HOW to BUILD the PILOT TELEVISION RECEIVER WASP Short Wage Receiver Has World -Wide Ranp.- Edited by HOW to DESIGN A

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HOW TO BUILD THE PILOT TELEVISION RECEIVER WASP Short Wage Receiver Has World -Wide Ranp.- Edited by HOW TO DESIGN A. C. Tube Sets for Best Results IM.B.SLEEPER RADIO PHYSICS COURSE for High Schoql Students 250 POWER AMPLIFIER, and Other New 4qtuTent

e4 Vol. 1, No. Pail Issue 10C COPY.4ailimp. EADIC IDESPIN The Greatest

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1,1.1 I 141.0 01. ny 0,11 red .11elf. ult It e 118010. yc cn 0t l" .CO1111111 111 VALUE Ever Offered in the History of Radio Set Building All About Television Beginners, who have never built radio sets be- By special arrangement fore, find Radio Design an adequate guide for withthePilotElectric constructing successful sets which give as good Mfg. Co., Inc., of Brook- lyn,N.Y., RADIO DE- results as the finest commercial equipment. SIGN will publishallthe Many successfulprofessionalsetbuilders details of Television equipment which is being devel- started in business by following designs cre- oped bythePilotengi- ated by the authorities whose articles are pub- neers. ThePilotCompanyis lished in Radio Design.Read the offer below. leading in this new science, andisnow making tests Students, who realize the importance of under- todeterminethepracti- cability of broadcasting standing the underlying principles of radio regular televisionpro- equipment, will find the Radio Physics Course, grams,bywhichpeople and their actions can be in Radio Design, just the useful information seen with the Radio Eye. they need to explain the thousand strange of-. Getallthisofficialin- formation right from Tele- fects which have seemed so mysterious. Don't. vision Headquarters, asit permit yourself to be ignorant of these funda- is published in Radio De- sign.Keep poSted on what mentals.Read the offer below. Pilot is doing, learn how to buildtelevisionreceivers, Custom Set Builders-don't let the other fel- and how toinstalthem. READ RADIO DESIGN. low take away your trade this Fall.Prepare yourself-be ready to give your customers the RADIO PHYSICS very latest designs in all -electric sets, short COURSE wave equipment and super -range receivers. TheRadioPhysics And make sure your prices are low enough to Course, n o wappearing serially in Radio Design, is meet all competition. Get on your toes-Read thecoursewhichA.A. the offer below: Ghirardi has been teaching for four years in the He- Four issues of RADIO DESIGN, equal brew TechnicalInstitute, New York City, one of the , toa 200 -page book, mailed to your foremosttechnicaltrade home, bringing in the four issues the schoolsinthiscountry. 25 details of the latest and finest designs. This course is suitable for worked out with scientific precision-Also, these allhighschoolstudents. Readitin RADIO DE- issues will contain Part 1 of the complete Radio SIGN. Physics Course. SEND 25c IN COIN OR STAMPS TO RADIO DESIGN PUBLISHING CO., Inc. 103-A BROADWAY BROOKLYN, NEW YORK, U.S.A. U. K. Krohne, who wrote the article on the power packs, is a German instrument maker by MAC IDIESICN trade, and a wonderfully skillful designer of HANDBOOK OF CONSTRUCTION FOR STUDENTS & SET BUILDERS radio equipment. Now an American citizen, he is the man who made the master scanning discs M. B.SLEEPER, Editor forthePilottelevision equipment, and con- GERSON LEWIS, Associate Editor structed the precision amplifying apparatus for the television transmitter. Published Quarterly by Frank T. Sullivan, whose name appears in the article describing the Air Hound receiver,is RADIO DESIGN PUBLISHING COMPANY, INC. Pilot's test engineer, the man whose job itis to find fault with -everything. Give Sullivan the EDITORIAL.OFFICES: parts for any new set and the layout drawings 103 Broadway. Brooklyn, N. Y. and he will assemble it,testit, check it and Phone,Greenpoint, 9604 before. he is through discovers so many faults that you feel ashamed to have let him see the Ten cents percopy, twenty-fivecentsperyearinthe design at all.But that's his job-finding out U. S. A. and foreign countries.Radio Design is published mistakes before they get out to trouble others, on the first of September, November, January and March. and he never lets one slip by. So you can feel When subscriptionsarereceivedbefore thepublication pretty sure of the Air Hound, since he has of Nts. 4 of any volume, the subscription is started with passed judgment on it. theNo. 1 ofthat volume and back numberssentif Many readers remember Alfred A. Ghirardi available,exceptonrenewalsubscriptions. as associate editor of Radio Engineering when that paper was published by M. B.Sleeper. (Application for entry assecond class matter made at For three years he has been instructor of radio Brooklyn, N. Y., September, 1928.) and electricity at the Hebrew Technical Insti- tute in New York City. The Radio Physics Course which startsin Vol. 1 September, 1928 No. 3this issue of RADIO DESIGN is exactly the course that Ghirardi has been teaching his boys. It is for that reason that itis being published YOU WANT TO KNOW- here-because it takes up such subjects as have been found useful to those who are seriously vvHETHER it's going to be a set for your- interested in radio, and presents them in a way self or fur one of your customers, before which has already been found understandable. you spend real, United States money for GersonLewis,whosearticleonthetaper - radio parts you want some pretty definite assur-tuned receiver appears inthisissue,isas:;o- ance that the design you're going to follow has ciateeditor of RADIO DESIGN, andisin been worked out with expert skill and scientific charge of the RADIO DESIGN laboratory. He thoroughness. is one of those unusual fellows who can assem- So, if you ask, "What has RADIO DESIGNble any kind of a set and make it work right done to assure me that the sets shown in this the first time. His success with the taper -tuned issue are going to be worth 100% satisfactory sets is no exception.It is the finest design we to me or my customers?" the answer is: have seen for a high -power, single -control re- Concerning television, the information on this ceiver, and embodies the most sensible method subject comes directly from the Pilot Electricfor overcoming thedisadvantages foundin Mfg. Company, which istelevision headquar- other one -dial sets. ters. The article is by M. B. Sleeper, who has Now about the short wave converter, with been connected with this work since its incep- whichS. W. stations can be heard on any tion, and has been 0. K.'d by John Geloso, chief broadcast set.This articleis by E. Manuel. engineerofthePilotCompany, andinventor who is export manager of the Pilot Company. of the Pilot television transmitter and receiver. He knows what's what in radio in every port In the coming issues these two men will keepof the world. RADIO DESIGN readersposted concerning An old-timer at short wave reception, Manuel further television developments. has devoted much time to the S. W. converter The first model of the Wasp short wave re-because, inforeign countries, thereisa tre- ceiver was built in R. S. Kruse's laboratory, it mendous interest in American broadcasting, and was tested by him, and in its final form bearshe has found that with the converter any set his O. K. As further proof ofitssuccessful in any country can bring in American short performance, Wasp sets areatthistime ofwave stations. writing in use by the U. S. Army in a number The 250 power amplifier, which also supplies of points in this country. A standard Wasp B voltages for any receiving set,is described has been used for the ground station in testsby W. R. Kaye.Thisisasubject which he with the Pilot Airplane Radio Laboratory, too.is eminently fitted to discuss, for, among other During these tests, using a 20 -ft. wire for an things, he is in charge of the transformer wind- antenna and an automobile chassis as a ground, ing department at the Pilot factory, and in this signals from California and North Dakota werecapacity Kaye "knows his transformers." picked up in the daytime. These brief notes are given so that you will The A. C. power packs have been in use in know that the equipment described in RADIO the 1ADIO DESIGN laboratory during theDESIGN is not the paper guess -work of inex- seven months which have been spent in work-perienced men, but apparatus skillfully planned ing out the Air Hound receiver. The A and Bby experienced engineers, chosen by this pub- packs have given several thousand hours oflication to assure your success and to establish operation during the development and life testsyour confidence in RADIO DESIGN-No wild on the Air Hound. ideas, but real stuff that you know is right. 21 Fig. 1.E. Manuel, sitting before the televisiontransmitter.The insert is the transmitting amplifier.Right, the combination television and broadcast receiver. ALL BROADCASTSTATIONS CAN TRANSMIT TELEVISION By M. B. SLEEPER

NOW you can build your own television re-lustrations, and saw the moving likeness of Mrs. ceiver! You can get in at the very beginning Geloso, 8 miles away, on the other side of the of a new science-vision carried by invisibleHudson River. waves-a science so entirely newthat its future For months, two groups of engineers had been developments and applications are still to be de- working inthePilot Laboratories to evolve a termined by those who are ready to undertakethe method of transmitting and receiving images of pioneer work ofunderstandingtelevision,and living, moving objects.The specifications which thinking in terms of its possibilities. had been giving them were: When the first intelligible radio telegraphsignals 1. Radio vision as clear as newspaper illustra- were transmitted over auseful distance, no one tions. expected that the foundations was beinglaid for 2. Full reproduction of details-not merely out- of tremendous lines or silhouettes. a world-wide communication system station commercial and political importance. 3. Transmissionfromanybroadcast No one dared to suggest that the firstsuccessful without altering in any way the equipment of the station. demonstration of radio telephony was the precedent 4. Transmission within a 10 -kilocycle band, to oftheentertainmentnow provided for every modern home in every civilized part of theglobe. preventinterferencewithotherbroadcaststa- The most profound students of radio engineer-tions. ing did not have the slightest idea, when theactivi- 5. A television receiver made up of standard ties of American amateurs were legislated downparts, so designed that it can beassembled easily below 200 meters, that short waves were to becomeand cheaply by set builders. By the first of August the Geloso systemhad so vital that they must besplit and allocated by During the second international agreement. passed the elementary stages. Mfg.week of August the equipment wasrebuiltin Nor did the founder of the Pilot Electric Sta- Company imagine, when the concern was organizedportable form, and the transmitter taken to tion WRNY on the west side of theHudson River, twenty years ago, that he would give tothe Ameri- in New can public the first practicaland successful meansand the receiver installed 8 miles away of seeing by radio, meeting through theefforts York City. And it worked!The first television transmis- of the Pilot engineering staff thetremendously in- easily and volved problems which have baf tiledscientists in sion, on Aug. 14th; was tuned in as their efforts, during the past 50 years, toextend quicklyas broadcast signals.As soon as the strange -sounding signals camein on the loud vision beyond the range of the human eye. speaker, the switch was thrown to theidio Eye, PILOT PIONEERS TELEVISION engineers On Aug. 14, 1928, John Geloso, ChiefEngineerand while a group of half a dozen long dis-watched the small enclosure, Mrs. Geloso was seen of the Pilot Company, achieved the first to walk before the transmitter.She smiled with tance television transmission whenhe looked into the extraordinary part the Radio Eye, shown in the accompanyingil- a little embarrassment at 22 Figures 2 and 3.A com- the first commercial broad- binationRadioEyefor cast and television set ever receiving television,and built.What willfollow, broadcastset. A snap what will be the future ap- switch changes theradio plicationsoftheRadio circuit from loudspeaker to Eye, no one can tell, but Radio Eye.The moving to -daywehaveactual objectsoranimatedpic- television at broadcast ture appear in the opening wavelengths,snakingpic- of the tuning control. This turesasclearasany receiver, developed by Pilot printed in the daily news- Electric Mfg. Company, is papers.

she was playing, waved her hand, and in a moment YOU CAN BUILD YOUR OWN RADIO EYE stepped aside.Others appeared before the trans- The first real Radio Eye is not merely a labor- mitter, each readily recognizable. atory demonstration.It works, and works mar- This private demonstration was repeated for the velously well.Considering the few months which benefit of newspaper reporters on August 21st, at have elapsed since the inception of the idea, the Philosophy Hall, New York University. equipment is truly wonderful.It is far more per- Meanwhile, work has been under way to developfect than the early broadcast sets. receiving equipment capable of even more perfect This work was undertaken by the Pilot Com- vision. The actual production of receiving sets and pany as part of its policy of keeping faith with equipment for the use of television set builders isthe set builders who look to Pilot to supply them being pushed ahead as rapidly as possible, for the with apparatus in keeping with the very latest de- Pilot Company realizes, of course, that transmis- velopments in radio art. sion is of no value without apparatus for receiv- Much has been published about "television bunk," ing. and much has been justified, for a number of com- Now that the equipment is being made available, panies have gone so far as to advertise scanning television broadcastingisa regularfeature on discs, for example, to receive the WRNY television WRNY. Moreover, the Pilot Company is prepar- transmission when the Pilot engineers themselves ing to furnish television transmitters to other sta- did not know how many holes would be used in tions throughout the United States.Thus seeing the final transmitter disc. as well as hearing by radio will soon be a part of But in making out specifications for this tele- regular programs. vision work the whole idea was to open the field to What is also of great importance, a start has experimenters, to make it possible for them to get been made towardthedevelopmentofspecial into this new science, and to encourage them in features which will make television highly enter- pushing ahead just as they did in the beginning taining, offering far more than a mere opportunitywith radiotelegraphy,thenradiobroadcasting, to see people bow and smile before the Radio Eye.and finally with short waves.

23 Fig.4.Detailed view of the amplifier and power pack.

Thespecificationspreviously enumerated ex- The mounting for the disc must have ball -bear- plain why it is possible for set builders, working in ings of the finest quality, of the type to take up their home laboratories, to use standard parts forend -thrust from the gears. buildingtelevisionreceivers, addingonly such The master disc, from which others are being special devices as the disc, motor and the neon made for regular production, calledfor such a lamp. degree of accuracy in locating the holes that it was The accompanying illustrations show how the necessary to rebuild what was already a precision first Radio Eye was arranged at the front and atmachine, in order to locate the openings in such the rear.However, there are various modifica- a way that they would not overlap, nor leave spaces tions which were made in the circuit, accountingbetween the holes. for the discrepancies between the wiring diagram Subsequent discs are being produced by a photo- and the parts shown on the pictures. graphic method, for the cost of machining scan- On the upper shelf are the television disc, bev- ning discs one -by -one would make the price pro- eled Bakelite gears, synchronous motor, and the hibitive. two 2 mfd. condensers. Neon Lamp:Another vital element in the tele- Below, at thefront,is thereceiver,shielded vision equipment is the neon lamp. from the amplifier and power equipment at the Until the advent of television, very 'ittle was rear.The lastthreetubes andtheresistance known about neon lamps except as they were ap- coupling units are enclosed in three cans. One can, plied to electric signs. The production of a suit- as you will see, has been removed. To the rightable type of lamp is not merely a matter of sealing is one of the new Pilot 250 type power packs, used metal elements in a globe filled with neon gas. to provide the plate voltage for the audio amplifier The whole combination ofthequantity and and neon tube. purity of the gas, the metals used for the elements, At the extreme right is a small Pilot B pack. and their arrangement and shape determine the re- That was not in the circuit, however, for it was sults to be obtained. found that 90 volts of B battery gave much better The illumination must change from zero light results on the R.F. and detector tubes. over the entire surface of the elements to a bril- As you will see from the diagram, the radio end liant illumination over the entire surface. is a standard receiver, to which the special audio If the lamp has a tendency to shine more bright- ly in one part than in another, reception is spoiled, amplifier has been added. just as a photograph is sometimes partly light - IMPORTANT NOTES ON TELEVISION PARTS struck. Scanning Disc:Most of thescanningdiscs The light response of the lamp must be accur- which have ben offered for sale are not worth the ately matched to the response of the photo -electric material used to make them. Some are even madecells at the transmitter.The degree of illumina- out of thin hard rubber, others of tin or galvan- tion must be proportioned to the voltage applied ized iron.Even if the holes were accurately lo- to it.If a slight increase in the voltage brings cated they would be worthless because they do not the lamp to full brilliancy, the picture is just a run true. bright blur. On the other hand, if the illumination Pilot engineers have found it necessary to use is very low until the maximum voltage is applied sheet aluminum 3/32 ins. thick, reinforced by a to it, the picture is very dark. disc of somewhat smaller diameter, as you will see A special Pilot neon lamp of exceedingly low in Fig. 3. resistance has been developed. There is only the Never buy a disc unless the shaft is furnished slightest voltage drop across it, yet it handles the withit.Any slighteccentricitywill absolutely high power required for clear images. ruin reception. Synchronous Motor:A synchronous motor of 24 No. 176 broadcast plugin coils are used, tuned by (.9 ct . zo No. 1617 Pilot .00035 mfd. condensers. Adjusto- hoZ In 0 s grads are used in the grid circuits of the first two ap tubes to prevent oscillations. 5 In the original receiver, Pilot Redi-Blox were 0 used to simplify the assembly. To prevent inter- action between the radio circuits and the audio end, the receiver was completely shielded, except at the front, where a Micarta panel was used. Audio Amplifier: There is so much opportunity for difference in opinion regarding the quality of audible reproduction that even a fairly large de- greeofdistortioncanbepermittedsuch an amplifier.. S For television reception, on the other hand, where distortionappearsvisually,theamplificationis either perfect or imperfect.

