INSTRUMENTS GENFMETER TUBE TESTER ALLMEER 20 ALL AUDIO FREQUENCIES Emission type perfected tube tester ONE Our superlative signal generator, direct reading for any and all types receiver tubes, The Allmeter, n 1,000 -ohms-per -volt d'Arsonval fundamental frequencies, 100 kc. tu 22 mc.. and including metal and metal-gin . s. instrument, instead of being just a volt -ohm- direct reading also to 100 mc., has modulation Tests shorts and leakage. Accurat,, ammeter, is such an instrument, plus a.c, read- on -off service, with bandspread audio frequencies simple, sturdy, direct ings for voltages and currents, also accurately 25- 10,000 cycles. Audio, in three band:, is saw- - English - reading $ r 0.40 measuring very low resistance, from below one tooth wave and useful also for (Bad - ?- Good). Ship- ohm, also high resistance, capacity, henries and oscilloscope sweep. Complete ping weight, 9 lbs. decibels, comprising twenty instruments in one. with four tubes. Shipping For a.c. 60 cycles for all 20 uses. Shipping weight. 10 lbs. $14.40 weight 6 lbs. 40 cy. $2 extra: 25 cy. $3 extra. 0-15 -150- 750 -volts and milliamperes, a.c. and d.c. -12 to -1- 30 decibles..03 -500 ohms. 500 -500,000 ohms. 5- 1.000 henries .01 -50 mfd. Continuity Tester. $1. 0.40

41140

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SUPERIOR INSTRUMENTS COMPANY Dept. RC -10 136 LIBERTY STREET N. Y. CITY Send for Our Catalogue PV in Colors - It's FREE! 1'h'osr Say Thnt You Sr,,,- lt in Itnnirt- ('RAFT 232 RADIO -CRAFT for OCTOBER, 1937

"LEARN -BY- EXPERIMENTING" Infinite Ohms Per Volt BEGINNERS' PRACTICAL RADIO COURSE with AUDIBLE TONE GENERATOR t e,1 from page 219) Fig. A; and the corresponding symbols for these small cells already connected internally, and parts, in Fig. 1A. thus is equivalent to 3 individual drycells of the same small size. Although larger cells will last longer, this size is sufficient, in this Experiment, EXPERIMENT-AUDIBLE TONE GENERATOR for operation over a few months. 5gC. MODEL 4900 ( "RADIO WHISTLE ") OBJECT: To study the Operation of the ANALYZING THE CIRCUITS OF A TUBE Vacuum Tube in Producing Audible Tones. 211, let us trace the 3 circuits known as audio fr/ vs,eney oscillations. Referring to Fig. 1 ZERO CURRENT of the tube in this arrangement. We will start with the "filament circuit" (or "loop "). The PRINCIPLES INVOLVED filament current which heats the tube is con- In this Experiment, the me r.,t inn of the vacuum trolled by the rheostat. Turning the knob to VOLTMETER tube as an amplifier of an input signal is modi- the right decreases the amount of resistance of fied so as to have the tube produce its own the rheostat being used, and so the current in signal which can be heard in the phones. Such the filament becomes greater, heating the fila- a "generator of tones" which can be heard may ment more. be called a "Radio Whistle" or more correctly The "grid circuit" contains the secondary an Audible Tone Generator. winding of the transformer in which "electrical The purpose for which each part, other than vibrations" (or oscillations) will be produced. the tube, is used in this Experiment is explained In the "plate circuit" when the key is pressed. in the following listing: plate current flows through the primary winding Rheostat (R). A moving arm making contact of the transformer setting up the electrical with resistance mire, that is, wire which opposes vibrations. These vibrations are transferred to the passage of the electric current through it. the secondary winding in the grid circuit, be- By turning the rheostat knob to the right, we cause -as previously stated-both primary and include less and less of this resistance in the secondary coils are wound on the same iron circuit, and thus allow more current to flow. core. These vibrations, in the grid circuit appear Transformer (T). A unit consisting of 2 coifs in turn, in amplified form, in the plate circuit- of many turns per layer and many layers of Since the plate circuit is continually feeding back This instrument may be connected insulated wire wound around an iron core. Cur- energy to the grid circuit the electric vibrations dis- rent is sent through the first coil, called the do not die out but are sustained so as to be to grids in any circuit without continuous at a certain rate (or frequency). For operation of set, built -in primary (marked p and b in diagram. Fig. 2A turbing and B). When this current is caused to change this reason this device may be called an "audible power supply furnishes balancing in any way, such as by electrical vibrations. tone generator" or more technically an audio - voltage, -adequately filtered. these changes are transferred by the iron core frequency oscillator. This instrument indicates: to the second coil wound on it. called the sec- The sound in the headphones caused by these Although Volts at ohms ondary (marked e and g, in diagrams). continuous vibrations can be controlled by the D.C. infinite these 2 coils are in no way electrically connected, key to send signals in the International (or Con- per volt the fact that they are wound on the same core tinental. as it is also called) Code, which is A.C. -D.C. Volts at 1000 gives the result that any changing current in shown in Fig. 1H. ohms per volt the primary winding produces corresponding We can also change the pitch of this tone by A.C. -D.C. Milliamperes changes in the secondary winding. When, as in adjusting either the rheostat or the optional ad- Ohms and Megohms this case, the number of turns of the secondary justable condenser. For example, by turning the is much greater than the number of turns in the rheostat knob to the right, the increased filament Microfarads, Leakage the secondary Decibels primary, the changes produced in current causes a lower pitch; this same effect are also much greater than the original changes can be obtained to a greater degree by adding Henries in the primary. This accounts for the name the greater capacity of the condenser to the cir- Wide ranges assure complete cover- "step -up" transformer, and, since it is used here cuit. This lower pitch indicates that the vibra- age for radio testing. in connection with audible sounds. it is technically tions are taking place at a lower frequency. The known as an audio transformer. principle involved in this case is that in any Variable Condenser (C adj.). A condenser con- such "oscillating circuit," if the characteristics Model 49555 sists, in general, of 2 conducting plates (usually, of the coil (its inductance) are kept constant, of brass or aluminum) separated by an insulator the frequency of oscillation will then depend (mica. air, etc.). Its effectiveness in any circuit upon the amount of capacity (condenser effect) Universal Volt is judged by the amount of its capacity. which in the circuit; the frequency, and therefore the means its ability to store an electric charge. pitch, becoming lower as the amount of capacity Ohm Milliammeter In this case we can make the capacity greater is increased. by turning the adjustment screw to the right. which brings the 2 metal plates closer together, PROCEDURE AND RESULTS Larger Meter - by the insulator though they are still separated A -Code Signaling which is a sheet of mica. Its use here is optional. More Ranges since its effect of making the pitch lower, which (1) Assembling. The appearance of the part?, is obtained by increasing the capacity, can be before and after mounting, is shown in the obtained without it, to a smaller degree, by photographs. Figs. A and B. The wiring between For Quality, Accuracy using the rheostat to increase the filament cur- these parts is shown pictorially in Fig. 2A and Fig. 213. and Dependability use rent which (by indirectly effecting the "tube in symbol form (schematically) in capacity") has the same effect. (2) Wiring. In making connections by solder- HICKOK TEST INSTRUMENTS Key (K). Has the same action as a pushbutton ing (The reader is referred to the article "How 1937, switch in closing a break in the circuit thus to Solder" which appeared in the July, ZERO CURRENT VOLTMETERS forming a complete path (e closed circuit) and issue of Radio-Craft.) the order in which the VOLT OHM MILLIAMMETERS current to flow. connections are made should follow the plan, allowing the of i shown in Fig. 2A and B, an made up the SET TESTERS A the vary- Pitones (Ph.). device for converting following 3 "loops' or circuits: TUBE TESTERS ing flow of electricity into audible sounds. This OSCILLATORS device will be considered in detail in the next Filament Circuit -The wiring, starting from OSCILLOGRAPHS Experiment. the binding post or connection terminal marked "A } ", will include the 2 terminals of the MODULATORS Battery (lts V.). A unit composed of a num- rheostat; "f +" and "f-" terminals of the socket APPLIANCE TESTERS ber of cells which generate electricity by chemical into which the tube is later to be plugged; and PANEL METERS action. Each cell contains a zinc and carbon back to the "A -" binding post. element operating in a chemical paste. Since Write for literature on the this paste, though always moist. is not in liquid Grid Circuit -The wiring, starting from the G terminal of the socket includes the g and e complete I IICKC) line. form, the cell is called a drycell. Such a drycell s could, for example. light a small flashlight bulb. terminal; of the transformer secondary; and "A binding post. If condenser C since each cell is rated at 11/2 volts, which back to the -" signifies its effectiveness in supplying the adj.. is used across the transformer secondary. HICKOK "electric pressure" required to force the cur- leave one wire unconnected until later. After the opposition the set -up has been worked without it. it can ELECTRICAL INSTRUMENT CO., rent through the circuit against its effect on or of the wire in the bulb. By connect- then be connected to determine the resistance circuit. 10413 Dupont Ave., ing 3 such cells, as shown in the diagram, we have a series connection and the voltage of the Plate Circuit -The wiring, starting from the CLEVELAND, OHIO entire battery is then 41/2 V. (or volts). A "C" p terminal of the socket includes the transformer battery of 41/2 V. is simply a unit containing 3 primary p and b terminals; (NOTE: If any s Please Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT for OCTOBER, transformer, other than the one used, it may be necessary to reverse these p and b terminals to get the device to work. To allow for this possibility. use long leads on these 2 terminals.) The circuit also includes the TOUCH BUTTON phone 115T that is. headphone) binding posts; the key for pushbutton) : and the "111 -" binding Post. The circuit is completed by the "ll -" terminal join- LATEST I8-TUBE MIDWEST TUNES ITSELF BY ing the "A--" terminal; if a "C" battery is used, it is connected as in Fig. 2A in which rase the "I3 -" is already connected within the ELECTRIC battery to the "A t ", thus completing the circuit. MOTOR! Notice that when using a "C" battery, which has the terminal designation shown in Fig. 1A, use the ( -4t_) terminal for minus I -); the Only Midwest's Direct - From - Factory ( -I)'/ terminal for -(-3 V., a and the ( - ) terminal for 4 V. Policy Makes This and Other Sensational (:3) Operation. Torn the rheostat to the right Features Possible at Amazingly Low Prices! up to about the first of the 10 divisions indicated on the dial plate. (CAUTION: When the fila- "The sensation of the radio world " - that's ment of the type 30 tube is operating at it cor- list experts said when they saw the amazing new rect temperature. there is no perceptible glow 1')38 MOTORIZED Midwest. You'll be astounded visible. lie sure to keep the rheostat turned well at the lightning -like motorized action -just touch a down Ito the left) to avoid a bright glow on button (on top of the radio) and its corresponding the filament, since this is injurious to the life ... of this type of battery tube.) station zips in. The famous Midwest factory -to -you Pressing the key should cause a note to be plan (proven by 18 years of success) is just as exciting! heard in the phones. If nothing, or only a It enables you to buy at wholesale prices - to "click" is heard, the circuit connections must save up to 50% - to make your radio dollar go he checked, before anything else is done, since twice as as far - to enjoy 30 days FREE trial in your the primary of the transformer may have to be own home - to pay as little as 50 cents a week. reversed, as explained before. Practice sending a short word, such as some name, by the code signals shown in Fig. 1H. 13- Changing the Pitch of the Note (1) Increase the filament current, noting precaution mentioned above. A change in the frequency of oscillation will be indicated by a change in the pitch of the note. Determine whether the filament current must be increased or decreased in order to give a lower pitch. (2) Connect the adjustable condenser, as shown in the diagram and determine the effect (of introducing this condenser) on the pitch; then note the effect of increasing its capacity (by turning the adjusting screw to the right), Now, you can enjoy the luxury of radio at its best- on the of the tone. No More Dial Twiddling! pitch you can tune your Midwest by merely touching ;t

Zip . . . . OPTIONAL ADDITION button! Zip Zip .. you can brtn f T in 9 perfectly tuned stations in 3 seconds. All this An additional diagram, Fig. 1G. is given for happens in'¡ second with Midwest Perfected MOTORIZED using this device from the A.C. or D.C. socket Tuning: (Sec above illustrations). (1-2) You touch button: power. Although it may be found convenient to (3) Electric motor speeds dial towards corresponding station: use this method in some practical applications, (4) Colorful Dull's Eye darts across dial and locales itself behind station: (5) Dial stops itself at station's exact center of where it is desired to operate a loudspeaker with. resonance and eye "winks" as program cures in perfectly tuned.' out the use of more batteries, it is not as suitable as the battery-operated outfit for the pur- 30 DAYS FREE TRIAL - pose of this Experiment, because, in the power - Enjoy the World's Most Advanced Radio For 30 operated case, a strong "hum" I humming sound) from the commercial power lines is superim- Days In Your Own Home! Don't Risk A Penny' posed on (added to) the pure note of the genera- Act at once on this unusual tor. However, for any who wish factory -to-you offer. We send a to use it, the Midwest radio you desire to your home. 18 diagram is given in a self- explanatory form, so You use it 50 days, and compare it with TUBES that it may he considered separately from the other radios you have owned or heard. List of Parts for the battery -operated unit. Then, you can return it to the factory, B WAVE BANDS if you wish, without risking a penny. You have a year top y, if you decide CONCLUSION to keep it. We trust you to give the a fair trial. You are g5 ,star,. II t o, Midwest triply Fundamental Principle. An protected with Foreign Reception audible note is produced in the phones by the Guarantee, One - Ycar Warranty electrical vibration of the vacuum tube at an and Money - Back Guarantee 04" audible rate (that is, at a rate or frequency 49 Pgi" which is within the range of hearing). This 18 TUBES for PRICE of 10 AC10a . sf \1' by he with an F íO1: device, therefore, is called an audio -frequency content ordinary lo, (' oscillator. 12 or 14 -tube set when you can tiny NEW 515 Super Datum 1theEe e CMA$Bti5 $rI Questions on Principles of Experiment No. I Motorized same Ques. 1. When the rheostat is turned to the money. It will uprise and delight 'ESr_ right to decrease its resistance, the filament cur- you with its brilliant world - wide- rent becomes (greeter) (less). reception on 6 bands, and range of 12,001 with -, Ques. 2. Increasing the filament current causes and more miles! It will thrill you its marvelous 6-continent overseas reception. the tone to become (higher) (lower) in pitch. Secures American, Canadian, Police, TERMS and therefore, indicates a (less) fre- (greater) Amateur, Airplane, Ship broadcasts .. . As Low quency. and the finest foreign programs. As Ques. 3. Increasing the capacity of the con- Send for FREE 1938 Catalog denser causes the pitch to become ( higher) (lower) and therefore indicates a (greater) (less) frequency. Sery/oe 50c piles. 4. Producing signals by interrupting the D W E S T Men: A WEEK! note Join nation-wide is accomplished in this Experiment by break- N WORLD -WIDE RADIOS ing the (grid) (Plate) (filament) circuit. Midwest service organira. jj ion. No Money Qnes. 5. The pitch. and therefore the fre- Dept. EE -12 CINCINNATI, OHIO Write for free details.J Send Now: quency of oscillation depends on berth the coil effect (amount of inductance). and the condenser PASTE COUPON ON 10 POSTCARD - OR WRITE . TODAY. effect (amount of filament) in the grid circuit. Answers to these questions appear un page MIDWEST RADIO 241 of this issue. CORPORATION Name Dept. EE -12 Cincinnati, Ohio School Radio Clubs are invited to write to Address of Send me your new Fuse catalog Radin -!'raft. attention this department. con- andd complete details of cerning the use of these Experiments for club 30 -day Fuca trial otter. Town State mq's. gr rspectal offer and Prier. pren rntr User -Agents Make Easy Extra Money. Check Here . I For details (Continued on page 241) asset dratipe direct with r.ewrr armut.> ¡1 Check Here for 1938 BATTERY Cetelo Please Say That You Saw It in RADIO-CRAFT 234 RADIO -CRAFT for OCTOBER, 1937 MODERN SERVICING OSCILLOSCOPES DEMAND (Continued from pape 222) KIT -TYPE SERVICING TABLE i (1500A) Cathode-Ray Oscilloscope Controls OSCILLOSCOPE UTILIZES A RI, R22, 0.5 -meg.: OGli //u04C 2 -IN. LENS (1500 -A) R2. 1 meg. ; THE INSTRUMENT, back and front views R10, R11, 0.1 -meg.; 50,000 ohms; of which are illustrated in Figs. D and E, R12, RESISTORS R13, 25,000 ohms; is a servicing oscilloscope available in kit form. R14, 3 megs.; The design, it is claimed, incorporates every SI. 2 -pole, 2- position switch; feature of the larger 3 -in. oscilloscopes, such as for S2, 2 -pole, 3- QUALITY- vertical and horizontal beam centering controls, position switch; S3, I -pole, 5- built -in linear and 60 -cycle sweeps, position switch. * ECONOMY - SERVICE provision Resistors for external sweep for alignment, both vertical It's more profitable to use Ohmlte Resistors. R3, R4, R20, 5,000 ohms; Built to last. they do a better job. and You and horizontal amplifiers and an efficient sweep R5, R6, 0.5-meg. ; pet ne profitless "call- backs ". Use ohmite. lock circuit for perfect synchronization. See Fig. It means "more R7, R8, 2 megs.; money in the pant's pocket." 2 for circuit. (Component values are given in Your jabber has them. R9, ohms; Table I at the end of this department.) 76,000 R15. 50,000 ohms; An outstanding feature of this kit is the use R16, 0.75-meg.; of a 2 -in. magnifying lens. This increases the R17. 40,000 ohms; size of the image on the 913 screen to a full Rit. 8,000 ohms; 2 ins. with unusually good definition. R19, 800 ohms; The arrangement of parts of this model R21, 200 ohms. T -11K16 kit oscilloscope has resulted in an ideal Condensers shape and size -6% x 10t/2 x 5 3/16 ins., just Cl, C4, C5, C6. C18, 0.1 -mf.; right for rack and panel mounting or easy 0.003 portability. The use of an etched panel and C2. C3. -mf.; C7, CR. C9, C10, 8 ml.; crackle-finish case give the completed unit a truly professional appearance. C11, 25 mf.; C12, C13, 0.5 -mt.; uiltlike Ohmite's big ustri units. with C14, 0.13-mf.; B lain a isturr of vitreous ,enamel. All C15, 0.04-mf.; standard values! NEW KIT -TYPE OSCILLOSCOPE C16. 0.007-mf.; HAS VERTICAL C.-R. TUBE C17. 0.0014 -mf. (I 500 -B) Names of manufacturers will be supplied upon BUILDING the oscilloscope from the kit of its receipt of a stamped and self -addressed envelope. parts naturally affords a keener insight into Kindly give (number) in above description of its possibilities, and the details of its operation, device. at the same time cutting its cost to a minimum. The oscilloscope shown in Fig. C was particularly designed for radio servicing. It uses the Dumont 2 in. cathode -ray tube. A feature of particular importance, seldom included in low - cost oscilloscopes, is the internal amplifier for wound unit at iWatt. increasing the sensitivity of the instrument to o inects in m: et l noiseless. All standard vlus!values! minute voltages. The saw -tooth sweep frequency (60 cycle line A.C., for example) substituted at will. Eight external controls are provided: vertical beam centering control; intensity control (and A.C. on-off switch) ; focusing control; frequency vernier (and sweep oscillator on -off switch) ; frequency selector switch; frequency amplitude control; vertical amplifier on-off switch, and vertical amplifier gain control. Greater familiarity with his instrument, and very much lower cost, are the advantages the The "standard" replacement resistor with Service Man derives from buying his cathode -ray higyh overload rapacity and edom from deterioration. Wire wound porcelain core oscilloscope in kit form and assembling it with ial high temperature e himself. f rBry en Fig. E

O Y VITIE MANUFACTURING COMPANY Fig. 2 4847 Flournoy St. Chicago, III. Schematic diagram of the new oscilloscope rear Manufacturers of view of which is shown RHEOSTATS - RESISTORS in the illustration above, TAP SWITCHES right. Figure D on page 222 illustrates ifs front t appearance. A 2 -inch C.-R. tube is used. ADVANCED HOME STUDY TRAINING FOR

"SERVICE MECHANICS" WHO WANT TO BECOME EXPERT SPECIALISTS Actually it is tacase of WANTING to become a Specialist-It is a NECESSITY! New developments mid Glandes to circuit designs make it NEW U. S. COAST GUARD AVIATION RADIO rient for you to keep pace the progress of Radio. The a rvlreman Who lacks the leresxary (Continued from pape 203) training is eliminating himself from a better position and hotter pay. homing device has and is proving itself of has only to follow the direction indicated by the THE START TRAINING NOW FOR FUTURE inestimable value in bad weather out at sea, etc.: radio compass. 1151 training In Radio 5 and Public Address work gives you thorough, bas knowledge of how since no time is lost in taking complicated bear- Most of the equipment involved in the Coast complex circuitstits work , mi what goes in muden, ,a,a,vrs tuna and learn all the facts. ings the plane for instance can proceed quickly Guard's new direction- finding loop antenna equipment appears in one of the views which shows the to the aid of a ship in distress. directional loop in the foreground. The radio operator aboard the plane wants The second development of interest is the FREE!yóetralld°es to locate a freighter sending distress signals, intercommunicating feature; the radio operator let us say. The loop is turned until it points at is able to utilize the audio system of the radio RADIO SERVICE INSTITUTE the source of the signals; though unlike a com- set for voice amplification in a "private" tele- SUBSIDIARY OF CREI pass needle which due to the earth's magnetism phone connection to the The earphone that Dept. RC 10, 3308 14th St., N. W., Wash., D. C. pilot. operates automatically the radio compass must is used for both the radio receiver and inter- be operated manually to maintain this directional communication services is shown in the second Turn to Page 2 t9 of this i -cue and read indication. However from then on as in the in- photograph in its mounting directly above the about the RADIO -CRAFT Special Offer! stance of using a magnetic compass the plane transmitter's flameproof telegraph key. Please Say That You Saw It in RADfo -CRAFT

