* 1940 IO and

Ç TELEVISION Data. Book

Published by ZIFF-DAVIS PUBLISHING COMPANY 608 South Dearborn Street, Chicago, Illinois

RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 3 1940 RADIO Radio & Television N EWS Data. Book

Edited by the staff of CONTENTS RADIO NEWS

William B. Ziff, Publisher, TELEVISION SECTION SECTION B. G. Davis, Editor, Television Occupations of the Soldering Tubing 5 Future 4 Karl A. Kopetzky, W9QEA, I. C. W. for 5 Meters 5 Television Fundamentals 6 Managing Editor, Crystal Dope 11 Building a Television Receiver.. 8 Learning the Code 14 Oliver Read, W9ETI, Television Words and Terms 10 Rapid Breakin With a Vox System 20 Technical Editor, Amateur 12 20-W Bandswitch Transmitter 23 E. Stanton Brown, U. S. Government Amateur Radio Associate Editor, SERVICEMEN'S SECTION Regulations 24 Herman Bollin, Art Director, Service Problems: Home Made Banana Plugs 37 Cross -Modulation 33 Selecting Wire 47 Eugene O. Gleeson, Variable Tone Modulator 47 Engineering Draftsman, Internal Cross-Modulation 33 External Cross -Modulation 35 Changing Crystal Frequency 49 35 Phone QRM 49 S. L. Cahn, Monkey Chatter How to Advertise Your Service INSTRUMENT SECTION Advertising Manager, 36 Shop Visual Deviation Freq. Meter 21 John H. Reardon, 36 Speaker Troubles An Electric Calibrator 27 Circulation Manager. Line Voltage? 37 What's the Home -Built Audio Oscillator 28 Equipment 37 Cushioning Radio A Vacuum Tube Volt Meter 30 Kinks 46 Meter Meter Readings 37 46 Magnified Handy Continuity Tester Increasing Meter Utility 47 46 Volt Home Made Pilot Light Socket.. Low Cost Tester 48 Dollars 46 Fuses Save Sharply Tuned Wave Meter 48 on 47 Published by Tips Radio Noises A.C.-D.C. Receiver Tube Tester.... 50 Plug-in 47 Ziff -Davis Publishing Company, Resistors Building a Good C. P. Oscillator... 50 48 Handy File System High Resistance Volt Meter 51 608 South Dearborn St., Now! 48 Fix It Low Cost Field Strength Meter... 54 Chicago, Illinois Practical Speaker Repair 48 Projection Device for CR 913 Tube 49 GADGETS-GENERAL SECTION Measuring Power Output 49 Fish Pole Antenna 47 Improving Quality 49 Single Tube Announcer 49 Soldering Iron Tip 49 Handles for Phone Cord Tips 50 Neon Lamp Substitute 49 Winterizing the Antenna 50 Copyright, 1939 Mark the Resistors and Save Time. 50 All Wave Tuned Antenna 51 Magnetic 50 Holder Test Leads 54 Ziff -Davis Publishing Company Replacing Speaker for Silent Microphone Ring 54 Concerning Doublet Antennae.... 60 Feverish Activity 56 Adapter for Determining Coil Pet Vs Pest 56 Frequency 60 New Application for 6E5 58 EXPERIMENTERS' SECTION Tinning Soldering Iron 60 Constructing a Polarized Relay... 29 Reaming with Tools Made of Soft Test Leads for the Experimenter. 35 Includes Articles by: Steel 60 Equipped Treasure Locator 42 Cure for Noisy Volume Control 60 Radio Alfred N. Goldsmith, Automatic Frequency Control Dual Diversity Coupler 44 M. W. Thompson, Measurements 60 Home Made Scratch Filter 47 54 Jones, W6AJF, Tubing Antenna Frank C. Home Made Antenna Tuning Raymond P. Adams, RECEIVER SECTION Condenser 60 The Jones 8 -Tube Special Superhet 15 Edmund P. Kelly, W9HPW, Radio Tuner for P. A. Systems.... 17 DATA SECTION Zeh Bouck, Antenna Mast for $7.50 19 Wire Table-Winding Turns Per Ernest A. Zadig, Better Reception with Good Ground 35 Inch 11 Fractional-Decimal Equivalents. 22 Joseph H. Appel, Jr., W2FDA, Increase Efficiency of Detector Tube 48 Common Word Abbreviations 26 S. Gordon Taylor, W2JCR, Reducing Drift in Receivers 59 R -S -T Reporting System 26 Lee Ward, DB 2-4000 Ohm Conversion Chart. 32 32 Chas. E. Chappel, SECTION DB -Voltage Power Ratio Chart Prevention of Oscillation in P. A Common Symbols Used in Radio McMurdo Silver, Systems 38 Diagrams 45 Lee Sheldon, Scotchman's Special Amplifier.... 39 Chart of Tap Clearance Drills 46 L. B. Robbins, A.C.-D.C. 4 -Watt Amplifier 40 RMA Color Code 51 56 Alfred Ghirardi, Making Your Own Records 41 International "Q" Signals Twin Triodes in Cascade 49 What is Electricity? 60 and others. Portable P. A. System 52 What is a DB? 63 Practical Remote Amplifier 58 Some International Prefixes .... 64-65 4 RADIO NEWS 161411 RADIO & TELEVISION DATA IiOOK TELEVISION TELEVISION OCCUPATIONS OF THE FUTURE

The above shows the operating technique which will be used in putting on the Television Show this spring.

ASTUDY of occupational possibilities looking and listening public. But the size of vision and receivers. Some of in the field of television before that the audience, its purchasing power, and its these men may be university-trained physi- interesting art has made its com- mood will all influence the extent to which cists who are prepared to enter the equally mercial debut is possibly premature and cer- the advertiser can justifiably support tele- complex but more commercial fields of tube tainly hazardous. It savors slightly of plan- vision broadcasting. Accordingly, there is research and design. The usual factory per- ning the Panama Canal shortly before the an action and reaction between economic sonnel will be required for television equip- discovery of America. At best, any voca- conditions and television success. If times ment construction, including test men, super- tional analysis of the television of the future are bad, the programs must be restricted visors, production and manufacturing engi- must be read with several provisos in mind. which, in turn, affects the public response neers, and the like. In the first place, a normal engineering de- that justifies the broadcasting of the pro- Transmitting Station Jobs velopment of television is assumed. That is, grams. Only in reasonably good times can Once the television transmitter has been it is taken for granted that technical knowl- this circle of effects be broken advanta- built and shipped, it must be installed in edge of television will increase apace, en- geously. Accordingly, those contemplating the television transmitting station and there- abling the practical solution of the remaining television as a career will watch closely for after maintained. At this point, an entirely engineering problems of television within a times of general economic recovery since it new series of openings will exist. Television reasonable time. is in such times that arts like television can station engineers will include field -survey In the second place, a normal economic be expected to flourish and to afford oppor- engineers who will determine the best loca- development of television must be regarded tunities for a multitude of new workers. tion for the station and its antenna system as probable in any analysis of its occupa- Opportunities in Manufacturing and who will study the strength and ac- tional possibilities. Television transmitting Let us start at the factory where the nec- ceptability of the signals throughout the and receiving equipment is elaborate and essary equipment for television transmission service range of the station. These men will relatively costly. Television program con- and reception originates. Here are needed also furnish the data which will satisfy the struction will be more complex and expen- apparatus engineers who are capable of governmental authorities that the station sive than radio program construction of to- doing research, development, and design is covering its territory with an adequate day. The television art is a comparatively work in that complicated field. These men service in the physical sense. The equipment luxurious one. Manifestly, such an art can must be technically trained and well -quali- must be maintained in good condition at all hardly be introduced rapidly on a large scale fied along conventional radio lines in order times, and emergencies must be met, and this in times of marked economic depression nor to meet the more difficult problems of tele- is the job of the maintenance staff of the can it be expected to win public favor under vision. These radio engineers are, in fact, station. such circumstances. The television programs electrical engineers with specialized training The television -station studios will require will be paid for, under our present system in the particular field of communications. In a staff of their own of considerable size and of broadcasting operation, by advertising the factory there are also needed tube en- of wide diversity of tasks. Considering sponsors in the main. The sponsors will in gineers who will handle the similar problems the technical men only for the moment, there this way purchase a portion of the purchas- of vacuum -tube and cathoderay-tube produc- will be lighting experts who will arrange ing power and general good will of the tion which are an integral part of the tele - and control the powerful illumination which RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK b

to meet the multitude of complicated, partly unfore- IC W for seeable, and sometimes uncontrol;able conditions 5 to be encountered in out- Meters door jobs. The outdoor camera man will neces- IN the old days of "Rock Crushers" and sarily be of somewhat the "Squeak Boxes" (spark transmitters to same type as the present you youngsters), a ham was known by his successful newsreel camera signal, as well as his call. In many cases if man who can meet an he should have forgotten to sign, it would emergency promptly and have made little difference anyway as by effectively. listening to the particular note, you could a fair of Since portion identify the man behind the gun. The dis- television may programs tinctive signal of the particular individual be, as stated above, from was just as much of a label, as his voice film, it will be necessary would be in a conversation. to film program material, recording both picture and No wonder "wireless" in those days had sound in the same way as the glamour and fascination to attract a fol- lowing. old time signals had a punch now done by the motion - Those picture studios and news- that somehow seems to be lacking today with reel companies. This will the pure flutelike CW notes. Even though lead to a demand for film the CW note of today is better in cases of camera men, sound record- interference, it seems to become more monot- ists, editors, cutters, and onous to listen to for any length of time, as F. J. Bingley (left) & B. E. Schni-zer, Philco television en- other men of the types compared to the old type note that was com- gineers, a live Philadelphia was full of over- monitor program from station. found in the motion - posed of several pitches and picture studios of today. tones. floods the sets (scenery) in the studio and The demand in these fields may develop Inasmuch as ICW is still a regular form the actors. These men must be skilled elec- fairly rapidly as the program "hunger" of of communication on the five meter band, tricians capable of handling, shifting, and television broadcasting rapidly increases after why not rig up a trick oscillator that gives a controlling illumination in any desired fash- its commercial inception. combination of tones, which when blended ion. There will be the microphone or sound would give an imitation of the old spark - men in the studio who will place and control Television Service Men type transmitter already discussed. Such an the microphone supports or booms which Still considering work of primary tech- hold the microphone close enpugh to the nical nature in the television field, it is clear actors to pick up speech or music, while that the television receivers of the future }.. still keeping the microphone outside of the must be installed correctly and kept in good field of view of the camera. Here men with operating condition. This requires the ex- AC steady hands, quick responses, and a cool istence of a good-sized group of television way of working effectively will be required service men. Such men must be familiar with (particularly in the stress of high-speed the circuits of television receivers, their oper- operations during the studio performance). ation, the testing of the receivers for faults, In the control rooms of the studio, there the location of the faults and their correc- will be sound -control men and picture -con- tion, and the best method of installing and trol men who will handle respectively the maintaining the receiver in the home. The quality of the sound and the picture which public response to television will depend in is being transmitted. some measure on the skill, honesty, and eaoTraloost Sometimes, the television transmissions diplomacy of these service men, particularly Circuit diagram of the tone modulator. may more difficult will be from sound -motion -picture film which during what be the or less of has been previously made. For example, a early days of commercial exploitation arrangement can easily be constructed using film newsreel may be transmitted. This re- television. a pair of quarter-watt argon tubes, used with quires that there shall be projectionists who Caution! a pair of triodes as a mixing device to pre- will handle and project the film on the tele- One final word may be in order in the vent reaction between the two argon audio vision pick-up whereby it is sent to the form of advice to the person who is think- oscillators. audience. Here too there will be necessary ing of entering the field of television. Don't film -sound control men and film -picture con- push and run-walk; and watch where you Referring to the diagram you will note trol men who will carefully monitor the are going. Speed in rushing into the field that one argon oscillator is used for low tones transmissions. will not be nearly so helpful as first know- while the other is used for higher tones, ing where your abilities lie, cultivating those each of these oscillators being resistance Camera Men abilities by training in fields similar to tele- coupled to the grids of their respective triodes The television -camera men will constitute vision, and then everlastingly sticking to (type 30's in this case for portability) for a new profession as well. These men handle the job of perfecting your talents and their mixing, and also to get some gain. It is then the television pick-up or "camera" which is application once you have entered the tele- only necessary to blend the two tones until trained on the action and carefully and con- vision field. Remember that television suc- the desired note is obtained. The pitch of tinuously focussed. The reactions of these cess will come rather as the result of a pro- either oscillator can be varied over quite a camera men must be instantaneous, they longed marathon of effort than from a brief range by means of the series resistors so must work with perfect coordination in gold -rush of enthusiasm. marked in the diagram, and the two tones groups where several angle -shots of the same [Reprinted by the courtesy of Occupa- blended by means of the volume control scene to be and they must low tone amplifier, are transmitted, tions, the Vocational Guidance Magazine on the input to the artistic in pictorial the saw be resourceful and their for April, 1938. (Copyright 1938.)) marked "Blender Control." With sense. tooth waveform produced by the argon oscil- The television -camera men in the studio Soldering Tubing lator it is quite easy to adjust the rig to give will be a part of a larger group, for it is In soldering the copper tubing and its quite a good imitation of an old fashioned clear that the outdoor television pick-ups will connections, a soldering iron is of little use, spark transmitter, or in fact an imitation of require the services of men of similar quali- unless it be one of the very large, heavy almost any type of note ever used in "wire- fications and perhaps as great resourcefulness type. Use a small, hot blow torch. less" or "radio" telegraphic communication. 6 RADIO NEWS 194e I;.ADIO & TELEVISION DATA BOOK TELEVISION FUNDAMENTALS and 49.75 mc. carriers, we automatically MICROPHONE TRANSMITTING ANT. RECEIVING ANT. secure the RMA standard sound interme- diate frequency of 8.25 mc. and the video intermediate frequency of 12.74 mc. CAMERA v---vmiRR°R ICONOSCOPE Whether one tunes to the 44-50, the 50.56 IMAGE SCREEN or the 78.84 mc. channel, the two carriers will and to their ELECTRON KINESCOPE tune correctly heterodyne SCANNING proper i.f. passbands. BEAM AUDIO CABLE CO -AXIAL Probably the easiest way to visualize the CABLE FOR VIDEO ELECTRON BEAM "pickup" and re-creation of television trans- CONTROL ROOM mission of a scene ìs to imagine that you TELEVISION THE AUDIO &VIDEO LOUD have before you, as a photoprint, the ARE CONTROLLED XMTR. SPKR. scene to be transmitted, as it would be at HERE RECEIVER any given 1/30 -second. You have a cur- rent -generating pencil, from which a wire leads to the transmitter-you draw a straight Diagram showing the various stages of the television and audio broadcast. line across the top edge of the picture, and, as you go over a black spot the current generated increases, while a gray spot pro- YOU gentlemen with more than the been assigned for this service between 44 duces less currei t, and a white area would average broadcast listener's interest and 108 megacycles, and another twelve result in no current flowing. Obviously, in radio, who intend getting ac- between 156 and 294 megacycles (see Fig- using a photograph, the current would quainted with Miss Television during her ure 1). This is necessary as it was only in constantly be changing. "coming out" parties of the next few this division of the useful frequencies that Now you draw another line as close to months, will find this fascinating new- enough frequencies were available to per- the first as possible, so that a total of 441 lines will comer speaks a new and strange language. mit a few channels with the relatively wide cover the picture completely. When you of Her sense of time is not that of seconds, sidebands required (a television channel is have finished, every point minutes and hours, but is in terms of "H" six megacycles in width). Here also, re- the picture will have been represented by and "V" -3H, 0.15H, 0.10V and 0.07V- flections from the "heaviside" layer occur a current, either strong or medium or weak, flowing from your a in which "H" is 1/13230th-second and "V" but seldom. Reflections would be disastrous, pencil. In television, is 2201/2 H's. as the difference in time between the arrival tiny stream (or beam) of electrons is caused of the ground wave and that of the reflected to travel, just as you did it, over the image There is much of merit in the develop- picked up by a lens and a complex variety ments of Marconi, Telefunken, Fernseh, wave would produce images in offset pairs or "ghosts." of cathode-ray tube called an Iconoscope. Mihaly -Traub, Scophony, Dumont, Farns- This is called "scanning" and it results in a worth and many others. While it appears constantly -varying current, modulated onto 3l rF?W II t..^1 r:r.^ that American practice will be developed a high frequency carrier, which, when re- around electron optical scanning systems, 441 56 88 78 98 108 MC ceived, can be re-created into an identical good based on the cathode ray tube, equally ES5 ºHsFas 1E22 picture by another beam on the end of results have been achieved with mechanical aE3 kin Fin i7r7 173 .'" QM 158 180 204 234 258 282 294 MC another type of cathode-ray tube termed a optical systems. Research into the work Kinescope. Figure I. done both here and abroad during the past While cathode-ray tubes, as used in tele- ten years, brings to light an almost unbe- vision, will be analyzed and explained in lieveable number of combinations of lenses, Each channel is complete in itself, that detail in the next article, I present in Figure apertures, prisms and mirrors mounted on is will it include both the video (picture) 3 a simplified sketch of the Iconoscope and drums, spirals and discs. As this is being and the audio (sound) transmission, and Kinescope, to make the current discussion written, announcement has been made by these will, in every channel, be a definite more readily understandable. The pickup Scophony, Ltd. (British) that a $10,000,000 distance apart. Thus they can be tuned -in of a scene is, in principle, not difficult to American affiliate will be formed to market simultaneously, heterodyned by one oscil- understand when an illustration is avail receivers utilizing mechanical optical de- lator, and each diverted into its own inter- able. The left wall of the Iconoscope, as signs. mediate . How this works out is shown in Figure 3, is of exceptionally clear, Allen Dumont has an excellent system illustrated in Figure 2. For this example, highly -polished glass, with a lens of the of television which involves no synchroniz- the channel in use at the Empire State order of f2.8 or f3.5 mounted at correct ing signals, has 4 -to -1 instead of 2 -to -1 in- Building (N.B.C.) transmitter is chosen- focal distance so the scene to be transmitted terlace, and utilizes two carriers. Over in the channel from 44 to 50 megacycles is reduced to proper size on the Signal Plate England they use "negative" modulation (mc.). within the tube. As the electron beam sys- which means that highest amplitude is It has been found that the wider the tematically covers the image on the Signal white rather than the synchronizing pulse video sidebands, the better the detail and Plate, a constantly -varying current is caused level in blackest black, and the sync pulse entertainment value, so, rather than trans- to flow to amplifiers and the transmitter. level is zero radiated power where our mit both sidebands (video) and have each At the receiving end, this varying cur- standards of "positive" modulation result in be 2.5 mc. deep, it will be the practice to rent which is stronger as the picture is white. Should one care to make a careful utilize but one sideband and have it, darker and weaker as the picture tends study of the work of many very brilliant roughly, 4.0 mc. deep. The other will be minds and form his own opinion of the suppressed. In Figure 2, the video carrier 44MC 50MC relative merit of each one's methods, it will is shown as 45.25 mc. and placed 1.25 mc. 6MC be interesting, and definitely instructive; the from the 44 mc. (lower frequency) edge 1-*-4.50MC APPROX. fact will remain, however, that the electron of the channel. Its sideband is about 4.0 .25MC optical systems are going to dominate com- mc. deep. The sound carrier is at 49.75 mercial television just as gasoline motors mc., placing it 4.5 megacycles above the outnumber diesels, there will be synchro- video carrier and 0.25 mc. from the 50 mc. nizing signals transmitted, 441 will be the (higher frequency) edge of the hand. This generally -used line frequency, and sync 4.5 mc. separation, and the 0.25 mc. plac- A signals will be above blackest black. ing of the sound are in recom- P CTURE SOUND carrier, the CARRIER mended standards. CARRIER First of all, television broadcasting is to 45.25 49.75 in If, at we oscillator be done the spec- the receiver, tune an Figure 2. trum, and, to start, seven channels have to 58 mc., and have it heterodyne the 45.25 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 7

as "V." These times are, of course, picture. This cycle continues through the SCENE TOBE SIGNAL TRANSMITTED 1/13230th-second and 1/60th-second re- last line of picture. PLATE spectively. You will note a vertical broken line iden- To see how they are used, I now refer tified as "Bottom of Picture-Field A." to Figure 5. The upper half illustrates This is the bottom edge of that which is FOCUSING the television signal covering the bottom visible; our electron beam will continue LENS edge of the picture in one scanning field swinging but the final 15 to 22 lines of ("A") and the top edge of the following the field will be blanked out or black. The TO XMTR ELECTRON field ("B"); the lower half of Figure 5' recommended standards say this period, SCANNING BEAM portrays the signal during transmission of known as "vertical blanking" shall be 0.07 YOLK CONTAINING BEAM the bottom edge of the second field ("B") to 0.10 of the time of one field (1/60 - CONTROLLING MAGNETS and the top three lines of what would be second) which is, roughly 15 to 22 lines (TRANSMITTING TUBE) a third field ("C"). This is necessary to of our 2201/2 per field. ICONOSCOPE show the differences in pulse arrangement, With the Kinescope held black, six nar- which explain how interlacing is accomp- row pulses termed "equalizing pulses" are CONTROLLED ELECTRON SCANNING BEAM lished. ,introduced. They are 0.04H wide and As in voice transmission, the carrier spaced at 0.5H intervals, beginning 0.01H provided for video transmission has a after vertical blanking began. Three of definite amplitude (voltage maximum) these are, in effect, horizontal synchronizing IMAGE HERE which it maintains evenly until modulated, impulses to keep the beam horizontally syn- LUMINESCENT COATING whereupon the voltage rise in each side - chronized; the three marked "M" are nec- WHICH EMITS LIGHT THAT VARIES WITH BEAM INTENSITY band varies with the impressed signals. In essary to assure proper interlace in the (REPRODUCTION TUBE) the television transmitters and receivers, it receiver, and their action will be described KINESCOPE is so arranged that full black (of the pic- in article three. Figure 3. ture) will be at 75 to 80% of maximum amplitude. The remaining 25% or 20% is toward white, varies the intensity of the to be used for synchronizing pulses. Thus, Il electron stream in the Kinescope as the all variations in the image transmitted are 1 beam scans the inner surface of the glass taken care of by variations in carrier volt- - 2 end of the tube. As this inner wall of the age from zero to '75 or 80% of maximum 3 tube is coated with a preparation (may be amplitude. - ,- 4 either a sulfide or a silicate of which zinc) Since we have full black at '75% ampli- 5 is highly luminescent, the original scene is tude, anything that may be done with the re-created in approximately 225,000 pin other 25% would not be visible on our - 8 points of light with surprising fidelity. The Kinescope, and it is here that we put the 7 negatively -charged particles that compose synchronizing pulses. At the left end of - e the beam are moving with velocities of the the upper half of Figure 5 we come into 9 order of 30,000 miles per second. the middle of the fifth line from the bot- I------IO Thus, what one will really see is a rapid tom of the picture of one field. As illus- VISUALIZATION OF INTERLACING sequence of pictures as "scanned" by a trated, it is going from dark to light (slop- lightning -fast electron pencil. To avoid ing down). The narrow upright pedestal Figure 4. flicker, it was known that 24 complete pic- shown represents the last 15% of this line, tures (movie standards) or better, would at the right edge of our transmitted pic- The vertical synchronizing pulse, which have to be created per second on the end ture. What is called a "blanking pulse" is comes next, requires the time 3H. It is of the Kinescope. The number 30 was injected which immediately jumps the car, composed, as shown, of six 0.46H pulses chosen, because, being a multiple of the rier to full black. In other words, we do and six serrations or slots which are 0.04H 60 -cycle supply frequency, hum difficulties not "see" the last 0.15H on each swing of each. bt should be noted that the front could more readily be avoided. Hum would, the Kinescope beam. edge of the vertical synchronizing pulse in this case, show itself as a dim pattern The narrower extension on the top of and two of these serrations (0) correspond moving across the picture. the pedestal is the "horizontal synchroniz- in their timing with the horizontal syn- Further to eliminate flicker, it was de- ing pulse," whose job it is to swing the chronizing pulses. The other three (N) cided to "scan" the image in a manner traveling Kinescope beam back to the left are necessary to make identical the vertical known as "interlacing" (see Figure 4). This for the start of the next line (4th from synchronizing pulses of odd and even fields means that, instead of picking up our lines bottom) while a condition of full black (see the vertical synchronizing pulse di- in regular 1, 2, 3, 4, 5 order, we pick exists. This horizontal synchronizing pulse rectly below in the following field). them up as 1, 3, 5, etc., until we have 2201/2 starts 0.01H after the front edge of the While these slots are shown with vertical lines and then jump back and get 2, 4, 6, blanking (full black) pedestal pulse. It sides, because they are so small in the illus- etc., through another 2201/2 lines-each lasts but 0.08H in time, then the voltage tration, the sides are really sloping, so complete operation taking not more than drops back to the blanking pulse level for there is a slanting fall on one side of each 1/60th-second. The full set of 441 lines 0.06H more, and, at its end, we are start- slot equal to 0.005H in time, and a slanting is known as a "frame" while each half is ing the 4th from the bottom line of the rise on the other side of 0.005H in time. a "field." EQUALIZING PULSES VERTICAL EQUALIZING PULSES Quite a few factors entered into the I` BOTTOM OF PICTURE-YNPULSE I`-- TOP OF PICTURE choice of 441 as the correct number of FIE LOW HORIZONTAL FIELD"B' scanning lines; any less than this did not I-- SYNC PLUSES M 3H give satisfactory detail from a complex LilrrJJ1L NONON I scene, while more than this created serious 1 l1 UU lJU 1 TIME BLACK problems. Important, however, as will be PICTURE LEVEL shown later, the number has simple factors and can be had by multiplying odd num- MAXIMUM --'-" WHITE k -H --i V- - f`H I - bers-3x3x7x7. This enters into the gen HORIZONTAL LTOP OF PICTURE oration of synchronizing signals at the FIELD"C' BOTTOM OF PICTURE I M I ¡.HM transmitter. FIELD1B- IONONO M To use the language of the RMA Rec- 1.-r ommended Television Standards Report, TIME FULL AMPLITUDE I will, hereafter, refer to the length of SLATEECONRD H a2H-+'i time required from the start of one line L +i ^ .SH tr'SH to the start of the next line in a field as PICTURE -4 I. VERTICAL BLANKING -15T022H VIDEOIDEO SIGNAL and the time required from the ONE LINE "H," Figure 5. A diagrammatic breakdown of a television signal. start of one field to the start of the next 8 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