1,1 Consequently, Pilot engineers found it necessary to develop a special audio amplifier that gives such perfect reproduction that it is not even possible to see the distortion. The three audio stages are assembled with Redi- blox. Instead of using the small stopping condenser ordinarily supplied, you will see that a pile of condensers are employed to give a total capacity of .06 mfd. Only two grid leaks are used.The other resistances are displaced by special units, mounted like grid leaks, but in the form of bobbins which serve as a combination of resistance and R.F. choke.In this type of amplifier a plain resistance is not ade- t quate, for it does not keep out the radio frequency distortion. Hence specially developed Resistochokes. § OE All three A.F. tubes take 220 volts, supplied from the heavy duty B power pack.This may seem strange, considering that 301-A tubes are used, but with the resistors employed and the C battery specified, this gives the best results. Power Pack: Ordinary B power packs cannot be used for the Radio Eye because, ratings to the contrary, we have not found any which will deliver 220 volts at 6o mils without overloading the chokes and causing A.C. distortion. The unit shown here is the new Pilot 25o power amplifier from which the heavy current is drawn. HOW TO OPERATE THE RADIO EYE HIV80'1 With the equipment assembled and wired according to the diagram, the television signal is tuned in by means of a loud speaker connected in place of the neon tube, or by putting a pair of phones in LL the plate circuit of the detector tube.As soon as the signals are brought up to maximum intensity, the phones are cut out and the motor started. With the disc rotating atfull speed, the set must be o+t, retuned to bring the signals in at the center of the resonance curve of each stage.Then the potentiometer on the 371 tube must be adjusted as well as the Resistograd in the plate circuit to the detector. The process is very simple; it actually takes less than a minute to adjust the controls to bring in z television clearly.The details of the method are clear enough when you are watching the effects of the tuning on the reception. IIIII o; ADDITIONAL INFORMATION ON TELEVISION O` BROADCAST 1/loth horse -power has been developed by l'ilut to If you want additional information on the equip- turn the disc. This is a very simple and inexpen- ment described, or concerning television broadcast- sive type, requiring no external regulation.It is ing from other stations in the United States, send simply plugged into the light socket like any other yourinquiriesaddressedtoTelevisionDept., electrical appliance. RadioDesign,103Broadway, Brooklyn, New Radio Circuits: The radio circuits are standard, York.In this way you can get additional details as is shown by the wiring diagram. Three Pilotdirect from the Pilot laboratories. 25 Fig. I. The Pilot Wasp has a world-wide receiving range. SHORT WAVE PILOT WASP HAS WORLD-WIDE RANGE

By JOHN GELOSO

THE new Pilot Wasp short wave receiver, for WASP COILS WIDELY RECOGNIZED 17 to 50o meters, certainly should be the last News travels very fast among radio engineers. word in this type of equipment.The coils The first coils were hardly produced when F. E. and the set were designed with the assistance of Handy, from A. R. R. L Headquarters, sent down R. S. Kruse, recognized authority in this country a hurry call for coils to use in a new receiver. on short wave communication.To speed up theThe Officers' Radio School at Fort Monmouth, progress of the work, the Pilot Airplane Radio N. J., ordered a quantity of complete kits to be Laboratory was used to carry the engineers back assembled by their students.A Wasp receiver, set and forth between the Pilot factory and Kruse's up in the shadow of the Statue of Liberty,is laboratory at Hartford, Conn.Such a long dis- handling U. S. Army traffic. tance collaboration would be difficultordinarily, Wasp coils were ordered for use in the short but the two cities are less than an hour apart via wave equipment designed for the Byrd South Pole the big Stinson monoplane. Expedition, which will carry 28 receivers.

Fig. 2.This is the Pilot Airplane Radio Laboratory, used for the development of aircraft radio equipment.This photo, taken at the Stinson Field, shows I. Goldberg, president of the Pilot Company, with Bert Hassell, the Rock- ford to Stockholm flier, who has been found in Greenland.

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OFFICIAL WASP DESIGN In other words, you can't take a schematic dia- Short wave receivers are not the simple matter gram of a short wave receiver and put the parts that set builders expect them to be, judging from together according to your own ideas of what looks experience with broadcast sets.Short waves are well or is convenient. very particular.They will not produce good re- Such an outfit will prove to be a most unsatis- sults in the obliging manner that broadcast signals factory bag of tricks.You must follow, to the come in on slip -shod sets.Nor is careful work- letter, the layout shown in the accompanying il- manship any assurance of success. lustrations. Short waves insist 'on designs which are based WASP ALSO RECEIVES BROADCAST upon a thorough familiarity with the vagariesof high frequencies, as well as the most careful as- While the Wasp isintended primarily asa sembly and wiring.Accordingly, we worked out short wave receiver, many splendid reports have an official Wasp short wave design, simpleenough been received concerning its operation on broad- for everyone to build, and taking into account all cast waves. the special kinks which must be considered, known The fivecoils provided have colored Bakelite only to those who have had long experience with finger rangs by means of which the wave length this sort of equipment. ranges can be identified.They are as follows : Fig. 6. The set of five Wasp coils covering all wavelengths from 17 to 500 meters. Each coil is identified by its colored Bakelite handle. Fig. 7.The illuminated dial controls the uxtvelength. The two center knobs regu- lateregeneration..When the broadcast coil is used, the upper midget condenser is put at maximum. For other coils, the condenser is set at minimum. All regu- lating is than donr with the lower condenser. On the right is the rheostat knob.

Red ring 17 to3o meters I 7 by 14 -in. Westinghouse Micarta front panel Orange ring 3o to52 7 by13 -in. Westinghouse Micarta base panel Yellow ring 45 to 105 9Pilot engraved binding posts Green ring 93 to 203 14 Blue ring 200 to 500 You will also need a length of spaghetti tubing, a few feet of No. 18 tinned copper wire, two dozen These wave length ranges apply when the pri- tinned soldering lugs, and some machine screws and mary coilisnot used, but the antenna coupled nuts. directly to the grid by the 5 -plate midget condenser, as shown in Fig. 4. How TO ASSEMBLE THE WASP The Wasp will bring in broadcast stations at The accompanying illustrations show very clearly full loud speaker volume over a range of several how the parts should go together, so if you layout hundred miles.Moreover, it is a convenient check, your panels carefully in accordance with the offi- when the set is first finished, to try it out on broad- cial panel patterns you should have no trouble at cast waves, to make sure it is operating properly. all.Fig. 3 gives the schematic diagram and Fig. II the actual layout as the wiring will appearin OFFICIAL. WASP PARTS the set.All the front panel parts should be as- Following is a list of parts which arc requiredsembled first, then the base panel parts assembled for assembling the official Wasp receiver: and wired as far as possible.Do not fasten the two panels together until that much has been com- o r No.180-4 set of Twin -Coupler plugin coils pleted. No.1282 Pilot illuminated dial It is very important to use only rosin -core solder. I No.16o8 Pilot .00014 mfd. condenser Do no use soldering paste under any circumstances. 2No.J-23 Pilot .000z mfd. midged condenser Be sure that you get the terminals of the sockets cr,No.J-5 Pilot .000015 mfd. midget condenser in the positions shown in Fig. it. I No.910 Pilot to -ohm rheostat As you put on the wiring, compare the directions I No.50-D Pilot .0002 mfd. fixed condenser of the wires and also the neatness of your work- I No.761 Jo-meg. grid leak manship with the photographs and the diagram in :1'No.750 Pilot .1 meg. grid leak Fig. It. 4No.5o Pilot grid leak clips t3,No.206 Pilot UX sockets How TO OPERATE THE WASP 2No.391 Pilot A. F. transformers When you have completed the assembly, plug in E No.212 Pilot UY socket one of the five coils, insert the tubes, and connect 41, No.35 Pilot I -in. Bakelite brackets a six volt storage battery from A+ to A-. Try

Fig. 8.In these illustrations, the No. 381 Pilot A.F.transformers are shown.The Waspkit. however, contains two of the new No. 391 transformers. The .1-nteg. grid leak,betweenthetwo A. F. tubes, is connected across the secondary of the firsttransformer to prevent howls when the set goes in and out of oscillation.

2s t:ig.g.By using a resistance -coupled amplifier, the Wasp can be employed for receiving the various television signals, broadcast from station 3XK at 46.72 meters. The present schedule goes on from 8.0o to g.00 P. M., Eastern Standard Time, on Mondays, Wednesdays, and Fridays.The transmitter is of 250 watts, and is being heard all around the country.

the rheostat to see that the tubes light properly. RESULTS OBTAINED FROM THE STANDARD WASP Then hook on the B battery, 90 volts from B- to RECEIVER B+Amp., with a tap at 45 volts to B+DET. Attach Already quite a number of reports have come your telephones to the binding post at the rear. in on actual results obtained with the Wasp re- If you have a regular broadcast antenna, hook it ceiver. For example, Staff Sgt. Edwin A. Red - on to the binding post marked SHORT ANT.Ii cling, Jr., in charge of the U. S. Signal Corps you have a small indoor antenna about 20 feet long, Station2SC, and WVP, Ft. Wood, N.Y., use the ANT. binding post. rersorts that "The Wasp was used in preference When you use the broadcast coil, set the upper to three other short wave receivers at this sta- midget condenser on the front panel at maximum. tion."This set was constructed according to For all other coils set this condenser at minimum official specifications. capacity. A very interesting communication was re- Tune with the big condenser for wave length, ceived from E. F. Whitcomb, 244 Gold Street, and adjust the lower condenser for regeneration. Brooklyn, New York. He sent a photostat copy You will also have to regulate the small condenser of an acknowledgment received from station at the rear of the base panel, in order to get a set- 4c)G, Brisbane, Australia.The card states that ting which will permit the coils to oscillate over an examination of the Official Log confirms the entire range. r. Whitcomb's report of reception. Beyond this, you must just experiment to get George.L.Jones,Hazardville,Connecticut, your own experience.There isa great deal ofreported on August zoth that he had received short wave broadcasting now, notonlyinthe 5 S \V, Chelmsford, England, on 24 meters, every United States but in foreign countries as well.If night (luring the previous week. Reception was you want to learn the code, you will have the whole obtained with an 18ft. antenna strung across world at your finger tips.In this issue of Radio a room about ft. from the ceiling. Design an up-to-date list of code and broadcasting Itis very interesting to observe the strange stations is given so that you can locate the callsthings which happen on short waves.Station you hear. WRNY, for example, reports that their short

Fig.to.There is no complicated wiring on the Wasp, even under thesubpanel. The grid condenser is field in place by the screrc's whichpassthrough thegridleakclips. Refer to this view as you assemble your set, for it will help you to put on the wiring cor- rectly.

29 A SHORT a- GNO ANT ANT A BATT BDET B 90v L.5. -

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N4 213 N9 213 SOCKET Q.r O SOCKET UX.201-A 184201

6 J23 J-23 .0001 ME (=IMF N4 910 COND CONE) RHEOSTAT r=1 1111III 10^ N41608 00014 M F 0° COND N91282 DIAL

Fin. I1. Picture wiring diagram of the Wasp short wave receiver. wave transmitterisheard by more peoplein BOOK REVIEW Australia thanin New York City.In other words, if -you are within a few hundred milesRadio Amateur's Handbook by F. E. Handy, pub- of a short wave station you may not hear it lished by American Radio Relay League,221 as well as signals from stations two orthree thou- pages, over 20o illustrations, $1.00. sand miles distant. On the other hand, the radio operators on the transatlantic ships find that they The Radio Amateur's Handbook which we re- can pick up KDKA or WGY, onshort waves,viewed in our last issue is now in its second print- as soon as they are out of New Yorkharbor,ing of the third edition.It has been most fully and hold the signals all the way across the At- revised and brought up-to-date. lantic. Sometimes amateur stations and commercial The Handbook still leads as a text on short- stations as well are difficult to hear, not be-waves and has more authentic material crammed cause of lack of efficiency at thereceiving set ill it than any other book we have ever seen. F. E. but because of defects in the installation atHandy, the author,isCommunication Manager the transmitter, which cause a slight swingingof the A.R.R.L. and knows just what both the of the frequency. You will notice occasionallybeginner and the old ham want to know about that when signals appear to be fading, if youbuilding and operating short wave receivers and change the tuning condenser youcantune along with them, indicating that the fading is transmitters. He has done a difficult job very nicely actually due to changing frequency at the trans-in the Handbook.Whether you have been in the mitting end. game since "way back when," or whether you are Ifyou hearapeculiarshortstaccatonote just starting you should have a copy of the Hand- soundingsteadily,but with varyingpitch,you book right beside you on the workbench. will learn to recognize it as a radio photograph As John Geloso pointed out in his article on the transmitter or one of the short wave television transmitters. Again, you will hear a high-speedWasp set, short waves have many strange charac- telegraph transmitter, clipping off a hundredteristics. Many of these puzzling things are dis- words or more a minute. cussed and explained in Handy's Handbook. Telephone or broadcast reception takes a lit- The Radio Amateur's Handbook can be obtained. tle experience and skill to bring in any satis-from the Book Dept., Radio Design, 103 Broad- factory manner, but once you learn where to it hunt for the foreign broadcast stations you willway, Brooklyn, N. Y. Bound in a paper cover, have no further difficulty. costs $1.00 postpaid, or $2.00 in a cloth binding. 30 Fig.T. Standard Pilot A and C power pack, and the B power pack. HOW TO DESIGN A. C. TUBE SETS FOR .BEST RESULTS By U. K. KROHNE

EVERY custom set builder who is planning forway below the values necessary tooperate the big business this fall is now selecting designs A.C. tubes, and with this increased current through for all -electric sets.You and I may havethe chokes, the inductance of the chokes drops our pet circuits that call for battery -typetubes, but from the rated value of 3o henries down as low as Mr. General Public, and particularly Mrs. General 5 or I0 henries.Then, under this overload, there Public, feel that any set that can't be hooked onto is a strong A.C. hum, usually blamed on the tubes the floor would be a discredit to the modern home. or the set. Now, the clever set builder knows that the real A POWER PACK DETAILS business comes from selling Mr. and Mrs. Public what they want-not what we think they would In Fig. 1, at the left, is an illustration of the want if they knew better. Pilot A pack, with the picture diagram in Fig. 2. The catch is right here: Custom-built sets can't This kit comprises the following parts: be exorbitant in price.Usually, they have to be 1-No. 386 Pilot Filament Transformer cheaper than factory jobs.Yet the battery sets 1-No. 959 Pilot double bias resistance which worked just as well with a little junk slipped 1-No. 951 Pilot singlebiasresistance in here and there aren't A. C. sets by a long shot. 2-No. 8oi Pilot mfd. by-pass condensers You CAN'T FOOL THE A. C. CIRCUITS 1-No. 718 Pilot binding post strip 1-No. 719 Pilot base board No, sir.You can't put anything over on the 110 volts, and you have to toe the mark when you use I-No. 723 Set of flexible leads the new tubes. 1-Package of wood screws That is, you must have the best thereisfor To this should be added a No. 200 Pilot potentio- the A and B supply circuits, and you must design meter of zoo ohms, to be used as a voltage control, the receiver with great care to provide the proper if you want it. C biases. The A transformer will operate one to three If you use poorly designed power transformers CY-327 tubes, one to five CX-326 tubes, and one or they will burn up sure as fate.This applies to the two CX-37I tubes. use of separate transformers for A andB supply, If the receiving set is made up of the 327 tubes as well as to the single transformerswhich furnish entirely, three or four can be operated from the both A and B voltages. transformer. The A supply must deliver a heavy current, and You will see that two special wire -wound re- operate continuously for hourst a time.There- sistors are supplied.The No. 951 resistor is to fore a heavy core and heavy 'winding must begive 45 volts C bias on the 171 tube, while the employed, together with a type of case which will 959 resistor is for biasing the R. F., detector, and permit the degree ofcooling necessary to the first audio tubes. design of transformer. B eliminatorsfor A.C. tubes must deliver a PLATE CURRENT DETERMINES C BIAS greater amount of current than isrequired for 301 -A's.That is, 301 -A's draws 2.5 to 3.o milliam- The C bias for the tubes is obtained by the drop peres, while the 326 draws 6.o milsand the 327, across the resistor when the plate currents flow 5.0 mils in the plate circuit. through them. Therefore, where a set using four 301 -A's and a The resistance values are such that the correct 371 would draw 3o mils, a similar set usingA.C. grid biases will be obtained when the rated volt- tubes will draw about 45 mils. ages are applied to the tubes. Many B power packs are able to handle 30 Now, if an inadequate eliminatoris used, the mils all right, but at 4o to 5o mils the voltage drops voltages will be below the rated values, and the C 31 bias willnot be right.That is why you must i-No. 96o Pilot B resistance use first class B power equipment. 3-No. 8ox Pilot i mfd. by-pass condencers 1-No. 253 Pilot socket How TO USE THE A PACK 1-No. 720 Pilot binding post strip Different circuits, with different combinations of I-No. 721 Pilot baseboard tubes, require various arrangements for the grid x-No. 724 Set of flexible leads bias.The standard Pilot No. 4 A pack has resis- The 280 type tube is recommended for thisset, tors to provide biases which are correct for the although a BH Raytheon can be used if you prefer. tuned R. F. receiver, described in Radio Design No. 2, and for the receiver shown in the accompanying NOTES ON THE B PACK illustrations, diagrams for which are given in Figs. In the standard kit, a buffer condenser issup- 5 and 7. plied, to be used in the regular way witha Ray- In Fig. 5 you will see that binding posts are theon tube, or connected as shown in Fig.3 for indicated in three different ways, to show those the 280. which should be connected to the A pack only,

NOV 50-60 110E, '"? 50-60'9 OFFICIAL CIRCUIT PILOT A&C POWER PACK NE 213 SOCKET FOR ALL- ELECTRIC SETS

PILOT 144400 400 ORM POTENTIOMETER 0 0 PILOT N9 377 II B- ELIMINATORla 10 NI so. CHOKE COIL MID. BY PASS COND 0 0 222 O

PILOT SUPER POKER 0 0 TRANS N? 386 FOP ci_2 A.C. FILAMENT TUBES I PILOT 749 377 B. ELIMINATOR CHOKE COIL Yf N9331 RESISTOR 2250^

EACH CONDENSER N9 559 RESISTOR NI 801 BY PASS I.Mra

A.C.(0 0 2k1V AC 0 jV A C 0

OFFICIAL CIRCUITCIRCUIT PILOT UNIVERSAL 3650 2150 2800 N? 960 RESISTOR C-40. C- SY. B - B -POWER PACK FOR U% 280 Fig. 2.Left. Picture wiring of the A and C power pack.Fig. 3. Right.Diagram of the B power pack.The 387-A transformer has only two primary terminals, but it runs either B- 6+45v 8.90V. 8+1350. B. 180V B. 2100. a BH or 28o tube. those to go to the B pack only, and those to be You will see that binding posts are provided for connected to both A and B packs. 180 volts and 220 volts.If you use the power pack For economy of space, the binding posts, as you on old style receivers, where separate C batteries can see in Fig. 7, were just machine screws with are employed, so that you will not need the biases battery thumb knots to take the leads. from the resistors in the A pack, you should use Since the bias resistors are supplied, no separate the 58o -volt binding post to get 18o volts on the C batteries are needed. 575 tube.If you use the A pack and the bias re- On the other hand, for the Air Hound set, sistors, you must connect to the B+ 22o -V. binding equipped with three 327 tubes, the bias resistors post so that you will have 40 volts extra to use are both of 2,25o ohms. for biasing. ARRANGEMENT OF THE B POWER PACK A RECEIVER FOR EXTERNAL POWER SUPPLY The B power pack is shown at the right in Fig. Figs. 5 and 7 show the circuit for a set similar to 1, with its diagram in Fig. 3.Here is the list ofthe Air Hound, arranged forexternal A and parts supplied with the kit: B power packs.This set has a stage of tuned R.F. 1-No. 387-A Pilot B transformer with a super -charger control, regenerative detector, 6-No. 9302 Pilot 2 mfd. filter condensers and two stages of audio amplification with an out- 1-No. 91 10 Pilot .5-.1 mf. buffer put impedance to operate the loud speaker.In 1-No. g000 Pilot condenser block clamp addition, the setisprovided with a jack for a 2-No. 377 Pilot 3o -henry chokes phonograph pickup. When the phonograph pickup 32

- _. Fig. 4. A very handsome effect is given by the new dials. is plugged in,it operates the detector, giving two 1 No.8o1 PilotI mfd. by-pass condenser stages of audio amplification. 3No. 35 Pilotiin. Bakelite brackets The set is assembled on a 7 x 18 -in. front panel, No.I3o Twin Coupler R.F. choke with a 7 x 17 in. base panel supported on three No. No. 52 Pilot .0005 mfd. condenser 35 Pilot brackets. 2 No 1255-W Pilot Bakelite knob Following is a list of parts required : 4Pilot engraved Bakelite binding posts

Z.MT UK -111 UY 221 0214 1111 SEC PRI 00015n4 P ri53010 iA.F.C11011:1 mos nI .000MI35 01 OUTPUT . \ Mtn UP Asia B IF 50500 P

TO M^4 A POWER PACK 0 10TO ri! 5 B POWER PACT 0 o 135, B- Si,C 200 1 C .455 A 1 GNP I S,C 010V VI TO A S 0 PACKS Fig. 5.Circui for the all -electric set, equipped with jack to take a phonograph pick-up. Note the legend for power pack connections.