RADIO -CRAFT for OCTOBER, 1937 235 NEW CIRCUITS IN MODERN RADIO RECEIVERS (Continued from page 211) $01)11°Z PRIZES Up to 3 V. peak signal across the last I.F. secondary (51) the receiver operates normally without A.V.C. at maximum sensitivity. When OPEN TO a peak exceeding -i -3 V. reaches the lower diode plate through the coupling capacity (50), this diode will start drawing current, building EVERYONE . all A.V.C. voltage across the 1 -mesa. diode load resistor (61) and the 0.33 -meg. tiller resistor. At the junction of the (61 and 5s) about % ra of the total A.V.C. developed is conveyed to the control -grid of the 667G I.F. amplifier. The total is conducted to the other grids through resistance -capacity filters. 642 (6) Suppressor Volume Expander THE $1,000 General Electric Model F -53. Making use of an ordinary triode power detector as the 2nd - CONTEST detector as shown in Fig. 1F, advantage is taken of the fact that the cathode becomes posi- rs4W tive in proportion to the average modulation intensity of the signal. The cathode is, therefore, connected to the suppressor -grid of the I.F. amplifier and as it becomes more positive, the signal is given additional amplification. When the signal is lower. the amplification is LET THIS Weer ?Axe, FIRST decreased and volume expansion is accom- PRIZE SECOND plished by varying the amplification in propor- PR) ' $250 tion to the signal strength. /938 WHOLESALE/MD/0 TMRD PRIZE $150 (7) Noise-Limiter Circuit :'$100 General Electric Model E -155. This receiver CATALOG deft/ fot iiow TO toy elk"',, ''' makes use of an additional 6116 tube to function $10, Jri: for delay bias in A.V.C. and a noise-limiter cir- OF PR OD cuit. See Fig. 1G. The signal voltage is taken WIN ONE THE /ZES $S00 from the 2nd -detector diode load nt the jttnc- tion of R21 and R22. the drop across R21 being Open to everyone ... servicemen ... amateurs .. engineers ... experimenters. So simple the desired signal. This is fed to the first audio anyone can win! Complete details on how to o 'lain these valuable prizes found on Page amplifier through a diode plate circuit (11 -13). ONE of the BIGGEST CATALOG IN RADIO HISTORY. Send for it immediately and get coupling condenser TC -55 and volume control R31. your slice of the generous awards. You can't afford to miss this wonderful opportunity! The cathode of section (11 -13) of the 6H6 Be one of the winners ... clip the convenient coupon now! The following well known noise limiter is maintained somewhat more people in the radio industry trill act as judges: Dr. O. H. Caldwell ... Editor, Radio Today; negative than the plate of the same section due Mr. Law Cochaday ... Edit", Radio News; Mr. Joseph Reiss ... President, Reiss Adverti.teg Agency. to its connection at a more negative point in o..Y the 2nd -detector load and hence a constant cur- EVERYONE!! Here's your lucky rent flows in this diode circuit as soon as any HURRY!! a'? chance to win the valuable signal is tuned -in. This current may rise to a one of prizes we are offering! f. HERE'S THE GREATEST predetermined maximum allowing full volume Here's your opportunity to obtain our wonderful catalog. output, but at this point the diode is drawing It's FREE!! And its contents will prove invaluable to you! CATALOG IN RADIO near -saturation current. A noise impulse or . its the biggest ... the best and any signal disturbance having greater ampli- for the SERVICER ... The greatest collet- ' ... will tude drive the diode into saturation. Above lion of up- to-date test equipment ... it has more radio bargains packed this point to reasonable limits, all additional rtea*\ 1 over 10,000 bargains in parts, tubes, signal drop will occur across the diode and between its covers than ever before! \t hardware ... at prices that cannot be hence be diverted from the A.F. system as the ' Imagine ... more than 10,000 real radio saturation current tends to remain constant in tibeaten! See this catalog ... learn why spite of increased plate voltage. thousands of successful servicemen "Buys" . at amazingly low prices! A\ 1\ In this way any noise which is above the buy the WHOLESALE way. Thousands of radio parts .. at lowest desired signal level is effectively eliminated. for the SOUND ENGINEER... Lafayette listings ... offered by the World's Larg- Well. fellows. how do you like this new de- P.A. systems are made in all sizes for est Radio Supply House! And NOW you partment in Radio.('raft? Constructive criticisms will be mutually advantageous. every possible requirement and speci- can make your purchases by the fication ... at prices that allow a handsome margin of profit. Complete WHOLESALE Easy Payment Plan. Use RADIO WITTIQUIZ beautiful NEW line described in de- your equipment as you pay for it. tail in BIG P.A. section. (Continued frum pay' _ 1;) Answers for the AMATEUR ...Thousands of "Hams" gjanfanbRit, !! ... THIS CATALOG (10,) 11311 (16h) buy the WHOLESALE way! It's the is 180 pages BIG ... and it's FREE! Send for it (lid) a (17d) Ill today get the details of the 51,000.00 con- (12d) i :u.) (19b) easiest ... the swiftest ... most re- ... liable . and economical way. test. See the new EASY -TO -PAY Plan now Contest Rules WHOLESALE maintains the biggest available. (1) An award of a 1 -year subscription to complete stocks of standard equip- Radio -Craft will be given to each person who submits a WITTIQUIZ that the Editors con- ment to be found anyullerc. SEND THE COUPONi/O* sider suitable for publication in Radio-Craft. (2) WITTIQUIZZES must be typed; use only one side of paper. (3) Submit as many WITTIQUIZZES as you 01R0«SM P0010 care to-the more you submit the more chance NEWYORK,N.Y. CHICAGO,ILL. ATLANTA, GA. you have of winning -but each should be good. 1 0 0 SIXTH AVENUE 901 W. JACKSON BLVD. 430 W. PEACHTREE N. W. (-1) Each WITTIQUIZ must incorporate ST., humorous elements, and must be based on some BOSTON, MASS. BRONX, N. Y. NEWARK, N. J. JAMAICA, L. I, term used in radio, public address or electronics. WHOLESALE RADIO SERVICE CO., Inc. (5) All answers must be grouped, by tntes- 100 Sixth A , Nw York, N. Y. E tion number and correct-answer letter, on a separate sheet of paper. Rush FREE 1938 Catalog No. 69 -3K7. (6) All contributions become the property of Radio -Craft. No contributions can be returned. Name (7) This contest is not open to Radio -Craft - employees or their relatives. (M) The contest for a given month closes on KS*" Address__ the 15th of the 3rd month preceding magazine - issue date. (For instance, contributions to De- Ws144 c47,. cember, 1937, Radio- Craft, on the newsstands about Nov. 1, must be received at Radio-Craft State _- City editorial offices not later than Sept. 15th, 1937.) MI

Plea se .Tay 7'1,,r Yo re .,,>,' f, ,, ! ;put- lit -tt 236 RADIO -CRAFT for OCTOBER, 1937

HOW DEPENDABLE ARE MILLIAMMETERS TO OSCILLOSCOPES ! YOUR METER READINGS? (Continued front page 213) shaft and the scale markings. which resists the "actuating" torque of the How much overload a given meter will stand movable coil, and then returns the coil and pointer depends upon its design, and how the overload to the "zero" position when the current is shut is applied. Overloads of reasonable magnitudes off. Any change in the "restoring" torque Pro- will not harm properly - designed instruments. If duced by the springs will cause a change in the the overload is applied for only a short time, and position of the movable coil and pointer -causing gradually, so there is no violent movement of the an error in the readings. pointer, the instrument will most likely stand con- Within the past few years, phenomenal metal- siderable overload without damage. (The meters lurgical advances have been made in spring of at least one prominent test instrument manu- design which almost eliminate the "fatigue" and facturer are designed to stand overloads as high "aging" of springs which manifested them- as JO times the normal value.) However, if selves in a "drift" of calibration in older in- the overload Ls applied suddenly, so the move- struments. The improved springs used in instrument is violent, a much smaller amount of ments of reliable manufacture render negligible overload will surely bend the pointer and also any probable error from this source, NO long as possibly dull the pivots or pit the jeweled bear- they are not subjected to mechanical or electrical ings with resultant lagging and sticky action. abuse. Incidentally, an overload of the wrong polarity, Of course, if the springs have become over- forcing the meter needle BACKWARD off -scale heated by prolonged abnormal current flow, they is very hard on meters and should be cautioned will lose some of their "temper ". This will against. It is always good policy to start measur- decrease their "restoring torque", and make the ing an unknown quantity with the range selector instrument more sensitive. (See Fig. 2, D and of the instrument in the HIGHEST range posi- E.) Consequently, its readings become inaccurate tion, gradually backing it down until a range is insofar as its original scale calibration is con- reached where the needle deflects without going cerned -and such errors may often be of con- off -scale to the right. This, of course, is the range siderable magnitude. This abuse of the springs where the user will receive his most accurate by prolonged overload is difficult to detect be- results, and this policy of working down to the cause, as a rule, the meter seems to operate in proper range will save many a meter from a a perfectly normal manner, no sluggishness or (;hlrardi's great, set, hang look gives you over 400 pages burn -out dice either to too much deflection for- stickiness being evident. of solid dose u all kinds o f radio test instruente-nr ward or, a disastrously high voltage or current ammeters. milliammeten, voltmeters. ohmmeters. volt - The springs may also become This con- "kinked ". ohm- nillllammeters. tCheatstone Bridges. output meters, of the wrong polarity (as far as the meter fault will frequently manifest itself by the fact vacuum -tube voltmeters, condenser testers and capacity nections are concerned). meters. tube checkers, set analyzers, test oscillators, that the reading at a certain point of the scale Catlssle -Ray oscilloscopes, etc For each type of Instru- (G) "Zero" shift. If accurate readings are will be different on "increasing" from "decreas- ment you get (a) a detailed explanation of the whole is that the must values. Another may theory of operation, design and construction : tb) de- desired, it apparent pointer ing" error creep in from scription of latest commercial models. with circuit dia- stand exactly at the "zero" point on the scale "softened" springs which sag. These cause un- grams and electrical m.aants, and explanation and voltage is applied to the torque, and abnormal illustration or special features; Ici full details ml build- when no current or even an "zero error" of the ing many prat( ira!, up -to -date testing instruments your - instrument. pointer. self- nllagrams, constants, etc.. included. This great 400 -page instrument section forms only If the pointer is not at the zero position to In general, the control springs of an instru- one -third of whole 1300 -page volume. The other two- start with. it is evident that all indications at ment should be maintained in as nearly perfect thirds explains how to toe for -e instruments In s ry lee be in error. Prac- a mechanical as work- brew to do rvu-u ts'! Votg,o got to get this book other points on the scale will condition possible by not abus- sometime GET IT NOW tically all commercial -type meters are provided ing the instrument by serious overload, rough Over 1300 Pages 706 Illus. with a zero- adjustment screw (see Fig. 2G), handling, etc. If the springs of an instrument which varies the tension of one of the control have received any form of damage, it should be CLIP OUT! '0'. MAIL NOW! springs, allowing the meter pointers "at rest" returned to the manufacturer, or an authorized position to be adjusted over several scale divisions, repair shop, for repair, if accurate measure- over the ments are to be made RADIO & TECHNICAL PUBL. CO. so that it may be centered exactly Posi- with it. 45 Astor Place. New York Dept. RC -I07 tion marked "zero" on the meter scale. (I) Bearing friction. The hardened and highly - Encl. find $4 for MODERN RADIO SERVIC- polished steel and the almost ING postpaid. (Foreign $4.501 Always make sure that the pointers on your pivots -frictionless Encl. find $0 for MODERN RADIO SERVIC- instruments are in the correct "zero" position sapphire jewel bearings which support the ING and RADIO FIELD SERVICE DATA. Incl. J Supplements to before taking readings! If the zero error is movable coil are subject to wear and damage. Far. 01 dr$e 6 found to be beyond the range of the adjusting (See Fig. 2E.) They are finely shaped and D Send free circular describing both books. screw, or if a sudden zero error of considerable polished, and accurately adjusted before the in- Name magnitude is observed, it is safe to assume that strument leaves the factory ; but friction may develop, due to excessively worn damaged Address the instrument needs checking and possible or repair. jewels or pivots. Rough handling of the instrument, overloading, dropping and tampering are When "zero " -adjusting a meter be careful to all common causes of damage to the bearings. MONET -BACK GUARANTEE avoid "parallax error" (explained later). This is particularly important when "zero"-adjusting Friction in the bearings usually manifests most ohmmeters, for in these instruments the itself in a stickiness and lag of pointer move- "zero"-adjustment screw does not adjust the ment. and a noticeable uncertainty in its zero TUBE meter pointer position directly but usually ad- position. Bearing friction will not usually cause MILLION in the readings, provided justs a resistor which compensates for variations errors the instrument TESTER in the potential of the battery supplied with the is gently tapped when the readings are being instrument. A fresh battery will, of course, taken; but since its causes are likely to be FEATURES apply a higher voltage to the instrument circuits productive of more serious results, they should be Emission than after it is partially discharged. Further- eliminated whenever possible. Metal Tubas more, because the resistors used in these meter Friction may also be caused by rubbing of Shorts Hot Leakage Hat circuits are not absolutely precise in value, there the pointer on the scale, or on fine fibres loosen- Resistance is some variation between the accuracy of the ing from the substance of a paper scale and Electrolytirs ranges of the instrument. Therefore, each projecting so By -Pass various out the pointer touches them. Condensers range of the instrument should be "zero " -ad- This trouble may become evident only during D'Arsonval justed separately -just before using. certain atmospheric conditions, and usually at Meter The Mcgohm ranges of ohmmeters are usually certain parts of the scale; and it may be difficult supply working to discover. MODEL powered by a miniature power CP from the house or shop line voltage. Variations Small particles of foreign matter which have in this line voltage can be, and should be corn - worked their way into the short air gaps of pensated -for by means of the Ohms Zero Ad- the magnet generally cause "sticky" operation $1395 juster, or whatever the manufacturer calls the and make the indications erratic. NET pointer "zero"- adjusting control. is to note that "sticky" meters and It interesting MODEL TM $16.05 Has 3" square meter Do not confuse simple "zero error" with that substances lodging themselves in continuous line voltage adjustment. due to foreign due to a bent pointer. If the pointer is very the movement seem to rank highest among the Direct orders require deptslt and name of ycur much off -zero because it is bent, it should not most frequent meter repairs not due to owner jobber. be brought back to zero by manipulating the negligence or carelessness. Sticky action is apt RADIO AND TELEVI- zero- adjusting screw: for such an adjustment to occur even in new instruments, due to the an position SION LABORATORIES brings the moving coil into initial jarring and shaking received during shipment. MILLION for different from that which it occupied when Although manufacturers take extreme care to 559 N. UNION ST., CHICAGO, ILL. the initial calibration was made. The bent insure receipt of the instrument in perfect con- pointer itself should be straightened! dition and despite the care taken in assembling (H) Spring errors. The springs play one of the meters, "trash" in the form of minute metal BE SURE TO READ THE the most important parts in maintaining the filings and bits of insulation or fibre may work ANNOUNCEMENT WHICH APPEARS accuracy of the instrument; for they not only into the movement. A meter service station should conduct the current to the movable coil, but remedy this because the average radio Service ON PAGE 250 OF THIS ISSUE also supply the "restoring" torque (or twist) Man is not capable of handling the delicate job t Please Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT for OCTOBER, 1937 237

of cleaning out ;, riti adjusting t he nu t veme n t. Anyway, the usual manufacturer's guarantee will generally cuver the cost of the adjustment, if it becomes necessary, within about 00 days of the .... e endorsed purchase date. A "sticky" meter may be detected immediately. Sticky or defective meters should be repaired at once rather than "borne with" as a man who By Leading Service uses an instrument which is not in 100(4, working order will subconsciously build up a psychological "mad" at the instrument's manufacturer. If it Organizations i repaired. he soon forgets that there was anything wrong with it. the * "Backlash" in moving parts is due primarily * to loose fits in them. This trouble is not common. nor serious, since errors due to it may be ma- HIGHEST QUALITY terially reduced by gently tapping the instrument while taking the readings. * (J) Electrical troubles. Under this classification are those troubles which may develop in the electrical circuits of the instrument after HIGHEST PROFIT it has been assembled, tested and calibrated. Poorly-soldered joints, loose or broken conductors, and partial or complete "short- circuits" or * * "grounds" are some of them. It is surprising how many loose or badly -soldered joints develop in FREE EQUIPMENT supposedly well -made instruments, unless the manufacturers are careful to inspect them rigidly at the factory. "Opens" due to breakage of the fine wire comprising the movable coil or that employed NATIONAL UNION for the multiplier resistors in voltmeters. have given trouble in some models of instruments. Of course, in such cases, the meter fails to operate RADIO TUBES either on one or more ranges -or altogether, so the trouble quickly makes itself evident. These National Union manufactures a complete electrical troubles can usually be detected by line of radio tubes-glass, metal and This "Sign of Efficiency" observation of the instrument for erratic action. G -type. National Union's high quality has When they are detected, they usually require a made them outstanding favorites in the Can Help You, Too. careful and complete repair before the instru- radio service All sales ment can again be considered reliable for service. profession. policies Get It - The copper-oxide rectifiers used in rectifier have been formulated with the idea of type A.C. instrument can cause an increase in making National Union radio tubes the meter inaccuracy. These copper -oxide rectifiers ideal replacement tube for the radio FREE from N. U. are inherently delicate and can be easily over - dealer. This has been backed up with a oaded. The average rectifier of this type will selling program that means real support pass a maximum of but a few milliamperes, and help to the wide -awake dealer. Deal- above which the rectifier "breaks down." This The NATIONAL UNION condition appears to be present in any A.C. ers and jobbers handling National Union measuring -meter circuit whether it be strictly a radio tubes are the leaders in repair parts WAY ... series- dropping resistor type or one in which and service. Through National Union's help, radio condensers and resistors are used. Care should service dealers everywhere have been therefore be exercised in the application of A.C. Free Equipment able to set up better equipped shops to voltages to these meters, for overload often re- Includes: do better work ; also to obtain mer- sults in a damaged rectifier and lowered A.C. chandise helps that produce more cus- voltage Tube testers, set analyzers, oscillographs, tomers. National Union has constantly readings. The rectifiers cannot be re- signal generators, modulators, meters and put the latest advances in scientific paired and are never guaranteed by the original equipment as well as modern selling manufacturer. Therefore, damaged rectifiers other servicing instruments. In shop aids within reach of the service dealer. .hould be replaced by the instrument manufac- equipment items available include stock The National Union Deal calls for a turer, or by some reliable meter repair firm, for cabinets, coats, display signs, electric dealer deposit which is rebated when the specified number of been they sometimes go bad even while being placed clocks, etc. All items absolutely free the tubes has in purchased. Over 70,000 completed deals. the instrument. The copper -oxide rectifiers National Union Way. Every service deader should investigate. should never be touched with the hands as chemicals in one's perspiration will usually cause early rectifier failure. The ratio of the rectified current to the applied THE ROAD TO Clip ! Mail Now ! current may change for a given rectifier. NATIONAL UNION RADIO CORPORATION Troubles such as the above cause this ratio to BETTER BUSINESS 570 Lexington Ave., Net. York City crop to sometimes half the original ratio. Varia- -Tell me how to get the Sign of Eabdenry Free. 1 . Full guarantee on 4. N. U. jobber stocks tions are also possible - --I am also interested in the following equipment due to variations of tem- highest quality ore complete...No lerature, humidity and the amount of current radio tubes. hunting for odd applied to the rectifier each time it is used for Name a measurement. In other words, the rectifier will 2. Cut price business types. have one when not solicited. Address ratio say 0.1 -ma. is applied, 5 Timely business another when 0.5 -ma. is applied. etc. 3. Price Protection. building aids. (K) Magnet weakened. Properly- designed permanent magnets of the types which are being used in recent high -grade instruments will stand a surprisingly large amount of rough handling before their magnetic strength will change s rficiently to result in incorrect readings. Other parts, such as the jewels and pivots, springs, e .G, which are more susceptible to damage by mechanical shock, are more troublesome in this NOW-WATER SAVINGS THAN EVER respect. However, the safe rule is to handle your IN NEW RADIOS AND EQUIPMENT instruments carefully and avoid all mechanical FRF jolts and shocks. We Carry Almost Every Radio Set Made (. - _-_ (3) Inaccuracies Due to Way Instrument Is Used, TREMENDOUS DISCOUNTS Or Conditions Under Which Measurements Are LATEST Made On Tubes, Amplifying Equipment, There are several inaccuracies Public Address Systems, Auto, Home, which are apt CATALOG and Farm Radios in Styles, Types, to creep >Ei AC- all into measurements made with electrical CONTAINING HUNDREDS jCßS011100HEs and Voltages. We can supply you with instruments simply because of the way the in- OF AMAZING any Manufactured Set. strument is used, or the conditions under which 67M1 the RADIO VALUES ALL MERCHANDISE GUARANTEED measurements are made. Errors which may Factory Sealed Cartons. No Seconds 1938 be present when a particular instrument is AT NEW CHOICE EXCLUSIVE TERRITORY used for one measurement may not occur when LOW PRICES AVAILABLE TO LIVE REPRESENTATIVES AUTO SET it is used again under different operating condi- LIST $54.95 tions -and vice versa! Some things to watch for will be pointed out in Part fl. DEP'TQN W ORK,NC OFF (Continued on page 247) POST RADIO CORP. 50', Please Say That You Saw It in RADIO-CRAFT 238 RADIO -CRAFT for OCTOBER. 1937