That is only 5/1000th of 1/13230th of a ception, except that it shortens the height field) which are 406, 408 and 410. At the second, but these slopes are necessary that of the picture by an infinitesimal amount right end of the lower illustration, a half a wave of the proper form be supplied if more are used. At the point marked video line is indicated following the finish to the deflecting circuits of the receiver's "Top of Picture-Field B" the vertical of vertical blanking, whereas above it, a Kinescope. blanking ends and slightly over four lines full video line is shown. In the upper draw- While the vertical synchronizing pulse of the next field are shown. ing, these top -of -field (B) video lines are has now thrown the Kinescope beam back The lower half of Figure 5 is similar in 1, 3, 5, 7, etc., while below, these first lines to the top of the picture for the start of its cycle of pulses to that of the previous are 2, 4, 6, 8, etc., of an even field (C). another field, there remain six more equaliz- field, but certain features should be stressed. When the fact that "an aspect ratio of ing pulses, which must be present for the Note that the last line of Field B (odd 4:3 is recommended to conform with exist- same reason as was the first group. A series field) is not complete when the vertical ing motion picture practice" is added, we of horizontal pulses then follows before the blanking begins at the bottom of Field B's have concluded our review of the more vertical blanking is removed, and the pic- picture. These are (presuming 30 lines of important introductory features of tele- ture is resumed. The number of such pulses blanking per frame) lines 407, 409 and vision. This quoted sentence simply means at this point may vary from approximately 411, and their timing must be 1/2H "off" that the height of the picture shall be 3/4 six to thirteen and this will not affect re- in relation to those above in Field A (even width, regardless of size Kinescope used. BUILDING A TELEVISION RECEIVER WITH television looming on the In this video set, which is based on the The first six tubes constitute the super- horizon an attitude of watchful Garod Model 100, certain refinements have heterodyne receiver and include one r.f. waiting is being assumed by the been avoided-refinements whose complica- stage, combined oscillator -mixer, 3 i.f. stages radio public in general. But neither the tions do not justify their advantages. It is and diode detector. This differs in a num- ham nor general radio experimenter is the believed by the designers, for instance, that ber of respects from conventional broad- type to sit and wait for someone else to do to build the sound and video receivers in cast superhets. First of all, every r.f. and i.f. things for him. Not so many years ago one unit would add complications not war- circuit must be capable of passing a tre- when there began to be some thought given ranted by the saving in space and a few mendously wide band of frequencies which to the possible practical value of short waves tubes that might result. Moreover, a sepa- constitutes the video signal. Even where for communication and broadcasting these rate receiver can be more readily used for only only a single side -band is transmitted men didn't wait for someone else to point other ranges such as the 5- and 10 -meter the receiver circuits are called upon to pass the way. They dug in and pioneered de- ham bands, the u.h.f., high-fidelity broad- a band approximately 2500 kilocycles wide velopment. There is every chance that they cast stations, etc., than can one whose cir- or more. This is accomplished by heavily are likewise going to play a big part in cuits are intertwined with those of the video loading the tuned circuits of both r.f. and evolution of television. Even the Radio receiver. i.f. with resistors as shown at Rl, R6, R10, Corporation of America recognized this pos- The complete circuit diagram for the etc. The r.f. and i.f. tubes are all of the sibility when over a year ago it made both video receiver and power supply is shown new ultra -high frequency type developed information and special television tubes in the figure. These are two separate units especially for television use. These tubes available to experimenters, and particularly as shown and are interconnected by means provide high gain at these frequencies- to hams. of cable and plug. gain comparable with that obtained at lower

ANT 1852 .0001MF 6K8 1852 12MC 1852 I2MC

Lie I TURN 120MMF .O5 MF

5OMA

5 150A LI STURNS SEETEXT SUA 5MÁ SOMA

.05MF 05MF Mr .0000Ó1 MF 2-6L7Gs 2-6F8Gs

IMEG 00M/n , 2005 5MEG 1 V V DUMONT !: C.R.TU8E", 2.SMEG .SMF 3MA 00085 350MÁ

370MÁ IMEG

002 MF 100Mn yMEG 200MÁ IODO HY

o,"H 1ö -r Ree II 879 SEE TEXT SOMA (D 2000 NY C.R.FII. 2.5V , 2.5V _ e00V SV ,00 YYYYu / 0 0 e li5v AL Circuit diagram of a home -built television receiver. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 9

frequencies from the 6K7, and the like. grid of the 6K8 converter (through the for the 1852 first video stage. This cell The tuning range is approximately 39 to .0001 mfd. coupling condenser). The oscil- will last for a considerable period, since no 63 megacycles, and the intermediate fre- lator is of the Hartley type, although the current is drawn. The output of the 6H6 quency 12 megacycles. The receiver is de- elements have been used in a somewhat un- is connected to the control grid of the signed to receive pictures from stations conventional manner. Note that the oscil- cathode ray tube as well as the synch. sep- using the R. M. A. standards of 441 lines, lator plate (No. 6 pin) is not used. It was arator. 30 pictures per second with interlaced scan- found that better stability was obtained The sweep circuit oscillators are of the ning. It can be adapted to other standards with the circuit as shown, than with the multi -vibrator type, are very stable in opera- by alteration of the sweep constants. conventional arrangement. The converter tion, and can be readily controlled by the The first and second video amplifiers is followed by three i.f. stages operating synch. pulses, which are introduced into the (1852 and 6V6G) function like the audio at 12 M.C. The 6H6 is used as a diode 6L7 tubes. Both sweeps utilize the same amplifier in a sound superhet except that detector in the usual way. The two chokes circuit arrangement, except of course, that they must be capable of passing a wider L8 -L8 together with the .00003 mfd. con- different constants are used for the hori- frequency range. There is also the differ- denser serve as a filter to remove the i.f. zontal (high) and vertical (low) sweep ence that the signal as amplified by these component from the video channel. The frequencies. The saw -tooth waves generated tubes contains not only the picture modula- 1852 and 6V6 act as 1st and 2nd video in such a multi -vibrator, are, if no, compen- tion, but also the synchronizing impulses by amplifiers respectively for the picture signal. sating means is used, logarithmic in form. means of which the viewing process at the A single 11/2 volt cell such as is used for Chokes L12 and L13 are therefore inserted receiving end is kept in exact step with the Pen -Lite flashlights supplies the "C" bias to correct this deficiency and produce a scanning operation at the transmitter. There saw -tooth, substantially linear, so that the are two groups of impulses, one controlling electron beam is carried across the tube at the horizontal sweep and operating at a uniform rate. 13,230 cycles per second, the other the ver- The synchronized sawtooth pulses are tical sweep, at 60 cycles per second. then fed to the two sets of deflecting plates The scanning impulses are of greater to scan the face of the picture tube by voltage amplitude than the picture signal means of the electron beam emitted by the and are separated from the latter by means electron gun in the neck of the tube. This of the 6H6 diode just to the right of the beam is in turn modulated (through the 6V6G video amplifier. This diode is biased control grid) by the picture impulses ob- by means of the potentiometer R36 so that tained from the output of the 6V6. it passes current only at voltages above a pre- Means are provided for centering the determined level appearing in the output of picture by varying the fixed positive poten- the 6V6G. Thus by adjusting this level (by tial on the two sets of deflecting plates. means of R36) to a point somewhat higher Other controls focus the beam by changing than the picture signal output the syn- the potential on the focusing electrode (R59) chronizing impulses are separated from the and adjust the bias on the cathode ray tube picture signal and cause current to flow (R56) to set the average brightness (con- through the 6H6 corresponding to the syn- trast). chronizing impulses. Then by means of Assembly and Wiring properly proportioned circuits, the high-fre- The assembly of the component parts may quency and low -frequency synchronizing be seen from the photographs and diagrams. impulses are separated, the former being All parts should be assembled as shown and fed to the control grid of the high -fre- checked against the circuit diagram to pre- quency sweep oscillator and the other com- vent any possibility of error. ponent to the low -frequency oscillator. Note that the end of the shield on the Separation of the synchronizing signals underside of the chassis is soldered to a lug after rectification in the 6H6 is accom- fastened under one of the screws on the plished through selection of the proper re- gang condenser. sistance -capacity filter values. C32, having Coils Ll, L2, L3, and L16 are wound a value of only .00001 mfd. will not pass with No. 16 bare wire. A %Z" diameter the low -frequency signal but will pass the form is used and removed after winding. high -frequency. impulses to the grid of the Turns are spaced approximately 1/4". The high -frequency oscillator. The low -fre- number of turns is indicated in the diagram. quency impulses are readily passed by C31 It is important that the wiring shown in to the grid of the low -frequency oscillator diagram be followed carefully. As each but the high -frequency impulses are blocked wire or component is put in, it should be out of this circuit by the high resistance of checked off. The grounds and heaters R34. Thus complete separation is effec- should be wired first, then the various B tively obtained. voltages, i.f. transformers; then resistors, The cathode-ray tube employed is one of mica and tubular condensers. All wiring the 5 -inch type in which the image has a should be as short and direct as possible. greenish tint. Tubes which provide a black Particular care should be taken in wiring the and white image can be used but have the video amplifier to avoid high grid or anode objection that for given anode voltages the capacities to ground, since this will result images are less brilliant, which is another in a loss of high frequencies with consequent way of saying that for equally brilliant pic- poor detail. This applies especially to leads tures the "green" tube is less expensive. from the Diode detector to the 1852 and All voltages for the cathode-ray tubes coupling condenser from 1852 to 6V6 as are provided by the 879, high -voltage sup- well as wiring from L11. These should be ply. The 5Z3 supply takes care of all other lifted away from the chassis %4 to 1/2 inch. tubes. Do not fasten the grid lead from the picture Construction Hints and Data tube to the chassis or wrap it around the The antenna primary L16 is connected other leads in the cable. to the Dipole (or other type) antenna CAUTION a twisted pair. The secondary is Approximately 1400 volts is supplied to the high through voltage Anode. This voltage should be treated with tuned to the carrier frequency by the first great respect, since under certain conditions it may section of the three gang condenser, and is be DANGEROUS. Be sure that the power switch is OFF or better still, remove the line cord from the fed into the grid of the 1852 r.f. ampli- outlet, when making any changes, or touching any fier. The plate circuit feeds through in- parts, other than the control knobs. ductor L2 as a plate load into the control The Television Receiver built up. With a high resistance (1000 ohms per 10 RADIO NEWS 1040 RADIO & TELEVISION DATA BOOK volt) voltmeter, measure all voltages, with Since we are operating near the voltage periods preceding the regular scheduled pro- respect to the chassis. Results should be limit of the ¶Z3 rectifier tube, it is imprac- grams. The i.f. system should now be re- approximately as tabulated. Variations will tical to obtain any improvement in this direc- adjusted by staggering the peaks to accept a occur due to line voltage conditions and tion. Amplifiers could be used to increase wide band of frequencies (2 megacycles). tubes. If there is any substantial deviation the sweep voltages, but this would compli- This will result in considerable improve- in voltage from that given in this table, cate matters greatly. The other alternative ment in picture detail, with relatively slight ascertain the reason, and correct it before is to reduce the 2nd anode voltage. Refer- loss in gain. proceeding further, or damage to tubes or ring to the circuit diagram, a 100,000 ohm The i.f. transformers are heavily loaded other parts may result. (R66) dropping resistor is indicated in (with 1500 ohms across each secondary). \YARNING series with the low voltage filter system. It is possible to omit these, with an increase are well insulated Be sure that the Voltmeter prongs a in gain if they so and use great care in making these measurements to This results in a larger picture, at only are carefully realigned avoid shock from the High Voltage supply. slight sacrifice in brilliance. The use of this as to stagger the peaks, with a resultant Alignment and Operation resistor is optional, depending upon which "square top" resonance curve over the band. Set the picture tube bias control (No. 1) characteristic is the more desirable. The r.f. circuits should now be realigned all the way to the right. Set the horizontal The image ratio should be 4:3. If the for best tracking. It may be necessary to and vertical sweep (Nos. 6 and '7) controls picture does not conform to this ratio, a re- adjust the r.f. coil inductances slightly to half way. arrangement of resistors in the sweep plate obtain the proper range and tracking. If Now turn the spot locating control and screen circuits will correct this. Poten- necessary the end plates of the variable con- (No. 3) all the way to the left and rotate tiometers could be inserted to control the denser may be bent to accomplish this. the other spot control (No. 4) through its voltages applied to the deflection plates, About 20 volts at the control grid of entire range. If neither a spot nor a raster but these additional controls are hardly the cathode ray tube is necessary in order (the scanning pattern) appears, move the necessary, since once this adjustment is made, to obtain a good picture. If everything is first spot locating control (No. 3) slightly it need not be changed, for a given set of functioning properly this should be easily to the right and rotate the other locating tubes. obtained from stations within range. This control through its entire range again. Con- After this has been satisfactorily checked, can be checked with a vacuum tube volt' tinue this procedure step by step until some- we may proceed to the i.f. amplifier adjust- meter or calibrated oscilloscope. thing appears upon the viewing screen of ments. An output meter or preferably an A little experience will enable the user the C -R tube. oscilloscope is connected across the output to tune in a station quickly and clearly. Now adjust the vertical and horizontal of the video amplifier (6V6 plate). A signal Proper manipulation of the controls is im- sweep controls until a complete raster ap- from a signal generator or equivalent source portant. pears. This should be approximately 4" is now introduced at the converter grid Ti -1500V. Power transformer 8C12 The intermediate frequency is 12 T.-Rcvr. power trans. 8K93 square (the actual picture will be somewhat (6K8). L15-Rcvr. Filter choke 20H No. IL 11R smaller due to the presence of the blanking mc. The i.f. transformers are now adjusted L14-HiVoltage filter choke 1000H No. 1 F45R and synch. pulses in the station carrier). for maximum output in the conventional Lie -Low frequency sweep choke 2000H No. 1 F47A L12 -High frequency sweep choke 300H No. 1 C42J By means of the spot location controls way. L11-R.P. Choke -SO MH L10-R.F. Choke-ISMH (Nos. 3 and 4) this pattern may now be Now introduce a signal, whose frequency L5, g-R.P. Choke -I20 MH centered on the tube face. is approximately that of the principal sta- L4.ES:5.6.7-I.F. Transformers -12 M.C., U100 The size of the picture is determined by tion to be received, into the antenna circuit. SIZ C-21, 23. 25, 28, 30, 33, 34, 39, 46. 47. 48- two factors, namely: the sweep circuit volt- Tune this signal by rotating the dial, then 525V. Peak net electro. age and the voltage applied to the second align the antenna and r.f. circuits for max- C-44, 45-2000V. (J347) C -41-1000V. (J345) anode. The picture increases with increase imum output by means of the trimmers on C -37-1000V. (J344) in sweep voltage and decreases inversely as the variable condenser. C-42, 50-2000V. (J346) After this has been done, the receiver is C-40, 43, 26, 5, 7, 9. 10, 12, 14, 15, 17, 18, 20. the square of the second or high voltage 22, 24, 27, 29, 49-400 volts. anode potential. The sawtooth voltage ready for a test on the air. It is best to C-51, 4, 13, 16-200V. developed by the multi -vibrators is a func- make adjustments on the fixed pattern trans- C-35, 36, 8. 52, 19, 31. 32, 38-Mica C -I, 2, 3-3 gaug variable tion of the "B" voltage applied to the plates. mitted by television stations during test R-64. 36, 52, 56, 44. 61, 62 -Wire wound pots. TELEVISION WORDS & TERMS

WORDS AND PHRASES COMMONLY ponent which appears as a steady back- Field Frequency Synchronizing Impulse: USED IN TELEVISION ground illumination of the scene being In order to keep the vertical scanning of Aperture : transmitted. the generator at the receiver in step with A loss of image definition of the scanning Direct Pickup: the transmitter, it is necessary to impose aperture. The height of the aperture is This deals with the televising of objects, a square topped impulse at the end of each equivalent to the height of one scanning scenes or persons, etc., directly from life vertical scanning of the picture field. line. and is not to be confused with the Frequency: Aspect Ratio: television method. Refers to the number of times per second This is known as the ratio of the width Even -line Interlacing: the frame area is completely scanned. to the height of the picture framed area. This refers to the number of lines scanned Frame: Automatic Background Control: in each frame and is an even integer. The frame is a complete picture. This is commonly referred to as "Black Field Frequency: Horizontal Blanking Impulse: Control" and refers to an automatic means The number of times per second the field Is a synonym for "Line Frequency Blank- of controlling the illumination of the cath- area is fractionally scanned is called the ing Impulse." ode-ray reproducer modulating the cathode- "Field Frequency" when used in interlaced Horizontal Scanning Frequency: ray intensity. scanning. Is the synonym for "Line Frequency." Composite Signal: The Blanking Impulse of the Field Fre- Ghost Image: When the video, blanking and synchro- quency: If the signals generated during the re- nizing signals are combined or are present Is transmitted at the end of each vertical trace time of the television camera scanning it is known as the "Composite Television scanning of the picture field in order to produce a ghost image signal, it is known Signal." erase the retrace path of the cathode-ray as the "Ghost Image." This is subsequently Consecutive Scanning: spot at the television receiver end. erased by the blanking signal. This refers to the method in television of Field Distortion: Iconoscope: scanning the image in which the field -fre- When the velocity of the scanning spot. This is the television eye and is a cathode- quency and the frame -frequency are iden or the departure from a rectilinear shape of ray type tube which has a mosaic plate and tical. scanning field takes place in the form of is so arranged that the positive charges D.C. Video Component: distortion of the shape of the object in thereon are neutralized so that the discharge This is that part of the video signal cotn- television, it is known as "Field Distortion." currents constitute a video signal. I;.\I)IO NEWS 1940 RADIO & TELEVISION DATA BOOK 11