2 No. 1617 Pilot .00035 mfd. condensers I 7 by 18 by Yee in. Westinghouse Micarta INo. 35o Pilot Resistograd panel 2 No. 1282 Pilot illuminated dials I 7 by 17 by A in. Westinghouse Micarta No. 1165 Pilot midget jack panel No. 54 Pilot .002 mfd. condenser No detail description of the assembly is necessary No. 121 Twin -Coupler three circuit tuner sinceitiswell illustratedinthe accompanying No. 123 Twin -Coupler R.F. coil pictures, and in the wiring diagrams. No. 51M .00025 mfd. condenser It should be noted that the No. 52 fixed con- No.756 Pilot 2 meg. grid leak denserisscrewed into the rear terminal of the No.211 Pilot UY socket Resistograd, and a leadforconnection drawn 3No.205 Pilot UX sockets off from this common point. 2 No.381 Pilot A.F. transformers The grid condenser, No. 51-M is mounted under No.383 Pilot output choke the base panel, and held in place by screws passing Fig. 6. Rear view of the all -electric four -tube receiver.

33 through the grid leak clips, through the base panel pression that a hum isset up when 326 tubes and into the threaded bushing of the condenser. areused. Thatismore probably due tothe Some of the leadsinthisset are cabled as extrafilamentwiringwhichmustberun much to improve the appearance of the set as around the receiver, inducing slight A. C. cur- to keep the leads properly separated from others rents in the R. F. circuits. in which a 6o cycle hum might be induced. The question frequently arises as to whether the The operation of the set is similar to that of the A power transformer can be mounted right in Air Scout. An ordinary broadcast antenna is re- the radio set without making trouble. Ordinar- quired with a first class ground connection. ily this arrangement is entirely satisfactory. In The two condensers control the tuning, while the Air Hound, for example, there is no hum the volume inthe R.F. and detector stagesis to be heard, even when no broadcast signals regulated by the Resistograd and tickler coils re- are coming in. spectively.Once you are familiar with the opera- Usually A. C. interference is only caused from tion of the set, you can adjust the Resistograd per - a filament transformer when itis overloaded

N0.4 PILOT A AND C POWER PACK MO. 5 PILOT B POWER PACK 0 O

1 1 CND AMT. A C --4p445. 4ityAc B Bso FI 1.35., AC L5-LS --O @,1

a PILOT eiP IkCr$ T B. TRANSFOPIFit P 10.381 G PT0:143r"Eg

.205

(P SUET P MO 205 SOCKET 1ST AG 4216 1 7/7 A.13oE CMOKI UX-22,

122 0 5i. m 1.1 CIRCUIT TUNER

SEC rtix 40.1623 .0005 WA CORD 000raPCOND

PILOT NO 350 RESISTOGRAO 54 MIDGET JACK

F. SUPER -CHAR 'ER CONTROL

NO.1282 DIAL NO.1282 DIAL Pig. 7. This set employs separate power packs for A and B. Note the connections for the phonograph pick-up. manently and control the volume with the tickler and there is, in consequence, considerable mag- alone. net leakage about the transformer. This set has a loud speaker range of r,000 or 2,000 miles, and issufficiently selective to meet USING POWER AMPLIFIER all ordinary cases of interference. If you want something very fine indeed, assemble an A. C. set such as is shown in Fig. 7, SPECIAL NOTES ON A. C. SETS or the regular Air Hound, but leave off the last A. F. stage.Instead connect the plate of There is now a decided tendency toward using thefirst audio tube directly to the new 250 all 327 tubes rather than specifying 326 tubes power amplifier. Then you will have radio re- for the R. F. and first audio. ception of the very finest quality and you can The reasonissimply that constructionis use one of the new dynamic speakers. More- greatly simplified by using all 327 tubes, and over,if you use the circuit shown in Fig. 7, the actual efficiency obtained from them is just with a jack to cut in a phonograph pick-up, as great as from the 326 tubes. you can get the 250 power amplifier results for Some set builders have been under the im- phonograph reproduction. 34 Be very careful in the selection of your phono- Radioisplaying an important part inthe graph pick-up.There are several types whichpromotion of safe flying. At all the Army posts have been dumped on the market, and are being weather reports are exchanged by radio early offered at very low prices, but the quality of every morning.As the day progresses, if any reproduction is on a par with the cost.Have change in atmospheric conditions occur, supple- the dealer demonstrate the operation of the mentary reports are sent out at once. pick-up for you.Otherwise you may get some- When the Airplane Radio Laboratory isto

Fig. 8. Here you can see how much it improves the appearanceofasetto cable the leads. This keeps thefilamentwires away from the grid leads, and, also reduces the A. C. hum. Filament leads for different types of tubes can be cabled together.

thing that sounds like the old-fashioned cannedstart on long flights, a report isfirst obtained music, instead ofquality from theamplifier from MitchelField, adjacent toCurtissField, that is superior to that from the phonograph as to conditions along the route which the plane from which, on the new style records, we get isto cover.Probably within the next year, music that sounds like the original orchestra orplanes will be able to get additional information the artist himself. inflight from weather reporting ground stations. THE PILOT AIRPLANE RADIO Experience gained during the operation of the LABORATORY Pilotplaneindicatesthatradioreceptionof The PilotAirplane Radio Laboratory has weather reports is practical on commercial planes flown more than 12.000 miles during test flightsoperating on regular schedule, even tho the pilot for trying out airplane radio equipment and on is flying alone.The use and practicability of radio trips carrying Company officials on emergencyfor privately operated ships is doubtful, however, flights.Between 250 and 300 men connectedfor the radio equipment must have the same in- with the radio industry have been up as pas- formed attention thatis given to the other parts sengers on trips around the country. of the ship, and radio equipment, until more ade-

Fig. 9.In many ways it is better to use separate A and B packs, for this methodofconstruction simplifies the design and wiring oftheset, and keeps all the A. C. equip- mentawayfromthe radio frequency circuits. This can be seen by com- paring these illustrations withthoseoftheAir Hound.