THE LATEST RADIO EQUIPMENT tC'outi,ocd from pave 221) CENTRALAB VOLUME CONTROLS cannot be $anall ! RHEOSTAT FOR PRIMARY NEW WIDE -RANGE SERVICE CONTROL ON SECONDARY OSCILLATOR (1297) VOLTAGE (1293) (Radio City Products Co.) (Ohmite Mfg. Company) ONE OF the latest in signal generator (or APARTICULARLY convenient control of "service oscillators') developments is the filament-transformer secondary voltages, in portable, A.C. operated instrument here illus- order to obtain maximum tube life (as in trans- trated (size, 8 x 11% x 5 ins. deep; weight. mitters, etc.), is afforded by means of a power 111/2 lbs.). rheostat connected in series in the primary cir- Five bands afford a continuous range of funda- An improved vitreous heavy-duty cuit. enamel mental frequencies from 125 kc. to 15 Inc.; rheostat suitable for this purpose is illustrated. harmonics extend the high -frequency range to It is constructed entirely of porcelain and metals 16 megacycles. and thus contains nothing which can char or burn. Of importance to the Service Man is the means -a full -vision direct -reading 4% -in. vernier -type airplane dial with multicolor calibration-pro- ORATOR -TYPE VELOCITY vided for speeding the reading of frequencies without recourse to charts or tables. Another in- MICROPHONE (1294) teresting feature that facilitates the alignment of says Mr. Owen O. Tressler' supersensitive radio receivers, as for instance AVELOCITY microphone which has been car -radio receivers, is the use of special lead - for and "desk of Elmira Heights especially designed pulpit coated steel for the case and chassis ; plus separate work ", or for all those applications where the shielding of the coil assembly, attenuator and "Sir," says Old Man orator generally assumes a fixed position, is R.F. circuits. Centralab, "I am illustrated. By an ingenious application of the overcome with pride directional "fins" developed for an earlier -type The possibilities of dead -spot effects are re- at this overwhelming microphone of the same make (Radio-Craft, duced through automatic shorting of unused vote of confidence. item No. 1438, August 1937, page 93), and by coils; and electrostatic shielding of the power placing the motor unit horizontally, an extremely transformer prevents R.F. feedback through But, (ahem) I can- the power not feel but that my wide angle of pick -up is obtained; this allows line. long years of smooth complete freedom of motion on the part of the Audio modulation of 30% at 400 cycles, sine - service to the radio industry merit speaker -within a radius of 3 ft. wave, is also available externally ; also, other, this recognition." This design is more sightly than the earlier external frequencies may be applied to the R.F. "banquet" stand type of mounting. The base may circuit. Sweep and "wobbler" circuits of cathode - Yes . Mr. Tressler is but one of be tilted to obtain best sound pick -up. Available ray equipment may utilize the A.F. modulation the thousands of radio men from with a noiseless rotary switch. Output level is from this signal generator. coast to coast who takes his hat off -65 db.: impedance either to grid or 200 ohms Panel and fittings are finished in MAN . . . . chromium, to OLD CENTRALAB (latter -type unit is equipped with a 25 -ft. length and who is doing a better and more aluminum and black. The cabinet is gray. of cable) ; frequency response 50 to 12,000 cycles; satisfactory service job because of weight, the smooth performance of these 3 lbs.; finish, gunmetal. world famous volume controls. 14 -26 WATT PORTABLE AMPLIFIER NEWEST RADIO SET FOR AVIATORS (1295) (1298) (RCA Manufacturing Co., Inc.) BRIEFED, the features of this amplifier are: electronic mixing of 2 microphones; pro- 6 -V. MILWAUKEE - WISCONSIN AVAILABLE for both and 12 -V. opera- visions for mixing 2 microphones and 1 phono- BRITISH CENTRALAB, LTD. tion, the new aviation radio receiver here graph; includes velotron microphone (on ban- Canterbury Rd.. Kilbourn illustrated features sensitivity and light weight. quet stand) ; has two 10 -in. dust-proofed dynamic London N.W. 6. England Only two type 6F7 tubes are used in the re- reproducers (said to be especially designed for CENTRALAB ceiver to afford the services of (1) R.F. ampli- P.A. work) ; tone control; beam power tubes. 118 Avenue Ledru -Rollin fication. (2) detection, and (3) A.F. amplifica- Paris xl. France Unit furnishes field supply; P.M. dynamics also tion in 2 stages, in a T.R.F. circuit. may be used. Speaker No. 1 plugs Frequency range of 200 to 400 kc. permits into the amplifier. Speaker No. 2 plugs into speaker No. 1. coverage of airport traffic control, and radio This placing beacon- weather broadcasts. White spot the permits the second reproducer a dots maximum of 50 ft. from the primary weather broadcast frequency of 236 kc., amplifier. and the airport traffic control frequency of 278 kc. Feather -weight headphones are utilized. Weight of complete receiver, power supply, cable and phones is 8.5 lbs. Dimensions for both receiver and power supply -6% x 5% x 3s/--. ins. deep biggest for each unit. Latest emis- AIRCRAFT MICROPHONE (1296) sion -type tube opportunities tester makes (Universal Microphone Co.) hot emission tests of all e still ahead ANNOUNCED as being "100 -per cent direc- types of tional and all extraneous noises excluded" is tubes. (1299) the aircraft -type microphone here illustrated. A In a decade radio has become a thumb-operated pushbutton is installed on the giant industry. The opportunities periphery. This is a double- contact switch. one by side of which closes the circuit for microphone created are being enjoyed current, and the other side operates the relay trained men. The International Cor- for throwing the transmitter into action. respondence Schools Radio Course. prepared by leading authorities and constantly revised, Wt's MAKE YOU A TRAINED MANI A fascinating book - FREE. 4Z INTERNATIONAL CORRESPONDENCE SCHOOLS

Box 6680 -C. Scranton, Penna. Send me- Irn-Infnrtnatn,n -unjeet rnecked: Radio pp Radio Service Man Radie Operator I] Electrical Engineer

Nanu New 14 -26 W. portable amplifier A wide -range oscillator with con- uses velofron microphone and 2 Addreaa tinuous range of fundamentals 10 -inch dynamic speakers. Input New aircraft mike. (1296) from 125 kc. to 16 mc. (1297) uses electronic mixing. (1298) Please Say That You Sato It in RADIO -CRAFT

RADIO -CRAFT for OCTOBER, 1937 23?

DEVELOPED for HIGH FIDELITY!

AND ONLY $1745

FROM FACTORY

TO The new "etched- foil" electrolytics. (1301)

EMISSION -TYPE TUBE TESTER (1299) YOU! (Million Radio 8 Television Laboratories) Tllhl TUBE TESTER illustrated on page 238 makes hot emission test of all types of tubes. Enelish- reading indications appear on the A WATT AMPLIFIER scale of a large meter. Neon test of shorts and 30 leakage is available up to 2 megs. Jacks provide COMPLETELY ASSEMBLED BUT NOT WIRED external use of the leakage test; as well as measurements of resistance in continuity test. USES the new 1221 Sylvania non- microphonic input pentode s.ltich permit, Operates on 110 V. A.C. The power circuit is you to use full gain of this powerful FOUR STAGE AMPLIFIER. Push fused; and all test circuits are insulated from the oil 6L6 beam power output with two input channels and faders for any type of microphone, radio or phonograph pick -up. INEXPENSIVE PRIVATE PHONE A RARE OPPORTUNITY FOR THE SERVICE MAN Just what you need for rentals; delivering anything from a whisper to full auditorium volume and (1300) Indies from one to four speakers, maintaining its perfect clarity at full volume. CARRYING the trade name of "Privaphone.'' K -30 HIGH FIDELITY AMPLIFIER; assembled complete with wiring diagram this intercommunication system requires only and tubes a built -in battery to operate it. Consequently, un- instructions less only wiring, chassis cover $17.45 like most previous types of such systems, it may 'entilated heavy gauge chassis cover, as illustrated 3.25 be applied in many services that do not have complete set of matched Sylvania tubes: 1 -1221, 1-6CS, 2 -6L6G, 2 -6JSG, 1 -5Z3 4.10 available a 110 V. supply. LIBERTY ST. The unit comprises a microphone and earphone, EASTERN RADIO & TELEVISION CO. NS Y- and a buzzer -all battery operated. May be used in connection with dictating, detective work, tem- porary point -to-point communication, etc. COMPLETE RANGE OF ETCHED- roir.i FOIL ELECTROLYTICS (1301) ('jsril I oJC (Cornell -Dubilier Corp.) r1_ BOTH THE types ER metal container rut! JR silvered cardboard container small -space WITH etched -foil condensers are now available in a BUILT-1N complete capacity range from 4 to 16 mf. at 200 to 525 V. rating. As a protection against excessive humidity and abnormal temperatures these rYCI SYMr units are triple -sealed. Uses No. 913 Tube with 1" NEW LINE OF REPLACEMENT Fluorescent Screen for Sharp CONDENSERS (1302) Images Controls Intensity, Focus IN ADDITION to the number of special uni- for versal- service condensers one manufacturer and Sweep Amplitude ( Continued on pape 247) Vertical and Horizontal De- flector Plates A.C. Operated A practical foundation unit for amateurs, engineers, sound and radio servicemen. With proper external additions it offers facilities for the study and adjust- Private interphone system. (1300) ment of countless circuit problems. May be adapted

for R -F and 1 -F alignment, resistor, condenser, vibrator and many other tests.

SEE YOUR JOBBER WRITE FOR CATALOGUE

READRITE METER WORKS 1016 College Dr., Bluffton, Ohio R9tttout. obligation please send rue m -.rt information on Model 840. I am also Interested In

Name ..

Address .. City .ate RANGER New line of replacement condensers. (1302) f 'lease Say That You Saw It in RADIO -CRAFT 240 RADIO -CRAFT for OCTOBER, 1937 Now-a high-powered- HOW TO MAKE "THE SEAFARER" 4 LOOP -TYPE BOAT RADIO SET (Continued from Page 208) right where we want to go? Then we simply 40 LOOP -POSITION INDICATION WI. take a bearing on it with our finder, adjusting sneer I For each Ioop, eru re or accurately draw a the loop for minimum reading or inaudibility. k as 360 -degree protractor of convenient size. (See sisn (The maximum- response reading is not as s,a, ! ,, - -- Fig. 1.) Cardboard affairs will do nicely. Center accurate.) Our pointer will read against the the protractor on the loop plug and fix it in settle and indicate the number of degrees this position in such a way that its 0- and 180 -deg. station lies away from our present line of direc- New markings are broadside to the loop (90 and 270 now tion. We note our course on the ship's compass The Library deg. markings therefore in line with the endwise .f comprises a re- and then simply correct our heading until course vised selection of plane of the loop antenna). Make definitely sure and signal are in line. We may now "ride the Radio books culled from that the scale will not slip and will turn only signal" into port without "much of any" trouble. latent McGraw - when loop and plug are turned. Bearing- station off- course. Is the bearing of Engineering Hill publications Place a pointer on the front of the cabinet's station ZZZZ unknown and do we wish this in the radio field. cover so that it will record against the scale. bearing? Then we note our course of direction, 4 Library Adjust the position carefully, making eure that as shown by our ship's compass, correct it for -especially selected by radio specialists of McGraw when the loop is turned to read zero (deg.) Hilt magnetic variation, get a direction reading on the publications or 360 (deg.) against the pointer, the finder is with our finder, find out its bearing from -to give most complete, dependable coverage of fact signal needed by all whose fields are grounded on radio exactly parallel- endwise -to the length, left to our present course by noting the degrees differ- fundamentals right, of the cabinet. ence between the 2 lines of direction, add our -available at a special price and tens. own bearing from true -North to this difference These books corer circuit phenomena. tube theory. net - -and get an actual true bearing on the signal. mks. measurements, and other subjects-give specialized OPERATION treatment of all fields of practical design and application. By extending this line seaward on our chart we They are books of recognized position In the llterature- In opertnion, the radio -direction finder is will have something to work on, for we'll at btuks you will refer to and be retened to often. If you are least we are on line! practical designer. researcher o engineer In any field positioned in direct line with the course of the know this based on radio. you scant these r books for the help they vessel. That is, the instrument heads directly Do we want a "true position "? Then we take give in hundred: of problems throughout the whole field this a bearing on 2 stations, if such bearings are radio toward the ship and the pointer indicates of engineering. line of direction of travel. not known, "triangulate" or extend both lines Svolames, 3064 , 2000U1mtratlons A chart of local waters will be renuired -a seaward, and note on our chart where they 1. Glasgow's PRINCIPLES OF RADIO EN- variation figures for cross. That crass or "fix" is our true GINEERING knowledge of magnetic position a and we know exactly where we are! 2. Hund's PHENOMENA IN HIGH -FRE- these particular waters, and ship's compass. QUENCY SYSTEMS These, of course, are common enough to any But these are matters for mariners. Your job 3. Chaffee's THEORY OF THERMIONIC mariner's store of seafaring apparatus and in- as a radio builder will be to construct a model VACUUM TUBES telligence. receiver, get it into proper working order, and 4. Terman's MEASUREMENTS IN RADIO All bearings and positions are taken with scamper down to the nearest yacht club for an ENGINEERING reference to a ship's course. exhibition. When you do-if you do -make such 5. Henney's RADIO ENGINEERING HAND- BOOK Bearing- station on- course. Is station ZZZZ, a trip, you may take along plenty of advance 30 days' examination. Special price. Monthly payments. which is coming in strongly, known to be exactly assurance of an immediate sale and some profit- $25.00 worth of books mat you only 123.50 under this in line with a desired course? position able orders for the season. offer. Add these standard works to your library now; pay small monthly installments. while you use the books.

SEND THIS ON- APPROVAL COUPON I McGraw-NM Book Co., Ins. I NEW TUBES FOR THE RADIO 1 ago w, 42nd St.. New York, N. Y. I Send me Radio Engineerin1,, Litrary, S V Isµ for I EXPERIMENTER days' examination on approval. In w days will d I2.50. pion few cents postage, d 83.00 i onthly till 23.50 Is ppsld. o returnre hoods paid. owe pay ( Continatd from page 204) ipostage o rders accompanied by remittance of teat nsuument.) Max. -signal plate current 60 ma. Screen -grid current (no I I Name No- signal screen -grid current 3 ma. signal) 5 5 ma. 1 Load resistance 2,000 ohms Screen -grid current (max. IAddress I Power output 3.6 W. signal) 12 13.5 ma. City and Brat. I 2nd- harmonic 2.5% Load resistance (plate -to- 3rd- harmonic 9 plate) 10,000 8,000 ohms Position ó (Data courtesy Raytheon) Power output 8.5 13 W. Company RC10-37 3rd -harmonic 3.5 3.5'/ [ 6V6G (glass) Unipotential- cathode Tetrode Total harmonic 4 4!: Power Amplifier. Transformed or impedance in- (Data courtesy Raytheon) put are recommended for use with this tube. If IF ITS TOUGH -DON'T CUSS resistance- capacity coupling is used the D.C. 1G5G Low -Plate- Voltage Power Output Pen- resistance in the control -grid circuit must not tode. This tube is designed especially for opera- Turn To RADIO-KINK -AIDS exceed 0.5 -meg. with self -bias. or 0.1 -meg. with tion from a 90 V. "B" supply and will be used fixed -bias. Note that the voltage between heater mainly in battery receivers, particularly where Praetial Repairs Per Over and cathode should be kept as low as possible. current limitations are a factor. Saa4 Hard -T.41z Radios. O N LY A direct connection is recommended. See Fig. ID. Resistance coupling may be employes) and the ton ar d,. as g. d. name Characteristics rated output obtained under class A operation. sad andd d do ar yco ." ">dog in vat doe Heater voltage 6.3 V. Larger power output is available by employing 9 5 heater current 0.45 -A. 2 tubes in push -pull service. (See Fig. 3E.) strike [roubles h.,,d Plate voltage 300 Characteristics in ,ha ,d.wain. (max.) V. 2 V. no 1.. dam. Y., :r. COMPLETE WITH Screen -grid voltage (max.) 300 V. Filament voltage 0.12 t METAL Plate and screen -grid dissipation Filament current -A. . ó (total) 12.5 W. Over -all length (max.) 4 11 /16 ins. f FREE"'"::: :r,ns caws Control -grid voltage -12.5 V. Diameter (max.) 113/16 ins. I AKRAD PRODUCTS CO. Amplification factor 218 Bulb ST-14 )'late resistance 52,000 ohms Base Medium G Type Octal No. 6 -X 362 WOOSTER AVE Akron. O. Mutual conductance 4,100 Operating Conditions and Characteristics IT..g out d.n .d, ,rue Nu,.. and Warn. ,tow . l'Inte current 45 ma. Filament voltage 2 V. ,.oat west ID -.,g.,,, .a sys and ...di at Screen -grid current 4.5 ma. Filament current 0.12 -A. Operating Conditions, Class A Amplifier Plate voltage 90 V. max. Plate voltage 2.0 V. Screen -grid voltage 90 V. max. Screen -grid voltage 250 V. Control -grid voltage -6 V. Control -grid voltage -12.5 V. Plate current 8.5 ma. Peak signal 12.5 V. Screen -grid current 2.7 ma. RADIOS Plate current (no signal) 45 ma. Plate resistance 0.135 -meg. Plate current (max. signal) 47 ma. Mutual conductance 1,500 umhos WHOLESALE Screen -grid current (no signal) 4.5 ma. Amplification factor 200 ma. Load resistance 8,500 ohms Our complete NEW line of FAMOUS Screen -grid current (max. signal) 6.5 ZEPHYR RADIOS open for your selection, Load resistance 5,000 ohms Power output 300 mw. at 50/ discount. Send for FREE catalog Power output 4.25 W. Total harmonic distortion 9 ó showing A.C.-D.C., All Electric or Battery 2nd -harmonic 4.5% (Data courtesy Hygrade- Sylvania Corp.) sets and Auto Radios. All latest modeis 3rd 25L6G (Glass) Beam Power Tube. This tube with -harmonic newest features -World -Wide recep- Operating Conditions, Class AB (2 tubes) has electrical characteristics that are identical tion, 5 IS tubes. Trial to 30 days -Money those of its metal the 25L6 de- back GUARANTEE. Earn EXTRA MONEY Plate voltage 250 300 V. to counterpart ask about our Agent -User Plan. Screen -grid voltage 250 300 V. scribed in the April, 1937, issue of Radio -Craft. Control -grid (see item in text However unlike the 25L6 which uses beam de- ZEPHYR RADIO COMPANY concerning input systems) -15 -20 V. flector plates the newer tube incorporates sup- 13141 Hamilton Av.., Detroit, Michigan Peak signal (grid -to-grid) 30 40 pk. V. pressor grids. (See Fig. 1F.) Plate current (no signal) 70 78 ma. (Tube is now available from RCA Radiotron, I'late current (max. signal) 79 90 ma. Raytheon, Sylvania, etc.) Please Say That You Satu It in RADIO -CRAFT

RADIO -CRAFT for OCTOBE R, 1937 241 "LEARN -BY- EXPERIMENTING" CRYSTAL BEGINNERS' PRACTICAL RADIO COURSE ,HEAD PHONES (Continued from page 233)

LIST OF PARTS FOR EXPERIMENT NO. I One general purpose, audio microphone transformer, T; SOUND CELL One adjustable condenser (optional). 0.0003- to ; LL 0.001 -mf. (equivalent to 300 to 1.000 mmf.) MICROPHONES One rheostat, 20 ohms, R; One 4 -prong socket, with screw terminals for type 30 tube: w Information on request One knob and dial- plate; Five binding posts ; BEFORE THE BRUSH DEVELOPMENT CO. One type 30 tube; or, type OlA tube may be 3312 PERKINS AVE CLEVELAND, OHIO used, with rheostat advanced to full, since this tube requires a greater operating current; YOU Three drycells, or one 4'_ V. "C" battery; One pair of standard headphones, 2,000 ohms resistance, Ph.: RADIO COURSES One key. may be home -made, as shown, or push- RADIO OPERATING: Prepare for Gov't button. K. License Exam. 'Names of manufacturers will be supplied upon t'y RADIO SERVICING: including Short WaveAMATEUR CODE receipt of a stamped and self -addressed envelope. ELECTRONICS TELEVISION How would you like to have a Day and Evening Classes- Dookiet Upon Requt I The author of this course has been identified good stock of nationally adver- New York YMCA School with the teaching of radio for many years in W. 64th Street. New York C,ty both private and public schools, and at present tised radio tubes on your shelves i is an Instructor in Radio in a New York City High School. His experience qualifies him ad- - without paying a nickel until mirably for presenting the technical material they're sold? BUILD IT YOURSELF of radio from the learner's viewpoint. That's how the Tung -Sol Con- You Can build this Trailer with ordinary ANSWERS TO signment Plan works for radio tools easily frroto our PROBLEMS Step-by-step constructional dealers who can qualify. You 'heats and large Shed blueprints. ON EXPERIMENT No. I ripest designed lr.ilee in existence. sleeps 4. Toilet. Simms'. Etto- pay for the tubes until (Sec page 233) don't Aer6?...t the cost by building it yourself. teed 2Sc for pisa. t. pweoaone end dead.. you've collected your cost and THE PLAN SHOP. 910 Palmolive Bldg. Chicago. II. (1) Filament current becomes gn'ater. (2) Tone becomes lower in pitch indicating a profit. That's worth looking into Blower or lower frequency. if you are eligible for (3) Pitch becomes looser indicating slower or -to see MODERNIZE YOUR OBSOLETE lower frequency. this unique plan. (4) Breaking the plate circuit. TUBE CHECKER OR SET (5) The amount of capacity in the grid circuit. More than 8,000 dealers have ANALYZER with "PRECISION" qualified -and are going places Write for details. Mention make and model in the tube business. number of your old instrument. BUILD THIS PRECISION APPARATUS CORP. Full profit -no investment-no 821 EAST NEW YORK AVE. BROOKLYN. N. V. "INTERMITTENT OPEN" dead numbers to write off at a CONDENSER TESTER loss. Easy to sell, because your (Continued from page 225) trade knows that Tung -Sol means RRDI05..5RVE;o50% will-insulated test prods and keep safely away top flight tube efficiency. DEAL DIRECT...FACTORY from the R.F. output of this "breakdown -test PRICES! Man odels to se- !vet( rom: AC- DC :AII- W ave; oscillator" in order to avoid high -frequency model.: automaeu 3 nflairinrear. radine: Farmeeta burns. that operate like city adios! Coil L consists of 76 turns of No. 24 enam. end tcard for NEW limeadeCatalog FREE. 9o. ^ wire wound on a form (preferably, air -core) nAY TRIAL pln nd 'nt-oser propoeitioni IV,. ins. in dia, Coils LI and L2 each consist of T RADIO CO. 50 turns of No. 14 enam. wire wound on a MICHIGAN OE. form 1% ins. in dia. The following List of Parts is suggested to builders who may want to try out this idea in a lab. set -up. Substitutions may be made by the PATENTS -TRADE MARKS experienced radio man as necessary to suit in- AU cases submitted given personal attention by members of the tiro. dividual convenience. Form "Evidence of Conception" and instructions LIST OF PARTS "How to Estblish Your RiOAts" -Free One Standard Transformer Corp. power trans- LANCASTER. ALLWINE & ROMMEL 1S PATENT LAW former, 650 V., 150 ma. sec. and a 2.5 V. sec., OFFICES T; l {ranChIS¢ 436 Rowan Bldg. Washington, D. C. Tung So limited One Standard Transformer Corp. filter choke, 1 se to a 200 ma., Ch.]; available can sä11 who One Hammarlund R.F. choke, 150 ma., Ch.: o) d¢aleta One Hammarlund variable condenser, 350 mmf., urn b¢" $500,000 GENUINE Ai 10 MAJESTIC- GRIGSBY GRUNOW CV; Wltolesal¢r REFRIGERATOR B UNITS Two Tung -Sol type 45 tubes, Vl. V2; a ualilY RADIO PARTS. GUARAN- One Tung -Sol type HO tube, V3; neatest 2000 01 YOU" REFRIG. TEED 18 MONTHS. Two Sprague condensers, No. TX- 24 -70, 70 mmf., ERATOR SEND FOR PRICE LIST. 1,500 V., C: UNITS G B G GENUINE MAJESTIC RE- One I.R.C. resistor, 25,000 ohms, 5 W. (no less), FRIGERATOR 8 RADIO PARTS SERVICE R; 5801 W. DICKENS AVE. CHICAGO, ILL. One Sprague condenser, No. TC -25, 0.005 -mf., 400 V., Cl; One Sprague condenser, No. TR -11, 0.01 -mf.. TUNG-SOL 5 TUBE SUPER KIT 800 V., C2; 56 K.C. 15 to SO Meters 200 to SSO Metes Two Sprague condensers, No. OT -21, 2 mf., 800 CJtfnz- f lvw Radio 04.,13-ea. Kit vi ,.i.1. of: I. F. Trans.. Var. Condenser. Chassie Pan. toils, Sn,-krls. Padding. Filter and Ity Pass V., C3; Condensers. its. i$ors. l'mver Trans. and Schematic One R.F. coil unit (see text for construction TUNG -SOL LAMP WORKS. INC. Drawing. Dept. F All above parts with G'e.' speaker $5.95 data) L, LI, L2; Radio Tube Division All Anne patio with 8° speaker . 6.95 One S.P.S.T. toggle switch, X; SALES OFFICES: Atlanta, Boston. 25 '. Depo.is Required With Order One bulb (and socket), 2.5 V. filament, V.: Chicago, Charlotte, Dallas, Detroit. FOR WRITE OUR NEW R PAGE FLYER Three 4 -prong sockets. Kansas City, Los Angeles, New York. ARROW SALES COMPANY Dent. 5 This article has been General Office, Newark, N. I. 631 WASHINGTON BLVD.. CHICAGO. ILLINOIS prepared from data supplied by courtesy of Sprague Products Co. Please Say That You Saw It in RADIO -CRAFT 242 RADIO -CRAFT for OCTOBER, 1937