Image Dissector: optically on the light sensitive cathode of A television cathode-ray camera type tube the dissector tube and should be distin- XTAL DOPE in which an electron image which corre- guished from the electrical focusing of the QUARTZ CRYSTALS USED IN HAR- sponds to the optical image of the scene electron image produced within the tube. MONIC TYPE OSCILLATOR CIRCUITS being televised is made to move in such Oscillight: Many amateur operators are disappointed a way that the electrons so collected con- Is a cathode-ray television reproducer in attempting to oscillate so-called 10 and stitute a video signal current. tube which is of the magnetically focused 20 meter crystals in the harmonic type of Interlaced Scanning Field: type. oscillator circuits. It is well to point out Is a rectilinear field in which the field Positive Polarity of Transmission: that 10 and 20 meter crystals are essen- frequency is a part of the frame frequency When increase in initial light increases tially cut to 60 meter fundamental and and in which the lines traced on each action the radiated power of the transmitter the therefore operate on their odd harmonics being scanned on the picture area are made polarity of the transmission is said to be rather than the even harmonics. For ex- to fall evenly between those of each pre- positive. ample, a circuit which attempted to use a vious fraction of one scanned line in order Picture Element: so-called 20 meter crystal would actually the picture to completely scan each picture frame. The smallest subdivision of put out a harmonic on 15 meters, which Interlace Ratio: area defined in the process of scanning. would fall outside of the amateur bands. Is the numerical ratio of the field fre- "Rain": It is therefore apparent from the above quency to the frame frequency. If a poor signal -to - -ratio exists on that in order to get good efficient per- Keystone Distortion: the television image it is commonly referred formance from either 10 or 20 meter crys- When the picture field assumes a trap- to as "rain." tals that they be used as a straight crystal ezoidal rather than a rectangular shape it Retrace Time: controlled oscillator and never to use them end results in an optical or electrical distortion The time which elapses between the as a generator of harmonic frequency. which is referred to as a "Keystone Dis- of one vertical scansion of the picture field Never attempt to use a crystal itself as tortion." and the start of the next vertical scansion. a power device. It is far better to use an Kinescope: Or else, it might be the time -elapse be- oscillator which is idling than one which This is the cathode-ray tube used in tele- tween the ending of one scanning line and has a high plate voltage supplied. It is vision which relies on an electrostatically the starting of the next consecutive line. always good practice to incorporate some focused cathode. R. F. Television Signal: The signal caused by the modulation sort of a fuse in the crystal circuit and this Line Frequency: may well be one of the popular type of of the R. F. picture carrier by the com- A saw tooth wave is used for scanning pilot lamps, possibly of the brown bead in a horizontal direction and is the line posite television signal. Scanning: variety. This particular bulb will pass 125 frequency that is equal to the number of ma of current at full brilliancy. Most lines per second scanned. When the dimensions, including the height and width together with the inten- crystals are designed to operate up to that Line Frequency Synchronizing Impulse: value never value, so sity of the picture, are being scanned by but exceeding that Is the same as the frequency of the saw if this were in the crystal means of a predetermined manner and that bulb used tooth waves, which is used for scanning in return circuit of the oscillator, any current the horizontal direction. from an electrical amplitude -time function representative of the illumination intensity in excess of 125 ma would blow the bulb, Line Frequency Synchronizing Impulse: thereby protecting the crystal. It should Is transmitted at the end of each scanning of each elementary area of the original image, the amplitude -time function thus ob- not be assumed that the crystal should be line to keep the horizontal generator at operated to light the bulb to full brilliancy the receiver end in step with the horizontal tained becomes a video signal. Scanning Interference: as such is not the case and the crystal cur- generator at the transmitter end. rent should be kept well below those limits. Line Frequency Blanking Impulse: When there is cross -talk between the is pro- Crystals suitable for frequency multiplying Is a square topped impulse transmitted video and scanning circuits and it duced on the television image, it is known are either the 160, 80 or 40 meter type at the end of each scanning line to erase and may be of any of the standard cuts. the return trace of the cathode-ray spot as scanning interference. Crystal cleaning: The quartz used for a receiver tube. Scanning Field: on television must be handled very carefully when Master Pulse Generator: Is the area covered by the scanning spot crystals cleaning and the best solution to use is This generator is used at the studio end either in dissecting or reproducing the tele- either alcohol or carbon tetrachloride, which to provide all blanking and synchronizing vision images. is available at the drug store in the form of signals for both the receiver and the trans- Synchronization: "Carbona." The face of the crystal must mitter. When the generators at the receiver are in step with the scanning generators feed- never be handled by the hand and a clean Magnetic Deflection: ing the television camera, both the trans- handkerchief or piece of soft paper should of a lateral or Refers to the directing receiver are said to be in "syn- be used when replacing the crystal to its ray spot by mitter and vertical motion to the cathode chronization." holder. field produced by a passing it through a Scanning Generator: coil through which the saw tooth scanning Is used to generate the saw tooth waves flowing. current is which are used for the electrical scanning Magnetic Focus Coil: of the television scanning tube or the Is a solenoid which directs the stream of WIRE TABLE cathode-ray type of reproducer. electrons emitted by the cathode-ray gun Winding Turns Per Inch a very fine spot on the cathode-ray Telecine Transmission: into d d screen. Refers to the process of televising and z z D.C.C. S. C. C. En- Polarity: transmitting motion picture film subjects. D.C.C. S.C.C. En- m Negative Transmission a7m amel Pa g amel When a decrease in the light intensity re- Vertical Blanking Impulse: c fre- sults in an increase in the radiated R. F. Commonly referred to as "the field 5.44 5.80 28 39.90 45.30 57.00 power of the transmitter it is known as quency synchronizing impulse." 7 8.08 6.23 27 42.80 49.40 64.00 8 8.80 8.94 28 45.50 54.00 71.00 "Negative Polarity." Vertical Synchronizing Impulse: 9 7.84 7.88 29 48.00 58.80 81.00 Negative Picture: Refers to the field frequency synchroniz- 10 8.51 8.55 30 51.10 64.40 88.00 11 9.58 9.80 31 58.80 69.00 104.00 When the polarity of a video signal is ing impulse. 12 10.82 10.80 32 80.20 75.00 120.00 reversed at the grid of the cathode-ray re- Vertical Scanning Generator: 13 11.88 12.08 33 84.30 81.00 130.00 14 13.10 13.45 14.00 34 88.80 87.60 140.00 ceiving tube it is called a negative picture. Refers to the field frequency scanning 15 14.88 14.90 18.00 35 73.00 94.20 160.00 generator. 18 18.40 17.20 18.00 38 78.50 101.00 190.00 Odd -Line Interlace: 17 18.10 18.80 21.00 37 84.00 108.00 195.00 When the number of lines which are Video Signal: 18 20.00 21.00 23.00 38 89.10 115.00 205.00 frame 19 21.83 23.80 27.00 39 95.00 122.50 215.00 being scanned during each picture When the cathode-ray tube in the tele- 20 23.91 28.40 29.00 40 102.50 130.00 230.00 become an odd number they are known as vision camera is used to scan an image, the 21 28.20 29.70 32.00 41 112.00 153.00 240.00 22 28.58 32.00 38.00 42 124.00 188.00 253.00 "Odd -Line Interlace." signal resulting from the scanning which 23 31.12 34.30 40.00 43 140.00 192.00 285.00 is being transmitted is called the "Video 24 33.80 37.70 45.00 44 153.00 210.00 275.00 Optical Focus: 25 38.20 41.50 50.00 This refers to the focusing of the image Signal," or one which may be seen. The complete Video Section hooked up reedy to transmit a picture. The section is not shown.

AN AMATEUR'S TELEVISION TRANSMITTER

THERE are two general television trans- The system of transmission of a nega- of a second. This will not do for television. mission systems in use today. First, is tive is quite unique in that it incorporates In picture transmission it is necessary that by means of the whirling disk and the the cathode ray tube as the heart. The the transmitter follow a variation from second by means of tubes. The second difference between our system and the Icono- light to dark in almost a millionth part of classification is divided between the Icono- scope was that while the Iconoscope scans a second. scope, used by RCA, and the Dissector, used an image inside of the tube, we were able In our transmitter the total numbers by Farnsworth on the West Coast. Neither to scan an image outside of the cathode of lines in the complete picture was 240 of these latter tubes are available to the ray screen. This was done by placing a scanned sequentially, and horizontally 24 amateur. negative flat against the end of the cathode picture transversals per second or 24 com- ray tube and transmitting the ray through plete frames per second. The line frequency the glass and the film, collecting it in an of our transmitter then was 5,760 cycles Eby cell upon which it had been focused horizontal deflection, and frame frequency by means of a series of lenses. This then of 24 pictures per second. Later we were would be our "Iconoscope." The lens we able to push out scanning lines up to 300 used was an ordinary photographic convex with some distortion and our horizontal de- type which can be purchased in any sup- flection ran 7,200 cycles. This distortion ply store. Our system had one drawback. was noticeable and not pleasing to the eye. There was not enough light hitting the Eby Before commencing the construction of cell to operate the modulator for the or- the amplifier it would be better to construct dinary speech input. the oscilliscope and its associated circuits. Our second big problem, therefore, was If two 908 oscilliscope tubes are available, to design an amplifier which would amplify one may be used with which to transmit, and the very small amount of energy obtained the other one to check the entire system by from the Eby cell sufficient to modulate a receiving the image. They may be hooked small transmitter. in parallel insofar as the power circuits go. A lot of different things had to be taken High voltage power supply for the cathode into consideration. Firstly, the amplifier had tube can be seen directly behind the am- to pass a very wide range of frequencies, plifier in the picture at the top of the page. from 20 to 1,500,000 cycles with a con- It uses a single 866 rectifier and operates on stant output over the entire frequency rate. the half-wave rectification system. The We determined we had to have at least a current drain from this power supply is one 60-volt output from the amplifier in order milleampere and it will not cause any to adequately excite the drivers and the voltage fluctuation in the power supply modulators of the transmitter. when this is used. A full -wave system could In order to avoid distortion, the capacity be used, but the cost would be exorbitant. of all of the parts had to be very small. The diagram fully explains the component The amplifier had to be hum -free, and each parts and their hook-up. It also gives the stage would have to be shielded so that there necessary voltages for checking. would be no interaction between them. After the high voltage supply has been Forgetting for the moment the video or completed, the sweep circuits should next transmission of television signals, we con- be commenced. The cathode ray sweep cir- centrated on the design of an amplifier cuit and its associated power supply is suitable for our purpose. Before going into shown. The controls in the front of the the actual construction itself, it might be panel are from left to right the horizontal well to state a few axioms of television. amplitude control, the horizontal frequency The simple basis of comparison with televi- control, blocking control, frequency control sion is the ordinary broadcast transmission and the vertical amplitude control. This and reception. An ideal broadcast or phone sweep circuit operates the horizontal and transmitter is one which can follow trans- vertical amplifiers of the cathode ray oscilli - mitted variations in one ten -thousandth part scope. It utilizes two 885 discharge tubes KADIO NEWS 1940 RADIO & TELEVISION DATA BOOK. 13

N OW ,J ; Nÿ U U 41- a u- 6 6 E di f .I° [.y. h I¢w O O .G .0 ~ ñti,~pNNOOte 6 6U.ési`t°e'^te ÿ.4Ô óppp0 0.EC w p.. .Q % O m m Ó p% II N Ó 0 8M CC la. % 00% E EOO.7 ó OOOÔOyyOMÔ 8 i nr,ti ti aab ro L.e II..(e,I `^`;@ e ó e L II1~ t.t. t.00 q1%0O : 00 e2 e O K aaaaaaaaaaw EcL Ea s -ú u Cr $ .7) óF E 6 i'.5E O ä,0 6$ 6 $ 6 ampnCió y$ ó mmNN ymt° my U2 CN e e y e 1v e e e o O ÿ m pmj i ° í°eEooEEEEEEEEEEö%

' iiiiiiiii ,0 `O `O A [. t. F. h t. t. aaaaaaaaaaaaaaaae e `0 'O e e J 111 U O TN/},, N 152J ' J lU W CC

.O rWWU x h 2Z-y ó zu

O V

> . ryryti titi...... _. H e Fa É ÉÉ ViÉÉE 0 6 6 .. 0 0 0 6 6 V 4 ., ó Ó000~~Em000"im°o Ó Ó Ó Ó Ó 0 e XOE 0 Ó Ó Ó e e Ó 0 Ó ÔOOMOtiI Oti..EitiO 2á227222

0 O ° sis N á n..ry h "i5E? 4 ó É° $v 4iii d'.5¡ Ú 11 J ói é ó2t É.. J 11.o aO %e. . á. aó 0 . ¢ mc Eÿ mmmmm%%% m4 E á ^Ery%ÉÉÉÉEÓóóÉE.I°.. áá W VGUaCaaaaNNNee~ N O

ti

%F ? i °? °p? -eaá ám$$$$$áW$$$` a$ ksá $ ßá$$am$$ o $ 2.a$á$ a$$4$$$g$$$p$$$p$$$á,$$44ó4a$$$8ÿ%ti%tititigsy y ,ti ti E b titiN Ey y^, .%w.%É E Ehe B EÿE E E Ero.E E E E Éÿ° E É É É É.%w.b,^íw.%ççEQQ ti".EEE.=.b ti EEteteteEEeyteteEEMteytnMEEteyyyEEEyyElEp°EEEEEEEEEEEyEEEtntnEÉ Éÿ É...btititi$Z+titi EEyE EEôbo EMyyy EteyNN NttOONNti00NNN ti00NN ...... iii1iiiiCd'iii4t'NeN N NOO hw 8;.% VVJVVVVVVVVVVVVUVVVVVVVVVVVVVV44 VVÚÚVVVÚÚVVÚVUVVUVVVVVVVVVVVVVUVUVVUVVe,!3!e!eee!!ede!e!ebe!e 14 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOT

and two '58 tubes. The associated power any hum is present, it will show on the Fire up your regular transmitter, call supply to which it is connected by means of cathode ray tube in the receiving position. "CQ Television," or "CQ Video." Do not a cable and plug arrangement contains a Hum must be removed before the amplifier turn on the video transmitter. When you power transformer a type 5Z3 choke and can be put into television operation. make a contact, inform the person receiv- the condensers in filter arrangement. Two By means of the lenses, focus the beam ing, that you wish to transmit a video sig- power supplies are mounted on this chassis, of the transmitting cathode ray tube upon nal. The person receiving will need the one for the sweep circuits and the other for the Eby cell. If everything is in order, a following information. First, the wavelength the amplifier. The transformers are mounted square frame of light should appear on the in KC upon which you expect to transmit along the rear side of the sweep circuit receiving tube at the other end of the ampli- your video signal; second, the horizontal chassis and 21/2 volt filament transformers fier. Both cathode ray tubes are connected scanning frequency, and third, the vertical are used to light all of the heaters in the in parallel as is indicated in the diagram. frequency of the image. transmitter. If the diagrams, pictures and hints herein Actually in practice, it works out some- After the oscilliscope power supply and contained have been followed, and the ap- thing like this. W9 ... calls CQ on 59.9 sweep circuits have been completed it will paratus tests ok, a picture can now be tele- MC. Receiving a reply, he advised the re- be well to test them with an oscilliscope. In vised. Place a sharp contrast negative up cipient to watch for the video signal on 58 the event that the sine wave input is not against the end of the cathode ray in the MC and gives him the horizontal scanning available for test purposes, 60 cycle current transmitting position. Turn on all filaments frequency of 5760 cycles and the vertical may be put upon horizontal or vertical and tubes. If everything is working right, frequency of 24 cycles. The recipient then plate through a .002 mfd. mica condenser. a positive reproduction should appear on tunes his television receiver to 58 MC and If everything is in order, the oscilliscope the receiving C. R. tube screen. You are sets his cathode ray sweep circuit to the should operate as is customary. now ready to put the television transmit- horizontal frequency of 5760 cycles and the The amateur is now ready for the con- ter on the air. vertical frequency of 24 cycles. By doing struction of the difficult part, the amplifier. Because of the wide frequency range of this, the transmitter and the receiver were Component parts are all listed in the dia- video signals, it is impossible through a in synchronization. Transmitted signal and gram itself. Procure a chassis 35 inches transformer plate to modulate any transmit- picture came through with considerable clar- long, 10 inches wide and 6 inches high. Di- ter. Grid modulation therefore will have ity. Audio or voice transmission must be vide this into six compartments, each of to be resorted to. The modulator and driver at least 1.5 MC removed from the video approximately 6 x 10 inches in size. The should now be constructed. We used a signal. tubes should be mounted in each compart, pair of 10's as modulators and a pair of The transmitter we described does not ment as is shown in the photograph, mak- 10's as RF final amplifiers. transmit any signal of a synchronizing ing certain that all wiring is as short as Feeding the output of the amplifier at nature, but it does enable the amateur to possible. Do not purchase anything but the points x -x into a pair of 45's in push-pull start on his way with television. As we very best parts. Check each resistor at the as is indicated in the diagram, we fed that see it, in the future amateurs will call "CQ time of the purchase, and be sure that the to 210's operating in Class A. Here again Video" and receiving an answer, will trans- values are exact and use the ohmmeter as a the diagram is self-explanatory. The out- mit their video signals. The receiving ama- reference rather than the printed label upon put of the 45 drivers is fed through a teur will set up the necessary components the part. A few ohms difference in the low impedance network to the modulators. in his receiving oscilliscope to synchronize various resistors might unbalance the ampli- These, in turn, grid modulate another pair with the transmission. Wide variation from fier and will make a great deal of difference of 10's acting as final RF amplifiers. The 60 cycles on the A.C. line will prevent the in the performance of the finished product. crystal and exciter circuit in the RF section picture from being received properly. Mount the Eby cell on the outside of the has not been drawn since it is well-known At the present writing, the television bands chassis to the extreme left and proceed with to almost every amateur. have been put down to 2.5 meters insofar the wiring and construction as is indicated In order that amateurs who have different as the amateur operator is concerned. This jointly by the diagram and the photograph. types of receiving sets, as well as any short means that extraordinary care will have to After the amplifier has been completed wave listeners who might be equipped to be used to prevent feedback. Any such mani- tubes should be inserted and it should be give you a report, can tune you in, the festation will spoil the picture transmission, checked for hum by turning on all of the following procedure is one we adopted with and may even make it unintelligible. Great filaments and the voltage to each tube. If considerable success. care should be taken to avoid r.f. feedback. LEARNING THE CODE THE Ham Maker consists of groups of ishes group two at the end of 15 seconds, his sentences containing all the letters. Obvi- letters, numbers, and abbreviations ar- speed is 8 words per minute. ously this is a difficult task in the first place, ranged in groups of five: in other words, code Some hams and would-be hams have at- and in the second place the code student words. tempted to solve the problem by making up unconsciously memorizes the sentences. There are fourteen horizontal rows of these code words, each row containing four- teen groups. They are arranged in rows 1 2 3 4 5 6 7 8 9 10 11 12 13 14 vertically and horizontally so that they can 1 zagwa seder fvt, gbyhn mju. ikolp 22q 32z poiuy trewq 98k 75m lkjhg 66b be read down or across. 2 ghjkl gfdsa trgfb boyar mlk7 78f qwsax 43g bvcaz ployg 74o m96 42m gtrwq This sheet was evolved after a long search for some economical, sure-fire way of giv- 3 gplfg hgjkp 92r r65 74d zzlpq jnoet 35x x01 23m mzqzm kdlpw hydra 90k ing code practice to aspiring hams. I have 4 w4dk fus2 jpjl ssdki mnbxc vzdfg hdsja k83 24y cantk leaky quick doggy zlipk tried sending from newspapers but the fault 5 crock swigq s7zq frtyu kyrwq awpja 12y kra9 w98 pinky boppq scram since ser, there is that only common letters appear 6 whose ink8 mgz7 35m kitty sweet kiddo zlkjw w3dg hurry w6tg wzk7 clunk tax, while z, x, j, q, and numbers seldom appear Also there is no way of estimating your 7 meete bendj moq. x -hi ill? xenia pjm, 62m as?m dew2 wait, break sox6 wheng speed when sending this way. 8 cgdew 7hot bghjk ,?j frogs soupy piggy io199 atf, s3vu equak 7-k xzz6 yucyi All these faults are done away with in the 9 aqzsw dxecf frvgt hby8 97j nkm4 29i lop, 90t Bog, dew2 tht4 585 h55 Ham Maker. Every letter and number is included at least once in each line. Abbre- 10 d57 49g ripto bit3 73k fplkj awrgq mkptg ,v, Imefq ivies tinko blabs w9gt viations commonly in use appear often. Fur- 11 egcgd ew9q jrkkt hisis w6gj r.ga kpsek rst4 82e st,s grips eomps etnxo b73 thermore the sender, by glancing along the 12 uraig 692 7zqp grhkm czdkf .r. frank poppy w60 48v cantl eak7 58f oru9 top of the page as he sends and keeping his eye on the watch, can keep a very ac- 13 gak? .aw15 34b glzfr jpltd ?,s yuhxs wdjna isu5 lijp twitt steep sleet ar-e curate check on his speed. Suppose he fin- 14 pl,o kmijn uhb7 ygv6 btfc rdx4 3ess waq2 8,e ?arh 606,1 dewb tnzob 73e RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 15 RECEIVER STCTIIN

THE .JONES 8-TUIZE SPECIAL SIJPEIi,IIET COMMERCIALLY built communica- tube; and a fine new noise limiting circuit. 160 meter coils but is tapped part way down tion receivers are being used by a The receiver was primarily designed for for the other bands. The coil table gives the great many amateurs. However, ex- code reception with a view to obtaining a turns and dimensions for all bands from 10 perimenters still like to build their own. high signal to noise ratio. It is quite satis- to 160 meters. Some of the experimental receivers have cir- factory for phone reception though no AVC Low C to L ratio is extremely desirable cuit improvements which can be added to or R meter circuits were included. It would for the signal frequency tuned circuits for existing receivers without too much effort, be possible to use AVC on the two IF stages weak signal reception. A low C oscillator thus bringing the nearly obsolete receiver with a separate amplified AVC circuit with circuit is unstable and tends to drift badly up to date in performance. For these rea- a 6B8 tube without disturbing the present while the receiver is reaching its normal sons, magazine articles on both simple and circuit layout. Plug-in coils, inside of rep operating temperature. These effects can be complicated receivers are of interest to nearly movable shield cans provide good efficiency nearly eliminated by using a high C to L all readers. The receiver illustrated here has and short r.f. leads with less difficulty in ratio in the oscillator circuit. It was found a number of good circuit improvements such construction than in the case of a band - that very good tracking of the tuned r.f., as high C oscillator, low C r.f. and detector switching system. detector and oscillator circuits was possible tuned circuits; modern tuned plate hexode Band spread over each amateur band is with a high C oscillator over the relatively mixer system; simple variable selectivity crys- accomplished by tapping the ganged midget narrow amateur bands. The trick is to cal- tal filter circuit; high IF amplifier frequency tuning condensers across the proper amount culate the values of inductance and capaci- with high image rejection; simple second of coil turns in each case. This tuning con- tance which will cause the oscillator to tune detector, AF and BFO circuit with a 6N7G denser is connected across the whole 80 and to about 1600 KC (1560 KC in this re -