Thanks to the dependability of the Stinson quate service is provided at airports might be as ship anditsWhirlwind motor, as well as the much trouble as it would be worth. skill of Louis Meier, the pilot, the big mono- In fact, the whole matter of radio equipment for plane has never had a forced landing. aircraft, and the methods of its use, will undergo Among the cities to which the ship has flownconsiderable revision within the next two years. are Washington, Detroit, Chicago,Cleveland, Much has been learned concerning this subject by Boston, Baltimore, and Hartford.The plane Pilot engineers, for it is only under actual average is a well-known visitor at Fort Monmouth, N. J., flyingconditions-not merelypleasant -dayhops where the laboratories of the U. S. Signal Corps around a flying field-that the scope and the limita- are located, as well as the Officers' Radio School. tions of airplane apparatus can be determined. 35 Jr OW a )e v "To meter band" reachesNote -The from International Jo to Short10-20 METERS Wave Amateur 15.641meterslengthWave PQW, Alfragide, Lisbon, Por- TransmittingCall Stations of the World Location of Station 16.71meterslengthWave- WBQ-WEBQ,Call Rocky Location of Station Point, 18.1Wave-lengthocation of Call Station daylightlengthtions10.7Wave- meterscan at long be andheard distances many there, additional only. especially sta- by Location of 15.70715.7 GLW, WFX-WEFX, RockyN.tugal Y. (Beam) Dorchester, England Point, 16.9316.78 KI7N-KEUN,WBC-WEQC, Bolinas, RockyN. Calif. Point,Y. 18.182metersI.18.17 CRNC, Loanda Angola, W. WJZ,CRHC, Bound Loanda Brook,Africa N. J. Angola, W. 12.25I10.meters I. AGK,IRG, Nauen,Call GermanyComo, Italy "Radiogiornale," Station Lake 15.74015.707 GLG, Royal Air Force, Hen - lowlow(Beam) 17.17. NKF,2BR,cg2BR,SPI, Rio Chelmsford, Chelmsford, de Janeiro, England EnglandBrazilD. C. Bellevue Anacostia, 19.419. .Vote -The ANK.OLQ, Malabar, SS. Slamat Java 20-30 METERS international amateur 14.13.8813-5 KDKA,WND,AGA,POF, Nauen, Ocean Nauen,East Pittsburgh,GermanyTownship, Germany N.Pa. J. 16.15.9315.86 WHR-WEHR,WDS-WEDS, Rocky Rocky N.Point, Y. Point, 17. 7. KNW,KKC,KFUM,PCG, Palo Palo Malabar, SS.Alto, Alto, Idalia Calif. JavaCalif. long-distancetions21.4"2o -meter meters may band"be and heardwave manyreaches andthere. additional fromat 20.8 sta- to itsIt is best a 0. 14.1314.0914.114.08 2XBC-WBU,KEL,KWE-KEWE, Bolinas, Bolinas, Calif. Y. Rocky Calif. Point, 16.0216. WTT,JPP,WSS,NKF,AGA, JYB, Rocky Rocky Nauen,Rocky JYZ, Poiht, Point, Point,GermanyTokyo N. N. Y.N. Y. Y. 17.417417.317.2 WKI,ANE,AGC,KNN, Newark. Nauen,HonoluluBandong, GermanyN. JavaJ. lyyour light,whenvery receiver. weakone or nearby both Twentystations and loud -meterare in at day- stationsa are frequent- i.e., both the transmitter and 14.414.291414.25 28 KMM-KEMM,FW,AG9,WQA-\VEQA, Sainte Nauen, Assise, Germany Bolinas,Rocky France N.Point, Calif. Y. 1616.077 146 GBJ,VNB, Klipheuval, 2XG, Rocky Point, N. (Beam)Y. Bodmin, S. Africa 17.717.5 GBO,GBM,GBL,WKC,ANH, Leafield,Leafield, Malabar,Newark, EnglandEngland N. Java J. 20.20.distance of moo miles or more. TUK,2XAW,WSS, Tomsk,Rocky Schenectady, Point, Siberia N. N. Y. Y. 14.814.8514.8 WQX-WEQX,WQQ,WGG,KSS-KESS, RockyNew York Point, Bolinas, Rocky N. N.Y.Point,Calif. Y. 16.28616.21616.17 VWZ,GB,, 2XT, Rocky Point, N. Y.(Beam) Grimsby, Kirkee, England 18.318.2718. PQS,POF,KFD, Nauen,Alfragidi,Denver, Germany Colo. Lisbon,tugal Por- (Beam) 20. NEPQ,NAL,CH,AGK, Quilicura, Nauen,Navy SS. ReliefYard, Germany Chile Washing-ton, D. C. 15.14.9514.9114.93 AGA,2XS,WQY-WEQY, Rocky Nauen, Point, Germany Rocky N. Y. N.Point, Y. 16.4116.35 WND,WEM-WEEM, Ocean Township, RockyN. N. (Beam)Point,Y. Y. Bombay 18.3618.3-18.7 WBQ,CRHA, Schenectady, N. YPortuguese,4XK,2XAP, E. San AfricaNew Juan, York P. R. Lourenco Marques, 20.20. PCH,OCTN, Scheveningen,landsFrance Mourillon, Nether-Toulon, 15.1.5. CH,2XAW,CG2BR,GLS, Quilicura, Ongar, Schenectady, Chelmsford, England Chile EnglandN. Y. 16.50116.49 CG, Drummondville, Montreal NPG,WLL-WELL, San Francisco RockyN. Y. Point, 18.18.18.818.62 PCLL,KEB,IRG,AND, Oakland, Kootwijk, Tjililin, Calif. JavaHolland "Radiogiornale," Lake 20.20. GLSQ,PUC,GER,PCRR,PDX, CuracacWinchester, SS.Kootwijk, Nauen, Olympic Germany EnglandHolland 15.57615.515.08 SPU, SPU,YNB,PUC, Rio CuracaoCapetown, de Janeiro, S. Africa Brazil(Beam) Santa Cruz, Brazil 16.716.616 574 GBK, KNW,WLL, RockyPalo Alto Point, N.(Beam) Y.(Beam) Bodmin, England 18.09418.18. CRHB, ICC,KTA, Coltano, Guam ItalyIslandComo, Italy Praia, Cape Verde 20.2520. JB,J-IPP,RR Johannesburg, P, Tokyo S.(B. C.) S. R. (Russia) Nijini Novgorod, S. Africa [1. 20 3 ANF, Tjililin, Java 22.02 WGY, Schenectady (B. C.) 25. HZA, Saigon, Fr. Indo China 28.5 PDRL, Leningrad, U. S. S. R. 20.82020.5 69 NKF,PCH,JKZB, Scheveningen,landsTokyo, Japan Bellevue,Tokyo Elect Anacostia, Nether- Co., 22.0922.2422.18022.1 Rio de Janeiro, Brazil (No call) GLH,2XE, Richmond Hill, N.(Beam) Y. Dorchester, England Point, 25.525.325. 5DH,FFW,PCRR, St.Dollis Kootwijk, Assise, Hill France HollandP. land0., Eng- 28.5828.8 KSS-KESS,AND,KMM-KEMM, Tjililin, Bolinas, Java Bolinas, Calif.(Russia) Calif. Scheveningen, Nether- 21. NKF,PCTT, Kootwijk, HollandD. D.C. C. Bellevue,Moscow, Anacostia, 22.822.522.3822.3 OLQ,WND,FY,WAJ-WEAS, Bordeaux, SS.Ocean Slamat Township, RockyFranceN. N. Y. J. Ft. Ind. 25.72825.5 VIZ, Melbourne, Australia NKF,B82,AGB, Brussels, Nauen, GermanyBelgiumD. C. GrinsbY,Bellevue, Anacostia, 29.29. OCNG,NKL,JPS,PCH,n Sapporo, Arlington, Japan Va.lands s Nogent-le-R ot r o u, 21.12721.4 PCH, Scheveningen, WDJ,RKV, Harrison, Ohiolands(Russia) U.S.S.R. Nether- 23.22.99 KNN,2XAA,WOWO.PKH, Honolulu, Houlton, Soerabaja, Me. T. Javah. (B. C.) Wayne, 26.25.906 GBH, AGA,FAMJ,AGC. Nauen, Nauen, SS. GermanyJean Germany d'Arc(Beam) En gland 29.28229.226 PCH,PCH, Scheveningen, Nether- landsFrance s Scheveningen, Nether- 21.521.421.48 WIK,KDZ,PKP,WIK, PointNew Rocky Brunswick,Barrow, Point, Alaska E.N. N. I.Y. J. Medan, Sumatra, I). 23.1823. WNP,RLT,RAU, Tommot,SS. "Bowdoin" U. S.(RussiaU. S. S. R. Tashkent, Turkestan, S. R. 26.26.086 GBK, VIS,WNU,VJS,ICJ, Sydney, Bengazi, Rabaul, New Australia Orleans,Cyrenaica,New Guinea La. Libia Bodmin, Eng la n cl 29.529.329.529.3 6XI,PCTT,KNR,SPW,KEL, Bolinas, Bolinas,RioClearwater, Kootwijk, deCalif. Janeiro Calif. HollandCalif. 21.5721.5215 WOP-\VEOP,GBM,GBO,GBL,'PP. Leafield, Tokyo, Leafield, RockyJapanEngland England Point, 23.723.523.423.323.25 GBM,WBQ,KNN,KTA, Osaka,Schenectady, Guam,Honolulu, Japan P. R. T.FFW,N. H. Y. Sainte-Assise, France 26.326.26926.2 CG, Montreal, Canada AGB,ANC, Nauen, Tjililin, Germany Java (Beam) 29.8329.829.71 3L0,WQX-WEQX, Rocky(B.N. Point, 1'. C.) Melbourne, Australia 21.6321.721.6 W PE-WEPE, Rocky KTF. Midway IslandN. Y.V. Point, 24. 2XAD,JES,GBL, GBO,New Osaka, Leafield, York Osaka, Japan EnglandJapan I 27.26.9226.3 ANH,AGB,2XAG,WDJ,KDKA, Harrison,Nauen,Malabar, New East YorkGermanyPittsburgh, OhioJava City Pa. 3o.30.3o. GBL,2XI,WQY-WEQY,IXAR, Schenectady Leafield, Manila, England Rocky P.N. Point,Y. I. 21.821.7521.821 8 GLS,WGT-WEGT,KEB,RRU,5DH, Ungar, DollisOakland, U. S. England SanHill. S Calif.Juan, England P. R. R. (Russia ) 24. JEW,KNW,GDKB,SSW,PKE, Osaka, Palo Chelmsford,Amboina, SS. Alto, Japan Dorsetshire Calif. D. England E. 27.527. RCRL,PKX,PCPP, Java Kootwijk,Central Hollandgrad, U. S. S. R. (Russia) Lab., Lenin- 3o.30.3o. KZET,JSK,JBK,GBO,GBM, Kagoshima,SS. Leafield, Manila, Shingo, England P. JapanMarti I. 2121.8 c22. 6 18, 2 XKI.L.HJG,KTA, A I), Bogota,SchenectadyBolinas, Guam, Colombia P.Calif. R. 24.624.524.3 CI,GLQ,FW,KFD, Sainte-Assise, Denver,Ongar, EnglandColo. France(Beam) Drummondville, C a n. 28.27.92727.5 6 WKI,5DH,WKC,PCMM,KKC, Dolliq Newark, Palo Newark. Kootwijk, Hill, Alto, N. England N.Calif.J. Holland J. 3030.530.2 630.2 PTQ,ARCX,PCJJ.ANK, Quartel, Eindhoven,Malabar, SS. Nielsen Brazil Java Holland Alonso 22.22. V IX,\ETA, *IT, Townsville,Guam Queensland,Australia Sydney, N. S. W., 24.924.7 NKF,VIY, D. (Beam)C. Melbourne,Bellevue. Anacostia.Australia 28.1528. KNN,FUL,POW, Beyrouth-Djedeide, Honolulu, Naren, Germany T. H.anon, Leb- Syria 31.30.9130.7 2XAL-WRNY,EAM,NAL, NavyMadrid, Yard, Spain Washing-N.ton, J. D. C. (B. C.) Coteyville, 22.22. VRABL, TZ.KGBB,RTRL, Rabaul, Haharousk, Tiflis SS. NewUngara GuineaSiberiaS. R. (Russia) Georgia, U. S. 2525.24.9 DCP,POY,cg2YT,NAA,PCMM, SS.Nauen,Arlington, Poldhu, Cap. The Germany PolonioHague.England Va. Holland 2828.428.26 5 2ME,SPW,WQA-WEQA,KWE-KEWE, Sydney,Rh de Janeiro, Austral' Rocky Bolinas, Brazil N.Point, Y.Calif. 31. 6XBH-KFQU,TVF..SAD, Flottans 'S. Soldevijk Alma Stations,holm,City), Stock- SwedenCalif. (B. C.) (Holy 31.04 32.5 34. RAV, Tashkent, Turkestan, (B. C.) 31.3931.7331.5 WFX-WEFX,8XAG,WDS-WEDS,PKP, Dayton, Medan, Rocky Ohio Sumatra RockyN. Y. Point, 32.9832.8432.7732.69 WEM-WEEM,2XAF,WND,IDX, Amara, OceanSchenectady Township,Italy Rocky (B. N.Point, N.C.) Y. J. 34.34. VNB,RKV,XDA, Capetown,Moscow, Mexico U. City, S.U. S.Mex.(Beam) S. R. S. R. S. Africa 36.36. LPO,KTA,3LO,DS,NPM, H. Buenos Guam, M. Honolulu, S. RenownAiresP. R. T. H. Melbourne, Australia 31.9632.31.8 2FC,WHR-WEHR,AYG, Sydney, Guayra, Australia, Rocky Venezuela N.Point, Y. (B. 32.9833. WLL-WELL,NPG,1FC, Puget Sound, Rocky Wash.School,N. Y. Rome, Italy Royal Frederico Point,Calif. Cesi 34.234.56834.013 GBJ,GBI, Grimsby, England RDI,HBC, Petrozavodsk, Berne, Switzerland U. S. S.(Beam) R. Bodmin, Engl a n d 36.536. FUTANF,OCBR,SAB, Tjililin, Rabat,Goteborg, MoroccoJava SwedenFrance Toulon -M our i 11 o n, 32. 3L0,2YT,2XG, Poldhu,New York England CityC.)(B. C.) Melbourne, Australia 33.33. CHO,AQE,6XAR, Telegraphic SS. San Francisco, Administra-Ross(B. C.) Sir James Clark 34.63448334.4 VWZ, Kirkee, Bombay, India VWZ,KNN, Kirkee,Honolulu, Bombay, T. H.(Beam) India 37.36.836.636.52 4XK,NPM,2XAP,KGH, San Honolulu,Hillsboro, NewJuan, York P. R.T.Ore. CityH. (B. C.) 32. 8XAO-WCX-WJR,6XAR-KJBS,9XD, Radio San Club Francisco, ofMich.Calif. Zurich, (B. C.) Detroit, 33. OCCO,IDO,KDO, Rome, SS. Italy EspartoFruit)tion, Oslo, Norway Conakry, Fr. (United W. 35.34.8634.7835. IRG,KWT,Standard'PP, Tokyo,Palo Wave Alto, Japan for Ships(Beam) "Radogiornale," Calif. Lake 37. KGBB,KFVM,KEL,GLYX,FUM, Rolinas,Montebourg, SS. SS. DerbyshireUngava Idalia Calif. France 32. ANE,90C, Malabar, JavaBerne,Zurich, SwitzerlandSwitzerland Tel. & .Radio SVC, 33. OCTN,OCDJ, Issy FranceAfrica Mourillon, les Moulineaux, Toulon, 35. 2X1,2XG,BWW, Schenectady Ocean Gibraltar, Beach, N. N. J. FrontComo, Italy 37. PCRR,OLQ,NPU,N PC, Tutuila,SS.Puget Kootwijk, Slamat Sound, Samoa Holland Wash. 32. FL,CF,ARDI,ANH, Drummondville,Eiffel Malabar, SS. Tower C. A. Java Larsen Montreal(Beam) 33.3733.3333.233. PCA,KTF,VZDK, Amsterdam, Midway SS. Jervis Island Holland Bay 35. BXY,BXW, Seletar, S in gap HongStraitsore, Kong Settlements Stonecutters I slan d, 37.2437.0137. WJD,6XF,WOBD, Los New SS. Angeles, York Radio Calif. (B. C.) 32. JHL,JB,IDO,HVA, Johannesburg, Hiroshima,Rome, Hanoi, Italy Fr. Indo-ChinaJapan(B. C.) S. Africa 33.533.4233 4 WQC-WEQC,KUN-KEUN,KNW, Palo RockyAlto, Bolinas, Calif.N. Calif.Y. Point, 35. BYC,BYB,BZE,BYZ, Horsea,Whitehall, Matara,Rinella, England CeylonMalta R. C., Eng-land 37.4 NKL,NKF,NAA,WCFL, Arlington, Chicago, Va.Ill.D. C. Bellevue, Anacostia, 32. OCNG.LY,PCLL, Bordeaux, Kootwijk, France HollandFrance Nogent-le-R o t r o u, 33.70833.5 VNB, Klipheuval, WNBT,NAJ,AQE, Great SS. Elgin, Lakes, Ill. Ill.Ross Sir James Clark S. (B.Africa C.) 35. NPM,BZF,VKQ,OCDA, Aden, Honolulu, Garden Dakar, Arabia Island, T.Fr. AustraliaH. W. Sydney, Africa 37.537.4837.43.37.43 WLC, Rogers, Mich. 2XAP, NewAND,6XAS, StandardYork Tjililin, California City Wave Java for All Ships (Portable) 32.12832. CG, Drummondville, Montreal VJZ,VIS,PKX,PKD, Sydney,Rabaul, KoepangJava NewAustralia Guinea 34.34.33.88 1FC,KUN-KEUN, Royal Cesi School, Bolinas,Italy Rome, Calif.(Beam) 35.0335. KGDU,\VQO,WGY,PCMN, SchenectadyRocky SS. Kootwiik, Four Point, Winds HollandN. Y. 37.537.9537.5 SKB,KFZQ,JKV,IDO, Rome,Kgnaswa,MS. SS. Gripsholm Robador Italy Japan 32.532.397 GBK, 2NM, G. Marcuse, Caterham,England(Beam) (B. C ) Bodmin, England 34. PCUU,NAJ.LPL,KNW,DCP, BuenosGreatS., PaloHague Cap Lakes,Alto, Aires Polonio Calif. Ill. 35.535.335.27 BZC,5DH,WJF, Detroit,Dollis Hill, Mich. EnglandlandSchool, Portsmouth Portsmouth, Signal Eng- 38.38. JPS,2XI,IST, SchenectadySapporo,GBA,3XQ, Chisimajo. MountainTobermorey, Japan It. Lakes,Somaliland Scotland N. J. 38. PCUU, Hague 41.95 FW, St.-Assise, France 44.03 KZA-KZB, Los Angeles 47. SUC2, Abu Zabal, Cairo, 39.38.538.38 KAV,OCMV, Norddeich,FUE,ANDIR,KEUN, Mont Mengam, Valerien, Malabar,Germany Bolinas, France France JavaCalif. 42.41.95 VRTRL,VIS, IT, SydneyTownsville, Tiflis, Georgia, Queensland,AustraliaS. U. R. S. 44.0344.4844.03 WAJ-WEAJ,SPI,WKI-WAQ,KOQ, Rio Houston, de JaneiroNewark Rocky TexasN. Y. Point, 47.447. SPM,KTA,ICX, Massawa,HelsingfGuam ors, EritreaEgypt Finland 39.539. OCRU,NAJ, JFAB,Great Ruf Lakes,Taipeh, isqu Ill.e, FormosoAfrica Fr. W. 42. SGT,PCUU,RRP, MS.Nijini Hilversum, Suecia Novgorod, HollandS. R. U. S. 45.44.7144.6244.5 OCMV,KPZH,WBO,ICK,SPI, Mont Dearborn, RioFairbanks,Tripoli Valerien, de Janeiro Mich. FranceAlaska 48.48. KNW,OCNG,OCTU,KNN, Honolulu Palo Tunis,Nogent Alto, Tunis - leCalif. France- Rotrou, 39.8"40 -meter band" isNote the -Thebusiest of all AGC,OHK, Nauen,Vienna, Germany Austria 40-50 METERS international amateur 42.542.5042.0842. FUA,TFA,KDZ,5XH,VJZ, Rabaul,Reykjavik, NewPt. Barrow, Orleans New Iceland GuineaAlaska Bizerta-Sidi-Abdullah, 45. OCNG,KEG,NPG, Vancouver,San Nogent Francisco - Wash.le - Rotrou,France 49.48.05 KSZ,ICF,KINT,KYI, McConney, Messina,Kings Palo Mill,Alto, Sicily Texas Texas Calif. intoertiesInsemithe addition, bands -local of 20 because andmeters it has "extreme someand will ofD work-X"the prop-wave. well daylight before it is both a good failing. It 4242.51 8342.9842.83 WTI,NPG,WJF,SS. Evansville,Masilia Detroit,San Francisco Mich. Ind.Tunis 45.0245. AIM,tAX, Meterological KEU,Rome, Los Angeles Hut, Oslo,ItalyNorway via Socioa 8o, 49.1549.5 TFA,KMV,KVR,KNR,WHD, Reykjavik, LasClearwater,Bandini,Sharon, Vegas, Calif.Pa. Iceland Nev.Calif. `)w 40. 40.40.411reaches from 41 to 42.8 meters. NPU,NQW,IXAO, Tutulla, SS.Belfast, Mexico SamoaMe. 43.43.42.95 VGIL,1MA,WIZ,KDKA, NewRome, East Brunswick, ViaPittsburgh, Bramantemander N. Pa. 3,J. SS. Canadian Com- 45.4345.3245.02 WHW, Highland Park, Ill. KEH,KFZG,KYU, PanhandleWichita Pt. Barrow Falls, City, Texas Texas 50.5o.49.97 2XAC,SAJ,OCTU,KWT, SchenectadyKarlesburg, Palo TunisTunis, Alto, Tunis SwedenCalif. 40. 6XBR-KFWB,NOSW,B82,NAS, Uccle, CocoPensacola, Belgium Solo, Fla.C. Z.(B. C.) Los Angeles 43. JOC,AtE, Otchishi, JapanBergen,Italy Norway Meterological H n t, 46.45.77 OAA,KQT,PCLL,KQS,KFE, LosThe PoncaLone Kootkijk, AngelesMossig Pine, City, Weini HollandCalif. Okla. Ain- 5o.51.50. AIN,WBZ,2XH, Casablanca Schenectady Springfield, Mass.C.) (B. 40.40. BAM,NPG,WNU,KFHW, SanTahitiNew Francisco Orleans SS. Pointsettia 43.0543.1443. WOP,WAQ,2XAI,FW, St.-Assise, WEOP, Newark,Newark, RockyFrance N. N. J. N.J. Point,Y. 46.46. KNN,OCMY, Honolulu Mont lofValerien,France 13, Austria 51.51.551. WQN,TSB,SAD, SS.Flottans Rocky Helder Point,Stations, holm,N. Stock-Y. Sweden 40.540.240 2 NAJ,J -IAA,ANC,AGC, Great Iwatsuki, Nauen, Tjililin,Lakes, Germany Ill.JapanJava 43.4543.3343.2 WLI,WLK,WPE-WEPE,KTF, Cleveland, Wheelwright, Midway OhioIslandRocky Ky.N. Y. Point, 46.4846.0646. WND,KGE,KGT,BVJ, Dartmouth,Medford,Fresno, Ocean Township,Calif. Ore. JerseyEngland New 53.52. ZWT,NPU,WLW,WGW,VAS, Bremerhaven, Lewisburg,Tutuila, Vieques,Cincinnati, Samoa P. NovaGermany R.0. (B. Scotia C.) 40.640.540.5 OHK,IAA,OCBA,JBK,SPX, Kagoshima,Iwatsuki, Vienna, Bamaku,Rio de Austria JapanJaneiro Fr.Japan Sudan 44-43.7443.643.52 OCMV,WOBD,KTA,KOS, GuamPampa, SS. Mont Radio Texas Valerie n, 47.46.9946.5 POZ,KGH,TSB,ICX, NorwegianNauen, Hillsboro, Massawa, Germany Ore.SS. Eritrea Helder 54.53.5453.554. KWJJ,AJF,NBA, Konigwusterhausen, Portland, Balboa, Ore.C. Z. (B.many Ger- C.) 41.741.541.341. SMHA,GDKB,ECBA,NKF, Stockholm, Bellevu Bamako, SS. Dorsetshire e, SudanSweden Anacostia,D. C. 44. GFA,WQO,SAA,KTA, Air Rocky Karlskrona,Guam Ministry, Point, London SwedenN.France Y. 47.47. DollisSPI,DNSC, Rio Hill, Royal de EnglandJaneiro Danishknown)yard, (call Dock- Copenhagen not 54.554.454. WQN,NKF,WEAO,8XJ, Columbus, Rocky Columbus, Point, Ohio 0.N. (B.D. Y. C. C.) Bellevue, Anacostia, Fig. I.This gives you an idea or the appearance of the finished set. TAPERED TUNING MAKES ONE -DIAL SET HIGHLY EFFICIENT By GERSON LEWIS iF you have played around with the constructiont;ng each condenser until maximum volume was of single control receivers, you probably know obtained.If this was dbne at one setting of the that there is a whole lot more toit than justdial, since each condenser would be at a slightly ganging up the condensers and matching coils.It different setting than the others, as they were all is almost impossible, even for the experienced pro- rotated together to tunein another station, the fessional set builder, to build a set of conventional stages would be unbalanced again due to the fact coils and condensers into a single -dial receiver and that the variation of capacity of this type of con- have every tuned stage exactlyin step over thedenser is not proportional to the angle of move- complete frequency range.Even if the coils and ment of the rotor plates.Therefore even though condensers are matched, thecapacities andin- all the condensers had been moved through the ductances due to the wiring, the internal capacities same angle the variation of capacity of each one of the tubes, the effect of metal objects near the would be different.This effect was especially no- coils-all add together to unbalance the tuning of ticed at the lower wavelengths, where the tuning the individual stages and decrease the efficiency of is sharp. the receiver, if not to make it altogether impossible In the Taper -Tuned Receiver each stage is de- to operate on account of whistles and squeals. signed to have a differentsharpnessof tuning. After a great deal of careful laboratory work,Starting at the first stage the tuning is broad. As Icame to the conclusion thatthe conventional thesignaltravels through toward thedetector, tuned R. F. amplifier would have to be changed each stage is more sharply tuned than the preceding for use in single -control tuned R. F. sets built by one.The detector stage is designed to give knife- professionalsetbuilders.Theresultwas the like selectivity without cutting sidebands.In this Tapered Tuning system of construction. way, by constructing the coils and laying out the set so that the stages are all electrically similar, TAPERED TUNING BIG IMPROVEMENT any slight detuning of one or more of the broad Experiments proved that in a single control set stages has no effect on the volume or operation employing straightlinefrequencyormodified ofthereceiver.The proof thatthis theoryis straight line frequency condensers, the set could sound liesinthe wonderful performance of the not be balanced up by tuning in a station and set- Taper -TunedReceiver. Thetuning is sharp Gig. 2. The newer Pilot variable condensers have mounting legs so that they can be secured to the base board of the set.

40 enough so that distant stations can be tuned in through thelocalsin New York City. The three stages of tuned R. F. with the close coupling give it tremendous sensitivity. The high grade audio amplifier gives wonderful tone quality when used with a good speaker, and the single tuning control gives ease of handling. - --"Ze LOSSER METHODS ARE INEFFICIENT There are two practical ways to make a Os tuned R. F. stage tune broadly.One is to insert resistance directly into the tuned circuit; the other is to use close coupling between the primary and secondary coils.The first method is a losser method and materially reducesthesignalstrength. The second method actually increases the signal strength, thepracticallimit being set by conditions of oscillation which develop if the coupling ismade tootight.The latter method of broadening the tuning was adapted sinceit was found that tremendous increase in sen- sitivitycouldbeobtained and by proper design ofcoilsand circuit theoscillation o tendency could be controlled very easily.