BUILD THIS "OPTIMUM TEST" TUBE CHECKER (Co sat iaHUl Irorn page 209) The features incorporated in this unit are The usual practice, in order to overcome this r.rouped in Table 1. The reasons as to just WHY defect of the "neon test," is to decrease the these various elements were considered essen- sensitivity of the lamp indication so as to be safe tial in the design of this new tube-resistance- on cathode leakage indication; but this auto- capacity tester make interesting and instruc- matically would show as OK some tubes having tive reading. troublesome high -resistance interelement leakage! This fault is overcome by keeping the neon indication highly sensitive and then making an DESIGN FEATURES additional cathode leakage meter test; this pro- (I) Accuracy. This is determined by the type cedure is considered by the tube manufacturers of test circuit used, as well as the accuracy of to be far more desirable. the component parts which comprise the circuit. (2) Protection against obsolescence. Some TYPE A review of the R.M.A. recommendations and assurance that the apparatus will not be out -of- consultation with the engineering departments date in a short time is essential when consider- of the largest and most progressive tube manu- ing the construction or purchase of a modern facturers emphatically concludes that the most tube tester. CONTROLS accurate test which can be made in a practical During the past 5 years there has been a commercial instrument is the emission -type text great deal of ballyhoo in the claims of tube- .. are available in a complete under line of exact duplicate replace- applied voltages and loads as recommended tester manufacturers as to their designs pro- ment types. by the A.M.A. This circuit was therefore adopted viding for future changes and additions. With after investigating power output and medium - an occasional exception it was necessary for . also, hot off the press comes price transconductanee circuits. It is true that the manufacturer to bring out one new model. the new IRC Control Guide a finer, more elaborate transconductanee tinter and sometimes two. every year as the previous listing replacements for almost could be built but every receiver. it would be a very costly model would be obsolete. It would not meet all laboratory instrument. difficult to operate, and of the requirements that were necessary for Ask your jobber -or write di- impractical for a dealer or Service Man. properly testing the tubes of the following year. rect to us -for a free copy of the The meter selected is a d'Arsonval moving - One of the primary factors is the complete Guide. Prepare to use the finest free- point, free- reference of both filament leads proved controls on EVERY job! coil type with an accuracy guaranteed within 2 %. The tolerance of each of the resistors as to all sockets without being tied into any active circuit bus at the same time. This design as INTERNATIONAL RESISTANCE CO. well as the regulation of the transformer must can readily be seen from the wiring diagram 401 N. Broad Street Philadelphia, Pa. be guaranteed within 5%. Even under extreme circumstances the total circuit error will not enables the complete isolation of the filament be as much as 5% as the tube under test has a supply to any 2 desired terminals of the tubs relatively high resistance compared to the other including shell and cap. (There is not to nu' circuit constants. With all that, we would feel knowledge another tube tester regardless cf highly flattered if any commercial tube tester price that has this feature.) (including this one) could achieve an accuracy Furthermore any other individual element can of 5,í in grading tubes. be isolated, as desired. so that it need not bs tied to the cathode or plate bus; which is not The aces racy of line- voltage indication is im- the case with all other emission -type tester... portant and here a time -tested circuit is em- The flexible plug in connectors A. Is, C, etc.. ployed utilizing the 6H6 tube as a rectifier. This provide this unusual and comprehensive protec- special circuit (described in detail in past issues tion and are operated the same as the conventional ... "The Name of Radio -Craft) was developed by the xeriter method for toggle switches. Tells You Its a and to -day is in Lase in many fine measuring There is provided a spare circuit (see diagram) Masterpiece" instruments. with full switching capacity as for any present Hot interelement short and leakage tests and element so that an additional element or a hot cathode leakage tests are fundamental re- 0 -prong tube presents no problem. (No commer- quirements, yet, most instruments use only the chd emission tester on the market seemingly 'LET ME TRAIN YOU sit Avrng. neon lump indication for both measurements! has such provision.) Space is also available on It is essential to note that interelement leakages the panel for the addition of several new sockets FORA GOOD, -as differentiated from cathode leakage-have should future tubes require new types of sockets. very high resistance values which necessitate the (3) Tests all tubes. A good tube tester must be use of a highly -sensitive neon lamp. However, sufficiently comprehensive to test all types of RADIO JOB" there is alwayss a permissible limit of cathode tubes that are now in use including metal, glass, leakage which would cause a sensitive neon bump M.G. (metal -glass), obsolete battery and A.C. 1iy Get in Line for Big Money W and A. G. Mohaupt glow erroneously indicate that a good types, as well as cold-cathode rectifiers. Very Uirvrlinu F.nwioser Ife :. I.t, [ )Iilrrn T naps ire IIIp1'.uAlly' trained experts fer tube should be discarded! few modern testers if any will test cold-cathode sennAre and mainten e. Y,.:t I be.nne(' such an expert rinht at home - . It T t 11.. _ 1- .ta i.::In

SWITCH POSITIONS ON SW.1 X. 5 GANG Be the ONE Man INCLUDED SWITCH, SW I 1. OFF Y FILAMENT in WITH OUR 2 L-V 2 1,000 3 SHORT SWITCH, SW 2 who understands e en'w:ng IlL TRAIN I N G 4 H NL -EON ill to know in order lo Ore 5 DIDOES "sure -fire' service to all kind- b.TYPE receivers. You can be the one man 6 who can take coo servire business 7 1E51 away Burn the old -time radio B'SPI "tinker."' 9.SP2 NEON lo Ia0000e14s LAMP, s v No Experience Needed 11 1 MEG / Even though you know nothing 12 CONnENSER uu about Radio you can quickly LEAKAGE CONT-GRID qualify the R.T.A. way to step right into a wellpaying position m start your own profitable business. Use your aparo time and ra_ VU H2 LEARN AT HOME EATERz_ This efficient time - ) HEATER H Rl, Most S.T.A. sera tart mak- insinCircú ize- Ci 1.MEG ing, money right front the begin - t u Analyzer mThe special servicing equip- and Resistance Tester ment which is supplied with t extra cost makes this possible. you te make e delay Don't wait -get s arted n. Write money without R4, R8 18,300 today for our interesting Dada,' Free Book tells Titer. you how. 20HMS OHMS)

1 BATTERY Don't Put Off-Send Now 25.000 , It Coupon o I- 131 MF OHMS/ RADIO TRAINING ASSOCIAT ON OF AMERICA is 5 525 Ravenswood Ave., Dept. RC -80, Chicago, III FUSE 6 R7 ) /' 20 R9 RADIO TRAINING ASSN. of AMERICA VR 2 RI7. 5.000 OHMS OHMS Dept. RC -80, 4525 Ravenswood Ave., Chleage. III. 8400 Loy 63V R 10,1,0000HMS, t Gentlemen: Send me details of your Enrollment elan QMS X OHMS ami informa on how tu learn to make real mulle» 9 X to ratto quirk C

Name 10575.12 R6 °, 220 25.000 Address f4 OHMS

110. AC ('Hy State Fig. I. Schematic diagram of the "optimum- test" tube checker. Please Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT for OCTOBER, 1937 243

rectifiers although there are a number of these One molded wire -wound resistor, 1 W., 2 ohms, tubes in use. R4; This design provides suitable voltage and load One molded wire -wound resistor, 1 W., 1,000 uncir,.ssand for proper test of such tubes at position "special ohms, RIO; No. 1" as seen in the diagram. An additional One molded wire -wound resistor. 1 W., 200 ohms, spare switch position is provided for some future Ru; bot /000 usas special voltage and load requirement. One molded wire -wound resistor, 1 W., 2,400 ohms, R12; "Comprehensiveness" must also include the One molded wire -wound resistor, 1 W., 5,000 complete number of tests fur properly determin- ohms, R13; ing the worth of a tube. This involves the quality One Dependable wire-wound rheostat, 200 ohms, emission test and sensitive inter -element leak- VR1; age indication with a less- sensitive cathode leak- Two molded carbon resistors, 1/4-W., 25,000 ohms, age indication. Shorts, opens and loose elements R5, R6; should be readily detected as is easily done with One molded carbon resistor, 1/4-W., 18,500 ohms, this instrument because of the feature of isolating R8; any element at will. On wire -wound resistor, 1 W., 20 ohms, R7; In addition the instrument also serves as an One insulated carbon resistor, 1 W., 8,400 ohms, accurate ohmmeter and capacity meter, and also RO; as a condenser leakage indicator. The extra One flashlight monocell, 1% V., Bi. been features have incorporated because they This article has been prepared from are so work date sup- necessary in service and on the plied by courtesy of Radio City Products Co., dealer's counter, and involve very little in addi- Inc. tional cost and no additional space to the tube tester. Ccmpl tt lmn:n.d (4) Optimum -quality parts. It is just as much WHAT SIZE OSCILLOSCOPE? of a fallacy to follow the assumption that "the MODEL best Ls cheapest in the long run" as it is to (Continued from pout 205) believe that "the cheapest price is the most as compared to the total value and cost economical." Here is where the optimum value of the finished instrument. The same comment plays the important role. in general might be applied to a comparison Dealer Price Only high -quality parts have been used in this between the 2 -in. screen size and the 3 -in. screen $ 1 instrument but not necessarily the most expen- size. 5.O° sive ones. Molded wire -wound resistors are used in values below 2.5110 ohms, and insulated and OTHER DIFFERENCES molded carbon resistors of ample watts rating Although we are used for high -resistance units. The line - have shown by the foregoing that L 1AC'/- (/j voltage power rheostat, rated to carry 25 W.. the oscilloscope instrument proper (less tubes) POf/lQC I OLL-V hm- is of the vitreous enamel type. Panel layout and costs nearly the same regardless of tube size, design is very pleasing; etched to give a 2 -color the performance of the several sizes may differ effect. Construction is sturdy so that the instru- considerably. Visibility Factor. ment should be good for at least 5 years' service The Visibility Factor may be AbLia//iin G tIQ L if it Ls not abused. defined as "the ratio of the smallest -size image useful for practical - For laboratory, shop or field use. (5) Simplicity examination to the largest of operation. This factor is size pattern which the area of the screen will realized in that there are only 2 selector switches. Handy pocket size yet sturdy and permit." A pattern 1/4-in. wide by 1 -in. high is The operation is similar to the conventional considered the smallest useful for precision built. emission -type tester only no special examination. there are while the largest pattern is governed solely by sockets or precautions that are necessary with the size of ray Uses Large 3" Sq. Triplett Instru- so many other the cathode tube screen. testers. It can be compared to band -spread on a radio ment. (6) Economical in Design. Economy is veri- receiver which permits micrometer adjustment tably the shining light that has automatically re- of frequency for fine tuning. Likewise, the AC -DC Voltage Scales Read: 10-50- sulted from simplicity and efficiency in design. visibility factor determines the extent to which 250 -500-1000 -volts at 1000 Ohms Just think -this unusual tester with its splendid an oscilloscope pattern can be enlarged to allow features and high- quality parts can be con- precise examination of its waveform. per volt. structed with little effort and at a cost to the Figures A, B and C (on page 205) give com- DC Milliampere Scale Reads: 1 -10- Service Man of only about $18. parative visibility factors for the several tube (7) Ohmmeter Tests. Resistance -test facilities, sizes. It is worthy of note that a "visibility 50 -250. with 2 direct -reading ranges, are included. Low factor" of 75 is obtained with the 3 -in. tube, Ohms Scales Read: Low % -300; range: 0- 10,000 ohms, with self- contained 1% V. whereas a factor of only about 8 and 23, re- flashlight cell. High range, 0 -1 meg., self -con- spectively, are obtainable from the 1- and 2 -in. High 250,000. tained power supply. tubes. From an examination of these figures Black Molded Case and Panel. (8) Capacity -meter operation. Condenser-ca- it can be seen that the 3 -in. tube benefits greatly by comparison with the smaller sizes. pacity tests may be made over 2 ranges from Low Loss Selector Switch. Effective Area. 1 approximately 0.001 -mf. to 10 mmf. Figure compares the area of the 3 tube sizes. The actual figures of effective Complete with Alligator Clips, Bat - area are given, at A, B, and C, page 205. It is ti'ry and Test Leads. LIST OF PARTS well to consider a cathode ray tube screen from One Dependable milliammeter, 0 -5 ma.. with the angle of effective usable area. because in DEALER PRICE $15.00 this way the true proportions of the combination scale dial, Ml; image can A Complete Instrument One Dependable etched and fabricated panel; be anticipated. for all serv- One Dependable special tube -testing transformer, icing needs. Can be used for all Ti; SUMMARY AC -DC voltage, current and resist- One wire -wound shunt rheostat, 200 ohms, VRI; It is entirely passible that servicing work in ance analyses. the near future will One Dependable vitreous enamel rheostat, 25 W., require more extensive use Leather Carrying 500 ohms, VR2; of full -size oscilloscope equipment. Ultra- Case, Model 669, supplied modern receivers and the possibility of servicing extra. Of attractive black, heavy leather One Dependable selector switch. 6 -pole 12 -posi- work to be done on television equipment make with finished edges and strap. Dealer tion. Sw.l ; it necessary for the wide -awake Service Man to Price $3 00 One Dependable filament switch, Sw.2; carefully consider the type of cathode ray equip- YOUR JOBBER WAITE FOR CATALOG Six sockets, VI, V2, V3. V4, V5, V6; ment to be purchased. Using the method outlined SEE te One insulated, double control -grid cap with lead, in this article to judge tube screen sizes will C.-G.; assist in making this decision. Eleven insulated tip -jacks, Red -P1, P2, P3, P4, This article has been prepared from data sup- P5, CP, Heater-Heater, Black -K1, K2, K3; plied by courtesy of The Jackson Electrical In- a ;LEr, Ten metal shell tip -jacks, NI, N2, N3, N4, N5, strument Co. NG, N7, N8, N9, N10; paecíai47%i Ten flexible lead connectors with insulation; LELECTRICAL INSTRUMENTS. One line -cord and plug; 1 IN. One Westinghouse neon lamp, 1/4-W., NL; The Triplett Electrical Instrument Co. One socket for neon lamp; 2 IN 1610 Harmon Ave., Bluffton, Ohio Three Dependable indicating knobs with insulated Without obligation please send me tips, Ill, A. B. C, D, E, F, G, 112; Spare 31N. --More Information nn Model GM1t. One Dependable round knob; --I am also hrttrtgtd in One fuse holder and fuse; COMPARATIVE CHART SHOWING One insulated carbon resistor, % -W., I meg., RI; THE RELATIVE SCREEN AREA. Name One molded wire -wound resistor. 1 W., 148 ohms, OF SEVERAL CATHODE-RAY R2; TUBE SIZES. Address One molded wire-wound resistor, 1 W, 240 ohms, R3; CRY late F; q I. Comparative C. -R. tube screen areas. a Please Say That You Saw It in RAMO -CRAFT 244 RADIO -CRAFT for OCTOBER, 1937

NEW SET TESTER PUT YOUR FEATURES LOW-OHM SCALE TEST EQUIPMENT (Continued from page 205) 2,000-ohm scale, again to take advantage of the TO BETTER USE ! very open scale distribution from zero to center READ scale, with each division representing 1.0 ohm. These low- resistance readings give very accurate checks of the resistance of transformer filament windings, resin joints, etc.; shorted turns in speaker voice coils ; contact resistance on variable- condenser shafts ; shorts and grounds in 6 -V. genemotor (motor-generator) armatures used on mobile P.A. systems, also armatures of rotary converters, etc.; and many other places Quiet Your Razor in electrical and radio circuits. I It is also interesting to know that the current drain from the battery on the 200-ohm range is to Quiet Your Radio! very low, in the order of 60 to 70 ma., instead Filternoys Suppressor FO1DH is an of several hundred milliamperes in the usual approved plug -in device to be at- circuit. This low current drain is accomplished tached to any electric razor and by a special combination shunt -series circuit of high accuracy, as shown in the schematic dia- plugged into the electric fixture. It gram of Fig. 1. It requires only a single 1.5-V. takes the noise of an electric battery for operation. razor's motor out of your radio The high-resistance range of this instrument programs. provides for every ordinary contingency ; the scales are: 0/2/20 mega. Requisite high voltages 64 Pages CONTINENTAL Filternoys 6 a 9 Inches are obtained front an internal power pack. The Over 75 FO1DH, list price $1.00, offers D.C. scales are: 0/1/7/35/140 ma. Illustrations radio servicemen a handy profit- SON. able item to sell on many service (For those technicians who require dimen- Flexible sions, etc., in order to determine whether the Covers calls. Carry a few in your kit. Any equipment will properly match existing apparatus, Become intimate with your set analyzer and other test CONTINENTAL CARBON dis- equipment! Know how they work . how to apply and soon, we add the following data: them PROPERLY and quckidoing. . and theey. will tributor can supply you. money for you more earn (The bronze panel assembly is mounted in a TURNOVER key to salol servicing. There's in SERVICING WITH SET ANALYZERS you quartered oak carrying case with a slip -hinge ever things cover. ample tool compartment and leather Here Are The Chapter Titles: GRUtON IItÁ1 RIXEILIL CARBON Inc.11 handle. Size 714 x 10!(: x 4pÿ ins. deep. Weight. Manufacturers Receiver Tubes only 9 lbs., complete.) l'oint lIs -Limitations o the Analyzer its Receiver Servicing. z.R PRINCIPLES -Switches, the 13914 LORAIN AVE.. Cleveland. Ohio For the Service Men who require a high - \'aro,uv Types and Their Uses- Meters. the More Com- Also. Toronto. Canada fy Used Types-Elementary Set Analyzer Circuits. Makers of Carbon Resistors. Paper Condensers, and sensitivity instrument (for laboratory work, etc.) TROUBLE SHOOTING WITH THE SET ANALYZER -Pre- Noise Suppression Filters there is available the type 542 aet tester. This liminary Checking- Tes.ing Tubes Under Operating Con- ditions-Isolating Trouble by the IT,aae of Elimination Enclosed find 10c In coin or stamps for my copy of Handy unit is similar in all respects to the model 541, -l'oint.to -Point Testing -Checking Individual Components. Pocket Data on Radio Interference Elimination. ASSOCIATE TESTING EQUIPMENT -The Vacuum Tube except that it employs a forged, cobalt -steel Voltmeter-The 'rest Oscillator -The Output Meter-Thu magnet, and a dead -beat, microammeter with a Oscilloscope. Name Address COMMERCIAL TESTING EQUIPMENT sensitivity of 40 microamperes at 25,000 ohms/ THE RMA SOCKET NUMBERING SYSTEM volt; and will measure current values as low as Send fifty cents in stomps, money order or City State 40 microamperes. amiss for a copy of S£Rt It YNG WITH SET ANALYSERS. It is mailed postpaid upon This article has been prepared from data sup- receipt of your remittance. plied by Cmote:ay of Supreme Instruments Corp. RADCRAFT PUBLICATIONS, Inc. BUILT FOR 99 -R HUDSON STREET NEW YORK, N. V. FACTORY TO YOU PERFORMANCE CORRECT PLAYBACK NEW REMINGTON NOISELESS PORTABLE! OF SPOT RECORDINGS (Continued from page 226)