TO ANT. 6J7 6J8G 6K7G 6K7G J h C7 cec> C C7= 2 c =C7 RF COILS R2 R3,2 sc Coll COIL'S COND. 123, ARE GANGED

6N7G PHONE JACK 41 R13 C12 1 63V -3A. CH S IF 1561 KC 001de RI7 /

110V AC. 400 ¿ Rle moon SW SPKR. FIE LI) = C7 400 65MA. T13 TC14

The circuit of the Jones 8 -Tube Super. 16 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

able 5 megohm resistor. This simple ar- rangement provides continuous selectivity from no crystal to full crystal selectivity without any appreciable detuning effect. Jr is quite easy to properly adjust the phasing condenser C11 for single signal reception even with a high frequency crystal. Con- denser C11 was mounted near the crystal socket and is not adjustable from the front panel. The second detector, audio amplifier and beat frequency oscillator are combined into one 6N7G tube which is a double triode similar to a 6A6. This portion of the cir- cuit is quite similar to the one used in the "Super -Gainer" receivers. For phone recep- tion the resistor R15 is set to a low enough value to practically short-circuit the external cathode coil which backs the second detector out of oscillation. This cathode coil is mounted underneath the chassis near the variable resistance R15 and the 6N7G socket. The resistor is controlled by a knob on the front panel and an extension shaft. The r.f. trimmer condenser C4 is also controlled by an extension shaft and knob for precise ad- stage. Underside the receiver chassis. justment with regeneration in the r.f. The second section of the 6N7G tube acts ceiver) higher in value than the detector and The first detector -oscillator is a 6J8G as an audio frequency amplifier with re- r.f. circuits. This can be accomplished with hexode which is much more effective than sistance coupling to the regenerative detector either a low C or high C oscillator circuit any of the older combination mixer tubes. section. The noise limiter is a full wave with a low C r.f. and detector circuit. It is fairly similar to the 6K8. A tuned plate diode type 84 tube in a push-pull circuit The oscillator circuit has an effective ca- oscillator circuit provides better frequency which limits both "positive" and "nega- pacity of about 3 or 4 times as great as that stability and less detector reaction than the tive" peaks of noise. This type of noise used in the r.f. circuits even though it is conventional oscillator tuned grid circuits. limiter or suppressor is quite effective for tuned to a higher frequency. The oscillator The 6J8G tube has an extra internal grid reducing auto ignition noise. The center - semi -fixed padder condenser C8 is set at connected to the oscillator grid for injection tapped choke Ta (the primary of a small nearly 100 mmfd. for all bands, while the similar to the 6L7 tube. push-pull output to speaker transformer) detector and r.f. padders C5 and C4 are set A high intermediate frequency was chosen reverses the "negative" peaks to "positive" 10 15 The oscillator to about or mmfd. in order to minimize image response in the peaks for operation on the diode plates C3 has to have about twice and to im- tuning condenser high frequency amateur bands which only work on positive peaks. as high a maximum capacity as the other prove the sensitivity for 10 meter band re, tuning condensers C1 and C2. The latter ception. The usual 465 KC IF causes the The diode plates act as a partial short each are 20 mmfd. and the oscillator con- oscillator to be tuned to more nearly the circuit across the audio amplifier during denser C3 is 35 mmfd. These three con- same frequency as the detector grid and periods of noise pulses greater than the densers are mounted on individual 10 ga. space charge effects tend to decrease the cathode bias on the 84 tube. This tends aluminum brackets about three inches high signal to noise ratio in the 10 meter band to punch a hole in the desired signal dur- by one and three-quarters inches wide, which region. This degenerative effect is reduced ing periods of strong noise peaks but since act as shields between condensers as well as when the oscillator frequency is far enough noise peaks are of extremely short duration, rigid supports. Flexible shaft couplings pro- away from the signal frequency so the ratio this causes no apparent distortion. The vide a method of single dial control. The of frequencies is more like that obtained in delay bias on the 84 cathode is ortained oscillator tuning condenser is nearest the the 80 meter band with a 465 KC IF. The from a small '70 ohm cathode bias variable front panel in order to reduce any tendency 1600 or 1560 KC for shaft and coupling backlash in the tuning IF is very desir- dial. A flexible shaft coupling between the able in a receiver oscillator condenser and the dial is a neces- designed for 10 sity to prevent any detuning effects from and 20 and even slight movement of the pront panel. 40 meter band re- The three plug in coils for each band fit ception. The gain into isolantite coil sockets mounted inside of is less with a 1560 the three large coil shields shown in the KC IF and so two rear view of the receiver. These coil shields stages are needed, have removable covers and are reasonably though in this case rigid though not as heavy as would be each stage is over - desired. biased enough to The r.f. stage is regenerative, controlled reduce the gain to by the screen grid potentiometer and the a value about cathode tap on the tuned grid circuit. A equal to a single 6K7 should be used in locations near strong 465 KC high gain signal stations such as broadcast stations IF stage. The ad- in order to prevent cross -talk into the short ditional tuned IF wave bands. In other locations a 6J7 sharp stages aid in selec- cut-off tube will provide a little better signal tivity. to noise ratio and higher gain. An 1853 or The crystal filter 1851 tube will provide even more r.f. gain circuit includes a but are not easily handled when controllable 1560 KC crystal regeneration is desired. shunted by a vari- Topside the receiver chassis. RADIO NEWS 1940 RADIO & TELEVISION 1)A'l'A BOOK 17 resistor connected in series with the normal R4-50.000 3's w. Aerovox R73-10 mug. 1/5 w. Centralab R5-300 3ít w. Centrelab Ri4-20,000 34 w. 350 or 400 ohm cathode resistor in the R6-50,000 1 w. Aerovox R16-1,000 pot. (2nd des. regeneration) Centrolab 41 power amplifier tube. This delay volt- R7-5,000 aft w. Aerovox R76-IO,000 aft w. Aerovox Re -10,000 1 w. Aerovox R77-25,000 343 w. Aerovox age is adjustable in order to set the noise Re-5 megohms (:tal selectivity control) Centralab Rí350,000 1 w. Aerovox suppressor starting action at any desired Rip-1,000 ohm 3h w. Centralab Ris-350 ohm 10 w. Ohmite Rit -100,000 1 w. Aerovox R2o-70 ohm rheostat (misc. silence bias) Frost level. R12-50,000 pot. (1F control) Centrolab Ra-25,000 10 w. Ohmite With no delay bias the noise reducing 8 Tube Communication Receiver COIL DATA action takes place on all audio signals and COIL R. F. DETECTOR OSCILLATOR distorts voice reception. A delay voltage BAND in All coils 13/4" diam. (except 10 osc.) of %2 to 5 volts eliminates this distortion METERS and allows that amount of audio signal to 4% turns No. 20 DCC 4% turns No. 20 DCC le turns No. 20 DCC 3'4" long 3/4" long %" long -13/4" diam. pass through without distortion. Cond. tap at 4 turns Cond. tap at 4 turns No cond. tap 10 Cath. tap at 34 turn Component Parts List Ant. -2 turns No. 26 Primary-4 turns No. 34 Grid -24h turns No. 2e Ci -20 mmfd. var. Bud 323 DSC interwd. DCC interwd. C2-20 mmfd. var. Bud 323 12 turns No. 22 DCC 12 turns No. 22 DCC 43á turns No. 20 DCC C3-35 mmfd. roar. Bud 322 134" long 13/4" long 1" long C4-15 mmf. roar. Hammarlund 11F15 Cond. tap at 5 turns Cone. tap at 5 turns Cond. tap at 2e turns C65-30 mmfd. trimmer Hammarlund 20 Cath. tap at 3g turn Ce -100 mmfd. man. padder Bud 321 Primary 8 turns No. 34 Grid -5 turns No. 26 DCC C7-.01 mid. 600 v. paper C -D Ant. -3%t No. 26 DCC DSC interwound %" long Cs-.1 mid. 600 v. paper C -D 24 turns No. 22 DCC 24 turns No. 22 DCC 10 turns No. 20 DCC Cg-.0001 mid. mica Mallory 11" long 11/4" long 13/4" long Ci0-.001 mfd, mica Ma.lory Coud. tap at 12 turns Cond. tap at 12 turns Cond. tap at 5 turns Cii-25 mmfd. roar. Hammarlund H 40 Cath. tap at 34 turn C72-.00005 mfd. mica Mallory Ant. -5 turns No. 26 DCC Primary-12 turns No. 34 Grid coil-7 turns No. 26 Cí3-.002 mfd. mica C -D closewound DSC interwound DSC interwound v. C -D C14-34 mfd. paper 400 40 No. 24 40 turns No. 24 DCC 15% turns No. 20 DCC v. turns DCC C16-34 mfd. paper 400 C -D 1%" long 13/4" long %s" long C76-.20 mfd. elec. 50 WV C -D No cond. tap No cond. tap No cond. tap C77-9 mfd. «lec. 450 v. C -D Cathode tap at 3/4 turn Cie -16 mid. elec. 450 v. CD 80 Ti-center tapped audio choke-primary of PP Ant. 8 turns No. 26 DCC Primary-20 turns No. 31 Grid coil-10 turns No. 26 pentode to loud speaker transformer- closewound DSC interwound DCC closewound to plate T2--3:1 interstage AF trans. coil CH-15 henry 85 ma. falter choke 80 tarns No. 26 E 80 turns No. 26 E 24 turns No. 22 DCC LC -2nd detector cathode coil30 turns No. 28- 1.4" long 1.4" long 1" long DCC random wound on a 54" diawater 160 No cond. tap No cond. tap No cond. tap porcelain rod insulator Cathode tap at 34 turn R1500 ohms 3$ w. Centrolab Ant. -10 turns No. 26 E Primary-32 turns No. 34 Grid coil-15 turns No. 26 R2-50,000 pot. (RF reg lion) Centralab closewound DSC closewound below DSS closewound below R3-20,000 1 w. Aerovox secondary plate coil RADIO TUNER FOR Y. A. SYSTEMS

Simplicity of control, including a phone jack, make The parts connected to each tube are grouped around that socket to give the best this P.A. Tuner the ideal for use by the serviceman. reception afforded by short leads and feed-back free operation on local signals.

AN efficient radio tuner for Public Ad- dent level to drive any succeeding amplifier contingent superhet. tuners might cause con- dress application is something more to proper output-something which a very siderable trouble. than "any old receiver which will simple set-up employing very few parts can The coverage is limited to the standard tune to and through the broadcast band." be made to do. broadcast band-the actual frequency range It is frankly an objectively engineered in- Physically, the tuner is quite compact and being from 530 kc. to 1600 kc. Tuning and strument, built specifically and therefore certainly portable-cabinet dimensions being tracking is very precise-and related to a functionally for P. A. service to meet the 8%g"x8%g"x13". In non -portable layouts, calibrated four -inch dial scale. particular requirements which program dis- by the way, and particularly in assemblies The Circuit tribution facilities involve. It need not be of dual -channel design, two of these units Four tuned stages are employed-antenna, an expensive item; as a matter of fact, the may be mounted on one standard 19 -inch the two r.f., and detector-with variable con- average job is neither costly nor complex, relay panel-and operated simultaneously densers in gang for single-dial control. The since it is called upon to do no more than without interference one with the other, detector-a diode-provides both an AVC pick up program stations in the broadcast TRF design of course precluding any neces- voltage and an a.f. voltage related to signal. band and produce an audio signal of suffi - sity for local oscillator circuits, which in The two -section a.f. tube, with its two output 18 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

test," so perhaps we had best present these pointers or suggestions here-with apologies to the more advanced and practiced builder to whom they may seem unnecessary-but with our advice to the general reader that they be borne carefully in mind. Mount the small parts-sockets, terminal strips, and the like-first. Solder each socket -saddle to the chassis at some con- venient point. Remove the flat strips between mounting bolts on the power transformer (these strips Io afford a tight press on the laminations), 0 3 GAF mount the transformer as indicated, then replace the strips below chassis. _rcm . BLACK T`=' Install the grommets for the gang con- denser stator or grid leads (lower). Bend Circuit diagram for the P.A. Tuner. (Meissner PA -61 the lower stator lugs until they clear the Ci-Integral with coil R7..-400 ohms chassis, solder 21/2 -inch long pieces of green C2, Cg, Cg, Ci2.-4 gang 365 mmfd., Meissner 21- R7-100,000 ohms braid covered stranded wire to the upper 5123 R4-50,000 ohms shield C3-.05 mfd. R-100,000 ohms stator lugs, then install the condenser C4-.0001 mfd. R6-100,000 ohms on the tuning unit, bringing the grid leads Cg-.05 mfd. R7-40,000 ohms, I watt C7-.0001 mfd. R,-40,000 ohms, I watt through the shield openings provided and Cg-.05 mfd. Rg-400 ohms terminating these leads with grid -cap clips. Cio-0.1 mfd. Rig -2,500 ohms C11.0001 mfd. Rii -25,000 ohms Mount the condenser on the chassis, after C13-.00025 mfd. 1112-25,000 ohms, I watt connecting the lower lugs to the green C14-.OS mfd. Rig-25,000 ohm pot. C15--0.1 mfd. R14-25,000 ohms, I watt leads (short direct tied) from associated C1g-10 mfd., 25 v. Rig -400 ohms r.f. transformers. C17-.25 mfd., 400 v. R16-500,000 ohms Cig-0.1 mid. 1117-500,000 ohms pot. Remove the plate leads from the r.f. Cto-0I mfd., 400 v. Rig 500,000 ohms transformers and replace with pieces of C2o-.01 mfd., 400 v. CH -30 Hy., 40 ma. braid -shielded wire, stripping the braid back C21, C22-8 mfd., 300 Y. electro. Ti-Melssner 14-1496 coil C23 -0I mfd., 400 v. T2, Ti, T4-Meissner 14-7860 coils an inch or so at each end of the wires. Con- C24-.00025 mfd. Tg-Power trans. (250 v.d.c. 30 M.4) C2150.1 mfd. SW-D.P.S.T. nect these new leads in circuit properly. R1-100,000 ohms J-Monitor jack See to it that the shield material makes no other than chassis contact, and solder the circuits, makes possible simultaneous head- The 6F8G plates, unlike the grids, are not shield material to chassis at both socket and phone (monitoring) output and amplifier paralleled but work into separate output cir- each of the transformer points. feed, the monitoring circuit, when in use, in cuits-one for headphone monitoring, one The chassis serves as one common lead for no way affecting the operation of the other. for tuner feed to the amplifier. Monitor- the filament circuit; connect the No. 2 lug of Consider first the detector circuit. Here ing des not affect the output in any way; all but the 5Z4 socket to it. Connect the we use a diode, its parallel plates connected neither the quality nor the level of the sig- 6F8G grids together by means of an appro- to the high side of the last r.f. transformer's nal supplied the amplifier is changed by priate length of green -braid covered stranded secondary through a small mica capacitor- headphone plug-in. wire-from the number S terminal of this rather than conventionally, which is to say Terminals 1 and 3 provide a 10,000 ohm tube's socket up through chassis to the grid directly. The return lead for the secondary match to the amplifier input, terminals 2 and cap. winding is then grounded, the effect being 3 a 2,500 ohm match. Terminals 4 and 5 Mount the tuning dial last-fastening it to provide for a tuned circuit here which will parallel the monitor circuit. Connections to to the chassis by means of a single mounting track with those preceding it. The diode, 200 or 500 ohm lines may be successfully screw. With the dial pointer set in line which with a conventional arrangement made to terminals 2 and 3-but advisable with the horizontal scale markers and with would have considerable shorting effect on practice (this really goes without saying) the variable condenser plates at full mesh, the secondary and in such a way as to make would of course be to provide a more accur- tighten the hub -screws on the shaft. track -tuning here extremely difficult (and ate line match by means of a suitable trans- Check and re -check for proper wiring which would take considerable power from former, its high impedance primary tied to continuity. the third 6K7 stage, lowering the gain of that 1 and 3. Alignment and Operation stage) has its own input circuit-in terms Layout Close the line switch (on the tone control) of physical make-up, a resistor connected The four -gang condenser centers along and check for these voltages (to chassis) : from the plates to the high side of the ef- the chassis, with the transformers (r.f.) to A. Common screen supply bus -75 volts. fective 250,000 ohm load component. the right and the associated tubes to the left B. R.f. plates-240 volts. The audio component of the rectified sig- of it. The 6H6 is forward in tube line-up, C. 6F8G plates -120 volts. nal develops across 200,000 ohms of the the 6K7 in the first tuned circuit toward the The total "B" drain will measure 27 ma. load leg and is coupled to the volume level rear and nearest the glass 6F8G. Power com- if the receiver is properly wired and all tubes potentiometer, which controls the input to ponents-rectifier, power transformer, and are drawing correct power at these potentials. both grids of the 6F8G dual -triode, 50,000 filter condenser are at the back. Tuned circuit alignment is made at one ohms of the load being used to limit the The potentiometers for volume and tone point-at about 1400 kc. If an accurate ad- amount of a.f. voltage available. The d.c. control are assembled on the front chassis justment is effected at this one frequency, component of that signal is used for pur- drop, the one to the left and the other to the the tracking will hold true across the band. poses of AVC, the total voltage developing right of the tuning dial. The phone jack No bending of outside condenser plates across 200,000 ohms being applied to the is on the front panel, which is extended should be necessary. first two r.f. stages and one-half that volt- forward from the chassis sufficiently far to As we have advised before, the .0001 mfd. age being applied to the third. Note, by the provide for ample dial -face clearance. mica condensers from plate to ground in way that .0001 mica capacitors are shown Wiring and Construction the first two 6K7 circuits should not be re- wired from plates to ground in the first twc Matters of assembly are, for the mosi moved unless maximum sensitivity is re- 6K7 circuits; this practice is desirable when part, fairly obvious to the reader who has quired of the tuner. In most tuner appli- the tuner is used largely for local signal studied the circuit and under -chassis dia- cations the sensitivity and gain will be en- reception (though gain remains high enough grams; and those of wiring are made clear tirely sufficient with the condensers in place. for extended range pickup) and if for no with similar study. However, a few pointers To operate the unit, connect to your am- other reason than to prevent any possible might facilitate exact reproduction and pro- plifier, matching the two assemblies prop- circuit oscillation. vide for proper tuner performance on "first erly at the screw terminals RADIO NEWS 1940 RADIO & TELEVISION DATA 1í00K 19 ANTENNA MAST FOR $7.50 WHEN radio reception was con- to strain. All guy wires should be made fast FIG I fined to the broadcast band, the to the mast before raising, and after the mast aerial did not present much of a has been raised the lower set should be problem. Any length of wire from 50 to ANTENNA drawn up to the stakes loosely as first, and HOISTING 150 feet in length and attached to a con- HALYARD then gradually tightening first one and then venient housetop, tree or barn would suf- UPPER REAR GUY WIRE another until the mast is absolutely vertical fice. Now, however, with short wave recep- and all wires are taut. The two guy wires tion very much in the picture, the call is for from the top may then be drawn up, but

all -wave doublets, double -doublets, spider - LOWER REAR these cannot be finally adjusted until after webs, and other complicated forms of an- GUY WIRE the antenna is erected and has put its strain tennae, all laid out to the most precise on the mast. LOWER FRONT specifications. It is much more difficult to GUY WIRE The approximate length of each guy wire find supports just the right height and just can be calculated in advance, by considering the right distance apart, and it is usually it as the hypothenuse of a right triangle, with necesary to erect a special support for at the mast as one other side and the distance least one end of the antenna. from the foot of the mast to the stake as Attempts to put up thirty or forty foot the third side. Then (height)2 plus (dis- wooden or metal masts or towers have often tance to stake)2 equals (hypothenuse)2. In proven to be expensive failures for the in- the case of a 38 -foot mast, with the stakes experienced, but it is really no trick if you 2 20 feet from the base, this would give know how. This article will describe a 38 - V (38)2+(20)2=V 1444 + 406= foot metal mast which is simple to construct, mast 22 feet high. The constructional details V 1844 = 43' easy to erect, and which is inexpensive- given here can easily be modified if masts as the length of each of the two top guy the whole job can be done for about seven of lesser heights are desired. wires. Add about five feet to this, for easy dollars, and will literally a "last lifetime." A 33" hole should be drilled through the handling and fastening, and cut it off later. This mast is constructed, fundamentally, smaller pipe about two feet from one end, The approximate lengths of the lower guy of two lengths galvanized of iron pipe, one and one of the machine bolts put through wires, to the same stakes, would figure out somewhat of smaller diameter than the other, it and tightened securely. This bolt pre- about 28.29 feet each. so that it will telescope within the larger vents the smaller pipe from slipping down For maximum efficiency, particularly if section at the joint between the two. A gal- within the larger one further than desired, the antenna is to be used for transmitting, vanized iron cap and pulley are provided at and also provides a convenient spot to strain insulators should be inserted in each the top of the mast a and galvanized mount- attach the lower guy wires, as shown. guy wire at ten -foot intervals. Such insula- ing flange the at bottom-these together Another 3s" hole should be drilled in the tors will break up these wires into short, with suitable guy wires, are all that are nec- smaller pipe about four inches from this electrically isolated sections of a length that essary provide to a strong, sturdy and pro- end, and the other machine bolt secured in will not absorb energy from the antenna if fessional -looking antenna support. this. This bolt serves as an anchor for the it is used for transmitting, or cause any A complete list of materials, with ap- top guy wires, as well as for the wire by "shielding" effects if it is used for receiving. proximate costs, follows: A metal mast such as this does not need Approximate which the pulley is attached, and prevents Material Cost any of them from slipping down. This end any annual painting or, in fact, any atten- 1-20 foot section l' iron pipe 52.10 1-20 foot section Ws" iron pipe 3.30 of the smaller pipe should be threaded when tion at all, once it has been erected in a I-1" pipe cap .10 I-Iy5 floor flange .25 you buy it, to take the cap as shown. This workmanlike manner. If a good grade of 2-% 52./2" machine bolts and nuts .05 1-Galvanized Iron clothesline pulley .10 cap is not absolutely necessary, but it does 200 feet No. IO galvanized iron wire .60 keep rain and snow out of the upper section, 20 "Egg" strain insulators .50 FIG.3 and gives it a finished appearance. CAP Total $7.00 The end of the larger pipe should also p . The actual costs of these materials will be to take the floor flange, which threaded, DOLT vary somewhat in different localities, but the in turn may be bolted or screwed down to prices given are about average, and the actual a block of metal or hard wood set into the total cost should not vary by more than ground, to give the mast a firm footing. GUY WIRE half a dollar from the estimated cost as Masts of this type not more than twenty Pulley and Top details. shown. The two sections of pipe, the pipe feet high may be guyed with a single set cap and the flange can all be obtained from of guy wires radiating from the top of the any good plumbing shop, the machine bolts, mast only, but taller masts should have two galvanized wire is used, to prevent rust, a pulley and galvanized iron wire from any sets of guy wires as shown. One set is mast of this type will give many years of hardware store, and the strain insulators attached to the top of the mast, and one faithful service, with no other attention from any radio shop. Iron pipe such as this set at or just above the center. These should than an annual inspection to detect cracked is always referred to by inside diameter, so be arranged in triangular fashion, as shown. insulators or guy wire stakes which may be the two lengths of pipe may be larger than One wire forward, in the same direction as loosening. And it will be far more satis- you would expert. The actual outside dia- the antenna, and two toward the rear, all factory and pleasing in appearance than any meter of those two sections are approximately equally spaced around the circumference of of the usual haywire antenna hung on 2" and 1 %" respectively, but the plumber an imaginary circle. All three are necessary tree limbs, bent and rotting 2x4 beams or won't know what you are talking about if at the middle of the mast, but only the two crumbling chimneys, such as are seen so you order them this way. back guys are needed at the top-the an- plentifully on every hand. The general appearance of the completed tenna itself will serve as the front guy at For those amateurs, desiring a vertical mast is shown by the sketch. Allowing for this point. radiator, the mast will more than fill the a two -foot overlap, and with 20 -foot sections Both top and middle guy wires may be bill. It may be used insulated from the of pipe, the height of the completed mast brought down to the same point, which ground, or not, depending on the type of will be 38 feet, as shown. Similar masts of should be a stake or pipe driven into the feed. 33' is the usual amateur length. This lesser height can easily be constructed, of ground at a distance from the mast of not can be made of two pieces 16' in length se- course, by using somewhat shorter lengths less than half the total height. This stake curely threaded together by means of a re- of pipe-two 16 -foot lengths will make a or pipe should be two or three feet long, ducing joint. A bolted antenna should not mast 30 feet high, allowing the same over- and should be driven into the ground at an be used for transmission because of loss at lap, and two 12 -foot lengths will make a angle, to provide the maximum resistance the bolted stages. 20 RADIO NEWS 1940 ItÀl10 & TELEVISION DATA BOOK AMATEUR TRANSMITTER SECTION

TI 37 T2 R4 885 37

R13

I,. R7 R12 R C2 885FIL. R8

R3 ti -- R9 RIO R11 37FILS. CH . SEE TEXT T SEE TEXT RELAY J R14. 1 11 RCVR. CLOSED RADIO NEWS SW. C4 VOX XMTR. OPEN Tc< SYSTEM 80 SW.

115 V. A.C. 1 RAPID BREAKIN WITH THE VOX SYSTEM

7DRi TO I SPEECH MOD olor DRIVER

VOX RCVR. SYSTEM XMTR

Block diagram of the VOX System.