GREATER SENSITIVENESS OBTAINED Referring to the circuit diagram you will see that the set employs an untuned antenna circuit with a 2,250 -ohm resistance connected between antenna and ground.The ground goes to the common grid return line so that the proper grid bias is put on this tube. .:-12:5:111315" This is followed by a stage of tuned R. F. amplification which is purposely made rather broad when considered in comparison with NeVY our modern sharply tuned R. F. stages.Os- cillation is controlled by a 5,000 -ohm Elec- trad non -inductive resistance shunted across the secondary of this coil.This resistance is of the proper range to control oscillation perfectly over the entire wavelength range of 55o to zoo meters and at the same time is T high enough to prevent any decrease in signal strength.By havingthiscontrol on the ' front panelitispossibleto keep theset under the oscillation point over the entire range,resultinginremarkablesensitivity. It also acts as an excellent tone control, for the volume can be reduced to a whisper by itsuse. The second and third stages have slightly sharpertuning,andemploythepopular "grid suppressor" means of oscillation control.The detector stage tunes very sharply and extra fine control for DX is obtained by the midget condenser. The phonograph pick-up jackisplaced ahead of the detectortube, just after the gridleak and condenser,sothatthe detector tube is used as an amplifier when the phonograph pick-up is plugged in.This results in more volume. 'Theaudioamplifieremploys two high qualityaudio transformers, anda171-A powertubefeedinginto anoutputfilter circuit. The A. C. line switch controls the A and C power pack unit and the B power pack. COMPLETE OUTFIT IN 2I -IN, CABINET The complete receiver, with A and B power 41

4 RADIO PHYSICS COURSE FOR HIGH-SCHOOL STUDENTS By ALFRED A. UHIRARDI

Chapter I-How Sound Waves Are Changed method is that it makes it possible to have a num- to Electrical Vibration and Back to ber of stations broadcasting at one time and still Sound Waves Again be able to select the program from any one station desired, without interference from any of the 1.BroadcastingSystemOutlined:Radio others.It is this latter feature which makes prac- broadcasting, as we knowitto -day, has forits tical our modern broadcasting system where a object the transmission of sound waves-speech large number of high-powered stations are operat- or music-from central distributing points, calleding at one time inthe same locality, while the broadcast stations, over long distances to the homes listener is able to select any one of them at will of thousands of people. The distance over whichby tuning his receiver. sound can be transmitted directly is very limited. An outline pictdre of the system is shown in

RADIO WAVE

ml)))))))

SOUND WAVE

GROUND 77-7 RADIO BROADCASTING SYSTEM FIG 1 Fig. I.Left, the transmitting station with the receiver at the right.

Even loud whistles or sirens can only be heard Fig. 1.Starting at the left, the man who is speak- overdistancesofa few miles. Anordinary ing sets up sound waves which are converted into speaker's voice cannot be heard intelligiblyover corresponding electrical current impulses by the distances greater than a few hundred feet. microphone M. These current impulses are sent Consequently, some means other than the direct into the transmitting apparatus B where theyare transmission of sound must be employed in modern combined with the wave -carryingcurrent.The radio broadcasting, where programs are to be sent resulting current, flowing in the transmitting aerial over thousands of miles.The great servant of A, produces electric waves which are transmitted man, electricity, providesthis means and isthe inall directions. At the receiving aerial C these main factor in the ever-growing radio industry. waves set up electric currents which flow into Instead of transmittingthe soundor speech the receiving set R. Here they are detected and waves directly, as in the case of one person talk- amplified sufficiently so that when they are sent ing to another across a room, they are converted into the loudspeaker L, they are converted back into corresponding electrical waves by suitableap- into sound waves which are loud enough to be paratus in the broadcasting station.These elec- heard by the listener.This outline of the com- trical waves are then radiated or sent out in all plete broadcasting system should be studiedvery directions from the aerial of the station throughcarefully since a thorough understanding of the the atmosphere for miles around to the receivingmain function of each unit will make the study of aerials of listeners scattered over the entirecoun- the subject interesting and simple. try.The electrical waves striking the aerials of 2.Sound: Sound isthe form of vibrating the receiving stations set up currents which flowmotion in an elasticmedium whichaffects the through the receiving apparatus. The function of auditory organs and produces the Sensation of hear- the receiving set is first to detect and strengthen ing.If we strike an ordinary bell so as to set it or amplify these feeble currents and then to con- vibrating, it will produce a ringing sound.If the vert them back into sound waves similar to the bell is large and the force with which it is struck original sound sent out from the broadcasting sta- is comparatively small, a series of slow vibrations tion. are produced, resulting in a low note.If the bell Thus, you see, electricity can be employed as an is small and it is struck a strong blow,a series intermediate agent, due to the fact that we areof rapid vibrations are set up, resulting in a high able to transmit certain electrical waves over long note. distances very easily through the atmosphere with- When the bell vibrates, it beats the air in front out wires, while itisimpossible to do this with of it and thus compresses it,while at the same sound waves. Another valuable advahtage of this instant the airin back ofthe bodyisrarified. 44 These changes of pressure occur very rapidly andand will be used almost entirely in our discussion. are transmitted from molecule to molecule of air If we could devise apparatus for measuring the in the form of expandingspheres ofincreased very small variations in air pressure caused by a pressures and decreasedpressureswhich travel simple sound wave at any particular point, we outward in alldirections.Any elastic body will would find that these variations could be shown transmit sound. in picture form by the wavy line or curve of Fig. The speed or velocity with which sound waves 2a,whereverticaldistancesrepresentpressure travel depends upon the substances in which they and horizontal distances represent time.The axis are moving. They travel at the rate of 1084 feetor horizontal linerepresents thenormal atmo- per second in air, and about 18,400 feet per second spheric pressure.When the sound wave comes in tempered steel. The velocity of sound in vari-along, the pressure gradually increases to a maxi- ous substances is given in the following table : mum from P to A, then decreases from A to B, Substance Velocity of Sound further to C, then increases again from C to D at in Feet per Second which point the pressure is again the same as at Air at 0°C 1,084 thebeginning. The next wave would continue Ash, along fibre 12,200 similarly along DEFGH. Point A, which is the Brass 8,9oo crest of a wave, represents a point of condensa- Copper 11,300 tion because at this point the air is condensed or Cast -iron 13,200 compressed. Point C, which is at the hollow of a Glass 17,050 wave is a point of rarefication, since at this point Lead 2,150 the air pressure is lessened or rarefied.

6 -DISTANCE WAVE TRAVELS IN 1 SECOND (FOR SOUND WAVES .1084

WAVELENGTH( ALSO ONE CYCLE) A IE

TIME FIG. 2 A 10 WAVES WAVELENGTH

FIG 2 8 6 WAVES -41 I'lWAVELENGTH

FIG.2 C 14 WAVES Fig. 2.Illustrating the terms cycle, wavelength, and frequency.

Mahogany, along fibres 14,500 It must be remembered that the actual pressure Steel, tempered 18,400 variations due to sound are very small. The varia- Water, fresh 4,700 tion due to the weakest sound which a person with Water, salt 4,770 average hearing can Eearisinthe orderof When a person speaks, his vocal cords vibrate.000000015 pounds per square inch. A painfully and set up tiny waves in the air which travel out loud sound would produce a pressure variation of in all directions. When these strike the ear drumabout .015 pounds per square inch.A consider- of the listener, each pulse pushes a little against ation of these figures shows that the human ear is it,causingitto vibrate inward for each pulse, an extremelysensitive anddelicate instrument, outward again during each interval between pulses. since itis able to detect these minute pressures. These vibrations actuate the auditory nerves, pro- One of the most important distinguishing charac-

ducing the sensation of sound to which the brain teristics of a wave is its frequency. Any wave, a responds.The number of these back and forthwater ripple on the smooth surface of a pond, a vibrations of the drum per second is the same as sound wave, or a radio wave, consists of a succes- the number of pulses of the wave that arrive atsion of tiny impulses, moving along one after an- the ear per second. That is,it is the same as theother. Simple waves, produced by a single to-and- frequency of the wave. The higher this frequency, fro vibrating motion, have a succession of regular the shriller this sound seems to the brain. Whatcrests and troughs as shown in Fig. 2a. A com- we really hear then is the frequency, not the length plete wave, or cycle as itis commonly called,is of the wave. Frequency is always a more charac- the part of the wave between one crest and the teristic property of waves than the wave length, orfollowing similarcrest.The lengthofa com- distance one wave travels before the next starts, plete wave is called the wavelength. This may also 45 be defined as the distancethe wave disturbance the wavelength is less.The relation between fre- moves while the vibrating body makes one com- quency and wavelength is : plete vibration or cycle. Velocity of propagation This term is similar to the familiar term "wave-Wavelength = length" assigned to broadcasting stations, with the frequency in cycles per sec. exception that in that case it refers to the radio The Greek letter X (lambda) is used to represent wave instead of the sound wave. thewavelength.Thereforeforsoundinair 4.Frequency:Thenumberofcomplete 1084 waves or cycles that pass a fixed point in onex- second is called the frequency. To show the rela- frequency in cycles per sec. tion betwen these familiar terms more clearly, let 5.Pitch: When discussing sound, frequency us refer again to Fig. 2, a.Suppose we have an refers to the pitch of the sound.Low pitched instrument atpoint P whichisproducing the sounds, like those of the bass violin, are low in sound wave shown, having afrequencyof10 frequency; high pitched sounds, like those of a cycles, or complete waves, per second. Then in one flute, are high in frequency.The normal human second the disturbance will travel 1084 feet-this ear is able to detect sounds of frequencies as low being the velocity of sound waves in air-takingas 16 and as high as 20,000 cycles per second. The it to point Q.In the space between P and Q there frequencies ofthe sound waves created by the are 10 complete waves, because10 waves have human voice during the course of ordinary con- been produced during the second.Therefore, the versation average 800 cycles. The actual limits of

FUNDAMENTAL

WAVE FORM OF LETTER"AFIG.3D Fig. 3. Diagrama tic representations of electric waves. frequency of the sound is 10 cycles per second.- audibility depend of course on the sensitiveness of Frequency is always expressed as the number of the hearing facilities of the individual as well as cycles per second.The wavelength will be equal the intensity of the sounds themselves. to the total distance PQ divided by the number of 6.Harmonics:Heretoforewehavecon- waves between P and Q, or wavelength=1084÷ sidered the most simple kinds of sound waves, that 10=108.4 ft. is,the "pure," fundamental, or sine -wave sound Now suppose the instrument at P is made to This type of sound consists of but one vibration produce a sound wave of lower pitch, having a fre- frequency and is very rare. A pure sound seems quency of 6 cycles per second. This wave is shownvery flat when heard by the ear and has no mu- in Fig. 2,b.Then in one second the disturbance sical value. travels1084 feet as before, but since there are When we hear a musical sound, we have no dif- only six waves produced during this time interval, ficulty in recognizing the particular kind ofin- the length of each individual wave must be longerstrument that produces it. The sound of the violin, than in the previous case. the piano, etc., each has its own peculiarities. The In Fig 2,c, the instrument is producing a wave characteristics which enable us to assign a sound of higher pitch, having a frequency of 14 cyclesto its source are called the quality or timbre of per second.In this case the wavelength is1084-1-- the tone.The physical explanation of timbre is 14=77.4 feet.Itis evident from this illustration that most sounding bodies vibrate not only as a that as the frequency is decreased, the wavelengthwhole, but also in various parts as does the string becomes greater, and as the frequency is increased of a piano. The quality of a note is determined 46 by the presence of tones of higher pitch, calledsame wave A with its secona, third, andtourth harmonics, whose frequencies are multiples of theharmonics. fundamental or lowest tone. To take a concrete case, The sound waves created during the course of let us consider the middle C string of a piano, human speech are very interesting due to their Fig. 4. When this isset into vibration by strik-wide variation of form.In Fig. 3d, the waves ing the key, the whole string vibrates as a unit,form of a common vowel is shown by the same producing vibrations of a fundamental frequencygraphical representation employed in previousil- of 256 cycles per second.At the same time, the lustrations. string also vibrates in parts, producing harmonic 7.Musical Instruments: The sounds created vibrations whose frequencies are exact multiples by musical instruments are practically always com- of the fundamental.Thatis,itwill produce aplicated and contain many harmonics. The violin second harmonic whose frequencyis 256x2=512 produces a very strong third harmonic, while some vibrations, or cycles, per second, and possibly aof the notes produced by a flute are perhaps the fourth harmonic of 1024 cycles.Thus while thepurest of any sounds that are generated by musical fundamental passes through one cycle, a harmonic instruments. ea.efate,t