The record's acetate coating is a tough, but only a semi -hard substance, while the pressing is what might safely be said to be flint -hard. The latter is formulated in a press under several Famous Remington tons pressure and is cured by the application of Noiseless Portable that heat, thus producing a very hard, firm, inflexible speaks in a whisper, only 10c a day, direct from disc with a highly glossy surface. factory. Standard keyboard- Automatic ribbon With the advent and use of a greater number reverse. Variable line spacer and all the conven- PLUS of instantaneous records, it is essential that the iences of the finest portable ever built. the NOISELESS feature. Act now. Send cou- user acquaint himself with, and fully recognize pon TODAY for details. not only the advantages but as well, the special and very necessary requirements for proper You don't RISK a Penny playback. We will discuss these in the order of We send you Remington Noiseless Portable for TRANSFORMERS FOR 10 days' free trial. If not satisfied, semi it back. importance. giving in each instance, masons for We pay all shipping charges. EVERY APPLICATION construction in the pickup to bring about maximum results both in the matter of quality of FREE Typing Course and Carrying Case You will receive FREE a complete simplified reproduction and in the life of the instantaneous home course in Touch Typing. Also FREE, a LABORATORY STANDARD record itself. handsome. sturdy carrying case. No obligation. (1) Freedom of Armature Movement. Of first Mail coupon for full details -NOW importance is the freedom of movement of armature of the pickup. Aside from the fact Remington Rand Inc., Dept. 189-10 Portable Broadcast 315 Fourth Ave.. New York. N.Y. that it should be as small as is to it possible Tell me without obligation, how to get a new Rem- construct and likewise as light in weight, it ington Noiseless Portable, plus Free Typing Course also must be damped in the very lightest manner. and Carrying Case, for 10c a day. Send Catalogue, General Purpose The damping adjustment (point C in Fig. 1A) Name therefore should permit free sideward movement of the armature and should require only Address Rep lacements State the very slightest pressure on the needle. City As a test. when the finger is applied to the Vest Pocket Adding Machine Separate Catalogs Describing The Vari- pickup needle. D, the physical movement of the Sturdy Steel Construction. Lifetime ous Kenyon Lines Of Audio and Power armature should be very easily and readily seen Pocket Companion. Adds, Subtracts. Units Are Obtainable From Your Multiplies. Divides. Capacity. 990.- with the naked eye. The armature should be 1,99.00. ` real machine-guaranteed years. We KENYON TRANSFORMER CO., Inc. abort (as stated above) and under no instances ship aeideiwr0 ey. postmanie ion. should it exceed in length that of the pickup 00000000 c,riss semi 840 Barry St., New York, N. Y. needle itself. In other words, the damping, using Frees u sy ba ti Export Dept.. 25 Warren St.. New York. N. V. the pivot of the armature as the center of a satisfied. Thousands Trial r aped lever, would resist the side effort in the groove Send no .$oOp al sana slacta"i eo.e ea agents II11111111II111111I I I II III1 1 1 1 1 1 1IIII I111111111I IIIIIIIIIIIIIIIIIIII III1111111111I111111111I II I III to move the armature between the pieces. pole SALES CO.. 21 West Broadway. New York, M. Y. Please Say That You Saw It in RADIO-CRAFT RADIO -CRAFT for OCTOBER, 937 245

If the needle were short and the armature long, the damping would have to be lighter and far Save Money more delicate than is possible to obtain in a practical assembly, therefore the armature is on everything made shorter from the damper to the pivot than it is from the pivot to the end of the needle. Any pickup with a stiff or over -damped armature NOW READY you buy ... will destroy frequencies (on a record) directly in ratio to tite excess of damping used. THE NEW SYLVANIA (2) Needle Pressure on Disc. The next point of The New importance is the matter of weight on the needle which should be in all cases as light as possible CHARACTERISTICS BAR GAI N -never over 3 ozs., and preferably less. A pickup having a heavily- damped armature of course will SHEET! BULLETIN require more weight on the needle to make sure Your Guide to that the lateral movement in the groove will Hundreds of Out- actuate the armature before causing the head standing Values. to jump out of the groove. (3) Needle Angularity, The third point that Write today for this must be followed for maximum reproduction and outstanding 'mew life of acetate discs is needle angularity. Ex- haustive experiments have proven that 30" BARGAIN BULLETIN - brings about longer life without affecting re- there is no obligation on your part. production (point E in Fig. 111). High quality merchandise at sen,a- In the case of certain pickups mounted at tionally low prices! Radio Sets. an angle of less than 30° to the vertical, a bent needle such a.s is shown at point G in Fig. IC is Parts, Sporting Goods, Watche.. resorted Clocks, Typewriters, Cameras, Nov- -to in order to correct the angle of the needle at its point of contact with the record. elties and many other items at real (4) Length of Pickup Arm. The next point of savings to you. Fair Dealing -Prompt importance is the arm length which should be and Courteous Service, always. Send maximum at all times. Longer arms create less for your Free BARGAIN BULLETIN side pressure on the groove, eliminating distor- now, try us, and be convinced of tion in the pickup ; and, in describing the arc our superior values and service. over the record being played, are less liable to side -wall wear because the needle has greater leverage (due to the longer arm) against any RADIO CIRCULAR CO., INC. friction in the pivot. DEPARTMENT RC Part If will discuss many problems in selecting 91S Broadway New York, N. Y.. the correct needle for playback of spot. recordings. This article has been prepared from data supplied by courtesy of Universal Microphone Coni. To Readers of RADIO -CRAFT pu n.y. FREE POSTCARDS MAY BE NAD UPON WRITING TO THE PUBLISHERS These post cards make it easy to answer advertisements which appear in RADIO - THE "RESONOSCOPE" CRAFT, without cutting valuable data which you may wish to save. NEW ELECTRONIC DEVICE Many times manufacturers request you to "clip the coupon" when answering their DETECTS "OFF -KEY" NOTES ads. Often this means destroying part of (Continued from page Let It Solve Your Tube an article on the reverse page you may need 200) later for reference. Save your RADIO - chromatic scale are calculated for a true tem- Characteristics Problems! CRAFT issues complete. If you should ever pered scale, which has the most practical use want to sell bound volumes, or certain copies for all types of tuning. The pitch of the scale No radio service man should be without of RADIO- CRAFT, the resale value of is 440 cycles- per -second for A, this being the uncut issues is very much higher than that International this complete tube characteristics chart. of mutilated ones. So send for a supply pitch " -musical reference point - of these free post cards and use them in for tuning. (This standard of pitch is the one It contains the very latest tube character- answering all RADIO-CRAFT advertiser, used in the present models of the resonuscope, istics information available - information but any other pitch can be had by substituting that can be found nowhere else. WANTED - MEN u new set of tuning forks.) to cast Christmas Goods. 5 and 19e Novelties, Toy UTILITY COVERS MORE THAN 180 TYPES Autos. Ashtrays, etc. t bo tone in aw spare The resonoscope seems definitely destined to room, basement or garage and no expericace neler- become an indispensable aid to every branch The Sylvania Tube Characteristics Sheet ar). A rare opWn(unity to di vi to spar., r full :0 ..1 the musical art, especially time 1 w.rk. glRITE UEI'r. ü. so when it is noted suits service men to a "T." It covers that skilled musical instrument will METAL CAST PRODUCTS tuners be more than 180 types . tube types are CO. ":f at least by 1/3 -cycle on their fundamental numerically listed . . characteristics 1696 Boston Road New York City notes, and more on the higher and lower octaves, are in usual ear tuning! While such discrepancies tabulated ... all characteristics and base may not be noticed in the individual notes. they diagrams are arranged on one side of the tit SOUND RECORDING' produce a general discordant effect which is displeasing paper- instantly available. Also contains TALKING PICTURE to critical musical ears. full information on PROJECTION The new "electronic robot ", on the other hand, the latest types of glass, TELEVISION -RADIO permits tuning to within a very minute part of metal and "G" tubes. Folds to pocket a cycle. Its tuning forks are tuned to an accuracy size- swell for your service kit! Sinner courses qualify you for good John. etrainingeasy to 'learn. Newest ye'ui , ent. F.tali of 0.002 -per cent! d 1915 Ear room and board whilewhile learn.ne. Cl'shoach It facilitates R. rR. fare "allowed "to I.. A. for Flt`" the tuning of such musical in- Best of all, it's FREE! Just fill in coupon 1100K. Address De rt. 10.RC, 4000 S. Figueroa St struments pianos, the as accordion reeds, harmonic below, and send it to us. You'll get your NATIONAL SCHOOLS--CH Anciefvf reeds, organs, and so -on, not only for fundamental notes but for all octaves. Each instru- Characteristics Sheet . . . pronto! ment of an orchestra or band may be so ac- "HAN" SPECIAL i::ór: curately tuned that an entirely new ensemble A highly efficient toile effect is obtained. Likewise a singer can de- teacher using heavy spe- termine precise pitch and adjust his or her cially prepared ed voice accordingly. In busy S Y LVA N I A paper tape. having sa two broadcasting stations rows of perforations. where musicians and artists hurriedly form SET -TESTED RADIO TUBES Writ. for Free folder A10. various groups in various studios, the device is We are the originators of Instrument with tapes this type instrument already being used to obtain correct pitch for r Prepared by expert aod individual instruments nude a and vocalists, so that no arse all for TELEPLEX CO. HYGRADE SYLVANIA CORP. :r' 107 III St 1.es. w'nnoutti..'rilator. 72.76 cocoanut Si.. N. time may be lost. Because the resonoscope permits the vocalist Emporium, Penna. to actually see just how his or her voice sounds, Please send me a FREE copy of the latest and to analyze its pitch and quality in the most Sylvania Tube Characteristics Sheet. critical manner, this instrument is being hailed COMING SOON! as a great aid in voice culture. The singer can Name New RCA Commercial adjust his or her voice. while watching the Sound Catalog. screen pattern, until it matches that of a great Address Watch for it! singer who is to be emulated. Because the instru- COMMERCIAL SOUND ment indicates pitch, character of note and City State .. volume, in a visual manner, it becomes Dealer Service Man RCA Manufacturing Co., Inc., Camden, N. j. the n 7 first electronic music master fur music lovers [1 Amateur El Experimenter A Service ofthe Radio Corporation of America everywhere. Please Say 7'liat You Saw It in RADIO -CRAFT 246 RADIO -CRAFT for OCTO°"".,

ON THE LATEST IN TEST APPARATUS No. I HIT PARADE FOR THE SERVICE MAN (Continued front poor , braced, direct- reading decibel sea!e su incorporated on the scale plate enabling db. readings from -10 to +63 db. in 5 ranges. The instrument incorporated in this unit has a base sensitivity of 400 microamperes at 100 TUNING ASSEMBLY millivolts and is of the modern, wide-open square The Meissner All -Wave Tuning Assembly is the entire type, size 4 x 4tß, ins., allowing all scales to "front end" of the radio receiver. Each unit is completely be easily read. The A.C. correction scale is wired and accurately balanced and aligned. READY FOR USE. Only six wires to be connected to any 456 kc. I.F. printed in red to readily differentiate between channel. A.C. and D.C. voltage readings. RANGES: A.C. voltage (at 1,000 ohms /volt), FEATURES 0/10/50/250/1,000 /2,500; V. D.C. voltage (at 1. Meissner Multi -Wave 5 -Band Coil as.embly; individual coils for each 1,000 ohms /volt). 0/10;'50 2 50/1,000/2,500. V. band; Meissner Align -Aire trimmers thru out, six -gang shorting switch; List D.C., 0/10/50/250/1.000 ma. Resistance, 0/400 fully shielded. ohms /1 /10 megs. Decibel meter -10 to +63 in 5 2. Meissner three -gang tuning condenser: low minimum capacity. Price ranges of 0/ (-14.!+2$/ +40 / +49 db. Output 3. Modern 8-in. oval dial; two -speed control; calibrated 5-Band scale: scale meter indications. for Band Spread. 4. Compactly mounted on rigid cadmium -plated steel chassis. As noted in Fig. F and circuit diagram, Fig. '38_' 2, all A.C. and D.C. voltages (except 2.500 5. All components including all resistors, by -pas; condensers, coupling con- V.). densers and AVC network. D.C. and resistance measurements are available 6. Every unit laboratory tested and completely aligned and padded. at only one set of polarized tip -jacks through 7. Available in two ranges. Model 7512 -5 to 555 meters (540 kc.-60 mc.). the use of the master range selector. This rotary Model 7511 -7.5 to 2140 meters 1140 ke. -40 mc.l. range selector permits speedy range change NOTE: See your dealer or write direct to Dept 1 for our New 32 -page descriptive catalog without the necessity of removing and re- insert- ing test leads. The Low -Ohms circuit makes use of the Shunt Method (back -up scale) for low -resistance measurements. Referring to the circuit diagram, MEISSNER MFG. CO. Fig. 2, it will be noted that when the range selector is rotated to the low-ohms position, a shunt is placed across the meter posts, and at the same time a section of the current -limiting Mt. Carmel Illinois resistor is shorted out, enabling full scale adjustment to be made through the use of the Adjust Ohms control. The combined resistance value of meter and shunt is exactly 20 ohms. New 1938 Radio Catalog The current drain of the low -ohms circuit is approximately 5 ma. It therefore be FREE!! Servicemen -Radio Salesmen and Agents -be- can readily seen that any low value of resistance placed come n' MODELL representative in your community without any investment. Earn up to $100 a week in commissions selling Nationally Known Radios. across the test tip -jacks of the multimeter, will Take orders from the largest and most complete catalog ever published, cause the current flowing through the meter to describing and illustrating the following 103$ makes: RCA- Philco- drop accordingly. An individually -calibrated and General Electric -- Zenith- Motorola -Delco direct -rending low -ohms scale is incorporated -Crosley- Stromberg Carlson- Since on -Grunow /_ J_ the meter scale plate for this low-ohms range. Kadette-Emerson-Fatia-Halson-Garod. 1839 1-ohm fs Join this nation wide organization by writ- v+ Resistance values as low as can readily ing for particulars. Territory is now being AGENCY DIVISION be measured. The 20 -ohms indication is located allotted to live wire men who are anxious write to Dept. D -5 and mail to at the center of this scale. to earn extra money in their spure time. address nearest you. (Precision Apparatus Corp.) Writ,. r... ,..- CHICAGO. ILL. Oa. NEW YORK. N.Y. log. S6 W. Washington St.l 57 rorayth St. SR Cortiandt St. BUSINESS PROBLEMS OF THE SERVICE MAN FREE! (Continued from roue 223) accessories, tubes and whatever else could be sold customer desired by Mr. Jerod and Mr. Holtz. HAMMARLUND is limited to those who would actually come down to the service department. A SOLUTION 25th YEAR The next point to he covered is. how much The better arrangement for Mr. Jerod and RADIO CATALOG the space worth? If offered the equivalent Mr. Holtz in the event that they insist on the in cash, would they service the store refrigerator North -West location, is to obtain the best store The most complete catalog ever pub- for this amount? The answer was decidedly - available for around $50 a month. This amount lished with special illustrations. NO! The rent was not worth over $40 a month usually is sufficient in smaller towns for a drawings, curves and a complete and upon examination it was determined that reasonably good location. Then. use about $750 16 tube description of the famous to up one man for of their capital for modest store fixtures and "Super -Pro." Write Inept. RC- 10 -37. they could not afford tie that amount. for putting in a reasonable stock of tubes small HAMMARLUND MFG. CO., INC. It readily becomes apparent that "something radio sets, replacement parts, electrical appli- 424 -138 West 33rd Street, New York for nothing is no bargain." Free rent in this ances. etc. The balance of their reserve is to rase was of no advantage, in fact it becomes a be used as a surplus fund for emergencies. If great disadvantage. the friends and acquaintances of Mr. Holtz come The store. of necessity, must be non-competi- through as expected their chances of success tive, therefore, it dews not attract the type of are indeed promising. QUALITYrecommends

SERVICE BENCH OF SUCCESSFUL SERVICE MAN (Coitt;i iid j coon pig, 223) checker. (3) volt- milliameter, and (4) signal tube, vibrator and condenser checker. Under this generator. The tools shown are mounted to is a panel composed iff jacks, which are con- hinged doors opening to a cabinet about 4 ins. nected to all instruments. and these, with the a9t4e'Vilir deep and 1$ ins. high, which forms the back of use of short wires and plugs as jumpers, will WET. ( OLA5) the bench. This cabinet is used to hold condensers, make most any test necessary. PAPER _ resistors, spooLs of wire. screws. nuts. bolts, The 2 meters to the left of the center are in MICA TRIMMER ... \ _ washers. The top of the bench is set off with the 6 V. D.C. circuit, one a voltmeter, the other Please Write lo, Derails etc. an aerial made up of about 30 ft. of wire mounted an ammeter showing current consumed by a 599 -601 Broadway .stand -off insulators. To this aerial is given set while being tested. The meters to the SOLAR MFG. CORP. New York City on two clipped the antenna leads of the sets being right are first an A.C.-D.C. meter and second, an tested or repaired. ohmmeter. Beneath these meters are 6 small The machine to the right of the bench is a lamps which are pilot lights, one of which lights RADIO ENGINEERING small air compressor and tank which is used with any equipment being used. RCA Institutes offer an intensive course of Idol to blow out the dirt from condenser plates. This prevents the soldering iron or tube standard embracing all phases of Radio. when not in cal training with modern equipment at New speakers and the house sets. (There are other checker from being left turned on York and Ch kale, schools. Also specialized pieces of equipment. not shown, such as bench use. Also to the left- center is a neon lamp which oturse: and Itrime study I 'ourses tinder "No can be plugged in any circuit for continuity or obligation' plan. Catalog Deot. RT -37. drill, lathe, emery wheels and portable drills.) Directly under the antenna is the rack for short tests. The two lower openings contain RCA INSTITUTES, Inc. spare tubes used for testing. The center of the slides on which are mounted punches and A Cor parution of Americo Service Radio back of the bench is built up from the Confidence chisels and socket wrenches of all sizes. 75 Varide St., New York 1154 Merchandise Mart, Chicago s Pleage Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT for OCTOBER, 1937 247 THE RADIO MONTH IN REVIEW (Continued from page 199) month, and heard in part over long distances. SLASH COSTS had much to do with the confusion attending the search for the lost Amelia Earhart, and caused reports to be sent in by listeners on short waves EARN MORE that they had heard signals of distress from the missing flyers. It. is difficult to imagine any precaution which could goon] against such a misunderstanding, unless such interpretative SAVE TIME programs are to be delayed until the excitement of the search has died down. R4V'O See your parts distributor or w rite ANNING S. PRALL, us about the new C -B free instruc- HEAD OF F.C.C., DEAD TRA/N/JVG! tion course. CHAIRMAN Alining S. frail of the Federal Communications Commission died at his sum- DEMAND CLOUGH mer hume, Buothbay Harbor, Maine, last month, -BRENGLE QUALITY at the age of 66 years. In memorium, practically every radio broadcast station in the United States and its territories, at the suggestion of the National Association of Broadcasters observed a 1- minute quiet period, on noon, Monday, July 26. T.t)tlk Mr. Pratt was appointed a member of the Radio Commission in 1934 by President Roosevelt. After the Radio Commission was merged with the Federal t'mmmnications Commission, Mr. l'rall was made Chairman of the Radio Division of th . Conlin-

Model 110 Signal Generator Model 120 Super Analyzer Finest engineering -Best materials - Sensitivity; 20,000 Ohms per Volt. Fault free. For 1 F and R F align- Makes all voltage, current and resistance ment. Also 400 cycle audio amplifier meaurements for analyzing reeeiv,r*.:mt lest. Model 110 $I :1.50 plifier,, etc. Model 120 S 13.50 $5.00 amen, It) months to pay. $5.00 down, to months to pay. Send for Catalog or see your parts dealer

The CLOUGH- BRENGLE CO. 2809 W. 19th St., Chicago, III.