R1-250,000 ohms pot. R_,-3000 ohms 1/ u megohms 1/2 U. R4-0.5 megohms 1/2 u. R-,-5000 ohms 1 w. R6-30,000 ohms 1 w. R;-2 megohms V.4 w. Rs -2 megohms Rs -2 megohms 1/.t w. R10-2 megohms % w. R11-2 megohms 1/.4 w. R14-10,000 ohms 2 W. R13-10 megohms w. R14-25,000 ohms 10 to. adj. C1-10 mfd. 25v. electro. C -1 mfd. 450,,. paper. C3-0.1 mfd. 450,,. electro. C4-8.8 mfd. 450v. electro. (Tobe 'Pluggin') CH -30 by choke (Stancor C-1706) RY-D.P.D.T. Relay: To make one and to The VOX System is simplicity itself. While the laboratory model is mounted on a break one. (Pull in at 15ma, drop out at Type 15-1000 A2 -B3). is no why this cannot be into the 10mo.) (Guardian separate chassis, there reason unit built xmtr. T1-Audio 3:1 (3000 ohm primary). (Stancor A-53). in that would permit "lazy operation and T2-Same as Ti. WITH the advent of more QRM -man" T3-6.3v. AC, 2.5v. AC, 5, AC, 250,,. DC the ham bands plus the skip and yet be fool proof and sure -acting. from filter. (Stancor P4045). fading that has been more than The unit employs a 37 tube as an ampli- SW-AC switch on R1. usually present these last few months, quick fier and isolator, coupled to an 885 gas dis- has which, in turn, controls the bias "breakin" for 'phone or even CW use charge tube hence my choice of them as amplifiers. become almost a necessity. Many ham in- on the 37 tube to operate the relay. Ap- The circuit is a simple one and the input stallations are so equipped, but then there proximately %2 volt of energy is required may be connected across the 500 ohm out- has always been a mess of switches to throw across the input terminals. The unit may line of the speech amplifier where it and the ability of getting at them quickly. be coupled with a condenser to one of the put goes to the modulators, or else the input In a rapid breakin QSO the switches speech amplifier tubes. may be connected in series with the plates "smoked" with their continuous "on -and - If 37 tubes are not available, '76's or even the speech tubes. Of course, off," and the average ham soon got to the 56's may be used without much change in of any one of necessary for the point that he did not care to use that type the circuit, excepting that the 56's will re, for operation it will be with means to re- of contact. I became determined to find a 2.5 v. a.c. for the filaments. I found that speech always to be on way out of the difficulties of throwing the 37 tubes had just the right amount of move the power from the modulators and switches and evolve-if I could-a system gain and stability to operate perfectly and r.f. section of the transmitter. Most hams RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 21 prefer to cut the power in the a.c. primary was done by locating that tube and its power After completing the placement of the circuit, although it can be done in the B- transformer to the extreme right of the transformers, the audio circuit should be side of the power supply. In this latter chassis while the other three tubes are located wired in. case it would be well to use a separate relay on the left-hand side. Care should be taken to see that the to prevent the high voltage, which might be Once the holes are drilled and punched respective input and output circuits of the lethal, from being present in the VOX out, the filament leads should be wired in, audio end be kept carefully separated in System housing. I am sure that there must being sure to use or make twisted wires so order to reduce feedback. be as many ways of connecting this little as to have the hum cancel out. After the If the circuit has been carefully wired in, system as there are different types of rigs. filament leads are wired in, the power cir- the VOX System is now ready for a test. Lay out a bent chassis similar to the one cuit should be wired in complete. It should Do not connect into the transmitter-receiver used in the model I built, or a standard then be tested and if the voltage rises above circuit yet. Connect power input to electric chassis 5" x 10" x 3" may be purchased. In 300 volts d.c., provision for a bleeder (R14) light lines, and replace the relay with a 0-100 experimentation, it was found advisable to and tapping of that bleeder should be ar- ma. meter in series with a 10,000 ohm re- isolate the power 80 tube and its associated ranged for. The VOX System operates on sistor. Turn on unit. The meter should read circuits from the rest of the VOX System exactly 250 v. d.c. under full load, and more between 20 and 25 ma. with the input to in order not to pick up too much hum which than that will make for unstable operation the first 37 set for the minimum gain or itself might throw the transmitter on. This of the 885 gaseous discharge tube. "ground" setting. VISUAL DEVIATION FREQ. METER ONE of the oldest phenomena known to the radio amateur is the effect, termed "zero beat." This occurs when two carriers of identical frequency are superimposed one on the other. The result- ing frequency, numerically, will be of zero audio amplitude and if either of the two fre- quencies are changed they will produce a beat note, the frequency of which is the difference, numerically, between the two car- riers. It was this condition of which advantage was taken and the frequency monitor was developed so as to have this beat note be- come visual rather than aural. To do this an oscillating detector was built with an amplifier, and in the output of the amplifier a simple a.c. voltmeter was placed. to a certain frequency per second in cycles tional phenomenon of which advantage was Since this a.c. voltmeter will read any and then drops off rapidly again to zero. taken in building the visual frequency amplitude of alternating current, and since This may be checked very easily by any monitor. a beat note is of that character, little or no amateur if he will put an audio oscillator The action of this visual frequency monitor difficulty was experienced in having the across an a.c. voltmeter and see that, rising is as follows: Supposing that the transmitter meter register the beat note which was im- from zero beat to say about five thousand is operating on a frequency of 3800 kcs. posed upon it. Fortunately for the author, cycles the meter gradually rises in the indi- The meter was warmed up to operating tem- the average a.c. voltmeter is not linear. By cation of the amount of a.c. voltage. From perature and set for a frequency of 3800 this it is meant that the higher the audio 5000 cycles to 10,000 cycles it drops off very kcs. This resulted in a zero beat signal or (a.c.) frequency, the less the response of the rapidly and beyond 10,000 cycles it fails, an a.c. (audio) component in the output of voltmeter to this frequency as long as the or refuses, to register any voltage whatsoever. the audio amplifier of zero volts. Now if voltage is varied with the a.c. component. The frequency has passed beyond the scope the transmitter frequency were to shift by The curve of the response of the meter rises of a normal 60 cps. meter. It was this addi- one thousand cycles, the 3801 kc. frequency of the transmitter and the 3800 kc. oscil- lating frequency of the detector would beat PICKUP ROD -+ . 2MEG OIMF 25A7G one against the other resulting in a beat note of 1000 cycles, which, if a pair of phones were placed in the output of the monitor, would be distinctly heard as a high pitched whistle. In addition to this, this 1000 cycle note has a definite a.c. component and is registerable in voltage on the meter. In using this theory in the construction of the visual monitor it was found in actual operating that this was not practical. This was so because on zero beat the meter did

TURNS16 SPACED TOÌLONG not register anything, and it took a consider- TAP AT SE COND TURN FROM GND C-10-IOMr 300V. I.SDIAMETER able "off-frequency" shift to make the meter FILS 1 30011 show an appreciable amount of increase of INSULATE D.P. ST voltage. Or the monitor may be loosely I10V AC PROD coupled to any one of the modulated buffer Circuit diagram of the Visual Monitor. stages; the higher the frequency the better 22 RADIO NEWS 1940 RADIO & TELEVISION DATA ROOT: since the transmitter oscillator frequency is A phone jack is provided so that the In actual use with a low power oscillator multiplied by the buffers. In order to check signal appearing in the output may be moni- it was found that a short piece of wire about whether the transmitter frequency has shifted tored. By so doing, the operator may in- one foot in length offered sufficient pickup beyond the range of the meter, a phone jack stantly tell the approximate change in fre- to the monitor even though located some 10 is inserted in the output circuit and it can quency required to change the reading on feet away. Do not use too much pickup as there be determined aurally that the fre- the output meter and by becoming familiar to do so will block the monitor signal. quency has shifted more than 500 cycles with this change he can estimate how many The extreme sensitivity of the meter makes and has shifted beyond the audio range. kilocycles the transmitter frequency has it important that the case be grounded to Still a third point presented itself, which shifted, assuming that the detector is oper- reduce body -capacity effects. A vernier dial was that the oscillating detector could be ating day and night or at least long enough in place of the knob shown will further add picked up in the receiver when in receiving to have reached a proper operating tempera- to the operating ease and precision adjust- position. This, of course, would be most ture. ment. annoying when tuned to receive a signal. The wiring of the various parts is sim- In conclusion it is well to repeat that the Therefore, the monitor frequency is detuned plicity itself and the only precaution needed monitor reads changes in frequency in cycles to produce a note of-say-500 cycles, and is to keep the wires short and direct. and is therefore fast reading if this condi- thereafter this setting and frequency of the It is important that the temperature in tion tákes place. A frequency change of but monitor is used as a reference point. the metal box be kept as constant as pos- a fraction of one kilocycle will cause the Thus it can be seen that the visual monitor sible. It would be even more satisfactory to needle on the output meter to drop to zero does not give the actual frequency during line the insides of the box with a layer of if care is taken in properly setting the regen- operation but rather shows any deviation Celotex or some other form of insulating eration and trimmer controls. whether plus or minus from the fixed fre- material. The use of heater -type tubes adds The users of this instrument will be amazed quency transmission. Summing up, then, with to the operating stability as a change of line at the drift in their transmitters, but it can the oscillating detector set at 500 cycles off voltage does not affect the operating tem- safely be said that if the monitored signal the frequency of the transmitter, any further perature of the tubes as much as would a stays on the meter in any position above 0 change by the transmitter will manifest itself drop in filament voltage on a filament type reading, that no change will be recorded at as change in a.c. voltage or audio on the tube. the receiving position. [Grand Island Sta- output meter, whether this change be up or Remember that in order to maintain an tion is the exception, hi, Ed.] The meter down. In other words, the note will become even temperature in the monitor cabinet cer- should not be relied on for exact edge -of - 500 cycles plus or minus whatever the fre- tain requirements must be met. It is not the -band transmissions. quency to which the transmitter shifts and necessary that plate voltage be applied when it is this particular change which is looked the monitor is not in service, but the fila- for on the meter and which indicates that ments should be left on at all times if the the transmitter is not operating on its proper rig is used every day. TABLES frequency. While the construction of the monitor Construction may be applied to various types of relay CONVERSION TABLE and is racks, etc., it is best that it be built in The metal chassis measures 9"x5" Factors for conversion, alphabetically arranged 2" deep. This size is convenient for the compact form so as to have it as close to the amount of parts which are to be mounted, operating position as possible or at least near MULTIPLY BY TO GET read. Amperes X1,000,000,000,000 micramicroamperes but any handy size may be used, if the enough to be clearly Amperes X1,000,000 microamperes various parts are not crowded. It was first Adjustment Amperes X1,000 milliamperes Cycles X1,000,000 megacycles intended that a standard full -wave rectifier When the monitor has been finished and Cycles X.001 kilocycles be used with a power transformer but after tested it should be allowed to run for an Farads X1,000,000,000,000 micromicrofarads Farads X1,000,000 microfarads making tests on the stability of the detector hour or so to reach a fixed temperature. The Henrys X1,000,000 microhenrys it was felt that a half -wave rectifier furnish- unit operates in much the same manner as Henrys X1,000 mlllihenrys Kilocycles X1,000 cycles ing a lower plate voltage to the tube would a regenerative receiver. The amateur bands Kilovolts X1,000 volts greatly add to the stability. are first located by means of a signal gen- Kilowatts X1,000 watts Megacycles X1,000,000 cycles A combination rectifier and output pen- erator or the signal from the transmitter. In Mhos X1,000,000 micromhos tode tube is used which receives its filament the 5 meter position the trimmer condenser Microamperes X.000,001 amperes Microfarads X.000,001 farads voltage through a resistor cord the same as is only is used to cover the band. Set the MIcrohenrys X.000,001 henrys a.c.-d.c. receivers. This tube is selector switch to the off position which will Micromhos X.000,001 mhos used in the Micro -ohms X.000,001 ohms wired in series with the combined detector disconnect the padders and tune the trim- Microvolts X.000,001 volts first tube. Filtering of the rectifier mer to a 10 meter signal. Advance the re- Microwatts X.000,001 watts and audio Micromicrofarads X.000,000,000,001 farads output is done with a 2000 ohm carbon re- generation control to the point where the Milliamperes X.001 amperes of the usual choke. Meter is tube breaks into oscillation. Millihenrys X.001 henrys sistor in place Miltimhos X.001 mhos 0.150 v. a.c. @ 100 ohms per volt resist- Tune for a whistle which will give a read- Milliohms X.001 ohms ing on the output meter and then readjust Millivolts X.001 volts ance. Milliwatts X.001 watts The controls on the front panel are ar- the trimmer for maximum indication on the Ohms X1,000,000,000,000 micromicro-ohms direct leads may meter. Now any variation in the signal will Ohms X1,000,000 micro -ohms ranged so that short and Volts X1,000,000 microvolts be made to the tuned circuits. The upper change this beat note or whistle and will Volts X1,000 millivolts likewise change the reading on the output Watts X1,000,000 microwatts right-hand knob is the trimmer condenser Watts X1,000 milliwatts which sets the frequency of the regenerative meter. Remove phones. Watts X.001 kilowatts detector to a point within a few cycles of The above procedure is followed for the the incoming signal from the transmitter. other bands and the initial adjustments are The band -setting condensers mount along made by adding additional capacity from the inside of the chassis in order that they the selector switch and its associated pad- may afford short leads to the selector switch ding condensers. A shorting type switch FRACTIONAL-DECIMAL as well as being readily accessible to tune must be used so that as the switch is rotated, EQUIVALENTS from the side when the bands are being set. the condensers will add to each other in Directly under the trimmer condenser is capacity. .0165 ¡Ss .4375 the special shorting type selector switch. A total of five positions cover the 1.10- = h .0312 1/l = .500 This switch is furnished with isolantite insu- 20.40.80 meter bands with the capacities _ shown on the schematic diagram. Each vari- A=.0468 5625 lation to further aid the over-all efficiency. = .0625 6 = .625 knob is able padder has a capacity range of from To the left of the switch control = .0936 12f = .6825 10 to 70 mfd. The 40 and 80 meter bands mounted the regeneration control. This con- 1/g = .125 _ .750 denser controls the amount of feed-back in are tuned with a higher capacity than would .1875 H=.8125 so addi- the detector circuit and is used to adjust the be reached with the padders alone 1A4 = .250 ?=.875 regeneration to a maximum indication of tional capacity is furnished by the fixed mica = .3125 _ .9375 the needle on the indicating meter after the condensers as shown. The high C greatly = .3750 trimmer condenser has been properly set. adds to the stability of the monitor. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 23 20-W Bandswitch Transmitter ing jacks and a built-in meter switch per- 6F6G .0001 MF I000V. OOOIMF ;;I000V iF 50-50MMF mits the reading of oscillator, amplifier, and 1 100-100 I' XTAL MMF modulator plate currents with a single meter . k) LINK and no plugs or jacks. BULB OSC.SOCKET The chassis parts layout is as follows, 1000V .002MF along the panel from left to right; amplifies' .00037 50Mn 002MF 1000V MF IW. R tank coil, amplifier tank condenser 807 (or F M! C W. RK39), amplifier tube, oscillator tank coil, T V. and oscillator tank condenser. U The ordinary TO ÌI° four metal tubes at the .01MF right end of the chassis are of the .OIMF 400V. .OIMF 400V. those 400V. 6J7 6C5 6N7 6N7 500M speech amplifier and modulator. Along the 250 100M rear of the chassis (foreground in the pic- (1IW w J ture) from left to right: the power trans- A-4712 4MF r former 5Z3 rectifier tube, filter power con- 50v 4MF 450V A5A0 o b 4MF450 M(1 densers; and the tapped modulation trans- 2MEG. IW á IOMF `BMA former. The crystal is to the left of the 25V. IOMF OMF25V .5W. IMF 25V. oscillator tube, and the pilot light crystal I SP.ST. 3M(1 400V. 3M(1 20/Aft IMA 100(1 0 IW r 1W 1W low. fuse is between it and the tube. 50Mn Iw The filaments should be wired first, along P-4004 with the primary circuit of the power trans- I 8.3FIL5. 8MF former and tested right away. Then the 450V. C-1515 plate supply connections can be made and Ii 83FILS 115V AC. T d the complete power supply tested. Next C-1412 J 105V AC. comes the R.F. Crystal oscillator circuit fol- -J00 20MÁ lowed by the 807 amplifier stage. It now LINE BMF 18MF 50W. becomes necessary to wind a pair of coils S.F. S T. TOre so that the R.F. section can be tested. All &p' MOO SZ3 of the coils consist of a single winding and it should not take long to make up the first OSC. COILS & PLUGS AMP. COILS &PLUGS 180M 20-10M 180-80M 40-20M 10-5M pair. All data for number of turns, wire size, base connections, etc., can be found in the coil table. If the data is followed carefully, little or no trouble should be ex- Schematic diagram of the 20 -watt all band transmitter. perienced in getting the tank circuits to resonate properly. IN building this transmitter, the factors of both in the oscillator and amplifier tank A reliable 80 or 40 meter crystal is flexibility, performance, and economy circuits so that the proper L -C ratio is ob- usually a great help in getting started on were carefully considered before the tained for all frequencies; and the sec - the "right foot"; so, with the proper coil final design was adopted. Complete cov- rions of both condensers are automatically plugged in the oscillator plate circuit, the erage of all bands with quick band change switched when the plug-in coils are inserted. oscillator can be tuned up. The meter was desired, and crystal control with a A 2 v. 60 ma. pilot light bulb is connected switch should be in the "Oscillator" posi- minimum number of stages. The all -band in series with the crystal to act as an indi- tion and the meter should read anywhere feature dictated the use of both phone and cator of the crystal current and also as a from 20 to 40 ma., minimum dip, depend- C.W. and, therefore, a complete speech fuse. Proper shielding in the amplifier stage ing on the frequency, crystal, tube, voltage, amplifier and modulator had to be included. is incorporated for increased stability and etc. When tuning the oscillator for the first Other features such as metering of all im- eliminates neutralization even at the higher time, it is advisable to leave the amplifier portant circuits, oscillator keying for break- frequencies. The antenna is coupled to the coil and tube out of their sockets. If the in operation, and front panel control were set by means of a link or by capacity coup- 807 is left in the socket and the amplifier worked into the set as the design crystal- ling to the amplifier tank circuit. coil removed, the full voltage is left on the lized, while economy was the deciding fac- The speech amplifier and modulator tube tube's screen. This will short life the ampli- tor in determining the tube lineup and the lineup is as follows: 6J7 input, 6C5 voltage fier tube considerably and might even cause use of a single power supply and meter amplifier, 6N7 Class "A" driver, and 6N7 its complete destruction. After the oscil- for the entire unit, as well as the over-all Class "B" modulator. Sufficient gain for lator is resonated, the amplifier coil and tube size. any crystal microphone or similar high im- can be inserted and also tuned to reson- The result is a complete phone and C.W. pedance input is provided; and different ance. With the meter switch in the "ampli- transmitter, including its a.c. power sup- load impedances are available at the modu- fier" position the current should dip to a ply, in a cabinet measuring 19" x 13" x 83/4" lation transformer by tapping the secondary value ranging from 5 to 15 ma. at reson- overall, and capable of operation on any at the number of suitable points. ance. When loaded the amplifier plate cur- frequency from 1.6 to 60 mc. with crystal The power supply uses a type 5Z3 full - rent should be from 50 to 75 ma., depend- control. Frequency change can be accom- wave rectifier and delivers approximately ing upon the input desired. plished in 30 seconds or less by means of 400 volts D.C. out of the filter, which uses Frequency doubling or quadrupling can two plug-in coils and a plug-in crystal; and condenser input. An additional filter sec- be employed in both stages of this trans- the rated input at all frequencies is 20 watts. tion is inserted to the supply power mitter, which makes it possible to cover all The modulator delivers 10 watts of audio circuit to the three speech amplifier stages hands with 160, 80 and 40 meter crystals. power which is capable of modulating the to insure humfree operation; and a tapped amplifier one hundred percent. The input voltage divider R 17 is used to obtain the The value of condenser in the oscillator varied can be increased to 30 watts if desired with proper voltage for the speech amplifier (300 circuit is fairly critical and can be one hundred percent modulation possible v. D.C.) and the oscillator screen grid (175' either way to obtain the greatest harmonic at voice frequencies on peaks. v. D.C.), while the screen voltage of the output. The radio frequency section utilizes a 807 (or RK39) is supplied through drop- The 2 v., 60 ma. pilot light bulb in series type 6F6G tube as a crystal controlled ping resistor R4. with the crystal indicates the crystal cur- oscillator, driving a type 807 or RK39 final All controls are mounted on the front rent, which should be kept to the lowest amplifier. Split stator condensers are used panel, including the microphone and key- value consistent with good output. 24 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK U. S. GOVT AMATEUR RADIO REGULATIONS