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Courtesy of National Bureau for Advancement of Music. Fig. 4. The complete piano key -board, showing the frequencies of the notes. passes through a number of cycles, depending upon 8.Sound Sensation: The sensation of sound what harmonic itis. as relayed to thehuman brainby the auditory Higher harmonics than the fourth are seldom en- nerve presents an interesting and important study. countered in ordinary practice.Consequently the Two sounds, which have the same physical am- single middle C piano string is really producing plitude but which differ in frequency, do not sound four sound waves of different frequencies at one equally loud.It requires a much greater ampli- time. These four waves do not exist separately in tude in low than in high tones to produce equal the air,but combine to form a resultant wave loudness sensation.-Notice the difference in ampli- whichisdifferent from any ofits components. tude of vibration, between one of the high note This is the wave which affects our ear. strings of a piano and one of the low note strings, To show how simple waves of differingfre- even though the sound from the two is equally quencies can combine to produce a resultant wave loud. different from each of them, let A inFig.3a, The energy of the vibration is proportional to represents one cycle of a fundamental sound wave. the square of the frequency, the amplitude remain- The horizontal distances, called abscissa, represent ingconstant.That is,if we had three sounds time,andtheverticaldistancesrepresentair having equal amplitudes but frequencies of 20, 40 pressure.Next, B, the wave of twicethe fre- and 6o cycles respectively the physical energies quency,isthesecondharmonicwave, emitted would be in the ratio ofI,4, and 9.However, simultaneously with A. The resultant wave formthese energy ratios do not exactly represent the is then represented by C.The wave C is notloudness of the sounds as they would be heard symmetrical and does not resemble either ofits by the ear because, for equal energies, the human component waves A or B.Also, notice that itsear hears sounds of very high frequency louder frequency is the same as that of the fundamental.than those of very low frequency, and sounds of Fig. 3b, shows the resultant wave C produced by mid or normal frequency better than either. Thus the combination of the same fundamental wave A, it is evident that a loudspeaker emitting low sounds with itsthird harmonic B.Fig.3c, shows the from an organ selection is really handling a much resultant wave produced by the combination of the greater amount of energy than when emitting the 47 higher notes of a violin selection, even though the the gamma rays which are the shortest known at (WOsound equally loud. the present time. Above theseis unexplored re- Fig. 4 shows the keyboard of a modern piano.gion of waves still shorter than the gamma rays. The lowest note on the keyboard has 27 vibrations The wave series is shown in Fig. 5, with the ap- per second, and the highest has 4096, on the physi-proximate frequency limitsfor each band.The cal scale. Middle C represents a frequency of 256divisions of radio, heat, light, and ultra -violet light cycles. The lowest C has 32 cycles. The C abovewaves are made merely for convenience.They this is an octave of it, and has a frequency of 64really all belong to one series, since they are all cycles.The octave of a frequency is a frequency electro-magnetic waves which travel through space twice as large. For instance, low C has a frequency at the rate of 300,000,000 meters or 186,000 miles of 32, the second octave a frequency of 64, theper second, and differ from each other physically third octave 128, the fourth octave, middle C, 256,only in the frequency of their vibration or wave the fifth octave 512, and so on. length.These electric waves are of an entirely The practical range of frequencies, with the at- different nature than sound waves, since waves are tendant harmonics, employed in the playing of a notelectrical and consist of actual to and fro selection on a piano ranges from about 32 to 600omotions of the airparticles.The speed of the cycles per second. This allows for the lower and higher keys which are seldom used.This is ap- 300,000, 000, 000,000,000 K. C proximately the range of sound frequencies which GAMMA RAYS FROM RADIUM are broadcast over the radio. Among the various 30, 000,000,000,000, 000 K. C familiar musical instruments the bass violin goes down to the lowest frequency of 4o cycles and the piccolo and piano employ frequencies as high X- RAYS as 096 cycles. NOTE I K.0= 1,000 CYCLES 9.Radio, Heat, and Light Waves:If we 10,000,000,000,000 heat a piece of iron or steel, such as a hack saw ULTRA -VIOLET LIGHT 759, 000,000 000 K.C. blade, in a gas flame, it gets hot.Continuing the LIGHT WAVES heating, causes the blade to change color first turn- 387, 000,000,000117C ing a dull red, then a bright "cherry red" to slightly orange and finally white hot.In this simple HEAT OR INFRA -RED RAYS experiment aseriesof waves ofdifferentfre- quencies are produced, giving rise to the different effects noted. When heat is applied to the blade, 300, 000,000 K.0 itsets the molecules of the iron into vibration, producing heat waves which are radiated inall directions. As more heat is applied, the molecules SHORT RADIO WAVES vibrate faster andfaster, causingthe radiated AND RADIO HEAT WAVES waves to follow one another more closely,i.e., the frequency is increased and the wavelength decreased. These waves coming off at higher and higher 13,000 K. C frequencies produce the sensation of light and of USUAL RADIO WAVES changing color ranging from dull red, for the lowest frequency, to cherry red, orange, and finally 30 K.0 bright yellow at the highest frequency. Just as the pitch of a sound is determined by the frequency of AUDIO FREQUENCY VIBRATIONS vibration of the body which produced it, so the color of lightisdetermined by the frequency of the vibration producing it.The color red is produced IS CYCLES by vibrations of lower frequency than those of the color yellow. Other colors are produced by vibra- WAVE SERIES FIG 5 tions whose frequencies are between and above these extremes in the order red, orange, yellow, green, Fig. 5. frequency greatly alters the aspect of blue,violet. vibrations. So far we have discussed sound waves produced by mechanical vibration of the air, having fre-electric waves is so great that they can be con- quencies between 16 and20,000cycles per second, sidered to move between any two points practically and in our experiment we produced heat waves instantaneously. The difference in frequency gives and light waves.These three types form onlythe various kinds of electric waves the properties a small portion of all the classes of waves known which are peculiar to them.Thus, radio waves to science today. The entire series is divided intotravel with perfect ease through practicallyall bands for convenience.Starting with low fre- substances, while light and heat waves do not. quencies we have the sound waves consisting of Just exactly what these radio waves are, and how simple mechanical between 16 and 30,000 cycles they travel, we do not know-any more than we per sec. Above these we have the waves employed know what electricity is.But just as with the case in radio, ranging from 30,000 to 3,000,000 cycles ofelectricity, we know how they behave under per second. Then come the short radio waves and various conditions, and we are finding out more radio heat waves recently discovered by Dr. E. H. and more about controlling them for our own use. Nichols, comprising a range from 3,000,000 cycles The question of how they travelisbeing in- to 300,000,000,000 cycles. Above these lie the heatvestigated by many of our most brilliant scientific waves, then the ordinary light waves, and ultra- men and, it is safe to say that the time is not far violet light waves or rays. These latter rays are off when we will know as much about the be- given off by X-ray tubes, the sun, and the electric havior of radio waves as we do now about simple arc.Following these we have the X-rays and then electric currents.Itis these radio waves which 48 make modern radio broadcasting possible, and their electrons passing through a conauctor intile production and use in broadcasting stations will be opposite direction to which we usually ascribe treated in a later chapter. to the electric current.Substances in which thelooseelectrons move aroundeasilyare called good conductors. Among these are gold, Chapter 2-About Electric Currents and Things silver, copper, brass, and iron.Substances in Which Happen in Electrical Circuits which there are no free electrons or very few. THE study of radio broadcasting necessarily are called insulators.These include porcelain includes a thorough understanding of themica, and dry air. action of electric currents since the trans- 12.Voltage: We have seen that the move- mitting and receiving stations deal entirely with ment of electrons along a conductor constitutes electricity.While itis impossible to present a anelectric current. However, if we take a complete electrical course here, an attempt will piece of copper wire and hold itin our hand. be made to give enough of the fundamentals to noelectriccurrentflows,sincethereisno enable the average person to grasp the ma- force or tendency to make the electrons move. terialinthe succeeding chapters and toact We must apply some external force to the wire, as a review for others. called voltage, to produce the current.If we 10.Current Flow:The flow ofelectricity take a strip of copper wire and one of zinc, partly immersed in a solution of dilute sulphuric acid, and connect them with a wire, AB-Fig. 6, chemical action will take place and electrons will be removed from the copper and given to the zinc.This results in the copper plate having less than its normal number of electrons and the zinc plate having more than its number. Theresultisanunbalancingofthe charges, and electrons will flow from B through FIG 6 the wire to A tending to equalize the charges again. This constitutes the flow of an elec- Fig. 6.The elements of an electric battery. triccurrentand we saythecurrentflows through the wire from A to B. We have here through a wire isalways a puzzling thing toa simple electric battery where A is the posi- the novice, possibly because the action isnot tive terminal and B isthe negative terminal. directly visible to the naked eye.We reallyThe battery serves the purpose of causing a do not know what electricity is, any more than continuousflowaslongaschemicalaction continuesatthezincthatis,aslong asa we know what gravity or magnetism is.But voltageispresent. like many other things, we can learn to use it 13. Current: An electric current consists of and controlit by studying its various pecu-a flow of electrons.If we measure the num- liarities.Many theories have been advanced byber of electrons flowing past a given point in prominent scientists to explain the reasons for a circuit in a unit of time, one second, we have the observed behavior of electric currents. Thea measure of the current.The unit of current one most commonly accepted at present is themeasurement is the ampere.Current isusu- electron theory. ally measured by means of an instrument called 11.Electron Theory:It is generally known that all matter, such as the paper upon which an ammeter. this is printed, consists of small particles called It must be remembered that a current of molecules. These molecules may be further electricity cannot flow ina conductor unless subdivided into what we call atoms.Thus a grain of ordinary table salt may be considered R. as consisting of many tiny particles, molecules, Rz R3 of salt held together by some force of attrac- tion. These molecules cannot be divided into smaller molecules of salt, but each one can be divided into atoms of different chemical substances.One molecule of salt can be split up into an atom of sodium and one of chlorine. Each atom in turn is believed to be made up of a center nucleus having a positive charge SERIES CIRCUIT RIG. 7 of electricity, around which revolves a number ofsmallnegativechargescalledelectrons. Fig. 7. How resistances arc wired in series. Under normal conditions, the positive charge of the nucleus is equal to the sum of the nega- thereissome force orpotential appliedtoit. tive charges around it, so that a state of bal-Just as no water can flow in a pipe unless there anceexists. Atomsofdifferentsubstances is some pressure applied. differ merely in the number of negative elec- 14. Resistance: When current flows through trons surrounding the nucleus. aconductor,itencounters oppositionorre- At least one of these electronsis loose orsistance, just as water flowing through a pipe free to circulate around among itsneighbors. encounters resistance due tofriction between When an electriccurrentflows, what really it and the walls of the pipe.The resistance happens is that these free electrons move along tocurrent flow depends onthematerialof the length of the wire, the movement giving which the conductor is made.Silver has the riseto the various external effects which we least resistance, annealed copper isnext low- associate with an electric current.Thus an est.The resistance also depends on the length, electriccurrentismerelyastreamoffree a conductor three feet long having three times 49 the resistance of one thatisone foot long, From these examples it will be seen that if other things being equal. any two of the above expressions either poten- Resistanceisalso inversely proportional totial, resistance, or current are known, the re- the cross sectional aera of the conductor.Con- maining one can be found by applying Ohm's ductors of large diameter have less resistance Law. than conductors of small diameter.The re- 16.Series Circuits:In order for current to sistance of most conductors also increaseas flow in any conductor, the circuit must be com- the temperature is increased. plete.In actual electrical circuits, parts are IS.Ohm's Law: We have now considered connected in either of two ways, or in a com- thethree fundamental thingsaboutelectric bination of the two. When they are connected currents-first the flow of electrons, constitut- in such a way that the total current of the cir- ing an electric current ;second, the potentialcuit flows through all of them, they are said or force which causes the current flow; third, the resistance or natural opposition which every R z conductor offers to the flow of current through it. 'Thereisa fundamental relationship between these threefactors, known as Ohm's Law. If current in amperes is denoted by I, potential, or pressure, is denoted by E, and resistance by the letter R, then Ohm's Law states that the current in amperes isequal to the potential in volts divided by the resistance in ohms; E that is I = - (2) SERIES PARALLEL CIRCUIT FIG. 9 R In order to fix this relation more clearly in Fig. 9.These resistances are wired in series - mind, let us consider a few examples dealing parallel. with electric circuits. (a) The filament of a vacuum tube has a to be in series.If two or more resistances are resistance of 24 ohms. What current will flowconnected in series as in Fig. 7, the total re- throughit when connected across a 6 volt sistance isequal to the sum of the separate storage battery? resistances. E 6 In Fig. 7 the total resistance is : Ans.I = - = - = 0.25 Ampere. R = R.: + R2 + (3) R 24 If 123 = 2 ohms, R2 = 5 ohms, R3 = 3 ohms, (b) What potential must be applied across and E = 20 volts, then the total resistance is a resistance of 24 ohms in order to send a cur- R = 2 + 5 + 3 = 10 ohms, and the current flow- rent of 0.25 amperes through it? ing in the circuit is : E 20 Ri I = - = - = 2 amperes. R 10 17. Parallel Circuits: When parts of a circuit are connected so that the total current is divided between them, as in Fig. 8, they are said to be in parallel with each other.When resistances

FILAMENT

PARALLEL CIRCUIT FIG 10 FIG 8 Fig. to. A rheostat in series with a tube. Fig. 8.Resistances connected in parallel. are connected in parallel, the totalresistance E is expressed by the formula: Ans. I=-orE=IxR 1 R R = (4) Therefore E = 0.25 x 24 = 6 volts. 1 1 1 (c) A 6 volt storage batteryisconnected -+ -+ - across a resistance and the current flowingis R1 R2 R3 found to be 0.25 amperes.What is the value Taking the same value of resistance as in of resistance? the previous example, the total resistance R E E of the three resistances connected in parallel is: Ans.I = - or R = - 1 R R = - 0.99 ohms. 6 1 1 1 Therefore R = - = 24 ohms -+-+- 0.25 2 5 3 50 From this it can be seen that connecting the picture of resistance may perhaps be obtained resistancesinparallellowersthetotalre- by the following consideration. sistance, since more paths are provided for the If we take a piece of wire of any definite current flow. diameter, length and material, it has a certain 18. Series-Parallel Circuits:If the parts of value of resistance.If we make the wire twice the circuits are connected so that some of them as long, its resistance will be twice as much, are in series and some are in parallel with each if we decrease its length the resistance will be other, then the total resistance can be found decreased. Now if we keep its length constant most easily by reducing the entire circuit to an but increase the diameter, or cross sectional equivalent series or parallel circuit, dependingarea, the resistance will decrease;if we de- upon the combination. Thus in Fig. 9 we have crease the diameter, resistance increases. R2, R3 and R. connected in parallel and this Kinds of Current:Fundamentally the elec- combination in series with IL and Rs is con- tricity itself is always the same in any current nected across the 6 -volt battery.To find the no matter whether itis produced by chemical total resistance of the circuit first find the total action in a battery, by a generator, or any other resistance of R2, Rs, and R,, and then consider way.Electricity, as we deal with it in our lives, the circuit as consisting of this resistance con- however, is usually in the form of one of three nected in series with R1 and R5. types of electric currents.When the current Let 12. = 5 ohms, Ra = 2 ohms, R. = 5 ohms, flows in but one direction through a circuit it R. = 10 ohms, Rs = 6 ohms. is known as direct current, commonly abbre- The total resistance of R2, R3, and RI, is then viated D. C.This is the kind of current sup - s

N MAGNETIC WHIRLS 11

I(111 1\\ / FIG 12 Fig. 12. A cycle of A. C. current. Fig.13.Magnetic lines of force FIG 13 A FIG 13C around conductors. FIG13 B

1 plied by all forms of batteries, and flows from R = - 1.25 ohms. the positive terminal of the battery, through 1 1 1 the circuitto the negative terminal.If the -+-+- current flows in one direction, but is pulsating, 2 5 10 that is, increases and decreases in strength, it The total resistance of the complete circuit is : is known as pulsating current.If the current R = 125 + R1 + R5 = 125 + 5 + 6 = 12.25 ohms. not only varies in strength but also changes its The total current flowing through the cir- direction of flow many times a seconditis cuit is called an alternating current, commonly ab- E 6 breviated A. C.This difference in the way in I = - = - = 0.49 ampere. which the current flows through a conductor R 12.25 givesrisetovariouseffects, whichwill be 19.Rheostats: Asstatedpreviouslyre- studied later.(To be continued.) sistance in a circuit opposes the flow of elec- triccurrent. Thereisa certain amount of resistance in every electric circuit due to the THE TAPER -TUNED RECEIVER connecting wires,etc. In some cases extra (Continued from page 43) resistance is added intentionally to reduce the current flowing.An example of thisis seen 3o enameled wire.The first coil contains 65 turns in the use of rheostats, or adjustable resistances, in the primary; the second contains 6o turns; the inthe filamentcircuitsofordinary vacuum third contains 5o turns; and the last is the regular tubes in radio receiving sets.Here the current coil with a 25 turn primary.The primary coils from a storage battery flows through the fila- are all wound so they start t/t6 inch frbm the ment of the tube and heats it to incandescence. filament end of the secondary.The secondary coils The amount of current flowing is regulated by are left untouched.Be sure to windthe wire connecting a variable resistance R inseries tightly on the forms and connect the ends cor- with the filament, Fig. 10. rectly. When the coils are finished the top end of Resistances are made in a variety of forms, the secondary should go to grid and bottom end depending upon their particular use.Low re- to filament return. The top end of the primary sistances for radio work are usually made of goes to B+ and the bottom end to P. The primary wire wound on some suitable insulating ma- is wound in the same direction as the primary. terial.Very high resistances of several thou- When wiring the set, the location of all wires sand ohms or more are made either of impreg- in the input circuit of the R. F. and detector tubes nated paper, or coated with carbon particles, should be kept short and as nearly similar for each or consist of a glass thread coated with a very stage as possible. The plate leads should also be thinlayerofmetal. Other adjustable high short. The two wires going to the oscillation con- resistances make use of carbon or graphite discs trol on thefront panel should be located very or powder which may hepressed together carefullyto preventfeedback fromtheother tightly to decreaseresistance, or allowed to stages. The coils may be placed as close as 3% separate to increase resistance. A clear mental ins. between centers without interference.

51 Fig.1.An ideal design for an all -electric broadcast receiver. ALL -ELECTRIC AIR HOUND IS MARVEL OF RADIO DESIGNERS' SKILL ByIRAN 1: T. StLiAvAN people seem to have the idea thatrealize at once the skill and cleverness which is itis now much cheaper to buy manufac- built into the design of the receiver.It is ex- ANYMtured receivers than to build one or have tremely sharp, although itcan be adjusted to one built by a custom set builder. give broad tuning.Out in the country, or when It may seem that such should be the case thisyou are fishing for DX late at night, too much season, but itis not.Radio Design is just asselectivity is a disadvantage.As soon as you much interested in showing new types of all -learn how to handle the two adjustments marked electric receivers to be built at the lowest pos-Super -Charger and Volume, you will be able to sible prices, as the set manufacturers, and as far asregulate the degree of selectivity as well as the bringing cost down, Radio Design seems to haverange of volume. been more successful. The set is absolutely free of hum, all the tricks Witness the Air Hound all -electric receiver. ofoperation have been eliminated, and the de- In tests which we have made, this set has donesign is so thoroughly substantial that, once the just as much and has done it just as well as veryoutfit is installed, it should function without any much more expensive receivers. In fact, in someservice whatever for an indefinite length of time. ways, itis a little better than other types. The filament lighting transformer gives the As for cost, the complete kit of parts comescorrect voltage for the tubes specified, and does to less than $45.00. Add a simple table cabinet,not burn out the tubes as has been the case and you will have as fine an outfit as is sold upwith so many manufactured receivers.With to $too.00. the tubes specified, the life should be from 2000 Moreover, you must remember this about cus-to 4000 hours.The radio frequency circuitis tom built receivers-each part is a finished piece highly efficient,being equipped with an R.F. of merchandise, while manufactured receiversSuper -Charger which serves for local reception are made up very crudely and, generally, designedas a neutralizer, and on DX makes it possible so that several parts can he hidden under eachto bring in stations at full loud speaker volume little box inside the cabinet. which otherwise would be heard only with the If anything goes wrong, itis expensive and telephones.In the audio end, the new moisture- takes quite alittle while to have the set re-proof transformers are employed with an out- paired. On a custom built receiver, each part isput filter.This gives excellent quality in the an individual unit which can be removed andamplifier circuit, while thefilter protects the replaced at once. loud speaker .from being burned out by exces- This is an important matter to the set owner.sive current and further improves the repro- Usually, if a set is going to go wrong, itis theduction. The Air Hound, mounted in a suitable morning before some important event is to becabinet, measures up to the latest standards of broadcast.Repairingamanufacturedsetis appearance.The vernier tuning dials have at- then a matter of days. On the other hand, atractive bronze plates, and are lighted indirectly custom built receiver can be fixed up in perhaps by small bulbs which shine through the cellu- half an hour. loid scales.With two walnut Bakelite knobs Again, a standard design of receiver, built byat the center, to match the front panel, the Air an established custom set builder, does not be-Hound will please the most fastidious customers. come an orphan, as is the case with so many AIR HOUND CIRCUIT DATA manufactured receivers built by companies that The Air Hound uses three CY 327 tubes for seldom stay in business more than a year. Con- R.F., detector, and first audio with a CX 371-A sequently, it is always possible to get competentas a power amplifier in the last stage.This not service for a custom builtoutfit, and repair only simplifies the wiring but positively assures parts are always available. freedom from all A.C. hum. With the No. 386 AIR HOUND IS A LABORATORY DEVELOPMENT filament transformer these tubes will giveas long life or longer than the CX 326 tubes. When you tune in on the Air Hound you will The filament supply circuit, you will see,is 52 Fig. 2. A special feature of this set is the moisture -proof transformersand filter. different from that specified for the standardtenna and ground across the primary alone and Pilot No. 4 A and C power pack.The reason tuning condenser across both coils.We have is that a special arrangement must be employed found this the most satisfactory way, although to give the correct biases on the three 327 tubes. you canuse inductivecoupling, putting the Cunningham specifies 9 volts on the 327, when tuning condenser across the secondary only,if used as a detector, with 90 volts on the plate,you desire. and, for R.F. and A.F. ainplication 9 volts bias The R.F. Super -Charger circuit in the R.F. with 135 volts on the plates. stage comprises a .002 mfd. condenser with a This works out very nicely in the Air Hound Resistograd. The center terminal of the Resisto- because it is possible to use one biasing resistor grad is threaded into one terminal of the fixed in the center tap lead of the 2.5 volt winding condenser, and a lead brought off at this point of the filament transformer, since the bias values for connection to the plate.The purpose of this of all three tubes are the same. adjustmentisto bring the R.F. tube to the A separate resistance of 2250 ohms inthe point of maximum sensitiveness for DX recep- center tap lead ofthe5 -volt winding puts the tion, or to neutralize it for local reception. bias of 45 volts on the grid of the 371-A in the The detectorcircuitisthe conventional3 - last amplifying stage. circuittuner arrangement, and has an R.F. You will notice that, although separate pri- choke in the plate circuit to keep high frequency mary and secondary windings arefurnished on the antenna coil, currents out of the amplifier. the primary and secondary The audio amplifier uses the new moisture- are connected together inseries, with the an -proof transformers, with an output filter,con -

Fig. 3. This set is complete in itself except for the No.5 B power pack.