ABC OF MODERN VIBRATOR SERVICING (rr,,t : sal t ,e, )at,, 220) PURPOSE OF THE BUFFER CONDENSERS tln' rarely, if ever, d, the poorer transformers pire trouble. Not shown in the drawings, but an important part of the vibrator function, are the 2 small buffer condensers which are either incorporated LOW "B VOLTAGES as a part of the vibrator or incorporated in the If the "It- battery voltages are low, the bat- power pack of the complete unit. tery voltage must be checked, as well as the re- These condensers form a very useful service sistance of all leads from the battery to the in limiting and suppressing the arc across the vibrator. Check AWNING S. PRALL contacts due to the making and breaking of the for high -resistance shorts in the rectifier current on the primary side. These condensers circuit. Check the rectifier tube and buffer con- are placed in the secondary instead of the pri- densers for worth, and for troubles which cause mary circuit since although the voltage must be low voltage in the usual home-radio set. The vi- THE LATEST very much higher, the capacity can be very brator should then be checked in a vibrator much lower as their action is reflected in the checker. RADIO EQUIPMENT primary circuit. (Continued f 239) The capacity of this condenser whether incor- HASH porated as an integral part of the vibrator, has added to his new line of condensers a series or Hersh is a problem circuit in the power should of design, shielding of 21 replacement units. Capacities range from pack proper, never be --both magneti., and electrostatic, proper changed as the entire vibrator has been designed radio- 14 -mf. to 65 mf. Representative styles are shown for frequency filtering, proper ground, mechanical in the illustration on 239. this particular capacity. arrangement page In the preliminary of the receiver, and the sensitive- check of the vibrator and ness of the receiver. Engineers the power pack. much have taken care guess work can be elim- of the hash problem inated by knowing the circuit and understanding in the design of' the receivers and if hash is present it should be DEPENDABLE ARE a few of the troubles, such as the following. traced HOW which to its source. Do not attempt to eliminate ha,h can occur to vibrators and their power by "doctoring" YOUR METER READINGS? packs. the vibrator. In severe cases, manufacturers of the vibrators do furnish hash (Continued frunt Palm 237) eliminators. Figure 2, on pg. 213, includes illustrations, of NO "B" VOLTAGE important elements in meter construction, which Shorted filter systems, shorted buffer conden- INTERMITTENT OPERATION the Service Man may be interested to note, as, sers, grounded filter systems, shorted trans- Intermittent operation can 1, a limited extent, they are self- be caused by defec- explanatory. formers, shorted wiring or shorted rectifier tubes tive vibrators due to sticking However, the detailed analysis of these elements contacts, loose may cause no "It" voltage. Also, no battery connections in the power pack and symp- (Figs. H to O. inclusive) constitutes important, other voltage may be delivered to the vibrator, which toms the same as in a conventional b :u lo knowledge which every technician should A.C. re- can be caused by a blown fuse, a burned -out ceiver. Eliminate these by checking the vibra- pc ssess. This information. and considerably more, switch, a broken "A" lend or any one of will the tor in a vibrator checker. appear in Part II of this useful article. numerous other suggestions which will come to mind. OTHER VIBRATOR TROUBLES Read Part II of this article; it will discuss After the cause for the absence of "B" voltage Inherent Meter Accuracy (or inaccuracy). has been discovered, correct same Vibrators with u n us wl mc_h :n iral noise are The and proceed author of this vital article is also author to test the vibrator in a good vibrator tester, as caused by the vibrator touching other parts of of "Radio Physics Course." "Modern Radio Serv- a shorted filter system and other shorts, such the housing, the internal assembly, or by loose cing," and "Radio Field Service Dala "-all of as buffer condensers, rectifier tube, transformer parts which vibrate with the operation of the 'hem valuable contributions to the field of litera- secondaries, etc., can damage the vibrator by vibrator. ture for the practicing radio Service Man. overloading the contacts. It might be stated here (Continued on page 255) Please Say That You Saw ft in RADIO -CRAFT 248 RADIO -CRAFT for OCTOBER, 1937 "AIR- TRACK" SYSTEM OF BLIND LANDING (Cantina. d from papy 202) Six important improvements have been incor- USEFULNESS OF "AIR- TRACK" porated in the Air-Track. Foremost among these AT CROWDED AIRPORTS are the facts that (1) the equipment has been so simplified and the design made no compart, that Usefulness of the apparatus for control of it is portable, slaking it Possibly to lend a pilot traffic at crowded airports has been stressed by in to n safe landing front either end of any run- pilots who have flown the system. Airline officials way on the field; (2) the radio signals. at first have pointed out that if all landings of air trans- liable to deviation and instability, have been port planes were made on this system, even made reliable, and a monitoring system installed in fine weather. a pilot would never make an which indicates to the operator whether accurate unusual landing, no matter what the weather signals are being broadcast: 13) both the might be. tornli:rr and the glide putt are quickly adjust- Despite the thoughtful and serious work of able and. (l) the equipment required in the plane airline operations managers and traffic managers has been made lighter and more efficient. in "staggering" schedules to avoid simultaneous The principles embodied in this system were arrival of several airliners at one airport at the originally worked out by an Aeronautics Re- same time, the airports at large municipalities Triumph 1", 2 ", and 3" search Division established by the Department of are already dangerously crowded at certain times. Commerce at the Bureau of Standards. A num- At one airport today, there are 18 transport ber of the radio scientists who developed the planes arriving within the space of an hour. system at the Bureau have been at work in a Increasing patronage will only aggravate this OSCILLOGRAPH laboratory at College Park Airport near Wash- problem, and bad weather complicates it to the ington developing the system from its early point of deadly hazard. experimental stages to the point where it is It is as if the engineers of a large number of WOB BULATORS now practical for air transport. Three years of trains were instructed to choose their own track such development and improvement work have and bring their trains in to a huge station with Buy your oscillograph and wobbula- resulted in hundreds of successful landings only the admonition to "be careful and not run tor together! Only with this com- "under the hood" and landings in fog conditions into other trains." The airline pilot has two -way which interrupted scheduled flying. voice communication with the airport control bination can you accomplish true Three experimental installations of this curved tower, and receives all the information available. visual alignment of r -f, i -f, afc, and beam type of landing system have been tested by but he does not have a definite "track" or path avc circuits. Model 77, I" Oscillo- Department of Commerce pilots, airline pilots to follow which will keep him clear of other graph Wobb. $49.95. Model 77, 2" and others. These are at College Park, Newark approaching aircraft. Oscillograph Wo6b. $59.95. Model airport, and the municipal airport at Oakland, A correct blind landing system may have a 180 -800, 3" Oscillograph Wobbula- California. In all, upwards of 1.000 safe instru- number of duplicate "tracks ", properly identified. tor with built -in signal generator ment landings huge been made on these installa- just as are the tracks in a railroad yard. and tions. the approaching pilot's orders will indicate the $100.00. track he is to use. Eventually, these engineers ELEMENTS OF THE AIR -TRACK SYSTEM believe. the "switches" may be set for the ap- TRIUMPH MFG. CO. proaching pilot. and his plane may be taken Briefly, the Air -frack system co ris i

RADIO -CRAFT for OCTOBER, 1937 249 GET THIS new BOOK --- NEW INSTRUMENT SPEEDS FREE -POINT TESTING (Continued from page 225) means of determining circuit conditions accurately since no current is drawn from the circuit under test. Current ranges on present -day testers have FREE! been used rather infrequently because of the time and trouble required in making a series Every Radio Man Can Use connection in the circuit. It to Advantage! THE "CURRENT MEASUREMENT" SYSTEM CO- ORDINATED f OF TESTING One of the most difficult parts of a radio set to test and one that has become the bug -a -boo SOUND SYSTEMS for Service Men is the A.V.C. and Q.A.V.C. circuits. Most voltmeters placed across these circuits, in order to make a voltage measurement, ~FO. draw current from them and more or less upset the high -resistance networks present. The purpose of these circuits is to control the current in the tubes to which they connect. A current measurement is logical therefore, since it does not upset the A.V.C. and Q.A.V.C. networks whatsoever. MAN 4 By (1) using an oscillator input at the POWER 1 antenna posts of the receiver, (2) plugging MI6 O I this new instrument into the sockets of the VII tubes controlled by the A.V.C. and Q.A.V.C. and (3) varying the signal strength put out by the oscillator, the plate current variation \ give an absolute of the will indication condi- ' - - /. tion of the A.V.C. or Q.A.V A. system. THE Editors of RADIO -CRAFT have prepared This method can be used for testing diode 2nd - a special hook for you. The new book -1937 L RADIO REFERENCE ANNUAL -is not for sale. detector circuits no matter how complicated the JI but available only to subscribers, both new and resistance networks connected to the diode may old, with a Seven Months' Subscription to be. Fixed minimum bias, A.F.C. or any other a JJ RADIO -CRAFT. The price of this Special Offer similar circuit may be tested by this method of ` Ifjill ` is only One Dollar ($1.001 -and as an additional current testing also. Service Men who do not I _ saving the book is mailed to you postpaid as well have an oscillator can make texts by tuning I{II111 as is the magazine each month. the Carefully outlined below is the contents of this on and off a powerful local station. In the audio new book ; it contains information which every end of the set, grid bias may be checked very radio man needs. The book contains 64 pages, accurately by taking plate current readings. An size 6 x 9, and is replete with illustrations. overloaded condition of the rectifier tube can Read these Interesting Chapter Headings of be checked easily by the current method for the power pack circuit need not be considered. As 1937 RADIO REFERENCE ANNUAL an example, it is the usual thing to check The LAFAYETTE line, one of the oldest. most complete lines in industry, Receiver Construction rectifier overload conditions by voltmeter read- the has Building 12 -tube All -Wave DX receiver -Ilow to make ings from chassis to rectifier filament or cathode always meant progress ... but never so a modern s -tuba Car Radio set- bullding up 2-tube but this does not necessarily give a correct much as in these NEW 1938 models. New Beginner's Set, with several different power supplies for indication for it does not take into consideration various uses -- Constructing a 2 -tube midget set for colors... stream -lined designs ... lightweight, whether the negative lead from trans- portable use -How to build a "talking" briefcase-no the power sturdy, non -corrosive steel cabinets special aerial or ground needed. former goes directly to chassis or through a filter ... Test Equipment -Construction or resistor network before connecting to the illuminated control dials ... here are sales Row to make an "Electronic Eye" output meter-How to chassis. This especially applies in A.C.-D.C. sets. features that make for EASY SELLING. construct an ultra -compact universal toll- Ohm- Mllllam- A couple of where lneter -Plow to make a Resistance -Capacity tester -flow to examples current readings for a wider margin of profit Build a Pocket Adapter for set testing- Building a come in handy are first, where an audio bias Portable Capacity bridge -Construction of a V.T. Volt- resistor has been so badly burned up that its byword of satisfied users meter In compact form -How to Make a Modern Set LAFAYETTE Analyzer. resistance value can no longer be read. A quick Audio and P. A. Equipment estimate using Ohm's Law will give the approxi- EASY TIME PAYMENT PLAN] ]staking an Audio Bass Booster, using direct coupling- mate value but only by taking current readings of NOW .. LAFAYETTE'S Easy Payment Plan, `` Stow to build and add a Dual -Channel Amplifier to your re+elver-t' nstrueting a high- Fidelity Amplifier -Con- the tube controlled by this bias resistor is it tailored to the needs of your business, will help t struetion of a 3 -tube A.C.- operated Preamplifier-Funda- possible to be sure that the resistor value is you finance the "big" jobs. .If mentals "Decibel Level" Decibel of and Cain." correct. Another example is in replacing a Articles for the Service Man volume control in an orphan set. By taking Servicing with the Oscillosrope- Servlctog with a Single HERE IT IS! Meter -"What's Wrong With Your Radio' chan- Tape'r5 current readings of the tube controlled it is M \'plume t'q¿ cols. and use f rious apes -Ideas for possible to check very quickly whether or not The FREES the Service Shop -Aligning All -Knave receivers. the taper of the new control is correct. Biggest 0/0 r Time and Money -Saving Kinks To sum up. by the use of the current method section by the experience of other .. In this you profit radio of making tests, analyses Radio Ale I /rOff ,/ men. These kinks are really valuable 'short- cuts" whirls of radio receiver faults +e Op, O save much tines and. very often, money. They are "pet" are very much simplified. By use of this instru- ... ,: Catalog %/ba óntosteD leH Ideas put into Ira,9i,e _ n ment current readings can be taken simply and ever assembled! 130 pages, R'5C oy,s. adon ero;/s Important Articles Which Have Appeared in without the cutting or unsoldering of wires. large RADIO -CRAFT (Incidentally, this device also may be used in ecttion. parts, 50 the yOCAT,q FRÉ6 taking the "usual" tests such as voltage General Interest Article. and LAFAYETTE Radio models. ° 'ri+ey s4orf0G. resistance.) test equipment and all at r e o/ Design of Treneformrrs ter ('lass ".U:" and "B" opera - ... tion -A table of Inter-Electrode Capmdtle: for 30 differ- Our Information Bureau will gladly supply lowest prices in history. ent tube types-now to make a Floating-G,-ld 7telay- manufacturers' names and addresses of any items Cunsuuctlon of a modern Treasure locator-How tu get DS on your All -Wave ltadio- ]taking a 5 -meter Trans- mentioned in 71- 4D104'1í:1 FT. Phase enclose a ceiver tor use in car or boat, stamped and to If -o11 r,sx.d , n e, lope, ill11011S11111111010 SEl1VICC CD.c. New Tubes Developed in 1936 Characteristics of the Newest Itovelvhtg Tubes of all NEWYORK,N.Y. CHICAGO,ILL ATLANTA, GA. manufacturers, giving uses, rhararteri stiu, present 00 uS IH a0l PI 02 rot W. 141510. 5405. .mw. NACHnn ...NAM equivalents any) tout all dita. (if pertinent OPERATING NOTES BOSTON, MASS. NEWARK, N. J. (Continued from page 227) BRONX, N.Y. JAMAICA. L I. RADIO -CRAFT eral small holes are provided in the top of the WHOLESALE RADIO SERVICE CO.. INC. 99 Hudson Street New York, N. Y. container to act as safety valves. in case this 100 Sixth A New York, N. Y. action takes place. This small leakage does not RADIO- CRAFT, 99 Hudson St., Now York, N. Y. affect the efficiency or change the value of the hush FREE 1938 catalog No. 69-3KA s Gentlemen: Enclosed seu w Ill flroi my remittance of One condenser in any way. Dollar 191.001 for which enter my subscription to RADIO -CRAFT Magazine for Seven Months. Send me STRIMaeltC,- CARLJON SOLgER NI,GGErs ARSOLT'TE 1.Y I'It :E. and POSTPAID, my spy d NAME 1937 RADIO REFERENCE ANNUAL Fada KA and U. S. Radio Model 10. Gassy 27s Name cause trouble in different sets in different ways. In a Fada KA. 2 of these tubes in the A.F. ADDRESS Address stage caused very poor quality of reproduction. In a U. S. Radio model 10, a gassy 27 in the City Stute 1st audio stage may cause a "jumpy" volume (Send remittance by check or money order. Resister your control. CITY. STATE letter It you send cash or unused U. S. Postage Stamps -) f RC.1031 PAUL. WELA ND Please Say That You Saw It in RADIO -CRAFT 250 RADIO -CRAFT for OCTOBER, 1937

C Tit CRostEr O ttAON WARNS I 1 57E`MART r"-----()_°4.1- 863 CORPO let -'gin CNASStS ST1pN 6 1 .

Oir/CIAL RADIO SERVICE MANUAL

.15 PHILCO RADIO & TELEVISION CORPORATION 37 -33 r a; Vow p1D34PHONOGPH CORPORA D140-D1423p 13eDI'- .. CHASSIS D

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150 PAGES ...... OF VOLUME 7 TO THE OFFICIAL RADIO SERVICE MANUAL ARE MAILED TO SUBSCRIBERS EACH MONTH

Compare other service manuals with the new GERNSBACK OFFICIAL RADIO SERVICE MANUAL (Volume 7) as it is published today. You'll find the GERNSBACK MANUAL, by far more complete in service information -more up -to -the- minute with present -day receiver diagrams -and published entirely differently than in previous years. Most important of many innovations are the month -to -month installment method of publishing Volume 7 -and the deferred payment plan which makes it convenient for every Service Man to own radio's greatest of service manuals. Write today for descriptive literature which gives complete information about Volume 7 of the OFFICIAL RADIO SERVICE MANUAL -and

the plan - which tells how to pay -as -you- compile your Manual. Mail the ro upo n below-TODAY'I

RADCRAFT PUBLICATIONS, Inc.. 99 Hudson Street. "NEW YORK, N. Y.

RADCRAFT PUBLICATIONS, Inc. RC 1037 THIS MANUAL 99 Hudson Street, New York, N. Y. Gentlemen: Please send me descriptive literature on Volume 7 of the WILL CONTAIN GERNSBACK OFFICIAL RADIO SERVICE MANUAL -and details for buying this edition on the deferred payment plan. OVER Name 1,800 Address PAGES City ... Please Say That You Sau' It in RADIO -CRAFT

RADIO -CRAFT for OCTOBER, 1937 251

HOW TO MAKE A CLASS AI PUSH -PULL NEGATIVE -FEEDBACK 60 -W. AMPLIFIER (Continued from page 215) The Best "BUYS'' stages, more adequate filtering is therefore One Electrad resistor, 100 ohms, 25 W., R28: * necessary in the filter network of this trans- One Electrad resistor, 15,000 ohms, 50 W., R29; Are Made for Casli! former. The output of the 5Z3 employs con- One Electrad resistor, 150 ohms, 25 W., R30; denser input, whereas, I'.T.1 employs the choke Six Hammarlund ft -prong isolantite sockets; t input method of filtering the rectifier system. Two Hammarlund 4 -prong isolantite sockets; RSS'ON Filtering of P.T.1 only need be sufficient to One Hammarlund 7 -prong isolantite socket; supply "B" voltage for the plates of the 6L6s; One 7 -prong special shielded plug and cable; regulation should therefore be better. One Kenyon transformer, type T255, T1: vtvtMßÁ ONS Sockets for the 6LGs and the GF6s should One Kenyon transformer, type T271, T2; have high heat resistance insulation such as, One Kenyon transformer, type T319, T3; isolantite. Great care should be exercised in the One Kenyon power transformer, type T215, T4: évy G1b wiring of the plate and screen -grid supply of One Kenyon power transformer, type T216, T5; GAIN1 the 61.6s. A heavier than usual or "normal" One Kenyon choke, type '1166, Ch.1; type of insulation should be used to prevent Two Kenyon chokes, type T152, Ch.2, Ch.3; possible arc-over between leads. Four Cornell -Dubilier condensers, type ED3 -100, 10 mf., 50 V., Cl, C2, C5, CO ; LIST OF PARTS Ten Cornell -Dubilier condensers, type DT -6P1, Two I.R.C. resistors, 3,000 ohms, 2 W., RI, R2; 0.1 -mf., 600 V., C3, C4, C7, CS, C11, C12, C15, Two I.R.C. resistors, 0.15 -meg., 1 W., R4; R3, C16, C19, C20; One Centrelab dual volume control, 0.25 -meg., R5, R6; Four Cornell -Dubilier condensers, 0.02 -mf., 600 Two I.R.C. resistors, 2,500 ohms, 2 W., R7, RS; V., CO, C10. C13, C14; Two I.R.C. resistors, 500 ohms, 1 W., 119, R10; Two Cornell -Dubilier condensers, 0.05 -mf., 600 Two I.R.C. resistors, 10,000 ohms, 1 W., R11, V.. C17, C18; R12; Three Cornell -Dubilier dual condensers, type Two I.R.C. 5,000 resistors, ohms, 1 W., R13, PE13-650x, ft mf., 600 V., C21, C22. C23, C24. *By CASH" R14; C25, C26; we mean your Two I.R.C. resistors, 15,000 ohms, 1 W., R15, R16: One Cornell -Dubilier dual condenser, type JR -216, jobber's regu- 16 mf., 200 V., C27. C28; lar terms. Two I.R.C. resistors, 10,000 ohms, 1 W, R17, R18; Two Sylvania type 6C8 glass tubes; Two I.R.C. resistors, 50,000 ohms, 1 W., R39, Two Sylvania type 6F6 glass tubes; R20; Two Sylvania type 6L6 glas tubes; Two I.R.C. resistors, 0.15-meg., 1 W., 521,1122; One Sylvania type 53 glass tube; Sylvania type During the years when "sinking -or- Four I.R.C. resistors, 0.1-meg., 1 W., R23, R24, One 5Z3 glass tube. swimming" was an everyday problem, R25, R26; *Names of manufacturers will be supplied upon One Electrad resistor, 10,000 ohms, 50 W., 527; receipt of a stamped and self -addressed envelope. a lot of business men, pressed for cash, got into "no investment" merchandise deals. One by one, most of them have fought their way back to sound business principles. And only by buying the finest quality merchandise at lowest possible cash prices have they been able to prosper. In the tube field, RAYTHEON offers the highest quality tube made-at cash' prices that save money for dealers every time they buy RAY - THEONS! That is why_RAYTHEON business has more than tripled in the last two years . .. why RAYTHEON dealers are prosperous business men! Ask your RAYTHEON jobber. Exact physical spec'lcations for ma g the arnp.:fier (left) and power pack chassis.

BUSINESS -LIKE "SILENT" SERVICING 1COP, li,nud lro,n ,.r,r 2iiL) perform every essential test required on a modern stages and tone compensation can be quickly radio receiver. analyzed with the oscilloscope across the output The technique of using these instruments is circuit and the audio modulation from the signal fundamentally simple. With the speaker voice generator supplying the steady sine waive. Re- coil open and preferable n dummy load resist- generation, phase distortion, overload, hum, or ance equal to the speaker impedance substituted "hash" from the power pack, all may be easily for the voice coil, a Service Man may first make identified on the oscilloscope pattern. Through- n voltage analysis of the receiver using a modern out all of these tests, not a sound is heard from 20,000 ohms/volt instrument. the pinker! Assuming that the power is properly dis- tributed, he next attaches the vertical plates PSYCHOLOGICAL VALUE OF "SILENT of the oscilloscope to the diode load resistor SERVICING" in the 2nd -detector circuit. With the signal gen- To the customer who wants to see this work erator feeding through the frequency wobbles done, this procedure is as marvelous as a major in the oscilloscope and then to the control -grid operation in a surgeons clinic. The Service Man of the last I.F. tube, that stage can be aligned has no need to fear that the customer will learn as indicated by the resonance curve on the the trieks of the trade because the instruments oscilloscope. Each preceding stage can easily alone are more expensive than most radio sets be adjusted to the same frequency. and the technique is quite beyond comprehension. Without mechanically "rocking" the conden- Like the surgeon,. the Service Man may charge ser, the oscillator or mixer padder can be n rate commensurate with his work. The flashy tracked at 600 kc. or any other frequency nA desig- instruments serve as indication that his work Vllló nated in the instructions for the particular is truly above the screwdriver mechanic's class. RADIO TUBES receiver. It is then quite simple to align the "Silent servicing" has raised the work of radio R.F. circuit at the high -frequency end of the Service Men to professional levels; which means 445 LAKE SHORE DRIVE, CHICAGO. ILL. dial. If the set has A.F.C., it is only necessary a decent living from a heretofore much abused 555 HOWARD STREET. SAN FRANCISCO. CAL to change one connection of the oscilloscope from and underpaid occupation. Furthermore the 420 LEXINGTON AVENUE. NEW YORK, N. Y. cus- 55 CHAPEL STREET, NEWTON. MASS. the top of the diode load resistor to thé cathode tomer is assured of a first -class repair job. 415 PEACHTREE STREET. N. E., ATLANTA. of the A.F.C. diode. This artirle has been prepared front data *ap- GA. Audio circuits, even with phase inverting plied by courtesy of Triumph Mfg. Co. Please Say That You Saw It in RADIO-CRAFT 252 RADIO -CRAFT for OCTOBER, 1937