FEDERAL COMMUNICATIONS Special Conditions a person holding a valid amateur operator's license, 152.50 Additional conditions to be observed by and then only to the extent provided for by the class COMMISSION licensee of privileges for which the operator's license is en- Washington, D. C. 152.51 Quiet hours dorsed. When an amateur station uses radiotele- ORDER 152.52 Second notice of same violation phony (type A-3 emission) the licensee may permit In a regular meeting of the Federal Communica- 152.53 Third notice of same violation any person to transmit by voice, provided a duly li- tions Commission held at its offices in Washington, 152.54 Operation in emergencies. censed amateur operator maintains control over the of 1938: emissions by on off re- D, C., on the 4th day October, PART 150 turning the carrier and when The Commission having under consideration a re- -DEFINITIONS quired and signs the station off after the transmis- vision of its rules in respect to the amateur service Sec. 150.01 Amateur service. The term "ama- sion has been completed. and having adopted the attached "Rules Governing teur service" means a radio service carried on by Examinations Amateur Radio Stations and Amateur Radio Oper- amateur stations. Sec. 151.15 When required. Examination is re- ators" to become effective on December 1, 1938 Sec. 150.02 Amateur station. The term "ama- quired for a new license as an amateur operator or IT IS ORDERED, That the following rules, teur station" means a station used by an "amateur," for change of class of privileges. which are now in effect, are hereby cancelled as of that is, a duly authorized person interested in radio Sec. 151.16 Elements of examination. The ex- December 1, 1938: technique solely with a personal aim and without amination for amateur operator privileges will com- 361 376 402, as amended pecuniary interest. It embraces all radio transmit- prise the following elements: 362 377 403 ting apparatus at a particular location used for ama- 1. Code test -ability to send and receive, in plain 364 378 404, as amended teur service and operated under a single instrument language, messages in the International Morse 365 379 405 of authorization. Code at a speed of not less than thirteen words 366 380 406 Sec. 150.03 Amateur portable station. The term per minute, counting five characters to the 366 (a) 381, as amended 407 "amateur portable station" means an amateur sta- word, each numeral or punctuation mark 367 382, as amended 408 tion that is portable in fact, but that is so con- counting as two characters. 368, as amended 383 409 structed that it may conveniently be moved about 2. Amateur radio operation and apparatus, both 370 384 410 from place to place for communication, and that is telephone and telegraph. 371, as amended 384 (a) 411 in fact so moved from time to time, but which is 3. Provisions of treaty, statute and regulations 372 385 412 not operated while in motion. affecting amateurs. 373 386 413 Sec. 150.04 Amateur portable -mobile station. 4. Advanced amateur radiotelephony. 374 387, as amended 414 The term "amateur portable -mobile station" means Sec. 151.17 Elements required for various priv- 374 (a) 400 415 an amateur station that is portable in fact, that is so ileges. Examinations for Class A privileges will in- 375 401 constructed that it may conveniently be transferred clude all four examination elements as specified in By the Commission, to or from a mobile unit or from one such unit to Section 151.16. (Sgd.) T. J. Slowie, another, and that is in fact so transferred from time Examinations for Classes B and C privileges will October 4, 1938. Secretary. to time and is ordinarily used while such mobile unit include elements 1, 2, and 3 as set forth in Section is in motion. 151.16. Table of Contents Sec. 150.05 Amateur radio communication. The Sec. 151.18 Manner of conducting examination. term "amateur radio communication" means radio Examinations for Class A and Class B privileges Part communication between amateur stations solely with will be conducted by an authorized Commission em- 150 Definitions a aim ployee 151 Amateur Operators personal and without pecuniary interest. or representative at points specified by the 152 Amateur Radio Stations Sec. 150.06 Amateur operator. The term "ama- Commission. teur operator" means a person holding a valid license Examinations for Class C privileges will be given PART 150-DEFINITIONS issued by the Federal Communications Commission by volunteer examiner(s), whom the Commission Section authorizing him to operate licensed amateur stations. may designate or permit the applicant to select; in the latter event the examiner gfiiving the code test 150.01 Amateur service PART 151 150.02 Amateur station -AMATEUR OPERATORS shall be a holder of an amateur license with Class A 150.03 Amateur portable station Licenses: Privileges or B privileges, or have held within five years a station Sec. 151.01 Eligibility for license. The follow- license as a professional radiotelegraph operator or 150.04 Amateur portable-mobile ing eligible to apply for license 150.05 Amateur radio communication are amateur operator have within that time been employed as a radio- 150.06 Amateur operator and privileges: telegraph operator in the service of the United Class A -A United States citizen who has within States; and the examiner for the written test, if not PART 151 -AMATEUR OPERATORS five years of receipt of application held the same individual, shall be a person of legal age. Licenses: Privileges license as an amateur operator for a Sec. 151.19 Additional examination for holders 151.01 Eligibility for license year or who in lieu thereof qualified of Class C privileges. The Commission may require 151.02 Classification of operating privileges under Section 151.20. a licensee holding Class C privileges to appear at 151.03 Scope of operator authority Class B -Any United States citizen. an examining point for a Class B examination. 151.04 Posting of license Class C-A United States citizen whose actual If such licensee fails to appear for examination 151.05 Duplicate license residence, address, and station, are when directed to do so, or fails to pass the super- 151.06 Renewal of amateur operator license more than 125 miles airline from the visory examination, the license held will be canceled 151.07 Who may operate an amateur station nearest point where examination is and the holder thereof will not be issued another Examinations given at lst quarterly for Class B; or license 151.15 for the Class C privileges. When required. is shown by physician's certificate to be Whenever the holder of Class C amateur operator 151.16 Elements of examination unable to appear for examination due various privileges privileges changes his actual residence or station 151.17 Elements required for to protracted disability; or is shown by location to a point where he would not be eligible to 151.18 Manner of conducting examination certificate of the commanding officer to examination for holders of Class apply for Class C privileges in the first instance, or 151.19 Additional be in a camp of the Civilian Conserva- whenever a new examining point is established in a C privileges tion Corps or in the regular military or region from which applicants were previously 151.20 Examination abridgment naval service of the United States at a eligible for C 151.21 Examination procedure Class privileges, such holders of Class military post or naval station and un- C privileges shall within four months thereafter 151.22 Grading able to appear for Class B examination. 151.23 Eligibility for reexamination appear at an examining point and be examined for Sec. 151.02 Classification of operating privileges. Class B privileges. The license will be canceled if PART 152-AMATEUR RADIO STATIONS Amateur operating privileges are as follows: such licensee fails to appear, or fails to pass the Licenses Class A -All amateur privileges. examination. 152.01 Eligibility for amateur station license Class B -Same as Class A except specially lim- Sec. 151.20 Examination abridgment. An appli- 152.02 Eligibility of corporations or organizations ited as in Section 152.28. cant for Class A privileges, who holds a license with to hold license Class C-Same as Class B. Class B privileges, will be required to pass only the 152.03 Location of station Sec. 151.03 Scope of operator authority. Ama- added examination element No. 4 (see Section 152.04 License period teur operators' licenses are valid only for the opera- 151.16). 152.05 Authorized operation tion of licensed amateur stations; provided, however, A holder of Class C privileges will not be ac- 152.06 Renewal of amateur station license any person holding a valid radio operator's license corded an abridged examination for either Class B 152.07 Posting of station license of any class may operate stations in the experi- or Class A privileges. Call Signals mental service licensed for, and operating on, An applicant who has held a license for the class 152.08 Assignment of call letters frequencies above 300,000 kilocycles. of privileges specified below, within five years prior 152.09 Call signals for member of U.S.N.R. Sec. 151.04 posting of license. The original to receipt of application, credited with examination 152.10 Transmission of call signals operator's license shall be posted in a conspicuous elements as follows: Portable and Portable -mobile Stations place in the room occupied by such operator while Class of license or privileges Credits 152.11 Requirements for portable and portable - on duty or kept in his personal possession and avail- Commercial extra first : 2 4 mobile operation Elements 1, 6' able for inspection at all times while the operator is Radiotelegraph 1st, 2nd, or 3rd : Elements 1 fßì 152.12 Special provisions for portable stations 2 on duty, except when such license has been filed Radiotelephone 1st or 2nd : 2 Cs' 152.13 Special provisions for non -portable stations Elements 4 with application for modification or renewal, or has Class A : Elements 2 of Amateur Stations 6' 4 Use been mutilated, lost, or destroyed, and application No examination credit is given on account of 152.14 Points of communication has been made for a duplicate. 152.15 No remuneration for use of station license of Radiotelephone 3rd Class, nor for other Sec. 151.05 Duplicate license. Any licensee ap- class of license or privileges not above listed. 152.16 Broadcasting prohibited plying for a license 152.17 Radiotelephone tests duplicate to replace an original Sec. 151.21 Examination procedure. Applicants Allocation of Frequencies which has been lost, mutilated, or destroyed, shall shall write examinations in longhand, -code tests 152.25 Frequencies for exclusive use of amateur submit to the Commission such mutilated license or and diagrams in ink or pencil, written tests in ink- stations affidavit attesting to the facts regarding the manner except that applicants unable to do so because of 152.26 Use of frequencies above 300,000 kilocycles in which the original was lost or destroyed. If the physical disability may typewrite or dictate their ex- 152.27 Frequency bands for telephony original is later found, it or the duplicate shall be aminations and, if unable to draw required dia- 152.28 Additional bands for telephony returned to the Commission. grams= may make instead a detailed description 152.29 Television and frequency -modulation trans- Sec. 151.06 Renewal of amateur operator license. essentially equivalent. The examiner shall certify mission An amateur operator license may be renewed upon the nature of the applicant's disability and, if the 152.30 Facsimile transmission proper application and a showing that within three examination is dictated, the name and address of the 152.31 Individual frequency not specified months of receipt of the application by the Com- person(s) taking and transcribing the applicant's 152.32 Types of emission mission the licensee has lawfully operated an ama- dictation. Equipment and Operation teur station license by the Commission, and, that Sec. 151.22 Grading. Code tests are graded as 152.40 Maximum power input he has communicated by radio with at least three passed or failed separately for sending and receiv- 152.41 Power supply to transmitter other such amateur stations. Failure to meet the re- ing tests. A code test is failed unless free of omis- 152.42 Requirements for prevention of interference quirements of this section will make it necessary for sion or other error for a continuous period of at 152.43 Modulation of carrier wave the applicant to again qualify by examination. least one minute at required speed. Failure to pass 152.44 Frequency measurement and regular check Sec. 151.07 Who may operate an amateur sta- the required code test will terminate the examina- 152.45 Logs tion. An amateur station may be operated only by tion. (See Sec. 151.23.) RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 26

A passing grade of 75 per cent is required sepa- a fixed amateur station: WIABC W1ABC W1ABC The following bands of frequencies are allocated for rately for Class B and Class A written examina- DE W2DEF DN3 W2DEF DN3 W2DEF DN3 AR. use by amateur stations using radiotelephony, type tions. Example 2. Fixed amateur station answers the A-3 emission: 1800 to 2000 kilocycles, 28500 to Sec. 151.23 Eligibility for reexamination. An portable or portable -mobile amateur station: 30000 kilocycles, 56000 to 60000 kilocycles, 112000 applicant who fails examination for amateur privi- W2DEF W2DEF W2DEF DE W1ABC WIABC to 118000 kilocycles (the Commission reserves the leges may not take another examination for such right to change or cancel these frequencies without privileges within two months, except that this rule WIABC K. advance notice or hearing), 224000 to 230000 kilo- shall not apply to an examination for Class B Example 3. Portable or portable -mobile amateur cycles (the Commission reserves the right to change following one for Class C. stations calls a portable or portable -mobile amateur service station: W3GHI W3GHI W3GHI DE or cancel these frequencies without advance notice PART 152 -AMATEUR RADIO STATIONS or hearing), 400000 to 401000 kilocycles. W4JKL DN4 W4JKL DN4 W4JKL DN4 AR. Sec. 152.28 Additional bands for telephony. An Licenses If telephony is used, the call sign of the station amateur station may use radiotelephony, type A-3 Sec. 152.01 Eligibility for amateur station li- shall be followed by an announcement of the ama- emission, in the following additional bands of fre- cense. License for an amateur station will be issued teur call area in which the portable or portable. quencies; provided the station is licensed to a per- only to a licensed amateur operator who has made mobile station is operating. son who holds an amateur operator's license a satisfactory showing of control of proper trans- Sec. 152.11 Requirements for portable and port- endorsed for Class A privileges, and actually is mitting apparatus and control of the premises upon able -mobile operation. A licensee of an amateur operated by an amateur operator holding Class A which such apparatus is to be located; provided, station may operate portable amateur stations (Sec- privileges: 3900 to 4000 kilocycles, 14150 to 14250 however, that in the case of an amateur station of tion 150.03) in accordance with the provisions of kilocycles. the military or Naval Reserve of the United States Sections 152.09, 152.10, 152.12 and 152.45. Such Sec. 152.29 Television and frequency -modula- located in approved public quarters and established licensee may operate portable and portable -mobile tion transmission. The following bands of frequen- for training purposes, but not operated by the amateur stations without regard to Section 152.12, cies are allocated for use by amateur stations for United States Government, a station license may but in compliance with Sections 152.09, 152.10 and television and radiotelephone frequency -modulation be issued to a person in charge of such a station 152.45, when such operation takes place on author- transmission: 112000 to 118000 kilocycles (the although not a licensed amateur operator. ized amateur frequencies above 28,000 kilocycles. Commission reserves the right to change or cancel Sec. 152.02 Eligibility of corporations or organ- Sec. 152.12 Special provisions for portable sta- these frequencies without advance notice or hear- izations to hold license. An amateur station license tions. Advance notice in writing shall be given by ing), 224000 to 230000 kilocycles (the Commission will not be issued to a school, company, corporation, the licensee to the inspector in charge of the district reserves the right to change or cancel these fre- association, or other organization; nor for their use; in which such portable station is to be operated. quencies without advance notice or hearing), 400000 provided, however, that in the case of a bona -fide Such notices shall be given prior to any operation to 401000 kilocycles. amateur radio society a station license may be issued contemplated and shall state the station call, name Sec. 152.30 Facsimile transmission. The fol- in accordance with Section 152.01 to a licensed of licensee, the date of proposed operation, and the lowing bands of frequencies are allocated for use amateur operator as trustee for such society. locations as specifically as possible. An amateur by amateur stations for facsimile transmission: 1715 Sec. 152.03 Location of station. An amateur station operating under this Section shall not be to 2000 kilocycles (subject to change to "1750 to radio operated during any period exceeding one month station, and the control point thereof when 2050" kilocycles in accordance with the "Inter - remote control is authorized, shall not be located on without giving further notice to the inspector in American Arrangement Covering Radiocommuni- premises controlled by an alien. charge of the radio inspection district in which the cation," Havana, 1937), 56000 to 60000 kilocycles, Sec. 152.04 License period. License for an ama- station will be operated, nor more than four consecu- 112000 to 118000 kilocycles (the Commission re- teur station will normally be for a period of three tive periods of one month at the same location. This serves the right to change or cancel these fre- years from the date of issuance of a new, renewed, Section does not apply to the operation of portable quencies without advance notice or hearing), or modified license. or portable -mobile amateur stations on frequencies 224000 to 230000 kilocycles (the above 28,000 kilocycles. (See Section 152.11.) Commission re- Sec. 152.05 Authorized operation. An amateur Sec. 152.13 serves the right to change or cancel these frequen- station license authorizes the operation of all trans- Special provisions for non-portable cies without advance notice or hearing), 400000 to mitting apparatus used by the licensee at loca- stations. The provisions for portable stations shall 401000 kilocycles. the not be applied to any non -portable station except tion specified in the station license and in addition that: Sec. 152.31 Individual frequency not specified. the operation of portable and portable-mobile stations (a.) An amateur station has Transmissions by an amateur station may be on at other locations under the same instrument of that been moved any frequency within the bands above assigned. authorization. from one permanent location to another permanent location may be operated at the latter location in ac- Sideband frequencies resulting from keying or Sec. 152.06 Renewal of amateur station license. cordance with the provisions governing portable sta- modulating a transmitter shall be confined within An amateur station license may be renewed upon the frequency band used. proper tions for a period not exceeding sixty days, but in application and a showing that, within three no event beyond the expiration date of the license, Sec. 152.32 Types of emission. All bands of months of receipt of the application by the Commis- provided an application for modification of license frequencies allocated to the amateur service may be sion, the licensee thereof has lawfully operated such to change the permanent location has been made to used for radiotelegraphy, type A-1 emission. Type station in communication by radio with at least three the Commission. A-2 emission may be used in the following bands of other amateur stations licensed by the Commission, (b.) The licensee of an amateur station who is frequencies only: 56000 to 60000 kilocycles, 112000 except that in the case of an application for renewal temporarily residing at a location other than the to 118000 kilocycles (the Commission reserves the of station license issued for an amateur society or licensed location for a period not exceeding four right to change or cancel these frequencies without reserve group, the required operation may be by any months may for such period operate his amateur advance notice or hearing), 224000 to 230000 kilo- licensed amateur operator. Upon failure to comply station at his temporary address in accordance with cycles (the Commission reserves the right to change with the above requirements, a successor license will the provisions governing portable stations. or cancel these frequencies without advance notice not be granted until two months after expiration of Use of Amateur Stations or hearing), 400000 to 401000 kilocycles. the old license. Sec. 152.14 Points of communication. An ama- Equipment and Operation Sec. 152.07 Posting of station license. The teu station shall communicate only with other ama- Sec. 152.40 Maximum power input. The li- original of each station license or a facsimile thereof teur stations, except that in emergencies or for test- censee of an amateur station is authorized to use a shall be posted by the licensee in a conspicuous ing purposes it may be used also for communication maximum power input of 1 kilowatt to the plate place in the room in which the transmitter is located with commercial or Government radio stations. In circuit of the final amplifier stage of an oscillator - or kept in the personal possession of the operator on addition amateur stations may communicate with amplifier transmitter or to the plate circuit of an duty, except when such license has been filed with any mobile radio station which is licensed by the oscillator transmitter. An amateur transmitter oper- application for modification or renewal, or has been Commission to communicate with amateur stations, ating with a power input exceeding nine -hundred mutilated lost, or destroyed, and application has and with stations of expeditions which may also be watts to the plate circuit shall provide means for been made for a duplicate. authorized to communicate with amateur stations. accurately measuring the plate power input to the Call Signals They may also make transmissions to points vacuum tube, or tubes, supplying power to the Sec. 152.08 Assignment of call letters. Amateur equipped only with receiving apparatus for the antenna. station calls will be assigned in regular order and measurement of emissions, observation of trans- Sec. 152.41 Power supply to transmitter. The special requests will not be considered except that a mission phenomena, radio control of remote objects, licensee of an amateur station using frequencies call may be reassigned to the latest holder, or if not and similar purely experimental purposes. below 60000 kilocycles shall use adequately filtered under license during the past five years to any pre- Sec. 152.15 No remuneration for use of station. direct -current plate power supply for the transmit- vious holder, or to an amateur organization in An amateur station shall not be used to transmit or ting equipment to minimize memoriam to a deceased member and former holder, receive messages for hire, nor for communication and to prevent the emission of broad signals. and particular calls may be temporarily assigned to for material compensation, direct or indirect, paid Sec. 152.42 Requirements for prevention of in- stations connected with events of general public or promised. terference. Spurious radiations from an amateur interest. Sec. 152.16 Broadcasting prohibited. An ama- transmitter operating on a frequency below 60000 Sec. 152.09 Cali signals for member of U.S.N.R. teur station shall not be used for broadcasting any kilocycles shall be reduced or eliminated in accord- In the case of an amateur licensee whose station is form of entertainment, nor for the simultaneous re- ance with good engineering practice and shall not be licensed to a regularly commissioned or enlisted transmission by automatic means of programs or of sufficient intensity to cause interference on re- member of the United States Naval Reserve, the signals emanating from any class of station other ceiving sets of modern design which are tuned out- Commandant of the naval district in which such sta- than amateur. side the frequency band of emission normally re- tion is located may authorize in his discretion the Sec. 152.17 Radiotelephone tests. The trans- quired for the type of emission employed. In the use of the call -letter prefix N in lieu of the prefix W mission of music by an amateur station is forbidden. case of A-3 emission, the transmitter shall not be or K, assigned in the license issued by the Commis- However, single audio -frequency tones may be modulated in excess of its modulation capability to sion, provided that such N prefix shall be used only transmitted by radiotelephony for test purposes of the extent that interfering spurious radiations when operating in the frequency bands 1715-2000 short duration in connection with the development occur, and in no case shall the emitted carrier be (Subject to change to "1750 to 2050" kilocycles in of experimental radiotelephone equipment. amplitude -modulated in excess of 100 per cent. accordance with the "Inter -American Arrangement Allocation of Frequencies Means shall be employed to insure that the trans- Covering Radiocommunication," Havana, 1937) Sec. 152.25 Frequencies for exclusive use of mitter is not modulated in excess of its modulation kilocycles, 3500-4000 kilocycles, 56,000-60,000 kilo- amateur stations. The following bands of frequen- capability. A spurious radiation is any radiation cycles, and 400,000-401,000 kilocycles in accordance cies are allocated exclusively for use by amateur from a transmitter which is outside the frequency with instructions to be issued by the Navy Depart- stations: 1715 to 2000 kilocycles (subject to change band of emission normal for the type of transmis- ment. to "1750 to 2050" kilocycles in accordance with the sion employed, including any component whose "Inter -American Arrangement Covering Radiocom- frequency is an integral multiple or submultiple of Sec. 152.10 Transmission of call signals. An munication," operator of an amateur station shall transmit its as- Havana, (1937), 3500 to 4000 kilo- the carrier frequency (harmonics and subbamonics), signed call at the end cycles, 7000 to 7300 kilocycles, 14000 to 14400 kilo- spurious modulation products, key clicks, and other of each transmission and at cycles, 28000 to 30000 kilocycles, to least once every ten minutes during transmission of 56000 60000 transient effects, and parasitic oscillations. The kilocycles, 112000 to 118000 kilocycles (the Com- frequency of emission shall be as constant as the more than ten minutes' duration: provided, how- mission reserves ever, that transmission of less than one minute dura- the right to change or cancel these state of the art permits. frequencies without advance notice or hearing), Sec. 152.43 Modulation of carrier wave. Except tion from stations employing break-in operation need 224000 be identified only once every ten minutes of opera- to 230000 kilocycles (the Commission re- for brief tests or adjustments, an amateur radio- serves the right to change or cancel these frequen- telephone station shall not emit a carrier wave un- tion and at the termination of the correspondence. cies without In addition, an operator of an amateur portable advance notice or hearing), 400000 to less modulated for the purpose of communication. or 401000 kilocycles. Sec. 152.44. Frequency measurement and regu- portable -mobile radiotelegraph station shall transmit Sec. 152.26 Use of immediately after the call of the station the f raction- frequencies above 300000 lar check. The licensee of an amateur station shall kilocycles. The licensee of an amateur station may, provide for measurement of the transmitter fre- bar character (DN) followed by the number of the subject to change upon further order, operate ama- quency and establish amateur call in procedure for checking it regu- area which the portable or portable - teur stations, with any type of emission authorized larly. The measurement of the transmitter fre- mobile station is then operating, as for example: for amateur stations, on any frequency above quency shall be made by means Example 1. independent of the Portable or portable -mobile amateur 300000 kilocycles without separate licenses therefor. frequency control of the transmitter and shall be of station operating in the third amateur call area calls Sec. 152.27 Frequency bands for telephony. sufficient accuracy to assure operation within the 26 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK frequency band used. may be imposed during the term of the license. Any 1715-2000 (subject to change to "1750 to 2050" Sec. 152.45. Logs. Each licensee of an amateur licensee receiving due notice requiring the station kilocycles in accordance with the "Inter -American station shall keep an accurate log of station opera- licensee to observe such conditions shall immedi- Arrangement Covering Radiocommunication," tion, including the following data: ately act in conformity therewith. Havana, 1937) kilocycle or 3500-4000 kilocycle (a.) The date and time of each transmission. Sec. 152.51 Quiet hours. In the event that the amateur bands. Incidental calling, testing, or work- (The date need only be entered once for each day's operation of an amateur station causes general inter- ing, including casual conversation or remarks not operation. The expression "time of each transmis- ference to the reception of broadcast programs with pertinent or necessary to constructive handling of sion" means the time of making a call and need not receivers of modern design, such amateur station the general situation shall be prohibited. be repeated during the sequence of communication shall not operate during the hours from 8 o'clock (b.) The frequencies 1975-2000, 3500-3525, and which immediately follows; however an entry shall p.m. to 10:30 p.m., local time, and on Sunday for 3975-4000 kilocycles shall be reserved for emer- be made in the log when "signing off" so as to show the additional period from 10:30 a.m. until 1 p.m., gency calling channels, for initial calls from isolated the period during which communication was car- local time, upon such frequency or frequencies as stations or first calls concerning very important ried on.) cause such interference. emergency relief matters or arrangements. All (b.) The signature of the person manipulating Sec. 152.52 Second notice of same violation. In stations having occasion to use such channels shall, the transmitting key of a radiotelegraph transmitter every case where an amateur station licensee is cited as quickly as possible, shift to other frequencies or the signature of the person operating a trans- a second time within a year for the same violation for carrying on their communications. mitter of any other type (type A-3 or A-4 emission) under Section 152.25, 152.27, 152.28, 152.30, (c.) A five-minute listening period for the first with statement as to type of emission, and the signa- 152.31, 152.41, or 152.42, the Commission will five minutes of each hour shall be observed for ture of any other person who transmits by voice direct that the station remain silent from 6 p.m. initial calls of major importance, both in the desig- over a radiotelephone transmitter (type A-3 emis- to 10:30 p.m., local time, until written notice has nated emergency calling channels and throughout sion). (The signature need only be entered once been received authorizing full-time operation. The the 1715-2000 (subject to change to "1750 to 2050" in the log provided the log contains a statement to licensee shall arrange for tests at other hours with kilocycles in accordance with the "Inter -American the effect that all transmissions were made by the at least two amateur stations within fifteen days Arrangement Covering Radiocommunication," person named except where otherwise stated. The of the date of notice, such tests to be made for the Havana, 1937) and 3500-4000 kilocycle bands. signature of any other person who operates the sta- specific purpose of aiding the licensee in determin- Only stations isolated or engaged in handling offi- tion shall be entered in the proper space for his ing whether the emissions of his station are in cial traffic of the highest priority may continue transmissions.) accordance with the Commission's Regulations. The with transmissions in these listening periods, which (c.) Call letters of the station called. (This entry licensee shall report under oath to the Commission must be accurately observed. No replies to calls or need not be repeated for calls made to the same sta- at the conclusion of the tests as to the observations resumption of routine traffic shall be made in the tion during any sequence of communications, pro- reported by amateur licensees in relation to the five-minute listening period. vided the time of "signing off" is given.) reported violation. Such reports shall include a (d.) The Commission may designate certain ama- (d.) The input power to the oscillator, or to the statement as to the corrective measures taken to teur stations to assist in promulgation of its emer- final amplifier stage where an oscillator -amplifier insure compliance with the Regulations. gency announcement, and for policing the 1715-2000 transmitter is employed. (This need be entered only Sec. 152.53. Third notice of same violation. In (subject to change to "1750 to 2050" kilocycles in once, provided the input power is not changed.) every case where an amateur station licensee is accordance with the "Inter-American Arrangement (e.) The frequency band used. (This informa- cited the third time within a year for the same Covering Radiocommunication," Havana, 1937) tion need be entered only once in the log for all violation as indicated in Section 152.52, the Com- and 3500-4000 kilocycle bands and warning non- transmissions untill there is a change in frequency mission will direct that the station remain silent complying stations noted operating therein. The to another amateur band.) from 8 a.m. to 12 midnight, local time, except for operators of these observing stations shall report (f.) The location of a portable or portable -mobile the purpose of transmitting a prearranged test to fully the identity of any stations failing, after due station at the time of each transmission. (This need be observed by a monitoring station of the Commis- notice, to comply with any section of this regula- be entered only once provided the location of the sion to be designated in each particular case. Upon tion. Such designated stations will act in an ad station is not changed. However, suitable entry completion of the test the station shall again remain visory capacity when able to provide information shall be made in the log upon changing location, silent during these hours until authorized by the on emergency circuits. Their policing authority is showing the type of vehicle or mobile unit in which Commission to resume full-time operation. The limited to the transmission of information from the station is operated and the approximate geo- Commission will consider the results of the tests responsible official sources, and full reports of rion- graphical location of the station at the time of and the licensee's past record in determining the compliance which may serve as a basis for investi- operation.) advisability of suspending the operator license gation and action under Section 502 of the Com- (g.) The message traffic handled. (If record com- and/or revoking the station license. munications Act. Policing authority extends only munications are handled in regular message form, Sec. 152.54 Operation in emergencies. In the to 1715-2000 (subject to change to "1750 to 2050" a copy of each message sent and received shall be event of widespread emergency conditions affecting kilocycles in accordance with the "Inter-American entered in the log or retained on file for at least domestic communication facilities, the Commission Arrangement Covering Radiocommunication," one year.) may confer with representatives of the amateur Havana, 1937) and 3500-4000 kilocycle bands. The log shall be preserved for a period of at least service and others and, if deemed advisable, will Individual policing transmissions shall refer to this one year following the last date of entry. The copies declare that a state of general communications Section by number, shall specify the date of the of record communications and station log, as re- emergency exists, designating the licensing area or Commission's declaration, the area and nature of quired under this section, shall be available for areas concerned (in general not exceeding 1,000 the emergency, all briefly and concisely. Policing - inspection upon request by an authorized Govern- miles from center of the affected area), whereupon observer stations shall not enter into discussions ment representative. it shall be incumbent upon each amateur station in beyond essentials with the stations notified, or other Special Conditions such area or areas to observe the following restric- stations. Sec. 152.50 Additional conditions to be observed tions for the duration of such emergency: (e.) These special conditions imposed under this by licensee. An amateur station license is granted (a.) No transmissions except those relating to Section will cease to apply only after the Commis- subject to the conditions imposed in Sections 152.51 relief work or other emergency service such as sion shall have declared such emergency to he to 152.54 inclusive, in addition to any others that amateur nets can afford, shall be made within the terminated.