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0 NS

s3eni.1N3vAri 'O'v 210A 95E 6N ONWell t13001 Mena. Jolla a

ZZYV .%800 11 0

-u U a

Fig. 4.The parts ai . al ranged in this diagram inthe same rc.'ative positions as they arc mounted on the finished set. raining a heavy choke coil and by-pass con- maximum signal strength on local, or fish for denser, in a case which matches the appearance distant stations.For near -by stations, turn the of the A.F. transformer. Resistograd almost all the way in, and put the tickler coil of the 3 -circuit tuner in a position for HOW THE AIR HOUND IS OPERATED maximum regeneration. Thiswillkeepthe Once you learn how to tune the Air Hound, R.F. tube from oscillating, and permit you to you will find it very easy to get adjustments for get the volume adjusted with the tickler.The 54 Fig. 5.For an all -electric set, this wiring is unusually easy to put on. left hand variable condenser willtulle alittle 2-Pilot No. 1617 .00035 mfd. tuning condensers. lower on the scale than the right hand con- 1-Pilot No. 350 Resistograd with 1255 W knob. denser, unless you use inductive coupling. 1-Pilot No. 42 toggle switch. When you want long distance reception, turn 1-Pilot No. 54 .002 mfd. fixed condenser. the Resistograd out a little bit, and it will throw I-Pilot No. 51 M .00025. mfd. grid condenser. the circuit into oscillation so that you can pick 1-Pilot No. 58 .006 mfd. fixed condenser. up squeals.Then by balancing the adjustment 1-Pilot No. 8o11. mfd. by-pass condenser. of the Resistograd against the setting of the I-Pilot No. 386 filament transformer. tickler work the controls togetheruntil you 2-Pilot No. 951 225o ohm wire wound grid bias biing the station up to full volume.You will resistors. have to readjust the tuning slightly, at the same2-Pilot No. 35 in. Bakelite brackets. time. 2-Pilot No. 391 audio transformers. Until you learn how to handle the controls, t-Pilot No. 392 audio output filter. the set may make some squeals but once you3-Pilot No. 215 UY sub -panel sockets. understand how to set the adjustments, you will 1-Pilot No. 214 UX sub -panel socket. have no 'trouble from this. I-Pilot No. 754 I meg. grid leak. 12 Pilot engraved Bakelite binding posts. ASSEMBLING THE SET Mount all the parts on the front panel and do Following is the complete list of parts for the as much wiring as you can.In the past there Air Hound: has been some misunderstanding about the two contacts, shown in Fig. 4, on the No. 1282 dials. 1-7 by 18 by 3/16 ins. Walnut Micarta front These are contacts for the electric bulb which panel. illuminates the dial. You will see that they are 1-7 by 17 by 3/16 ins. Micarta sub -panel. connected to the 5 volt A.C. supply running to I-Twin-Coupler No. 123 R. F. coil. the socket of the 371-A tube. 1-Twin-Coupler No. 121 three circuit tuner. When you mount the R.F.Super -Charger, 1-Twin-Coupler No. 13o R. F. choke. thread the rear terminal of the Resistograd into 2-Pilot No. 1282 illuminated dials. the .002 mfd. condenser, and then mount the 2-No. L-43 5 volt lamp for illuminated dials. Resistograd on the front panel. Check the ar- Fig. 6.Compare this illustration with the picture wiring diagram.

55 Fig. 7. The Air Hound has ii distinctly commercial aptearance about its compact design. rangements of the parts as shown in the illus- to melt and run freely.Use No. 18 tinned cop- trationsagainst your assembly work as you per wire.Cut this in lengths about 20 ft. long proceed. and stretch the wire about 2 ft.Then, laying Fig. 6 shows the method of obtaining connec-the wire down on the floor carefully, cut it into tions for the two A.F. transformers and filter. 18 -in. lengths.That will give you straight pieces Double lugs are slipped over the binding postswhich can be bent neatly into the necessary and on to the screws which hold the trans- shapes. formers to the base panel. Then all connections Where insulationis required, use small Em- are made to the mounting screws underneathpire tubing. Do not use wire with cotton insula- the panel.In this way, no wires need to be tion,forthatcollects moistureinthe damp brought up to the top of the base panel. weather and makes short circuits for the R.F Itis recommended that you use the official currents. panel patterns in laying out the set, so that the parts willfit properly and all errors avoided. These panel patterns are full size, and can be NEW CONDENSER FEATURES applied directly to the Micarta panels and the This season the Pilot variable condensers, isoo centers of the holes marked through with aand 1600 series, are made with shafts which center punch. can be removed without disturbing the plates. Do not use soldering paste.All lugs on Pilot The condensers can be mounted at either end, equipment are silver plated.Consequently they givingclockwiseoranti -clockwiserotation. take rosin core solder very easily.Just watch Mounting feet are provided, so that they can out that you apply heat enough for the solder be mounted on the sub panel.

Fig. 8. The new A.F. transformers and filter are contained in polished Bakelite cases 56 HOW TO MAKE ANY BROADCAST SET TUNE TO SHORT WAVES By E.MANUEL IN foreign countries the short wave adapter time to give your broadcast set a world-wide has suddenly become the most important receiving range.The few parts for the Con- adjunct to broadcast receivers. Where ordi- verter can be assembled in two or three hours. nary broadcast sets can bring in only a fewFollowing is a shopping listthat shows what local stations, in some places not more than two you need: or three, the short wave adapter makes any Micarta panel 9 x 7 x 3/16 ins. city a neighbor to countries thousands of miles I Micarta sub panel 8 x 7 x 3/16 ins. away. I No. 1282-L Pilot illuminated dial. For example, such stations at WGY, KDKA 1 No. 92o Pilot 20 -ohm rheostat. and WRNY can be picked up readily, on their 2 No. 1252-W Pilot Bakelite knobs short wave transmitters, from Buenos Aires, 2 No. J-23 Pilot midget condensers. 6,000 miles away; Rio de Janeiro, nearly 5,000 No. 206 Pilot UY socket. miles away ;the Phillipine Islands,1 r,000 miles No. 212 Pilot UX shock -proof socket. distant,and Australia,half -way aroundthe No. 50-D Pilot .000i mfd. grid condenser. world. I No. 761 Pilot Io-meg. grid leak. In the United States, the short wave adapter No. 1608 Pilot .00014 nifd. condenser. makes it possible to receive transmitters in for- 2 No. 35 Pilotr -in. brackets. eign countries equally distant. Iset of5 Twin -Coupler plug-incoils. There are Pacific Coast stations which can be 6 Pilot engraved Bakelite binding posts. heard in New York, for they send their regular programs of short wave and broadcast trans- CONSTRUCTION NOTES mitters simultaneously.Similarly, the eastern The two panels can be cut from a piece of stations can be heard on thePacificcoast. Micarta 7 x 18 x 3/16 in.There are varieties WRNY, for example, sends all programs on of finishes, so that you can choose the sort of two transmitters. panel material that will match the set you have Of course, for the very finest short wave re- at present. ception and the maximum efficiency the stand- You will notice that two No. 1252-W knobs ard Wasp circuit is recommended in preferenceare in the parts list. These are walnut finished to the Copverter, but exceedingly fine results Bakelite, to match the knob on the illuminated can be obtained with the Converter on practi-dial. One controls the rheostat, while the other cally any type of receiver, whether it is operatedis for the midget condenser on the right hand from batteries or A.C. supply. side of the front panel. However, the one tube in the Converter must Black Bakelite knobs are furnished with the have a battery supply for the filament, becauserheostat and midget condenser, but by substi- if it is run from A.C. there will be an objection-tuting the walnut knobs you can make the front able hum.If you use a 201-A tube in the Con- panel more attractive in appearance. verter, that will require four dry cells to run The front panel carries the rheostat, tuning the filament. A 199 can be operated for longercondenser, and one J-23 midget regeneration time on three dry cells, but the 199 is not quitecontrol. On the base panel are the shock -proof as good for broadcast receiving.This filament tube socket, plug-in coil socket, J-23 condenser batteryisonly neededif you have an A.C. forregenerationcontrolatbroadcast wave operated receiver.If your broadcast set is bat- lengths, grid leak, and binding posts.Under the tery operated, then the filament of the tube in sub -panel are the grid condenser, antenna series, the Converter can be run from your 6 -volt variable condenser, and R.F. choke. storage .battery. How TO ASSEMBLE THE CONVERTER WORLD-WIDE RANGE AT Low COST Mount the illuminated dial on the front panel It will cost you about $1o.00 and an- evening's at the center and up high enough so that the

Fig.1. This little Verter. At the left unit, added to any is a rheostat, and broadcast receiver, at the right, a mid- willbringinall get condenser which the short wave sta- regulatesthere- tions. None of the generation. Diff er- tuning controls on ent coilsare thesetareused. plugged in accord- All tuning is done ingtothe wave- with the illuminated lengthrangede- dialonthecon- sired.

57 Figs. 2 and 3.Top and bottom views showing details of the converter. bottom of the mounting bracket is Y8 in. abovefasten them with nuts underneath.Note also the bottom of the front panel.The centers forthat a %-in. hole must be made to accommodate the rheostat and midget condenser areiin. the nut on the end of the shaft. from the edge and 2 in. up from the bottom of The coil socket must be mounted in such a the front panel. way that the C and F posts are toward the The holes for fastening are Bakelite brackets front, and the tube socket with the F and 1' on the front panel are in. from the edge. toward the front. The lower hole is Y8 in. up from the bottom of the front panel, and the upper hole is I% in. from the bottom of the panel. When the parts CONNECTING AND OPERATING THE CONVERTER have been put together, fasten the base panel to the brackets so that the rear of the base Schematic and picture wiring diagrams are panel extends out beyond the brackets Y8in. clear and can be followed readily.The only Space the tube socket, coil socket, and midget catchisthat the lower contact on the lamp condenser along a line DA ins. from the front of socket of the vernier dial must be connected to the base panel.The grid condenser and grid leakthe front F post on the tube socket, and the go directly behind the two sockets and betweenupper lamp socket terminal soldered directly to them.The six binding posts and the antennathe frame of the dial. series condenser are lined up 34 in. from the To attach the Converter to your broadcast rear of the sub panel. The R.F. choke is under-receiver, connect the flexible lead, shown at the neath the panel and behind the J-23 condenser.right in Fig.6,to a brass pin which you can There is a trick to mounting the J-23 con-insert in the plate contact hole of the detector denser.The two screws which hold the fixedsocket in your set.If there are any R.F. tubes plates are used for mounting. Make two holesin the set, remove them as well as the detector. for these screws through the base panel and Connect four dry cellsin series across' A+

Under the base panel, at Fig. 4.The wiring of the the rear, is the little an- converter is only a matter tennaseriescondenser of putting on a dozen which must be adjusted leads. Each joint must be until the circuits oscillate solderedperfectly,for smoothly.To the left is shortwaves-highfre- the R. F. choke, and on quencies-have a way of the rightthe grid con- doing strange things that denser.This is held by do not happen in ordin- the samescrews which arybroadcastreceivers. passthroughthegrid leak clips.

58 OFTO DLATCOriMO-ETETSttE T IN BROADCAST RECEIVER, F CHOKE

0001,4F

.000010 ME.

20 DIAL

SHORT ANT. RIND. A B- A - ANT. Fig. 5.Schematic of the short-wave converter. and A-on the Converter, or to a six volt storage If you are using an antenna connected to the battery, and connect the B- binding post to theSHORT ANT., adjust the small condenser at B- terminal on the broadcast receiving set. therear of the base naneluntil the circuit If you want to use your regular broadcastoscillates at any setting on the tuning dial. antenna, connectitto the SHORT ANT. on There are many tricks about operating this the Converter.If you have a 20 -ft. indoor an-set that you will have to learn by actual experi- tenna put it on ANT. Do not use two antenna ence.The rheostat setting has a considerable on the set. influence on the results.Changing the value of For short wave reception, put the J-23 con-the grid leak makes quite a difference.If, when denser which is mounted on the base panel at you tune out of oscillation, the set squeals, put a zero, with the movable plates all the way out. I-meg. resistor across the secondary of the first Plug in any of the coils except the broadcastaudio transformer. coil, tulle in your station with a variable con- To tune broadcast stations, plug in the broad- denser, and use the midget on the front panelcast coil and set the J-23 condenser at the base as a volume control. panel at maximum capacity, and operate as before. SHORT A+ G140. ANT ANT. B - A -

TO PLATE TERMINAL OF DETECTOR SOCKET IN BROADCAST RECEIVER

NO 130 R.F. CHOKE

PILOT WASP

NO 212 ... COIL SOCKET SHORT WAVE CONVERTOR OFFIelAL CIRCUIT

C0 -301-A 0 No 200, FO SOCKET J-0.3 .0001 PKF. COND.

N9 608 - 23 00014 MV. 000 1 NE. N9 920 COND. COND. RHEOSTAT 20 -A-

N°1282 DIAL Fig.6. The actual arrangenzent of the parts and the wiring arc shown here. 59 LAST MINUTE NOTESON TELEVISION RINGS are happening very rapidly in the that is not objectionable.In fact,it adds to the field of television developments.Atuch that mysterious impression you will get as you "see the is appearing in the radio press contributes transmission." more to confusion, unfortunately, than to progress. Before we can all talk the same language about On the other hand, with a variable -speed motor, television, we must agree as to what a television if you do succeed in putting it in step for a mo- transmitter is. By the nature of the word, a "televi- ment, the unstable resistance of the rheostat will siontransmitter"isone which transmits actual change just enough to throw the images out again, images of moving or still objects. or else someone will turn on an electric light and drop the line voltage sufficiently to slow down the A device which can transmit only black and motor. white objects is distinctly a silhouette transmitter, It is no economy to buy a cheap motor.Get a and not a televisor. Co -cycle motor in the first place if you want clear Thus, when we refer to the Pilot television trans- reception. mitter, or televisor, itis understood that, at the The scanning disc, as has been pointed out else- receiving end, true, detailed images will be seen. where, must be a precision job.We have used The eyes appear distinctly, the teeth show when discs of aluminum and of brass.The former is a the person smiles, and the smoke of a cigarette little easier to handle, but the finest discs are made is clearly visible. of brass, 3/32 in. thick. One of the fascinating things about television receiving is the strange, positively ghost -like ap- First, holes are drilled .022 in. in diameter. Then each hole is filed out .026 in. square.During the pearance of the images.When the receiveris filing process the workmanship is tested frequently slightly out of phase, the images float across the by revolving the disc, with a light held behind it, opening like spirit pictures. to test for overlaps or spaces between the circles Reference is made frequently to the screen of formed by the holes.Given the best equipment for the television receiver.There is no screen.That receiving television, if there is the slightest error is probably the reason for that fact that television in the location of holes, the images will be dis- images look like nothing you have ever seen be- torted.It is clear, therefor, that a cheap disc is fore.They are not reproduced on any flat sur- the expensive one. face, as is the case with printed pictures or photographs.They are formed from individual dots Inevitably some parts manufacturers have started of light from the flashing neon lamp, these dotsto advertise apparatus for television which is en- being distributed by the holes in the scanning disctirely unsuitable.Thisiseven true of one or in such a way as to form a complete image at eachtwo highly reputable concerns.You must be care- revolution of the scanning disc.This is similar ful, therefore, to satisfy yourself that any equip- to the method employed for projecting moving pic- ment advertised for television has actually demon- tures, where one picture after another is thrown onstrated its ability to perform. the screen in such rapid succession that the eye One company, for example, is showing resistance receives the impression of continuous movement. coupled amplifier kits which we know cannot give Altho thePilot Company will be ready very good television reception because we have already shortly to supplytelevisiontransmitterstoall found the ordinary amplifier, however well it may broadcasting stations, the only one in operation at sound on broadcasting, to be entirely inadequate this time of writing is at WRNY, the Radio News for television.Every company selling television stationoperated from thestudiointhe Hotelapparatus should give you the answer to this ques- Roosevelt, New York City.Station WRNY trans-tion, "Have you actually used these partsin a mitstelevisionon boththe standard broadcast televisor, and how can I be sure that the results transmitter and the short wave transmitter for five were genuinely satisfactory?" to ten minutes starting on the hour, every hour PersonallyIhave always doubted the signifi- that they are on the air.This is the first stationcance of amplification curves of audio transformers to provide a daily television schedule for experi-which are so commonly shown to prove that the menters, and the only station sending television on transformers give perfect, straight-line amplifica- broadcast waves. tion.Television has demonstrated that such curves The use of broadcast waves is highly important, are absolutely meaningless.If the transformers since the vagaries of short wave transmission are were as perfect as the curves show them to be, the avoided. Itisenough to handle thetelevision transformers would be just the thing for television receiver without having to contend with the pe- amplifiers.But when you see the amplification culiarities of short waves.On the other hand, the results in the televisor, you know that, curves or no short wave transmitter at WRNY can be used if curves, transformers are not perfect. you are far enough away to get good reception. More than that, it seems as if we do not want Several papers which have publishedarticles perfect audio amplification for perfect visual recep- about apparatus for Pilot television have recom- tion.If you tune in your set to get the best music mended the use of ordinary fan motors to turnfrom WRNY, and then switch to the televisor the disc, the speed being controlled by variable high when the television program starts, you will have resistors.The authors, it may be suspected, haveto retune- your set.And when you are getting the not had much experience with television, or theybest television, you will not get good musicalre- would know that this method is not practical.It production. is absolutely necessary to have a synchronous motor Why thisis so we cannot explain yet, but we for the disc.If the A.C. supply at the transmit-shall understand this, and many of the other strange ter and receiver are not perfectly synchronized, thephenomena as we delve further into this fascinat- images will move slowly across the opening, buting science. 60 Fig. i.This power amplifier also supplies all B voltages to the set. HOW TO BUILD A POWER AMPLIFIER AND B SUPPLY By \VILLIAM R. K:\\ -E THE first model of the 250 power amplifiercondensers tohandle the high voltage. But was not intended for radio builders, butthat was allright becauseitkept thegirls was constructed to please a group of four happy.Since then, we have piped the music hundred girls who gather for lunch every noonto other floors, so that everyone can enjoy it. on the sixth floor of the Pilot factory. Soon after thefirstamplifier was finished, It happened in this way.These girls, who John Geloso came along and, looking atit, wind transformers, operate the filter condenser said, "Ah, that's just what I need to supply B machines, and assemble rheostats, got the ideavoltage to the television receiver." that, working in a radio factory, they ought to To keep peaceall around, we made up a have music with their meals. dozen sets of parts.One amplifier was used So we built the original power amplifier forto operate a Racon dynamic speaker for dance their use, hooked itup to a simple receiver, music.The power amplifier gives much better and ran leadsoutto some big Racon loudmusic for dancing than can be obtained from speakers. ordinary amplifiers becauseitbrings out the We had to wind a special power transformer low notes which supply the rhythm of the music. and extra heavy chokes, and make special filterAnother went intoapublicaddress system Fig. 2.This unit is built to stand up under all conditions, and without attention.