A COMPLETE ADVANCED DESIGN LINE OF NEW ''RESOLUTION TESTER" MICRO -BEAM POWER AMPLIFIERS FOR CATHODE -RAY TUBES NEW NOW AVAILABLE FOR ALL P. A. APPLICATIONS

for television reception) images quite frequently appeared to be entirely Out of focus. AU previoua efforts to correct this misbehavior were fruitless! Exhaustive tests revealed that nothing was wrong with the "electron optic,' of the cathode- ray tubes. Finally, they hit upon the basic trouble. Those spots of light, or picture elements, which "build" the television image did not assume the circular form they had presumed, but were partly of Write For Complete Details and Attractive Proposition streamline shape. AMPLIFIER COMPANY of AMERICA But how to verify this was the problem. To understand the difficulties involved one must 35 -45 WEST 20TH STREET NEW YORK CITY, NEW YORK consider that it takes only (see note) 1/13,230 - second to "paint" one line of a television image over the full width of a fluorescent screen, and every line consists of thousands of closely arranged light dots each with a diameter of ap- NEW 1V proximately 1/50,000-in. I Mr. Burnett solved the problem in a very in- "how -to- make -it" genious manner. He omitted 2/3 of the light dots by sending "blocking" impulses into the PUBLICATIONS tube. The main trick to produce the patterns for was done by sending 2. 5 or even 10 frequencies Experimenters varying between 30 cycles and 2,000 megacycles into the tube. Since ti constantly changing mix- ture of frequencies between 30 cycles and 3,000 WE list below a large number of radio, short -wave, and mechanical "low- to-make-it" designa. megacycles (as used in actual television trans- Each is a special publication originated by masters in their respective fields. mission) produces complicated images with a For the first time, at the low price of TEN CENTS. you are now enabled to buy a complete design with photographic reproductions, complete mechanical layout, and full description to make it possible for anyone to build the protect wealth of little details, one will readily under- In question. stand that a cathode-ray tube must produce The name of "Radio Publications" has become a household ord because this company has for many years specialized In radio and other literature of .pedal interest to the experimenter. specific patterns when specified frequencies are PLEASE ORDER EACH PROJECT BY ITS PUBLICATION NUMBER, and use the special coupon below. sent into the terminals. We accept manes- -orders. rash. cheeks or new IT S. .LIMPS. (No foreign stamps or currency e n be accepted. ) If you The send cash or stamps, register your letter to safeguard against loss. Money refunded if you ate I. ,.1 -ücl main difficulties to be conquered did not ANY TWELVE PUBLICATIONS lay in the actual production of the patterns FOR ONE DOLLAR shown on this page, but rather in the Problem to design a master oscillator which was able to PARTIAL LIST OF NEW 10 CENT PUBLICATIONS produce exactly all the specific frequencies de- II sired, and a great number of them at one time. How the master oscillator of this system SHORT -WAVE RECEIVER PUBLICATIONS looks is shown in Fig. A. In short it is a nice, NOW TO MAKE THE 2 TO S METER TWOTUBE LOUD. HOW TO RUILD THE NAMAND "PEE 2- TUBER. but complicated, piece of test equipment, but SPEAKER SET. This receiver may he used with batteries -WEE" A dandy receiver with high efficiency and hamtspread as mentioned is with A C po erpaerect eÌh c a tg wa of o tuning. Works a loudspeaker yet the entire receiver is before, it merely the initial HOW TO BUILD THE CIOAR -SOX 1 -TUÉE "CATCH ALL" no larger than your hand. Works with either butteriez nucleus of the instruments which the Service RECEIVER. An effective short-wave battery set which fits or an A.C. power pack No. 115 into a agar -box, unstring high portabiNOy Muir, of the future who intends to do television aí cf( vinais yet work will require. MOW TO [MILD THE SHORT -WAVE MOW TO RUILD THE DUO- AMPLIDYNE. The Ideal 1 -tube PORTABLE MINIDYNE for the beginner. One of line finest 1-tube stets: it Uses 110 aerial. nd. The total1 weight is 3t/ IDs, a measures w5 x,3 inches. really gives 2 -tube performance. Made for battery opera contained batteries, tube, condensers. and loop. IlighlY Don- With only [nlout entpta 4rltngs ut the good sensitive circuit No. 114 turopomn stations No. 115 Note -This addition to the tools of the elec- RADIO BROADCAST AND tronic specialist is a most important one. Re- RECEIVER SPECIAL RADIO PUBLICATIONS gardless whether HOW TO BUILD A SUER -SENSITIVE ALL -WAVE CRYS- HOW TO ROILS A -TUBE BATTERY ALL -WAVE "FARM of a television program is "on TAL SET. Just the thing for ',manners who wish to have PORTARLE" SET. ranging from 12 tu 2.100 meters. A the air," transmitting and receiving equipment an asy.to. operate crystal sut ail -waves and winch real portable that pulls in Use alatluua...... No. 8126 will separate all the striions. Can be made for less may now be tested by means of the "synthetic" than $2.00. Uses no tubes or batteries No. 121 HOW TO MAKE AN A.C.-D.C. ONE -TUBE "DEAF AID." video afforded by this resolution tester. HOW TO BUILD THE 2-71111E ',PENTODE PORTABLE An excellent aid for Om hanl.ofDearing and deaf. for program theatre, churches.. d lue home. A godsend for SROADCAST SET -the lightest.test. a allest set giving I 1 The one here illustrated was designed several speaker volume on Mtleries. Weighs less than 12 mono.. afflicted persona. Can be built fur :, few dollars. No. 127 Built an a IL portable case 112 years ago; when 343 -line fidelity was being em- No HOW TO SUMP A PIANOTRON. For less than t.vn dol. HOW TO SUILD THE RADIO TREASURE" FINDER. This lars. plus a few lank sparts which you have. you can ployed. It is described on the basis of operation is a really sensitive amt practical 'Tri sun finder. make a beautiful musical instrument. Aerated In- three "on Simple tu bulled and guaran1av,I 1 work. Uses 4 tubes. radin tubes. It has al actual keyboard. andI you , play the air" at approximately this image-line Can be built for less limn 313.00 No. 123 tunes. Warka n n A "' and n" batteries. great no it frequency; that is, with a resolution -meter fre- NOW TO BUILD THE GERNSBACK ONE -TUSE PENTODE due ln the unusual music which issues from the loud- SET. This as the best one-tube loudspeaker Ho. 12S quency of 336 lines or 30,080 c.ps. (The fre- fkaI, t ver constructed. Il works oit batteries. A is ur broadcast reception. Extremely sensilive NO. 324 MOW TO BUILD THE ONE -DOLLAR RADIO. imposa ihle quency of 13,230 c.p.a. mentioned by the author thiugh it nds, for one dollar you can build radio HOW TO LS apparently based on 441 BUILD THE WORLD'S SMALLEST ONE TUNE set which Ìm-lptes a radio tube and a pair of head - -line operation for BATTERY RADIO. So 11 that it i actually built ha phones and batteries. You make everything't which the resolution as cigarette c . The set of the last New York ide of the three last mentioned items. from woodsl meter has not yet been radio shuwas No. 125 and spare metal parts No. w129 redesigned. In general, however. the actual points MECHANICAL PROJECTS PUBLICATIONS discussed are relatively similar.) MOW TO BUILD A PEE-WEE AUTOMOBILE. An ultra - HOW TO USE AN A.O. . I1 automobile that ran be built for less than 10 ARC Companion publica- Although, as the author states, up to 10 fre- dollars. Will carry two 17- year-old boys. Runs 35 miles tion o the on listed directly before. Very Informative: hour and especially.specially to the garage mechanic who has had quencies, constituting in the aggregate a com- Per 100 to 125 miles on one gallon of no ex rienre with welder. Contains many Ne Ì es, imis,rtant. and photographs of actual work done plex "A.C. voltage mesh" which appears on the HOW TO MAKE A SAND SAW FROM OLD AUTO PARTS. with an welder No. 143 end of the cathode-ray tube as Made eon] Chevrolet par. Capable of an intricate fre- delicate and satisfactory Uses 25-gauge HOW TO MAKE YOUR OWN MICROSCOPE. A microscope quency pattern, may be used the practical appli- JO and 12.inch band saws. Assembly la easy for each which the home mechanic can easily build in his shop. Its allotted No. 135 The lenses are obtained from the finders of a cam. cation of the resolution meter does not require port tills place perfectly Although simple and easy to build. It is a thoroughly NOW TO BUILD A REAL LATHE FOR 55.00. Requires practical and efficient instrument No. 144 such an extensive design. The more complex few hand tools. about 55.00 worth of raw material d HOW TO MAKE A WIMSHURST patience to build. The lathe is capable ill - ELECTROSTATIC MA. mosaic is of use mostly for demonstration pur- g. trimming. boring and thread cutting No. 135 CHINE. An easily constructedtn,cted generator of nt. lie electricity callable f discharging a fat three -melt spark. poses; for ordinary, practical work it usually AHOW TO SIMLri useeAIce. F Used In schools where electricity is taught. can be refrigerator. Does The cooling unit built for less than $2.00 No. 145 is sufficient to utilize only a 2 megacycle fre- from fire. EasyBand nexpensiveto obus d. Excellent for boats. e NOW TO MAKE A POWER DRILL PRESS FROM SCRAP quency. its 3rd- harmonic of about 6 megacycles Picnics. etc No. a 13S PARTS. An excellent practical drill n that will make and a frequency of about '700 kc. The HOW TO work easier ñn the mechanic. About $2.00 worth of pattern BUILD LARGE TESLA AND OUDIN COILS GIV- raw material and scrap re,luirements IHO . iron are the only thus produced is a checkerboard. IS -INCH Interesting highfre,iuency ali. No. 145 parata with which many mgt- fre.luency and x y - pei"enÑ can be performed. Capable of producing HOW TO MAKE NDdEXPERIMENT WITH AN EELECTRO. Editor t15.000 this (Continued on page 255) n with static lecctricitvuman be performed. Mane HOW TO MAKE AN ARC WELDER. A 1 a welder p- able of doing commercial fobs satisfactorily. Uses heavy re iñese experiments re thoroughly laced nn D- uty transformer which operates from the 110 -volt A.C. Ìualrated No. 1{B in. The output of the machine ranges from 15 to HOW TO MAKE AN ARC WELDER FROM AN AUTOMO UM amperes No. 142 RILE GENERATOR No. 149 RADIO PUBLICATIONS 99A HUDSON STREET NEW YORK, N. Y. "R.-C." STAFF CHANGE a -1037 RADIO PUBLICATIONS, 99A Hudson Street, New York, N. Y. RC Bert Nussbaum, formerly Assistant Ad- I enclose s f a. the publication. listed by m ber at I I I I IS right, t loe a y (ONE DOLLAR FOR ANY TWELVE: lUH1.ICA- 107 114 116 vertising Manager of Radio-Craft maga- TIONS.) These áuDlléatlens are be be sent m postpaid. I have zine, has joined the staff of Reiss .Adver- Placed number which t 121 122 123 124 125 Snd a me also your listof tr publications. tising (agency). His former associates on 126 127 128 129 132 "R.-C." feel sure that the ability he ex- 135 136 138 141 142 Name Address hibited during his tenure of almost 8 yrs. 143 144 145 146 148 will -be a valuable contribution to his city State 149 new Position.

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RADIO -CRAFT for OCTOBER, 1937 25: IMPORTANCE OF MODERN TEST EQUIPMENT The LAST in Formerly WORD Sold (Continued from page 207) for PERFORMANCE . a . R $15,00 audible range. This type of equipment will allow the Service Man to check the response characteristics of the receiver from the antenna term- The Last Word in Long Life! VARIABLE to speed induc- inal the input of the loudspeaker, giving in- tion typo .self- starting. Ili) all, 25 to 60 cycle, AC. with dications of the quality which may be expected. speed control. Plug and cord. Speed range from 5 to 200 MODEL 321 RPM. Can be installed in ()lace of old-fashioned. hand - New opportunities are periodically being pre- winding speed motor. Outside Diane. 11 ". height sented to the Service Man due to the fact that Shaft IVs". (Clam. 54') developments are continuously being made, and TUBE TESTER O.E. Electric Phonograph motor as de- S A .95 scribed the public is becoming more aware of what it may expect in the way of radio reception. At the Sin going weight -12 Ib.. MULTITESTER f:s present time the set owner is beginning to realize that much of the radio interference WESTINGHOUSE which he was formerly led to believe was a necessary evil may be mitigated or entirely elim- $4950 UNIVERSAL MOTOR inated by filtering apparatus which causes radio 110 Volts noise. The Service Man who has made some Whatever you pay for a tube tester -multi- AC sad OC study of this type of man -made static is in a tester, you can't duplicate comprehensiveness. $x.55 good position to pick up much profitable business. engineering, performance, of Radio City's new Shipping Model 321. Consider these features: Weight Public -address systems have long been more 3 tbs. or less neglected by the average Service Man as Tube tester provides most modern R.M.A. load, separate ions, 1/30 an added source of income. A thorough acquaint- function, open, short. leakage 11 I' Ir:d(-porates on either tests. Absolutely free reference to full floating A.C. or 11.1'., 110 volts. ance with the circuits commonly employed ea filaments. Hum and noise tests. Double fuse 5000 R.P.51. Rheostat well as the ordinary troubles encountered in this protection for can be used to vary spin i meter and tester. type of apparatus is well worthwhile. Height :iW, Length 3 % ". Multitester tests condenser Width 1%', Shaft t/s'. ono leakage, opens and Inch long. Can be used to shorts, electrolytic paper, mica types. 5 range drive Sewing Machines, Mod- AC voltmeter 9 -5 -25- 125 -500 -1250. 5 range els. Buffing lathe. roil.hing THE ABC OF A RESONANCE CURVE DC voltmeter- 0-5 -25- 125 -500 -1250. 5 range ]toad, Drills. Grindstones. To return to the cathode-ray oscilloscope as a ohmmeter-low 1 /20th ohm to high 30 meg- etc.. etc. means of obtaining a visualization of the reso- ohms. Current -6 ranges -low 10 microamps, high 25 amps for vibrator MOTOR only $2.55 nance curve, it might be of interest to show the testing. D.B. measurements from down 15 to up 40. 5 out- á355 manner in which a curve is actually traced on MOTOR with Arbor ar.1 11" Chuck put ranges. Protect- the screen. In order to obtain such a curve it is ed against burn out Add 25c for sperint packfng and mailing necessary have a frequency anywhere ro 11. S. A. to -modulated signal -and obsolescence. generator. A TUBE Frequency modulation of a signal generator MICROPHONE and RECEIVER as opposed to ordinary amplitude modulation, TESTER TAANSMarrn where the amplitude of the radio frequency out- EAR CAPE "rat SET put of the signal generator varies at an audible (say 400 cycle) rate, consists of varying the Set Tester pause NATE frequency of the signal produced by the signal combination generator at a given rate, usually 60 cycles. It should be noted that in frequency modulation the that can't get amplitude of the signal does not vary with time but the frequency does. Curve B of Fig. 1 shows out of date 2e rt the manner in which the frequency produced by EASY the signal generator varies over a complete MODEL 306 Ana

(Continued from preceding page) represents the picture which actually appears on the screen under the above conditions. HOW A CYCLE "PAINTS" ITS IMAGE GERNSBACK TRANSFORMERS The intersection of horizontal lines drawn through points of curve C representing various OFFICIAL RADIO SERVICE points in the cycle. with vertical lines drawn through the corresponding points of curve A. determine the pattern which is traced on the screen of the 'scope during a complete cycle. The reader can readily follow these points as MANUALS they are numbered consecutively. For instance, at point O the moving spot is in the center of AND the screen as regards its horizontal position ; at this same instant of time the frequency -modulated signal generator is producing the frequency to which the set is tuned so that the response of HANDIBOOK the set (applied to the vertical deflecting plates) is a maximum. At point 1 on curve A the spot has moved slightly to the right as regards to its ARE AVAILABLE AT horizontal position. At this instant of time the frequency produced by the signal generator is FOR THIS slightly higher than the frequency to which the JOBBERS set is tuned and the response is correspondingly * 100 WATT lower. The remainder of the picture traced on MODULATOR '122' the screen may be understood by following the consecutive points indicated on the drawing. inexpensive * DISTRIBUTORS HIS but efficient modu- T lator delivers 100 clean watts of audio with 800 volts on the plates of the modu- THE "SERVICE TECHNICIAN" lator tubes. Built on standard Relay Rack The Service Man is becoming more and more, * MAIL ORDER and PaneL as the years go on, a technician. In the successful TUBES: 6C6 Pre -amplifier, 76 voltage pursuit of his work he must have a fundamental amplifier: Push -Pull 76's: 6A3 Drivers: understanding of the various principles under- HOUSES TZ -20 Class B Modulators. lying each and every individual circuit which STANCOR TRANSFORMERS: Push -Pull goes to make up the radio receiver. These cir- Input, XA4206: Push -Pull Interstage, cuits. when individually analyzed. are not ex- XA4208: Push -Pull Driver, XA4212: tremely difficult. However, they do require a Output, XA2908. thorough understanding of the operation of FREE BLUEPRINT AND LAYOUT TEMPLATE each of the component parts entering into the circuit. Not only must the Service Man have a good physical picture of circuit operation, but Here they are: STANDARD he must also be thoroughly acquainted with the various types of test equipment which he uses 1936 Official Radio Service Manual TRANSFORMER 1.200 PAGES OVER 2.500 ILLUSTRATIONS in analyzing receiver faults. He must know the Looaeleaf Binder -Stiff, Hard t'cpers CORPORATION applicability and limitations of this equipment Size 9 z 12 Ingle; Pries 67.00 he the tí50 BLACKHAWK ST., CHICAGO and. as a consequence, must understand principles on which it operates. 1935 Official Radio Service Manual s The standards for efficient Service Men are OVER 1.000 PAGES OVER 3.000 ILLUSTRATIONS being constantly raised. Their professional serv- Looseleaf Binder -Flexible, Leatherette Corers ices should demand increased remuneration. Radio Size 9 z 12 Inches Pries $7.00 service racketeers are finding that it is becoming increasingly difficult to hoodwink the public. 1934 Official Radio Service Manual Zew CATALOG Probably the day will arrive when no Service OVER 400 PAGES OVER 2.000 ILLUSTRATIONS Man not having a diploma from a creditable Looaeleaf Binder- Flexible. Leatherette Cuvcra OF AMPLIFIERS school will be allowed to practice. Size 9 z 12 Inches Price $3.50 All types, embodying I:Ae :t principles of design and construction. Superior 1933 Official Radio Service Manual OVER 700 PAGES OVER 2,000 ILLUSTRATIONS quality. Many new features and advan- Corers tages. Superb salles, remarkably low - Looaeleaf Bindrr- b'Irrible, Leatherrtr. Size 9 z 12 hale, Price $5.00 priced. Used by leading P.A. Men. Write for free catalogue now! AMPLITONE SERVICING I1PRODUCTS CO., 135 Liberty St. N.Y. 1932 Official Radio Service Manual QUESTIONS AND ANSWERS OVER 1,000 PAGESOVER 2.000 ILLUSTRATIONS Binder. Flexible Covers (Continued from pace 227) Looaeleaf AMPLI TONE Siac ti z 12 luches 19íko $5.00 your 4 -tube set. the plate voltage is generally 1931 Official Radio Service Manual Courses In much higher, and this is responsible for the Correspondence OVER 650 PAGES (Including Supplements) resistor on the primary side of the No. 255 audio OVER 1.500 ILLUSTRATIONS RADIO 3 d UURKM £NGIN££RING transformer burning out. Looaeleaf Binder -Flexible, Leatherette Corers You ask what the correct voltage should be Size D x 12 luches Prim $4.50 ELECTRICAL ENGINEERING ofG" goo group p ..al fie .1. Prepare yourself. at Low Cost. for secure fu- on the plate- return of the 1st audio stage. It is Rtor kern. hfi ed.Y you fané to 1935 Auto Service Manual fcan ,rader douicki . advisable "juggle' the voltages from 45 to Official -Radio ADIOENGINEERING fir ,here,,, pñip-eleiirie a. 135 in order to determine the best results. OVER 240 PAGES OVER 500 ILLUSTRATIONS furervhe man. real v tithe Leatherette Corers to, lor r,óuu 6qetá kas furnished. Diploma on completion. Remove the 3 -to-1 audio transformer and re- Looaeleaf (tinder- Flexible, Toil u.n, ill,` r cour Deferred payment plan. Sine 9 z 12 Ini -lies Price $2.50 cale¢¢ 255 for r plena chool tudent connect the Silver- Marshall No. unit, magazine,. complete dealte. SEED NOW! since you only burned -out the primary resistor, FREE 1933 Official Auto -Radio Service Manual LINCOLN ENGINEERING SCHOOL, Ba 931 -43. LINCOLN, HEIR. it is merely necessary to replace this resistor OVER 250 PAGES OVER 500 ILLUSTRATIONS with one having a value of 0.2 -meg. See Fig. Looseleaf Binder -Flexible. Leatherette ('opera R M C Q27. It is not necessary to open the transformer, Sigo 9 z 12 in -lies Price $2.50 RELAYS to get at the resistor ; merely shunt this cluding P.E. Cell wu k signal aand alarm resistor across taps 1 and 2, and this unit will Official Radio Service Handibook circuits. etc. Pure silver contacts I rating. 0 n 3 to 4 M.A. be as good as new. OVER 1.000 PAGES OVER 1.000 ILLUSTRATIONS h rlerre o Beautiful Linea, (old Sta +n nrd corer 10000omtes ohms-other vauellistante yid mile. 16oethS Size fi z 9 holies Price $4.00 Dealer Net Price . $2.85 postpaid 25r7c Deposit Require) ou C.O.D. LOUD HUM AND WEAK SIGNALS If your Jobber or mail order house cannot supply (!x I Floyd Coomber, Wal worth, N. Y. you. order any of the OFFICIAL RADIO MANUALS or the OFFICIAL RADIO REGAL MANUFACTURING CO. (Q.) 1 have an RCA model 4 -17 -M set. It has SERVICE 1906 S. Grand Ave. Los Angeles. Calif. SERY iCE HANDIBOOK from the publishers. a loud hum and only faint reception of the Send your remittance in form of check or money nearby. powerful. local stations. Tubes were order -or. it you send cash or unused U. S. RADIO CHASSIS CRADLE checked and found to be OK. Postage Stamps. be sure to register your letter. For more `afile and (A.) The reason for a loud hum and only ALL ORDERS ARE FILLED PROMPTLY. .a receivers o faint reception of nearby local stations of your BOOKS ARE SENT TO YOU POSTAGE PRE- lifierslnL noun service PAID. Address Dept. RC -1037. .hop needs the RAIr1O eGIR- RCA model 4 -17 -M 4 -tube receiver is due to the nient )clamps tcradle,. Equip- ment le filter condensers capacities being below their he adjusted toh. x de- designated rating. The only remedy is to INC. sired angle. Conveniently ac- replace RADCRAFT PUBLICATIONS, commodatesdates a nr chassis these filter condensers. and in doing so, make '19 21 inches. Excellent for displaying receivers to cut sure that the correct polarity of the replace- 99 Hudson Street, New York, N. Y. ment condensers is maintained. Voltages will W 'lt f a /wtrated circular RC! WM. A.THOMAS C0.321 CAROLINEST., NEENAH,WISCONSIN read from 60 to 100 V. on all sockets. Please Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT c- OCTOBER, 1937 7rî NEW "RESOLUTION TESTER" FOR CATHODE -RAY TUBES IT'S BONUS TIME TABLE I No. 5- Deflection: Vertically, 30 c.D.s. saw - HOW THE PATTERNS OF FIG. B tooth ; horizontally, 3,780 c.p.s. sine -wave plus WERE OBTAINED small components of 1,260 c.p.a. and 180 c.p.s. Phase is shifted slightly from No. 4. Grid: 1. No. 1- Deflection: Vertically. 30 c.p.s. saw- 30 c.p.s. square -wave, negative portion the width IN RADIO'' tooth ; horizontally, 10,080 c.p.s. sawtooth. Grid: of the vertical- deflection return -line time; 2. 1. 30 c.p.s. square -wave, negative portion the 3,780 c.p.s. sine-wave; 3. 70.560 c.p.a. square - width of the vertical - deflection return -line time; wave. 2. 10,080 c.p.s. square -wave, negative portion the width of the horizontal-deflection return -line No. 6- Deflection: Vertically, 30 c.p.s. saw - Are You Getting time; 3. 2,222.640 c.o.s. sine -wave; 4. 740,880 tooth; horizontally, 3,780 c.p.s. sine -wave plus c.p.a, sine -wave; 5. 246,960 c.p.s. square-wave; small components of 1.260 c.p.s. and 180 c.p.s. YOURS? 6. 70,560 c.p.s. square -wave; 7. 1.260 c.p.a. Phase is shifted slightly from No. 4. Grid: 1. 30 c.p.a. square -wave, negative portion and width Tills year -ltuho s bane square -wave; 8. 180 c.p.s, square -wave. ought to pay you a it of the vertical- deflection return -line time; 2. 3,780 Boyars-tn. San not, No. Deflection : Vertically, 30 - 2- c.p.s. saw c.p.s. sine -wave: 3. 70,560 c.p.s. square -wave. every month. But IS lt i lino, d- tooth; horizontally, 10,080 c.p.a. sawtooth. Grid: uf Sprayberry trained men aree mak- No. Deflection: Vertically, 30 c.p.s. saw- ing that much extra out of in- 1. 30 c.p.s. square -wave, negative portion the 7- rsed salaries, tooth ; increased profits width of vertical deflection return -line time; horizontally, 3,780 c.o.s. sine -wave plus from their own businesses from $175 A MONTH small components of 1,260 c.p.a. and 180 c.p.s. sparo -time earnings. Meet my student 2. 10,080 c.p.a. square -wave, negative portion the So can you. Joseph Artr:Nalu width of horizontal- deflection return -line Phase is shifted some from No. 4, is almost b .ay, time; Ì m ne hangs f 3. 740,880 c.p.s. sine -wave; 4. 246,960 c.p.s. same as that for No. 5. Grid: 1. 30 c.p.s. square - BIG OUTFIT SENT rroair scierie wave, negative portion the width of the vertical - square -wave; 5. 1,260 c.p.s. square -wave. Tho Sprayberry course Is entupiste. 1ributorr-a peraran. deflection return -line time; 2. 70,560 c.p.s. square- AI /VANCE!) Includes - eut Job. Thanks to No. 3-Deflection: Vertically, 30 c.o.s. saw - latest Wave ; 3. 246. 960 c.p.s. square -wave. aids and spirits' serles of spare -time w.'q;rin¿éreátln¢ r'dñ, tooth; horizontally, 3,780 c.p.s. sine-wave plus BUSINESS BUILDINGS. Also big to under- small component of 1,260 c.p.a. 1. No. 8- Deflection: Vertically 30 c.p.s. saw- PROFESSIONAL OUTFIT OF stand. I'm making Grid: 30 c.p.s. REAL RADIO TOOI.ä. Tltl l'LIITT square -wave, negative portion the width tooth ; horizontally 3,780 c.p.s, sine -wave plus ÿóu ". ñ domiiti.i.! of the TESTER, 7 -RIDER MANUALS, writes today. Co t vertical- deflection return -line time; 2. 70,660 small components of 1,260 c.p.s. and 180 c.p.s. EBY ELECTRIC EYE. ETC. the rectal c.p.s. square -wave. Phase is shifted considerably from No. 4. Grid: 1. 30 c.p.s. square -wave, negative portion the EASY TO START No. My 4- Deflection : Vertically, 30 c.p.s. saw - width of the vertical-deflection return-line time; terms, as low as $2 a month. make It easy to start, tooth; horizontally, 3,780 c.p.a. easy to keep on. easy to mils'' big dividends as you go. sine -wave plus 2. 70,560 c.p.s. square -wave; 3, 246,960 c.p.a. New FIEF: BOOK. "Moro Money in ]radio'' fully ex- small components of 1,260 c.p.a. and 180 c.p.s. square -wave. plains. /:et )'our copy. Write me, or use the handy Coupon. Phase of horizontal deflection is changed from that No. SPECIAL COURSE FOR SERVICEMEN in 3. Grid: 1. 30 c.p.s. square -wave, Note -All patterns were made on 9 negative a -in. Servicemen! -ask about my Soeelal Course for YOU. Also portion the width of the vertical- deflec- cathode-ray tube using full magnetic deflection fully explained in my big book. "Moro Money in Radio,'. tion return -line time; 2. 70.560 c.p.a. square and a second -anode potential of volts. Send fur a copy -get complete facts. wave. 6,000 All f rwturncirs are synch ro rt izoI. -MAIL NOW FOR FREE BOOK1