3 -WEAK SIGNALS. COMMON WORD ABBREVIATIONS 4 -FAIR SIGNALS. 5 -FAIRLY GOOD SIGNALS. ABT about GA go ahead ND nothing doing TNK think 6 -GOOD SIGNALS. AHD ahead GM good morning NG no good TR there AHR another GN good night NL night letter TT that 7 -MODERATELY STRONG SIGNALS. ANI any GT get, got NM no more UD it would 8 -STRONG SIGNALS. BD bad GG going NR number UL you'll BK break NW now 9 -EXTREMELY STRONG SIGNALS. HA laughter from BUG speed key HI laughter -high OB old boy VB BN been very bad HR hear-here OL old lady VY very 84 before HW how OM old man BI by HV have OP operator WA word after BCUZ because OW old woman WB word before TONE BTWN between I "ok" WD would BIZ business IC I see PLS please WF word following 1 -EXTREMELY ROUGH, HISSING CK check K go ahead PSE please WK work CN can LID poor operator PX press WL will-would NOTE. LIL little CUL see u later R ok WN when 2 A.C. C see LST last RI radio inspector WL wavelength -VERY ROUGH NOTE -NO CW continuous wave LTR letter SA say WT what TRACE OF MUSICALITY. DE from MI my SS single signal WX weather DX distance MA milliamp. SIG signal X interference 3 -ROUGH, LOW-PITCHED A.C. DA day MSG message STICK pencil XMTR transmitter NOTE -SLIGHTLY MUSICAL. DH dead -head MILL typewriter SKED schedule VF wife DC direct current MST must TFC traffic YL young lady 4-RATHER ROUGH A.C. NOTE - ES and MNI many TKS thanks YR your MODERATELY MUSICAL. FB fine business MI my TNX thanks 30 finish FM from MK make TK take 73 regards 5 -MUSICALLY MODULATED NOTE. FR for MO more TMW tomorrow 88 love and kisses 6 -MODULATED NOTE -SLIGHT TRACE OF WHISTLE. 7 -NEAR D.C. NOTE -SMOOTH RIP R -S -T REPORTING SYSTEM PLE. 8 -GOOD D.C. NOTE -JUST TRACE READABILITY 4 -READABLE WITH PRACTICALLY OF RIPPLE. NO DIFFICULTY. 1 -UNREADABLE 9- -PUREST D.C. NOTE. 5-- PERFECTLY READABLE. 2 -BARELY READABLE - OCCA- IF THE NOTE APPEARS TO BE SIONAL WORDS DISTINGUISH SIGNAL STRENGTH CRYSTAL CONTROLLED, SIMPLY ABLE. 1 -FAINT SIGNALS B ARELY PER- ADD AN X AFTER THE APPRO- - PRIATE NUMBER. 3 -READABLE WITH CONSIDER- CEPTIBLE. ABLE DIFFICULTY. 2 -VERY WEAK SIGNALS. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 27 INSTRUMENTS AN ELECTRIC CALIBRATOR

quickest and most simple check on a receiv- er's calibration in the home as well as in the shop. Plugged in on any a. c. line, 11 fre- quency checks are supplied on the standard broadcast band employing the 100 kc. funda- mental, plus one check right in the center of the band, at 1000 kc. on the 1000 kc. fundamental. On the higher frequencies there are many more checks per band-every 100 kc. and every 1000 kc.-up to the limits of the har- monics which are above the range of the average set. Naturally every 1000 kc. har- monic coincides with a corresponding 100 kc. harmonic. For instance, on 9 mega- The Piezo-Electric Calibrator set up to cycles, on the high position, the 9th har- measure the efficiency of the receiver. monic of the 1000 kc. fundamental will be heard. On flipping the toggle switch to the crystal calibrator affords accurate cali- the low position the 90th harmonic of the bration of vernier dials, greatly facilitating 100 kc. fundamental will be received-"right the identification of stations by their known on the nose!" frequencies. Start counting in 100 kc. steps The 1000 kc. steps are used for spotting from a positively identified 1000 kc. har- rather than calibration. It might often be monic. These steps will be consistent- impossible to identify a 100 kc. harmonic. evenly spaced-and relatively weak signals For example, several 100 kc. harmonics will between these steps are spurious and should be located close to 9 megacycles, but only be disregarded. The Electric Calibrator. that one coinciding with the 9th harmonic A similar curve on an amateur receiver of the 1000 kc. fundamental locates 9 mc. WITH DX bands becoming more provides an immediate answer to a request It is then possible to count in either direc- for a frequency check. Explanation of the crowded, and the hunting of DX tion in 100 kc. steps, and calibrate the re- a national sport, a well calibrated use of the calibrator will furnish the answer ceiver or oscillator in a series of 9.1 mc., to the inevitable government license exam- receiver is almost a necessity. There are 9.2 mc., 9.3 mc., etc. Care, however, should many calibrated receivers on the market, but ination question, "Explain how you would be taken to observe and reject image fre- determine whether the frequency of your few of them, unfortunately, are accurate. quencies on the wavelengths below 25 meters. a dis- transmitter was within the amateur band?" The RCA Piezo-Electric Calibrator is the all -wave oscillator is one of the While The quartz crystal and plates should be tinct asset toward calibration. serviceman's most useful tools, its utility is cleaned frequently. As soon as the har- If you figure its cost in dollars per ounce, considerably lessened when it gets out of monic output of the 100 kc. fundamental be- or dollars per cubic inch, it comes pretty calibration. Such oscillators are readily cali- gins to weaken around 20 meters, or when high! Actually, its cost is about half that of brated with the aid of the Piezo-Electric cali- a tap against the side of the instrument is a good all -wave oscillator, and in value per brator. The set-up is shown in the figure- required to obtain a vigorous response, the dollar it is, in the estimation of the writer, a Hickok oscillator in the background, an crystal holder should be dismantled and the the best buy in radio test equipment today. It receiver to the left, and the cali- all -wave plates and crystal cleaned with carbon tetra- consists of a 955 acorn tube, a special cir- brator in the center. The frequencies to be chloride or alcohol. Do not disturb the 1000 cuit, and a crystal with two frequency nodes. checked are located on the receiver, and the kc. trimmer. After cleaning do not touch This provides a wealth of harmonics with oscillator tuned to zero beat. Needless to the plates or crystal with the hands. Use a an accuracy as high as two parts in one say, the all -wave oscillator should be given clean soft handkerchief to prevent grease million. The instrument is of equal value to ample time to warm up. The same holds from the skin from filming the cleaned parts. the serviceman, the short-wave fan and the for the crystal oscillator-but to a much amateur. less degree. The crystal is then replaced and the plates The crystal's fundamentals are 100 and To the serious short-wave experimenter, evenly tightened until the crystal will not three 1000 kilocycles. A toggle switch selects oscillate. Letting up equally on the nuts thus loosening the plates until the 100 either frequency. Operated from 115 volts 16 MAIN DIAL SETTING kc. harmonic on a high frequency coincides 60 -cycle a. c., raw a. c. is applied to the plate 15.6 STARTS AT 13.9 MC. a -cycle modulated with the 1000 kc. harmonic. of the 955 providing 60 Iss output. With the removal of a jumper across Occasionally the oscillator should be two posts and the substitution of 90 volts 15.4 checked against a reliable broadcasting sta- of "B" battery, a pure d. c. output is ob- 15.2 tion, or better yet, WWV's standard fre- tained. The 1000 kc. harmonics are readily 2 Is quency transmissions. These occur daily at detectable as high as 30 megacycles-the g14.6 5000 kc., the 5th harmonic of the "high" thirtieth harmonic-and the 100 kilocycle 14.6 116.2 top or 50th harmonic of the "low." Beat signal. If a zero harmonic at 15 megacycles-the 150th har- 14.4 the oscillator against the results the instrument is OK, if not.. monic! Ordinarily the device is merely 14.2 beat near the receiver-no input neces- determine by heterodyne beat method the placed 14 VERNIER DIAL sary. With closer coupling one can go even amount it is off and mark this up for ref- IS 20 5 10 o 5 IO 15 z0 5 10 1s 20 5 to higher. o 0 ó erence. should then be made for all fre- This instrument will fit readily even into A receiver calibration. The A chart to maintain accuracy. a small service kit, and therefor provides the vernier dial setting graphed. quencies 28 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

The front of the unit. The dial controls the pitch of the audio note, the meter is used in the Vacuum tube voltmeter.

CHI CH2 340v. 4B3 78 r R25 0+82R" b C34 2sov C30 I C31 C32 C33 O4BI3sv. C29 i -L 0 T cas

FOR INFORMATION ON `vJ©QD © SEE TEXT While it seems complicated, the wiring is The circuit of the B.F.O. combination V.T.M. extremely simple. Shielding should be fol- lowed wherever indicated for best results. A HOME -BUILT AUDIO OSCILLATOR WITH high fidelity audio amplifiers paratively high output, the unit proved such The layout is compact. The component and audio by-pass filtered circuits a good performer that it has busily been go- parts are so placed that the path of the signal becoming more and more common- ing the rounds on loan to other laboratories. is progressive and long leads are eliminated. place, the laboratory of the advanced ama- The very uses to which a beat frequency The front panel is simple and businesslike. teur and serviceman is not complete without oscillator is put, make a vacuum tube volt- The power supply is grouped in one corner an audio oscillator, sometimes termed "Beat meter a necessity. In this unit the meter is with the power output tube adjacent to it. Frequency Oscillator." Unfortunately this brought out to a separate terminal; the cus- The most sensitive circuits, those of the oscil- apparatus is expensive when purchased com- tomary practice is to bridge it directly to the lators, are placed well away at the other end experimenters plete and, therefore, many output terminal within the instrument. Cali- of the chassis. The variable condenser is and engineers have preferred to work with- to eliminate brated readings in both the input and output mounted on rubber grommets out it. microphonic effects which could otherwise circuits of amplifiers are therefore possible. The working circuit of the Beat Fre- become annoying. (Only one section of the quency Oscillator is difficult to obtain be- A separate voltage divider is provided for standard two section broadcast variable con- cause it is rarely published and the one the vacuum tube voltmeter. This improves denser is used.) power supply regulation (the current for herein described resulted from an enforced The oscillator inductances and the tuned the meter does not pass through the chokes) session with a slide rule and a soldering iron. tank are made from ordinary single tuned and frequency flutter in It includes a vacuum tube voltmeter thereby eliminates intermediate frequency (IF) transformers. output when the volume is sud- brought to its own separate terminal, an in- the control The rated frequency is not important, but novation which greatly increases the flexibil- denly turned full on with the meter con- the three should be identical. Mica dielectric ity of making measurements. With a com- nected. trimmers were used in the unit being de- scribed, but air trimmed transformers are Parts of the Audio Oscillator. preferable. CI -Trimmer of IF C24-5 mfd 450v electro. Rs 10000 ohms 10 ,r. The transformers are carefully removed C2-.00025 mfd mica C25-5 mfd 450v electro. Ro -.25 megohm 5 w. C3 -.0l mfd 200v paper C26 -.I mfd 450v paper R1Ir-100000 ohms 2 w. from their cans and the following changes C4-.01 mfd 200v paper Cr7-.002 mfd mica R11-13000 ohms 10 w. are made. As soon as each has been recon- C5-.01 mfd 200ro paper C28-.01 mfd mica RIS -.25 megohm 10 w. C6 -Trimmer of IP C23-.01 mfd mira R13-100000 ohms 10 w. nected, it should be returned to its can and C7 -.0000I mfd trimmer Ca3-0 mfd 500v electro. R14-25000 ohms 1 w. marked to eliminate the possibility of error C8-.01 mid 350e paper C3l-8 mfd 500v electro. R16-50000 ohms I w. C9-.O1 mid 350v paper Ca2-8 mid 500v electro. R16-10000 ohms 1 w. in placement. C10-.00025 mid 400v mica C33-8 mfd 500v electro. R17.-.500000 ohms 5 tr. C11-.01 mfd 350v paper C34-8 mfd 500e electro. R58-25000 ohms S w. For the variable oscillator inductance: The C12-.00025 mid 400v mira C36-8 mfd 500v electro. R19-10000 ohms pot. trimmer is disconnected. The primary and C13-5. mid 450ro electro. C36 -I mfd 450v paper R70-100000 ohms 10 w. C14-.1 mfd 450v paper R5-25000 ohms 1 te. R21-.25 megohm 5 u.. secondary of the transformer are connected C15-.1 mid 450v mica R2-50000 ohms 1 w. R22-1000 ohms 10 w. in series so that both windings run continu- C16-.1 mfd 450v paper R3-10000 ohm. 1 to. R23-5000 ohms 10 w. C17-.0002 padder air cond. R4-.5 megohm 1 w. R24-5000 ohms pot. ously in the same direction. The trimmer is Cig-35 mold var. midget R6-.50000 ohms 1 w. R25,R76-40000 ohms 25 w. o,l j. connected to one end of the primary and one C16-.00025 mid mica R6-7500 ohms 10 w. Z-2 megohms l w. Cur -Trimmer of IF R7-100000 ohms 10 w. SW -4C switch end of the secondary. Three leads are C21 -.0I mfd 200v paper Meter -0.50 Milliammeter with internal shunt removed. two from the trimmer and one C22-.01 mfd 200v paper L, L5, L, -Rebuilt 1F transformers. See text for details. brought out, C23-.00001 mid trimmer RFC -.Standard broadcast band, radio frequency chokes. from the junction of primary and secondary. Q -Insert .01 mfd at pt Q When the windings have been replaced in RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 29 the can, a zero adjuster is made from a small much the better. These precautions will be Another way, and the one used for the in- right angle bracket, a piece of fibre rod filed appreciated when the beat frequency oscil- strument being described, is to check it to a screwdriver shape on one end, and a lator is used in connection with sensitive re- against a broadcast station making a fre- knob. This is clearly shown in the illustration. ceivers or to modulate the output of a signal quency run at night after the programs cease. For the fixed oscillator inductance: The generator. It is customary for the large broadcasters primary and the secondary are connected in The wiring diagram should prove self- to make these frequency runs at regular in- series so that both windings run in the same explanatory as far as connections go. The tervals. They do this by modulating their direction. The trimmer is connected to the RF chokes are the standard broadcast type transmitters with audio frequencies from the two open ends left. Three leads are brought wound in pi form; the values are not critical. lowest to the highest. A telephone call to out, two from the trimmer and one from the The trimmer marked C is a padder for the the operator will identify the frequency in junction. variable condenser; it enables the full audio cycles per second; the identical frequency on For the tuned tank: The primary and the scale to be spread over the entire dial. the oscillator is then logged by dial degrees. secondary are again connected in series and Putting this beat frequency oscillator into The lowest frequencies, that is harmonics the trimmer is connected across the two out- operation is easy. Turn the unit on (the and sub -harmonics of sixty cycles, can also side ends. Only two leads are brought out, switch is the knob under the dial) and touch be obtained by beating against the power however, one from each side of the trimmer. the grids of the oscillators with the prong supply using two speakers or phones, one The front panel is of aluminum and mea- of a high resistance voltmeter. If they are connected to the AC line through a resist- sures seven inches high by fourteen inches oscillating properly the grids will show ance, the other to the oscillator. wide. The chassis is of plated steel seven negative. The vacuum tube voltmeter is quickly cali- inches deep, thirteen inches wide and two Next connect a pair of phones or a small brated in RMS values by means of the 25,000 and a half inches high. loud speaker to the output terminal and ad- ohm potentiometer and the AC voltmeter The output volume control (marked A vance the volume control slightly (the knob hooked up as shown in the diagram. The in the diagram) is an ordinary 5,000 ohm under the meter). Tune the tank to the tube is of course first set practically at cut- wire wound potentiometer. It would be well fundamental frequency of the fixed oscil- off by means of a variable cathode tap on its worth the slight additional expense, however, lator. This can be done in various ways as, voltage divider. The plate tap is set at a to substitute an L pad at this point. Such for instance, by watching a meter in the plate value which will allow the tube to draw a a pad would keep the output impedance of circuit. The dial is then set to zero and the maximum current just enough to swing the the beat frequency oscillator constant regard- zero adjuster on the can of the inductance meter full scale. The false zero will be less of the output level. In the described is turned cautiously until zero beat is heard. slightly above the actual zero on the meter; unit, this output impedance changes with (Later zero beat adjustments are made much the needle is set back before calibration by each change in volume. more accurately with the vacuum tube volt- means of the screwdriver slot on the meter Degenerative coupling is used in the out- meter ) face. put for the sake of its response-improving - The padding trimmer C is then manipu- The power transformer is the standard and -flattening effect. The 10,000 ohm wire lated until the highest audible frequency broadcast receiver type. The chokes are the wound potentiometer (marked B in the dia- comes at the high end of the tuning dial. small ones usually found in low priced re- gram) serves both as a cathode bias resistor The coupling trimmers D and E are turned ceivers. Three wet electrolytic condensers and introducer of out -of -phase signal volt- to the positions (usually around their lowest are used in the two pi section filter and a age. It should be noted that the 5 mfd. low capacities) which will give the purest notes. dual dry electrolytic is used across the taps voltage electrolytic at this point is connected The degeneration control B is also set at the of the main voltage divider. from the cathode to the potentiometer arm best point. An oscillograph is a great help A milliammeter of 0.50 range was in- and not to the ground. at this point in inspecting the wave form, corporated in the beat frequency oscillator Both sides of the primary of the power which should be pure. being described because it was the only one transformer are connected to the chassis When everything is running smoothly, a available. The internal shunt was removed through .01 mfd. fixed condensers. If a calibration chart of the beat frequency oscil- and it was then possible to get full scale de- transformer with an electrostatic shield be- lator is prepared. The easiest method, of flections easily with the type 76 tube when tween primary and secondary can be had, so course, is to compare it to a standard. measuring the output of the unit. CONSTRUCTING A POLARIZED RELAY THERE is always considerable use for in "squelch" circuits used to reduce, or cut relays in the equipment of experi- off entirely, the output of radio sets when the menters, especially in photo electric signal input reaches a certain predetermined, cell applications. Relays are not hard to minimum value. build, but the average home -constructed re- With no current flowing in the coils the lay is very insensitive to feeble currents of a armature is attracted equally to either pole. milliampere or less. However, if a current is passed through the The relay to be described is very sensi- coils in the direction shown, the polarity of tive; the one constructed operating well on Nj will be strengthened, and the polarity to the op- currents as low as 250 microamperes. In one of N2 weakened or even changed tends to move the experiment, it operated on 50 microamperes, posite. This, of course, toward N1. The action is reversed although the reliability was poor for this armature by changing the direction of the current. sensitivity. The current controlling capac- The completed polarized relay. Simple, com- pact and efficient, it will give excellent service. The parts needed are very easy to obtain. ity however is quite low, when operating The magnets can be obtained from an old at such low currents, due to the small sepa- rent reverses direction. It remains on the magneto from any motorcycle shop or air- so an auxiliary relay ration of the contacts, other contact until again reversed. port repair station. The poles are made of not over .25 drawing an energizing power of This also makes it applicable as a circuit laminated iron of good permeability. The watt should be used. breaker. It can be made to close on a given cores of old audio transformers are especially Auxiliary relays should always be used current in a predetermined direction, and good. The coils can be obtained from a when the sensitive relay is operating on cur- open again as the current is reduced. The vibrating spark coil of the model T Ford rents of a milliampere or under. Those current change to open, when the relay is variety. Both coils in series should have a working on up to two watts are satisfactory. being held closed by the minimum current resistance of about 3,000 to 5,000 ohms, This relay is polarized so as to operate required to close, can be adjusted within each being half that value. on currents of a certain direction. Single rather wide limits. About 250 microamperes The drawing is more or less self explana- pole, double throw, it can be adjusted to is the minimum, when the closing current tory. The dimensions, of course, do not stay closed in one position until direct cur - is a milliampere or over. It is very useful have to be followed exactly, but can he 30 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

Con/ads `Si/ver - - , ; , .^. . ioo ,,, o0o aoo.,. miaimmol= - v i-; ---- 111111/111wee =+ Imagems ram