61 and so on until our small supply of parts was 1-No. 402 Pilot power amplifier transformer exhausted. 3-No. 375 Pilot 85 -mil choke coils Checking up on their performance, we found 1-No. 381 Pilot A. F. transformer that they were all giving such splendid service, 14-No. 95o1 Pilot 5oo-volt1. mfd. filter con- and cost so littlefor the magnificent results densers delivered, that we decided to build the trans- 2-No. 9302 Pilot Soo -volt 2. mfd. filter con- formers, chokes, and filter condensers in regu- densers lar production.That's the story of the new 1-No. 956 Pilot 1,2oo-ohm resistor No. 402, 375, and 9501 units required for the 250 2-No. 96o Pilot B pack resistors amplifier.All other parts required are stand- 2-No. 213 Pilot Bakelite UX sockets ard Pilot devices. 2-No. 9000 Pilot condenser clamps How TO USE THE 250 UNIT 1-No. 9oo1Pilot condenser clamp Thepoweramplifier should beconnected 1-Binding post strip to the first A. F. stage of any receiving set. 1-Base board 19 x 714 x ;/4in. Only when exceptional volume is needed should 49-% -in. No. 6 R. H. wood screws it be put on the second stage. 8-t -in. No. 6 R. H. wood screws No B power pack is required for the receiv- The illustrations show how the brackets are ing set, because the power amplifier is equippedarranged to hold the bank of fourteen I. mfd. with terminals for 45, 90, 135, 18o, and 40o volts. condensers.Do not squeeze them too tightly, The 400 -voltpostistohandleany specialbut see that they are firmly clamped. Con- c9,;:ipment. necting links are supplied with the kit to slip

Fig. 3. Not an inch to spare, vet the parts are not crowded.

The power transformer isfitted with bindingover the condenser binding posts as shown in posts as follows : Fig. 3. Check each condenser carefully to make Nos.I,2, 3 deliver 7.5 volts and up to 2.0 certain that it is a No. 9501, and not one of the amperes.No. 2isthe centertap.This two No. 9302 condensers mounted separately winding lightstherectifyingtube, CX-381. for the output filter. Nos. 4,5, 6 deliver 7.5 volts and up to 2.0 When you mount the two resistors, compare amperes. No. 5isthe center tap. This the terminal markings with those shown in winding lightsthe power amplifiertube, Fig. 5.If you make a mistake and reverse the CX-35o. position of one of the resistors you will not Nos. 9 and to deliver 60o volts at .o6 ampere. get the right voltages at the binding posts. This is the high voltage which isrectified A special set of clamps with short rods are for the B supply of the amplifier tube. providedforthe twoNo. 9302 condensers. Nos. 7 and 8 are for connection to the A. C.These are of 2. mfd., and are of a lower voltage supply. This must be of Ito to 120 volts, 5orating, since they are connected in the output or 60 cycles. filter. The voltage drop in the rectifier tube, chokes, CONNECTIONS TO YOUR SET and resistors brings the output voltage down No changesinthereceiver arenecessary to 400 on the amplifier tube. when you use this amplifier except that you Because of the high potential employed inwill have to switch the leads from your present. this unit,itis important to put the amplifierB pack to the posts on the amplifier. in a well -protected place where no one will get On the amplifier is a post marked PLATE his hands on it by accident.If you can do it,INPUT in the diagrams.This is the only lead arrange a lever -operated switch so that, whenrunning to the receiving set.If you are going the cabinet is opened at the back, the currentto use only thefirst A. F. stage in your set, to the power transformer will be cut off. disconnect the wire running to the P contact SUGGESTIONS ABOUT ASSEMBLING on the socket of thefirst audio tube.Then The base board must be ofwell -seasoned connect the lead from the power amplifier to wood, 19 by 7% in., and Y4in. thick.Fig. 3the P post on the socket. Rives the general plan of the layout, with fur- If you use the second stage in your set, go ther details in the picture wiring diagram, Fig. 6.through the same process, removing the wire Start the assembly at the power transformerrunning to the P post on the second audio end, and wor': across.Space each part care-socket, and put on that post the lead from the fully,and makesurethateachdeviceis amplifier. fastened down securely.The complete list of This puts 135 volts on the tube in the set to parts isas follows: which the power amplifierisconnected, as 62 you will see by referring to Fig. 5.If you want Never usecotton insulation for the wiring a higher or lower voltage on that tube, changeon the power amplifier,In damp weather the the resistor end of the lead running from B+cotton will absorb moisture and offer leakage on the No. 381 transformer. For 90 volts putpaths for the current to flow where it does not the lead on the terminal of the resistor which belong. isconnected to the 9o -volt binding post.To Be very carefulabout thesoldered joints. get 180 volts on thelast tube you are using Don't apply so much heat and solder that you in the set, change the lead to the resistor ter-will damage the instruments.Have your iron minal connected to the 18o -volt binding post. very hot and perfectly clean, so that the solder will flow freely and quickly. USE WITH TELEVISION AMPLIFIER There is some misunderstanding in the minds When youusethepoweramplifierasthe of set builders concerning the relative merits of platesupplyfor a televisionreceiver you willthe 310 and 35otubes.Eithertube can be notneed some ofthepartsspecified. Leave operated on 40o volts plate supply, although the out the power tube socket No. 381 transformer,310 takes 35 volts C bias and the 350 requires the output choke and 2. mfd. condensers, and 70.5 volts. the No. 956resistor.Connect the remaining When you consider that the 310 has an am- parts according to the diagrams. plification factor of 8 against 3.8 for the 350, it Without the load of the amplifier tube, themay appear that the 310 is a better tube. That voltageatthe18o -voltbinding postwillbe is not true, however.

Fig. 4. The shape of the base panel fits most console compartments.

approximately 220volts,asspecifiedinthe The undistorted output of the 35o tube is 3,25o television receiver diagram.This is the only milliwatts, while the 310 can handle only 1,500 type of heavy duty power supply now available milliwatts without distortion.In order to ob- that can supply sufficient voltage, without over- tain the most perfect reproduction, a big reserve loading, at 6o mils drain. of power must be available to handle the low notes. From the figures given, you can see that, SPECIAL NOTES when the 310 is at its maximum, the 350 is re- If you are not familiar with this type of equip- livering only half its rated power. ment, the following notes will he helpful. In the average home, high amplification is not

O L.S -

OL.S +

N9315 N9310 3011 30M 0,..0 6+ AMP. ASO"- 2250.- 2800

N9 40 N9 381 0 8+ ISO V. POWER TRANSFORMER A.F TRANS. 2800.,

F2E'. CX.350 0 8+135 V. 4 SF 4 MF. F.1 2230+ 110V.60., A.C. 8+ 90V. LINE 36E00. 10 5+ 45 V. IMF 4000A. 0 B-

6 orrifJ-v

Fig. 5. Schematic diagram of the amplifier and B voltage supply. 63 important, for big volume is more often objectionable. Quality is the thing. And that is what BOOK REVIEWS the 35o tube will give you. The Radio Manual, by G. E. Sterling, edited by Put a good dynamic speaker on this power R. S. Kruse. Published by D. Van Nostrand amplifier, connect up your old set, and you will Co., Inc.Over 900 pages and more than 1,000 think you have a whole newreceiver.The illustrations. power amplifierisan excellent adjunct toa Perhaps for the first time we have in one hand- battery -operated set, sinceitfurnishes all the book an entire course of training for the Depart- ment of Commerce's examination for any grade of operator's license.It was prepared by two men who were perhaps best fitted to do so; R. S. Kruse and G. E. S.erling.Sterling is Radio Inspector and Examining Officerof the Radio Division of the Department of Commerce.Kruse, who edited the Radio Manual, was for the past five years Tech- nical Editor of QST, theofficialorgan of the American Radio Relay League. The sixteen chapters, carry the reader from elementary circuits right through to the details of the newest commercial equipment, so that a beginner, with hardly any knowledge of electricity, can get fromthe book a thorough knowledge ofradio operation. The book isa thorough compilation ofradio information, and has some new information which had never been published.It has a complete description of the Western Electric 5 K.W. transmitter in use at most of the large broadcasters ; and a description and circuit diagram of the W.E. superheterodyne receiver type 6004-C, as well as a most complete description of the standard Navy 2-K.W. spark transmitter.A very valuable sec- tion, worth the price of the entire book, is devoted to Radio Laws and Regulations, and handling and abstracting traffic. Complex mathematics have been avoided and the different topics, introduced in a well -planned sequence. The mechanical make-up of the book is generally praiseworthy. The Radio Manual is now on the press and will be ready October first.The regular price of the publication will be $6.00.By a special arrangement with the publishers, Radio Design can offer this book to its readers at the special price of $4.95 postpaid.Orders should be sent to the Book De- partment, Radio Design Magazine, 103 Broadway, Brooklyn, N. Y. Practical Television, by E. T. Larner, published by D. Van Nostrand.Price $3.75, 172 pages, 100 illustrations. This first up-to-datebook written on the subject:Practical Television gives the layman 'a clear understanding of the fundamentals and principles of seeing by radio. The first part of the book is devoted to the work of early pioneers, starting with Abbe Caselli, who in 1862 sent drawings and diagrams over wire.The use of selenium, which was the firstlightsensitive element known, and its characteristics are discussed as an introduction to the development ofthe modern photo -electric cell. A chapter is devoted to the use of the cathode ray as a light sensitive cell. This method is one which has been more highly developed in Europe Fig. 6.You can follow the layout of the parts as than in the United States.Much space is given shown here, for they are laid out just as in Fig. 3to the Baird Television and to trans -atlantic television. Whether you intend to build television receivers, experiment, or just want to have a working knowl- B voltages, andplugs directlyinto the lamp edge of this new art. socket. Then you will need only the storage This book will be mailed to you postpaid if you battery to light the filaments in the set itself.will send $3.75 to Radio Design, Book Department, No current is drawn from the storage battery 103 Broadway, Brooklyn, N. Y.This is a special to light the tubes in the power amplifier. introductory offer to Radio Design readers. 64 /46w/what B16 money hese fellows have madehall showyoutoo in the RADIO BUSINESShow to start a spare $375 One MonthSpare Time I t I made $377. intime or full time one month in my spare timeinstalling.servicing. selling Radio sets. And, Radio Business not so long ago,I earned enough in one week to pay for my course." ofYour Own EARLE CUNIMINGS, IliWebster St., Haverhill, Mass. 61597 In Five Months without capital "TheN. H. I.is the best Radio school in lb..I \ Radio's amazing growth is making many big job,. The world- hare made $ I ?Y."it,h,. wide use of receiving sets and the lack of trained men to sell, months.I shall s.I,II my friends that1 ow.nr, install and service them has opened many splendid chances success to you." for spare time and full time businesses. HENIli: J. NICKS, Jiv, J.E. SMITH Pres. 302 Salford Ave.' Ever so often a new business is started in this country. We Li\e seen how Tarpon Springs, Fla. !he growth of the automobile industry, electricity and others 'mole men rich. S1164 Spare Time Profits Now Radio is doing the swim thing.Its growth Iris already made many men "Look at whatI havemade rich and will make more wealthy in the future. Surely you are not going to sinceI enrolled, $1,16 pass up this wonderful chance for success. money I would not have I Will TrainYouAtH In Tour had otherwise.I nmcer- More Trained Radio Men Needed SpareTimeHome tainly glad I took tip Radio A famous Radio expert says there are four I bring 111V ir,rining to )011.Boldyourjob. with N. R. I.I am more g...1 jobsforeN ery Mall trained to hold them, c,iye me only part of your spare time. You than satisfied.- Radio has grown so fast that it simply has bea college or high school rt. rtrAKKINEN. don't have io nut got the number of trained men itia..441s. Many of my graduates 110W Mak- 123W. Erie St., Chicago, graduate. Every year there are hundreds of line jobs ing,' big money in 11.1.1iii didn't, 1,1,nfinish the Over $1000 InFour Months N111011g its many branches suchas broad- grades. Boys II,15 years old andmenup "Nly (*Ilionof the N. It. I. castingstations,Radiofactories,jobbers, to 60 have finisli.11 my emirs,successfully. course is that it is the I-I dealers, on hoard ship, commercial land sta- You Must Be Satisfied to hehad atanyprice. tions, and ninny others.Alany of the six to When 1 enrolledI didn't million receiving sets now in use are only I will give you a crrillrn agreementthe day 1110W a condenser from a 12.?, to 411%efficient.This has made yonr ynn enrollto refundy,uurmoney if you are ti,msformer, lint from De - big chance for a spare time orfulltime not satisfied cctic the lessons and instruction ,tillertoAprilImade business ofyour ownselling, ins. ailing, service wlwri sou complete the course. You ell over $1000 and I only tug sets. are the only judge. The resourcesuf the N.11.1. ked in the mornings." So Many Opportunities You Can Make Pioneer and 1...12est Houle -Study Radio school Si JOHNSON, Extra MoneyWhile Learning in the world stand back of this agreement. lino Shelby St., Sandusky, Ohio. Many of our students niake $10, $20, $30 a Get My Book Week extra while learning.I'll show you the Find out what Radio ofl'crs you. ply 6t -page bans and ideas that have proved .1.nnt, "Rich Rewards in Radio - successfulforthem-slimy you points out the money making op- how to begin making extra 1110110y shortly after 3iJ Book portunities the growth of Radio you enroll.G. W Page, 1807-2Ist Ave., S., oat alitat has mathe for soli.I the cou- Nashville, Tenn., made $933 in his spare time 4110 °tea pon. Send itto f111.. YOU won't What! taking my course. be obligated in the least. I Give Ton Practical Radio Experience With My Course etit;L:t)lb" Address Mycourseis not just theory. Mymethod gives you practical Radio experience- J. E. Smith, Pres. -0u learnt'-.11t 1 a nil he - of practically evcrs is pc of Radio Dept. 9G3 set mad... This give. you C01111- fit.111I` t.0 tarkle:111) HAI° problems and shows lip in pair pay envelope too. National Radio Institute Washington, D. C. You can build 100 circuits with the Six Big ( ttifils ofRadio parts gi,e .our The pictures here ,how only three of them. My book explains my method of giving prac- J. E. Smith, tical training at home. President, Get your copy I Dept.,9G3. National Radio Imlilule, Washington, I). I. Dear Mr. Smith: Send .ateyour book. I Want to know more about the opportunities in Radio and your practical method of teaching at home in spare time.This request does not obligate rice14, enroll and I understand no agent .till call Oil me. Name Age Address City Slate

65 the Important RADIO BOOKS

Hereisaspecially selected \i' group of radio books which you will find in constant use on the desks of radio engineers and custom set builders. These books will bring your library up to date. I SIGNAL CORPS OFFICERS' RADIO MANUAL 1929 EDITION. Used by all officers of the Signal Corps as a reference book on radio subjects. Completely illustrated with Cabinets for circuits and diagrams.Explains newest equipment,includingdynamicspeakers PILOT TELEVISION SETS and television, as well as newest circuits and used in the Signal Corps. BROADCAST RECEIVERS Price, postpaid $1.00 This type of cabinet is approved by John Geloso forthePilot Television receiver.Also used for radiosets,with built-in loudspeaker. Write for PRACTICAL TELEVISION prices on this and other beautiful cabinets. By E. T. LARNER. The only modern MAXWELL RADIO CORPORATION book on this new subject.Written for N South 6th Street, Brooklyn, N. Y. experimenters who are working on television development. 172 pages, 100 illustrations. Price, postpaid $3.75 TWIN COUPLER RADIO AMATEUR'S HANDBOOK Twin Coupler Coils are sold in KRESGE, By F.E. HANDY. The third,revised edition.All about short wave transmit- KRESS, GRANT, and tersandreceivers.Entirely "howto make it."Used as a guide by amateurs other stores thruout all over the world.211 pages, 200 illus- the U. S. A., Canada, trations. and foreign countries Price, postpaid $1.00 THE RADIO MANUAL By G. E. STERLING and R. S. KRUSE. This is the most complete book on modern commercial radio communication that has ever been written.900 pages, 1,000 illustrations. Largest Radio Coil Price, postpaid $4.95 Manufacturers in Combination Offer$9.95 the United States These 4 books, postpaid GENERAL OFFICES AND FACTORY Radio Design Pub. Co., Inc. TWIN COUPLER CO., Inc. 103 Broadway, Brooklyn, N. Y. POUGHKEEPSIE NEW YORK

66 Al. FA1R1R 11 S IF YOU CAN'T BUY WHAT Box 83, Station W YOU NEED FROM Brooklyn. New York YOUR LOCAL DEALER, Officigl M. B. Sleeper Panel Patterns ORDER FROM Be sure you're right when you assemble expensive radio parts. Use the Official Panel Patterns so as to reproduce exactly and efficiently the sets shown in Radio Design. Pilot Air Hound:Panel patterns of this new all - electric high -quality broadcast set - - - $1.00 Fastest Radio Mail Short -Wave Wasp:10,000 -mile range,17to 500 meters, finest of short-wave sets.Panel patterns.$1.00 Service in the Workl 250 Power Amplifier:Combination 250 power amplifier and B supply for receiving sets, patterns. $0.50 SPEED isheadquarters forall Pilot Scanning Disc:Full mechanical drawings of OfficialPilotscanningdisc.O.k.'d by John Geloso. Pilot parts and Twin Coupler $1.00. coils, as well as special television PILOT TELEVISION RECEIVER apparatus. cfOn September 15th John Geloso will release the hook-up of the redesigned Pilot Television Re- SPEED can furnish the kits for ceiver.Complete patterns and circuit, with all building the Pilot television re- constants and data - - $1.00 ceiver, special amplifier, and power pack, as well as discs, neon lamps, I I T I I \ P \ N. P 1I R \ I I TV', I \ ID and synchronous motors, alloffi- cially OK'd by John Geloso, for \VRNY television. SPEED carries in stock the kits for the Air Hound, Wasp short \vaveset,250 poweramplifiers, w No. 4A power pack, and No. 5B are included in the Mer- riam Webster, such as power pack,aswellasallthe aerograph,broadtail,credit separate partsfor sets described union, Bahaism, patro- inRadio Design. genesis,etc. 11ew names and places arelisted suchas Cat her,Sana'burg, Stalin, AND Speed ships all orders post- Latvia, etc. paid the day they are received. Constantly improved and kept up to date 1:emember, Speed is WEBSTER'S NEW INTERNATIONAL AS NEAR AS YOUR MAIL BOX DICTIONARY Get The Best SEND STAMP FOR The "Supreme Authority" LATEST PRICES in courts, colleges, schools, and among Govern- ment officials both Federal and State. 452,000 entries including 408,000 vo- cabulary terms, 32,000 geographical subjects, 12,000 biographical entries. Over 6,000 illustrations, and 100 valuable tables. Send for Free, new, richly illustrated pamphlet ConkTent:sharteaffo:eLof the

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