F. L. SPRAYBERRY, Pres., ABC OF MODERN "AIR-TRACK" SYSTEM OF SPRAYBERRY ACADEMY OF RADIO. 20.1- University Plate, N. W.. VIBRATOR SERVICING BLIND LANDING Washington, D. C. FREE "More Money -' (Continued from. page 247) (Continued from page 248) and) lilas9aÌ your neww tyta o trainingü,iin. Name Age A vibrator tester's primary purpose is to de- their development. They have not released much Address tact defective vibrators which will no longer on their development. but we understand that City State function or operate properly with their asso- it is still fixed in position, although it retains Paste Coupon On Penny Postcard, Mail ciated circuits. The Triplett Laboratory in work- the fundamental principles of the Bureau system. a ing out the design of their Vibrator Tester The 4 major Airlines, AA, TWA, UAL and Model 1670, secured a number of vibrator.' in EAL, meeting with Bureau of Commerce and various stages of deterioration and worked Federal Communications Comm- isaion representa- closely with the manufacturers of vibrators so tives recently set forth recommended specifica- a tester could be designed which would enable tions for instrument loading to be adopted on o Service Men to make every needed test. national scale. In the analysis of vibrator trouble, it was It is interesting to note that Air -Track exceeds found that defective vibrators had two distinct the operating requirements of these specifications, characteristics. meets all the requirements described as "prac- ticable,' and most of those which (I) The vibrators would fail to start properly are called on very low voltage "projected developments." For example, the speci- such as 5.6 V. on a 6 -V. fientions suggest that glide battery. path and locslizer in- NEWEST T- dications should be separate. The Bureau started QUIPMENTES ET (2) The vibrators would operate unevenly, with TOOLS thus separate transmitters and we regard them RADIO SOOfS causing a variation in the output voltage. as essential to safety and proper operation. RECEIVER We believe this instrument landing situation A UTO SETS S has implications which make it the biggest story \ REQUISITE TEST FACILITIES in radio or aviation at this time. Entirely aside In toue design of the Triplett tester, these facts from the safety angle, its economic angle is sure were carefully taken into consideration and the to have a tremendous effect on the history of unit was designed to: air transportation. (1) Accurately measure the input voltage. (2) Control the input voltage to the vibrator. CREDITS (3) Accurately measure the output of the vi- When a curtailment of funda necessitated a brator on a GOOD -BAD scale. discontinuance of Department of Commerce ac- The Rtdolrk 1937 (4) Accurately check the regularity of the vi- tivities on radio aids to flying in 1933, scientists NEWEST BOOK Profit Guide is the brator on the meter. who had been employed at the Bureau were set mt , 111n4a0 o I up-to-date radio Parbt txnk up in a new laboratory at College r lubl i shed. 164 pagers M rallo buying Infer (5) Check the output voltage in per cent with Park where motion. TF4'1INIC:U, information and helps for they continued their research and experiments. ., nici nun are featured throughout the boot. an increase, of the input voltage, of 0.5 -V. Among these men were Comer L. Davies, Dr. (6) Place a 5,000-ohm load across the filtering Frank G. Kear, Gerald H. Wintermute, and 12,000 PARTS T't" Right rrplacemem the ,, system so the vibrator would work r items ter :cry radin into the late William H. Orton, who are largely responsi- that > will service., A complete nee. selection approximate load it works into in normal opera- ble for the improvement of the Air -Track and of ICerr'irers. Amplifiers. Test Equipment, Tubes. tion. This was Terms, and Books-always In stork-ready for found to give a vibrator test its adaptation to commercial needs. pr, opt shipment. approximating the actual condition under which The first job of instrument landing is to save the vibrator would operate. lives. Its second job is to make possible the The has been FASTER SERVICE "ÁI121 :5kn sow tester designed for extreme sim- completion of every trip interrupted or can- log the radioman. Our organization Is plicity geared -no using a minimum number of sockets and celled because the terminal airport is "closed to servo you best -to give you what yon i a rota.,, switch to select the proper circuits when you want It and at the RIGHT I9tG'FS. for in ". and thus to guarantee flying on an an- This BIG now book is FIIEEI Send for the vibrators under test. A your D.P.D.T. toggle nounced schedule. The story of its contributions mpy NOW I switch is used to switch the measuring instru- will be the first chapter in an entirely new ment in either the input or output. circuits. A epoch of human flight. potentiometer is used to control the input voltage, Airlines of the country took a big step toward a RA DOLEK and second switch is used to place buffer con- 100% in safety and regularity of scheduled opera- 601 W. Randolph, Chicago. Dept. C -10 densers in the circuit of the vibrator when they tion when they recently agreed upon specifica- Send mo tho Radolok Radio Front Guido FREE. are not a definite part of the vibrator. tions for an acceptable instrument landing Most Service Men seem not to realize the tre- system. Name mendous progress that has been made in vibrator - As a result, it appears that a workable system Address type power supply systems. It is hoped that this will have been tested and accepted before the Serviceman? article, therefore, will be useful to these men. arrival of bad flying weather this winter. Dealer? Experimenter? 1 Please Say That You Saw It in RADIO-CRAFT 256 RADIO -CRAFT for OCTOBER, 1937 CORNELL -DUBILIER BOOK REVIEWS mnhhuuubu69uum9uunuuuuh9numhuu9hu9uuu9uuunnumuun ADVERTISERS' INDEX DRY ELECTROLYTIC MARCONI -THE MAN AND HIS WIRELESS, by Orrin E. Dunlap. Jr. Published by The Mar - A millan Company. Size, 6 x 9 ins., 360 pages. 16 Arroyo: r1,rp,rati.nl CAPACITORS .tkrad Products Corneal* illustrations. Price, $3.50. Allied Radio Corporation This is the life story of Marconi ; the emphasis American Television Institute, I... I.. . . Amplifier Co. of America is on the man's work and on his personality. .tmplitone Produts Company Starting with the birth of Marconi, Mr. Dunlap, Anew Sales Corporation Jr., portrays in a technically- accurate and most vivid narrative manner the entire history -making B sequence of Marconï s life to within several short The Brush Development Co 241 months of his death. C histori Compactly designed The author very ably interprets. with 238 TYPE JR. the rule that Central Radio Taboratorie for maximum utility, accuracy and scientific acumen, C nnaudagraph Corpnat ion Cla Marconi played and the significant steps in the Cluirh- Itrengle Pompa,,' 217 Convenient mounting the Type JR capacitor Continental Carbon. Inc epic of "wireless" (radio). Cornell- Dubllier Corp 16 feet. will fill the majority The book touches on many historic events -the Coyne Electrical School 195 of servicing require- heroic and dramatic role of Marconi wireless in Long color -coded in- ments. Expensive de- the Republic disaster and the Titanics mid - E Eastern Radio & Television Co. 239 sulated terminal lays and costly shop- ocean tragedy. The period of the World War to develop new leads. ping tours are entirely which started the hectic rush G radio devices and led to the development of short eliminated by stand- O & O Genuine Maiestio Refrigerator and Smallest size ... waves (on which Marconi was working when Radio l'art. Service 241 mode possible by ardizing on C -D death claimed him) is fully and most interestingly us1gcts Magazine 248 Goldentono Radio Company 241 etched foil process capacitors. covered. of manufacture. Have you received Incidentally, Marconi himself thoroughly H checked the final proofs so that the book would your copy of the Ilammarlund 31ig. ('empara' 246 Available in o com- be accurate in facts about radio and historically 16..kuk El.r. Instrument I o 232 245 plete capacity range New Catalog No. correct in personal details. Ilygrado Sylvania Corporation at 250 and 525 volts 151A? Many new 1 Peak, innovations in con- International Correspondence Schools 2238 international Resistance Company "42 denser design, and Dual and multiple K the full C -D line of AUTOMATIC FREQUENCY CONTROL SYS- section units in popu- by John F. Kenyon Transformer Company. Inc 244 capacitors illustrated TEMS. by John F. Rider. Published lar capacity combi- 71/2 ins., cloth Rider, Publisher. Size, 51/4 x hard L nations. in complete detail. cover, 144 profusely illustrated. Price, $1. pages, Lancaster, Apwine & lbnnntel "41 Automatic Frequency Control is radio's biggest I.Wco.n Engìncei ilia Smoot 251 WORLD'S LARGEST EXCLUSIVE MANUFACTURER Man's latest head- development -and. the Service M ache, unless he knows what its all about. OF CAPACITORS MICA ... DYKANOL ... PAPER McGraw -llilt Book Company 240 The author evidently had this thought well in 246 AND DRY ELECTROLYTICS. ]Itisaner Mfg ompans' .. WET mind for A.F.C. is explained from its funda- Metal Cast Products Ceml'any 215 its various developments up to Midwest Radio C,,rporatlun 233 mentals, through Million Radio & Television labs 236 which the circuits assume in 2216 CORNELL -D UBILIER the final forms M , dell ELECTRIC CORPORATION various commercial receivers. A review chapter 'I he Muter Cump ny 228 of inductance and New covers that part of the theory N South. Plainfield, Jersey upon which A.F.C. depends. phase relations National Radio Institute Automatic Frequency Control Systems Ls an- National Schools 193 other Rider book that should be on every Service National Union Radio t'orp 237 Man's bookshelf. New York YMCA Schools 241 O The Type Ohmite Manufacturing Company 234. \ E P HANDBOOK. by Frank C. JONES ANTENNA The flan Shop 241 Jones. Published by Frank C. Jones. Size. 6 x 9 Pod. it,dio Corporation 237 20 -C AMPLIFIER ins., 64 pages. Price, 50c. Precision Apps atus Corporation 241 If it serves no other purpose than to clarify in R as the mind of the reader conflicting opinions RCA Instituts. Inc "-48 to relative merits of various arrangements of ItC.t Manufacturing Company. Inc 245 Antenna Handbook will have Radio & Technical Publishing Co 236, 2.,3 antennas the Jones Radio Circular Company 245 effected a worthwhile achievement. Merely to list Radio City Posduc s tbmpaU' 253 chapter headings -which is all that space Radio l'ublicat Ions 252 the Itadlo Service Institute 234 permits in this column -is hardly to do justice Indio Training Association of America. l' 12 to this valuable reference work. Contents: An- Itadolek Company n5 Corporal:onn 251 : Antennas for Transmitting ; Di- Raytheon Production tenna Theory Iteadrito Meter Works rectional Antennas; Antennas for Receiving; An- Regal Manufacturing Company Special Pur- Remington Rand. Inc 844 tennas for Ultra -High Frequencies: 196 pose Antennas; 160 -Meter Antennas; Antenna John F. Rider Coupling Systems; Antenna Charts ; Measuring S Equipment. Solar Manufacturing Company 240 Sp -ay berry Academy of Radio - 20 Watts output nsand ad Transformer Porlanatpm 214 gprier !mermen( Company 231 Dual mike input Inside Front Cover Electric Eyo Monitor AIR CONDITIONING IN THE HOME, by Elmer Supremo Instruments Corporation.. Torok. M. E. Published by The Industrial Press. T 39 Modern in appearance and Size, 6 x 9 ins., 296 pages, 50 illustrations, Tavela Sales Company 241 performance tables. Price, $3. Telepl.z tbmtxuq' 215 William A. Thomas Comparu' i book that no 213 line of sound systems We find upon reviewing this Triplett Electrical Instrument Cu A complete concerning its makeup can Triumph Manufacturing Company better cross-section Inc 241 for every application illustrated be prepared than is contained in the author's Tung Sol Lamp Works. in U.S.E.'s new 16 -page catalog. preface. from which we quote: U "The. first 2 chapters deal with the benefits, Write for new catalog No. 107 United Sound Engineering Co 256 and effects and functions of air conditioning. Chan- proposition ters III and IV describe in detail various types w of air -conditioning equipment and systems. Chap- Wellworth Tr :Ants Compmu' °'t Corp Bac" Cover ter V is devoted exclusively to the subject of in- Weston Electrical Instrument United Sound Wholesale Radio Service Company -..a. 219 stallation and operating costs. If the reader tVrlght- DeCOstcr. Inc 218 wished to go into the matter more in detail. Engineering Company Chapter VI, written in question and answer 2: on the principles of air Zephyr Radio Company 240 of Electronic Equipment form, will enlighten him Manufacturers conditioning. If one finds simple calculations more 2239 UNIVERSITY AVENUE fascinating than solving crossword puzzles. Chap- St. Paul Minn. ters VII to XII will give him a generous amount (While every precaution is taken to insure of material in the form of tables. examples, and accuracy, we cannot guarantee against the Licensed by arrangement with F..R.P.I. possibility of an occasional change or omis- by solutions." of this index.) under patents owned and controlled Men can well use this book as a guide sion in the preparation A. T. T. and Western Eire. Co., Inc. Service to work in the new. profitable field. Please Say That You Saw It in RADIO -CRAFT GREATER OPPORTUNITY THAN THIS LmGR

D TELEVISION

TRAINED TELEVISION MEN WILL BE NEEDED SOON! Already Commercial in England! Television engineering will be the next high salaried profession. Will you be ready to cash in with this new industry? Leaders of radio recognized their opportunity some fifteen years ago, and they as engineers have since earned millions! Now the future of television is assured. Are you going to make it your oppor- Every student receives this giant tunity lt:: success? Trained men will make television cathode ray tube as tart of his equipment. front S2.500 to 820,000 per year. THE AMERICAN TELEVISION INSTITUTE was established in 1935, to provide skilled men for television development in the United States. A. T. I. was founded by U. A. Sanabria, internationally famous inventor of the interlaced scanning system, now universally used. The Institute possesses one of the best equipped television experimental laboratories in the world, and it is here that students complete their courses under the personal supervision of Mr. Sanabria.

A. T. I. TELEVISION TRAINING AN UNPARALLELED VALUE qualifies you (luring the first fees- months tit AMAZING OFFER take your R kl)IO TELEPHONE FIRST * uCCetiri ! * GOVER\\1E\ I' LICENSE E\A\ll \ATI( Equipment You Receive From and get into a good paving jolt in the radio 7/17/37. The Nation- American Television Institute field while completing your television instruc- al Resources Commit- Is not small, ordinar instruction equipment, but a full sized professional television lab- tion. Many of our graduates are successful tee reported to Presi- in dent oratory used for public exhibitions with a radio and sound motion pictures. Roosevelt that steel rack and panels nearly six feet high, t h e most important two feet wide and eight inches deep mounted M. B. Foster of Prairie Du Chien. Wis., writes: on rubber tired casters; R.C.A. amplifier and "As a graduate of the class of 1036. I ran highly development work in recommend A. T. I. training with practical equip- television to a s com- modulator tubes throughout with A.T.I.'s ment. Since graduating. I am a technician with giant photo -electric cells and î" x 21" cath- the Ampro Motion Picture Corp., making a good pleted, and that only ode ray receiving tube, together with all salary. I feel secure in knowing that I am able to do nearly anything in sound motion pictures or t h e conlntercial ar- other parts to stake a complete television radio now. and that I am ready for television." rangements remain to transmitter and receiver worth a thon -:old dollars to one taking E. D. Carter of Bethany. Ohio. writes: "I spert be made to provide this training. a1I of years this i- included with the A.T.I. and two in college and have investigated other n a t i onal television course training in radio and the allied arts, and 1 have is ours to keep. It is all amazingly low in yet to find anything nearly so comprehensive as SV'riire. price nd on terms arranged to you. the A. T. I. training in television, which include.+ suit It all any practical man needs to know about radio. costs you nothing to thoroughly investigate I have earned an average of $2,300 per year since This means trained this opportuuil'. loin cannot afford to pass studying with Mr. Sanabria doing television and tele;.hone work." men must be ready. it up if you want to get in to television. Send Coupon . 'trocs

THIS MAY MEAN YOUR FUTURE IN TELEVISION - The Man of Ability Will Succeed MAIL COUPON Jn n ! a W... accept only applicants who can AMERICAN TELEVISION INSTITUTE pass the examinations on the first 433 E. Erie St., Chicago. III. RC -1037 four lessons. We will actually send Gentlemen: Please send me your free book, and first four lessons, with which I would like to be tested. It is four lessons without cost or ob- understood that all this is free. ligation, so may you determine how Name Age A. T. I. training will benefit you, and a equip you for a future in radio and Street television. Clip coupon at right, now, and mail it to us without delay! t- ty State wESt0N 772 ANALYZER VW"' MODEL P 20.000 ohms VIESION measures SERVetE actually full scale0 77S MODEL .p peL condenser meg complete test, Con.. on 30 P. portable. leakage test really l the feature scale. tains 712Tube- ohm odels ly1M and 773 checker.

WEBION LURE. CNECMas.ttER MODEL 773 spProv all Special, circuit spare r tubes noise tes, socket I

W ESION 771 CNECRMASIER ign MODEL dependable d de field estimator E' Ideal checker lt- tube in engineering of usefulness tester. wISION ronge continuity SEMER wide 713 LURE in simplicity DEL the operatingésence {eptures in Containsof 794131 abe, turcs in, rapid w obsolescence .. in low for sere can ereneeliandsome F°l. possibilities Insu Invest profit P d ¡shed case .. in Ra WESToN ish ol ..,c and remember, eSC óNenient purchasedPurchase pla +,. a Weston Electrical Instrument Corp., 599 Frelinghuysen Ave., Newark, N. J. ment OS Send full data on all Radio Instruments. ST warne Address GET ALL THE FACTS- RETURN COUPON TODAY City State