111ÏIIÌ114 711i1Ì111 111Ì1114

G-32 SC¡es recess 'Vas The drawing clearly shows details. Diagram of how the circuit works. changed to fit the material available. If L brass or aluminum is used for the double holes for ¿o/Ting /o shaped laminations of the dimensions shown purpose of a mounting for the contact panel, A--" pole pieces are not available, the laminated spacers be- and to hold the pole pieces in their proper tween the two permanent magnets can be position. The method of mounting the contact varied to obtain the same air gap between The angle is slotted to allow the arma- points which are really activates. the pole pieces. ture to move from side to side. The screws The armature is held to the pole piece used to hold the panel and the ground bind- at the bottom by a piece of light spring brass. ing post are countersunk in the angle so as one pole piece or the other, depending upon This acts as a hinge. The laminations of not to interfere with the pole pieces. The which side of center it is released. The the lower pole piece are cut to form the mountings for the adjustable contacts are contacts, however, hold it in the position de- small recess shown so as to obtain more flexi- made from binding posts, the horizontal holes sired. The relay will be most sensitive when bility in the brass spring and still allow the being tapped out the size of the contact the armature is nearest a central position. armature to come dose to the pole piece and screw. It is advisable to slot these length- To adjust as a sensitive simple relay, one form a good magnetic connection. A strip wise for a short distance and bend slightly contact is screwed to just past center so that of brass with contacts attached is clamped be- together to make the contact screw self the armature when pressed to this contact, tween the laminations of the armature. This locking. with no current flowing in the coils, will just should be very stiff and have no appreciable A small panel can be fastened to the fall back to the other position. Then with bend as the relay operates. The upper pole permanent magnets to provide connections the current desired to close the relay, flowing pieces are held to the magnets by the U- for the coils. It is advisable to use four in the coils (in the proper direction), the shaped clamps. The lower one is held by binding posts so as to provide series or other contact is moved up until the relay the piece of IV sheet steel cut and bent as parallel connections for the coils. This will trips. shown in the drawing. furnish one-half or double the resistance of This last mentioned contact controls the The adjustable contacts are shown in Fig. each coil, as a total resistance. closing sensitivity, and the former contact 2. A piece of nonmagnetic angle such as In use, the armature will be attracted to the release sensitivity. A VACUUM TUBE VOLTMETER ALTHOUGH cathode ray oscillographs, A few points concerning the signal generators, b.f. oscillators, input circuit will be explained. and a.c. and d.c. meters of every The parts specified are not description, make, range, and style abound critical and good components in the modern experimenter's shack and the of the same values can be up-and-coming service shop, one instrument substituted. Wire wound re- which is not found in many labs as often sistors and paper condensers as its usefulness warrants is the vacuum must be used where specified. tube voltmeter. High cost, low sensitivity The sub -panel brackets were and complicated, battery operated designs revamped from one standard have been some of the reasons. Eliminating 21/2" by 6" aluminum bracket many former defects this v.t. voltmeter is by cutting it in two length- completely a.c. operated, of reasonable high wise and filing the two halves sensitivity and accuracy, and at the same where required. The angle time stable and rugged in operation. The bracket for the four plate re- 2.5 so called because of its two stage circuit sistors and the bias resistor and five self contained ranges in either cir- was bent up from a piece of cuit employs two type 53 tubes in bridge scrap metal. circuits, one as the voltmeter, the other as The socket for the volt- a direct coupled d.c. amplifier. By this meter tube is mounted di- A 6"x9" hardwood cabinet houses the entire unit. means, the sensitivity has been boosted to rectly on the range switch in less than % volt. Throwing a single switch order to obtain the shortest possible leads. socket as close to the switch plate as possible and re -adjusting the milliammeter to zero, This keeps down stray input capacities. The without shorting the contacts. It may be takes the amplifier out of the circuit and wafer socket is easily mounted by removing necessary to file the holes in the socket ears connects one section of the 53 as a conven- the two screws which hold the switch con- slightly oblong, as their center distance is tional plate circuit v.t. voltmeter, giving less tact plate to the indexing plate. Two 1" slightly different from that of the switch sensitivity and higher accuracy on high fre- bolts, of the same size, with two nuts on plate. quency measurements. each will mount the socket and also hold Mount resistors, switch contacts. Note Construction of the 2.5 is quite simple. the switch plate solidly in place. Mount the that metallized resistors were used in the IADIO NEWS 1940 RADIO & TELEVISION DATA 1100K 31

Under chassis view, showing resistor bank. All connections should first be carefully checked with an ohmmeter. Do this with the amplifier switch on both the off and on positions to make sure that the switch has been properly connected. Tap t4 should be set at about the center of the bleeder, its The mounting of component parts. actual position not being very critical. Place t2 near the high voltage end of the re- original 2.5. Substitution of precision, wire be connected to their respective cathodes. sistor, temporarily. The connection between wound resistors is a worth while invest- Mount the milliammeter last, and leave the t2 and the cathode of the voltmeter tube ment, since the accuracy of the instrument leads temporarily disconnected. If a sep- must be broken at some point and the will be much greater. Also, a calibration arate 1000 ohm per volt meter is not avail- milliammeter connected in series so as to made on any range will then hold for all able for the final adjustment of the v.t. measure the total cathode current of the the other ranges. However, it is now pos- voltmeter, it will be necessary to connect voltmeter tube. Now, with the amplifier sible to obtain metallized resistors on spe- the milliammeter of the 2.5 cial order in high accuracy units, around in series with one watt 2%. If either of the above methods can- metalized resistors to make not be used, it is possible to use the stand- a temporary voltmeter. ard commercial metallized units, and either The circuit adjustments VT VOLTMETER select them from a large number so that are made by changing the Q9 values sufficiently close to the correct ones positions of taps on R1, Q9SL0 , can or else to make a separate be found, R2 and R6. These adjust, ''''-TRANSFORMER range. For serv- calibration curve for each ments are important and Sw ice work, the commercial units will prob- must be carried out care- ably be sufficiently accurate without selec- fully if the meter is to Test circuit used for calibration. tion or separate curves. operate at its best and give For DC calibration, substitute a 2-6 volt battery for the trans- former and use DC meter. After mounting the range resistors, wire the sensitivity of which it o switch, Connect + side of meter to center terminal of the 2-5, and the socket to the connecting the is capable. the to bottom terminal. switch arm to the grid terminal nearest it. Calibration- made as above will he accurate on any frequency, including RF. The socket should be mounted so that the filament terminals are at the bottom. Plate A.C. SERIES COND. 53 53 cathode and filament leads about 10" long BALANCE SECTION VOLTMETER AMP. SECTION C2 SECTION should be soldered to the socket with two o SW2 shorter leads for connecting the input ter- A.C. e minals switch unit. Now mount the D.C.r to the FIL. LIELDEADSEDARE Re 102 SH entire socket unit on the panel and proceed X X IC X x Re RIO to wire according to the diagram. The fila- 10s SÇCTINOÑ

Ru I 4 ment center tap for the 53's must not be 0 1 s

I I R12 grounded unless a transformer with sep- O 20 I Ru is 0 R3 arate filament windings for each tube A.C. 0 DC. - MULTIPLYING used. In this case the center taps should 0 -IMA. 4 FACTOR -

SW 3 I OFF AMP. -.-ON `__- 4I -

02 03 74 RI R2 RT The circuit of the 2-5 Vacuum Tube Voltmeter.

Sw2-Single gang, shorting type selector switch. RH-200,000 ohms, Vs se. metalized Single circuit, six pole. Yaxley 1216L. Ri2-100,000 ohms, 1/2 se. metallized Swr-SPST toggle switch. R13-100,000 ohms, % w. metallized Sw3 Six pole, double throw switch Yaxley No. Ci -8 mfd. 500v. electro 3263J, non shorting type. Set adjustable stop C2-1/2 mfd. 200v. paper for two position operation. C3 and C4-% or I mfd. 400v. paper Ri-1,000 ohm, 10 w. adjustable wire wound 0-1 MA milliammeter R2-15,000 ohms, 50 w. adjustable wire wound, Power transformer. 2.5v. @ 4.4; 5v. @ 2.4; 300. Electrad Truvolt. 0-300 83-90,000 ohm wire wound, 20 w. Aluminum or electraloy panel, size 1-16 by 62 R4-100,000 ohm wire wound, 20 w. by 9 inches ohms. universal wire wound R3-10,000 Yaxley Aluminum or electraloy sub -panel, size 1-16 by SW1.1 volume control. Linear taper. Rs -10,000 ohms, 10 w. wire wound 51 by 81/2 inches AC R7-10,000 ohms, 10 w. wire wound Cabinet. 1/2 inch hardwood, with a slip hinged 110V Rs -2 megohms, 1/2 w. metallized cover. Size, inside measurements, 6 by 9 inches Rs -1 megohm, 1 w. metallized by 5% inches, in depth. The lid was 6 by 9 The power supply of the 2-5. Rio -600,000 ohms, 1/ w. metallized by 11/ inches deep. 32 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

switch on off and the amplifier tube out of with the amplifier in the circuit. Discon- the position of RS, which should again be its socket, short the input circuit (range nect the milliammeter. Turn the amplifier in about the center of its range. switch on 0), apply the power and allow switch on, the range switch on 0, and plug Tighten all taps thoroughly so that pull- ten or fifteen minutes for the voltmeter in the amplifier tube. Connect an ammeter ing them slightly in any direction will not tube to become thoroughly heated. with a range of 0.2 ma. or higher in series change the meter reading. This is impor- Next, carefully adjust the cathode tap, with the cathode lead of the voltmeter tube tant, since a loose clip will ruin the cali- t2, until the milliammeter reads .55 ma. (the lead going to tl, with the amplifier bration curve. The sensitivity with the total cathode current. Slightly lower val- on). The milliammeter in the 2.5 may be amplifier on may now be checked by ap- ues will give a little better accuracy, but used by connecting a temporary shunt di- plying an a.c. input. Full scale should be less sensitivity. Higher values only cut rectly across its terminals. Set tap t3 as reached at %2 volt or less. With the am- down the sensitivity. Replace the milliam- close to t4 as possible, tl about in the cen- plifier off, if the milliammeter reads back- meter in its regular position, apply an a.c. ter of Rl. Allow tubes to become thor- ward with a.c. input, reverse the meter input to the meter and check the voltage oughly heated. Now adjust tl until the connections. Then, if the knob of RS turns necessary for full scale. This should be cathode meter reads 1.3 ma. total current in the opposite direction to the meter needle, about 4 volts on range 1. The meter is to the voltmeter tube. change the wire leading to the outside ter- adjusted to zero before applying the input A 1000 ohm per volt meter with a range minal of R5 to the outside lug on the other by turning RS. If the zero adjustment of of 250 volts should then be placed across end of the potentiometer winding. Now, RS is too critical for easy operation, con- R4. The reading should be about 45.50 if the meter reads backwards with the am- nect a 1000 ohm, wire wound resistor in volts. Connect a voltmeter with a range plifier on, reverse the leads going to the series with one of the leads going from the of 100 volts across R7. Then carefully ad- grids of the amplifier tube. When adjusting single cell flashlight battery. Attempting just the cathode tap, t3, of the amplifier R6 for a zero meter reading with the am- to use a tap on the bleeder resistor to sup- tube until the meter reads 25 volts. This plifier on if sufficient resistance cannot be ply the bucking -out current for zero adjust- adjustment is very critical and varies as obtained, reverse the two plate leads from ment, in place of the battery, will result R5 is turned. Set R5 at about the center the amplifier tube to the plate resistors. in greatly decreased accuracy and sensitiv- of its range whole making the adjustment. The meter is calibrated by using an a.c. ity. The life of the battery is practically its Then adjust the end clip on R6 until the voltmeter and the filament winding of a shelf life. milliammeter in its regular position reads power transformer to supply the input volt- Next step is adjustment of the voltmeter zero. This adjustment will also vary with age, according to the diagram. DB 2-4000 OHM CONVERSION CHART DB -VOLTAGE POWER RATIO POWER VOLTS POWER POWER VOLTS POWER LEVEL 500 OHM WATTS LEVEL 500 OHM WATTS DB LINE 0-6mw DB LINE 0-6mw CHART

-20 0.1730 0.00006 +26 34.5590 2.3886 -19 0.1990 0.00007 +27 38.7760 3.0071 -18 0.2180 0.00009 +28 43.5070 3.7857 POWER DECIBELS VOLTAGE io RATIOS RATIOS -17 0.2340 0.00011 +29 48.8160 4.7660 100 IOOM 7 80M -16 0.2730 0.00015 +30 54.7720 6.0000 i 5 0 4 60M -15 0.3000 0.00018 +31 61.4550 7.5535 J 3 95- 50M -14 0.3390 0.00023 +32 68.9540 9.5093 2 40M -13 0.3890 0.00030 +33 77.3680 11.9716 881 90- 30M -12 0.4450 0.00039 +34 86.8080 15.0713 -11 0.4860 0.00047 +35 97.4000 18.9747 400 20M 300 85 -10 0.5477 0.00060 +36 109.2850 23.8865 200 - 9 0.6145 0.00070 +37 122.6200 30.0710 100 80 10M - 8 0.6895 0.00090 +38 137.5820 37.8570 m 70 8M z 50 - 7 0.7737 0.00110 +39 154.3690 47.6600 8M - 6 0.8681 0.00150 +40 173.2050 60.0000 38 75 5M 20 - 5 0.9740 0.00180 +41 194.3400 75.5350 4M - 4 1.0928 0.00230 +42 218.0500 95.0930 f io 70- 3M - 3 1.2262 0.00300 +43 244.6600 119.7160 2M - 2 1.3758 0.00370 +44 274.5100 150.7130 3 65 - 1 1.5437 0.00470 +45 308.0100 189.7470 2 0 1.7321 0.00600 +46 345.5900 238.8650 80 IM + 1 1.9434 0.00750 +47 389.0700 300.7100 5ÓS 800 } 2 2.1805 0.00950 +48 435.6000 379.5000 ---55= 600 3 2.4466 0.01190 487.0100 474.3700 500 + +49 2ÓÓ 400 4 2.7451 0.01500 +50 547.7200 600.0000 + 1óO0 + 5 3.0801 0.01890 +51 616.0300 759.0000 50- 300 6 3.4559 0.02380 +52 688.7400 948.7500 50 + 40 45 200 + 7 3.8776 0.03000 +53 770.4000 1185.9400 + 8 4.3507 0.03800 +54 871.2000 1518.0000 20 + 9 4.8680 0.04740 +55 974 0300 1897.5000 10 40 loo 7 80 +10 5.4772 0.06000 5 Impedance DB 60 +11 6.1600 0.07590 35= 50 +12 6.8100 0.09480 4000 Ohms Add 9 40 +13 7.7368 0.11970 2000 Ohms Add 6 700 30 30 +14 8.7100 0.15070 6000hms Add 1 E=JWZ 20 +15 9.7400 0.18970 500 Ohms 0 where - 25 +16 10.9285 0.23880 250 Ohms Subtract 3 E= AC volts 2 +17 12.2620 0.30070 24 Ohms Subtract 13 across load. 100 20 lo +18 13.7578 0.37850 15 Ohms Subtract 15 Z =loaded line 70 a 50 +19 15.4369 0.47660 10 Ohms Subtract 17 impedance. tn 40 6 +20 17.3205 0.60000 8 Ohms Subtract 18 W=watts. ~ 30 15- 5 +21 19.4340 0.75530 6 Ohms Subtract 19 20 4 21.8050 5 20 in 10 10 3 +22 0.95090 Ohms Subtract Cond. Series 7 +23 24.4660 1.19710 4 Ohms Subtract 21 with DB Meter 5 4 2 +24 27.4510 1.50710 2.5 Ohms Subtract 23 = .25 Mfd. 3 +25 30.8010 1.89740 2 Ohms Subtract 24 2 o RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 88 SERVICE PROBLEMS design of the set, the way it is connected 4. Lack of line filter. Next in importance to its aerial and ground system, the loca- as a cause of overload and distortion is the tion it is being used in or perhaps the pres- case of the power line acting as an aerial. ent condition of the tubes or adjustments The presence of a good aerial and ground of the set. Likewise, external modulation does not help much unless the power line is due to external causes, such as defects is further prevented from acting as an aerial. of the aerial and ground system or of the Seemingly miraculous is the cure of some old wiring and piping in or near the location and some new sets when .01 mfd. con- of the radio. densers are connected from the line to Of course, both types of cross may be ground. This also helps to control volume present at the same time along with several on local stations. other troubles. AUDIO A-Internal Cross Modulation and Distortion When there is internal cross modulation, usually there is distortion along with it, al- with- though it is possible to have either one AMC. out the other; however, inasmuch as the cure for one is frequently the cure for the other, it will be assumed that the troubles are interchangeable. I The cause of this trouble is always the Fig. 3-Original Circuit. The author adjusts a wave trap. overload of some tube to such an extent that AVC. AUDIO signal present from the interfering station RECENT developments in the broadcast- is large enough to cancel out the bias on this ing art, such as the new single tower tube, thus causing the tube to act as a de- vertical aerials and automatic vol- tector.. ume control devices installed in the audio The causes of this overload may be: system of the transmitter have so increased 1. Lack of preselection (two gang con- the efficiency of many stations that they densers). There are probably some sets hav- have an effective range of from two to four ing three gang tuning condensers in which times that previously obtained. This re- this is still the real cause of the trouble, sults in much stronger signals in the vi- especially when shielding and design are cinity of the stations and relatively less at bad. Fig. 4-New Circuit. 2. Lack of a good ground. For years X-1 megohet. Y-100 mfd. - A8 other parts ore the same. engineers have stressed the value of a good I ground connection, but the lack of one is 5. Many early all -wave aerials of the so- I el still a major cause of poor operation of called noise reducing type are causes of over, modern radios. Why does a good ground load on the broadcast band because the trans- 1

I help? Simply because radios are usually mission line acts as an aerial. If the aerial L-- .0 --i L _ _ _--- J built with the idea of having the aerial wire has no transformer at the aerial end of the pick up the desired signals rather than the transmission line, this undoubtedly is the Fig. I-Two Basic Types of Wave Traps. power line; and, unless a ground is con- case. Make sure the can does contain a nected, the power line may be putting more transformer. Many cans formed only a distant points. Both phenomena add to signal energy into the radio than the aerial, junction box for the leads. To test this, the problems of the serviceman. and, the line may High Percentage Modulation makes itself be introducing the Fig. 5-Old Circuit. known when you are near the station, as signal directly to the 24A 24A distortion. This fact alone complicates serv- first detector while icing by causing the distortion to be inter- signals from the mittent and dependent upon the carrier level. c aerial must travel must be Recent trends in receiver design through the tuned give n their full COUPLER TRAP circuits of the de- share of responsi- tector and r.f. LINE bility for the serv- SCT stages, if any. iceman's woes. It is G the purpose of this 3. Several cases Fig. 2-Wave Trap. article to help the of cross modulation serviceman solve recently occurred in A B some of the problems caused by the above which the trouble Fig. 6-New Circuit. changes. was due to a very 24A 24A Cross Modulation short aerial (10 ft.). Although the term "cross modulation" is Even though a by definition "a type of intermodulation ground was being due to the modulation of the carrier of the used, apparently desired signal in a radio apparatus by an more energy was undesired signal," it has come to be neces- still being intro- sary to divide the trouble into two distinct duced by the power types to be known as "External Cross Mod- line than by the ulation" and "Internal Cross Modulation." aerial, because in- The internal type will be discussed first. creasing the aerial A X B Internal cross modulation then, it will be length immediately 4 to old volume control. B is old screen rests or. X to a new resistor to be inserted (2-S wett size). assumed, is due to something about the cured it. :14 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

Tilley's Radio Service of Ancon, Canal Zone, features a fi ne service bench of solid mahogany with a linoleum fop.

make a simple continuity test of the trans- lem is to know which type to use. Two basic to appear that previously was not present. mission line. If open, there is no trans- types are available; one in series, the other This would seem to indicate too good a job former at the top. There is at least one ex- parallel tuned. This difference is very im- had been done, and the temptation is to ception to this in the case of a popular all - portant. throw the set slightly out of balance again wave aerial shipped with each set from the Type A is a new article commercially and or perhaps put back one of the old, weak factory. Small mica condensers were placed works by allowing only the undesired sig- tubes. The real trouble is the outdated de- in series with the line just inside the trans- nal to pass through it, rejecting all others. sign of the set or else some trouble we have former housing. It must, therefore, be connected in parallel missed. Suggestion: Check all the bypass If the set is overloading due to excessive with either the antenna coil, if an L aerial, condensers in the AVC feed line. Replace aerial, whether it be due to too much top or across the transmission line. As such all those that show any leakage whatsoever. or the combination of top and lead-in being it is very effective provided the transmis- Leakages of 10 or 20 megohms will cause too much, matters not. If you cannot sell sion line is acting as a true line. If not a trouble. Make sure none of the tubes have the customer a modern noise reducing aerial, true line, the effect will be nil and the only any cathode leakage. This applies espe- there is an easier and better way to cure solution is a type B trap in each wire of cially to the tubes used in early AVC the trouble than by going up on the roof the so-called line. Type B is an old friend cuits. Occasionally, the tubes being con- and cutting off the aerial. In the first place, that you have used for years; its action is trolled by AVC voltages develop defects you cannot be sure just how much aerial one of absorption. The undesired signal which cause them to draw grid current. Most to cut off, and no aerial is ever too long. is absorbed within the tuned circuit and the tube testers are incapable of detecting this The reason for this is that long aerials always trap must, therefore, be connected in series defect. When in doubt, try new tubes. give better reception on distant stations with the circuit for best results. This is It may be helpful in some modern sets to both in signal strength and noise ratio. ideal for L type aerials and may be used separate the detection and AVC actions. A. But to get back to curing the overload. with some success, if connected as shown in This is easily possible if a duplex -diode The easiest way to reduce signal strength Fig. 2, on transmission line couples. triode is used. The reason for the improve- is simply to connect a small mica condenser C. There is another gadget available which ment is that for detection purposes one can- in series with the lead-in at the aerial ter- does a good job of removing cross talk, at not make the detector load resistor more minals. If an L aerial, only one is needed; the expense of the weaker stations, however. than .5 megohms; .35 megohms, or even .1 if a twisted pair lead in, two of equal size It frequently reduces their level down into megohm, would give better audio quality, are required. The size will depend on the noticeable hiss. It is a cross talk elimina- but if the same resistor is used to develop amount of signal reduction needed to cure tor, whose action is that of a selective shunt, AVC voltage, obviously more could be de- the cross talk. Usually the size will vary for it is merely a small r.f. choke of low veloped across a larger resistor. The change between 50 and 100 mmfd.; but less than resistance which is connected across the is illustrated in the circuit below: 50 mmfd. will almost always cause excessive transmission line. Its impedance is suffi- F. So much for the newer sets. There are hiss on distant stations. Check this with a cient to prevent short wave signals from many older sets that can be much improved weak station at the low frequency end of being by-passed. by some modernization. If the changes are the dial. The exact size can be quickly D. It is obvious that there is very little made at the same time as repairs, the cost determined without making several trips to hope of removing cross talk unless all coils, will be very little more than the repairs alone, the roof; and there is no loss of the noise tubes and long grid leads are shielded. and the result will be a job that you will reducing effect of the long aerial. E. Much cross talk and distortion would get paid for. The customer seldom ques- A word about local -distance switches. not occur if there were sufficient automatic tions a bill if the set performs better than What serviceman has not made fool trips volume control action to properly bias the ever; whereas, if merely routine repairs are to someone's home to find the antenna tubes. This whole problem is a very com- made, the general pepping up of the set switch open? Secondly, any radio is sub- plicated one of the vicious circle type; for often results in distortion or lack of con- ject to any one of a dozen troubles if oper- as soon as the r.f. voltage is available and trol of volume on locals which the customer ated without an aerial even if it be only on the gain decreases, the available voltage says he did not have before. So, rightly or local stations. To enumerate only a few of also decreases with which to cut down the not, he questions your bill and probably re-. them, they are: fading or sudden change in gain. The real problem arises from the fact fuses to pay at all. The solution is simple volume when light switches are thrown, that it is a characteristic of most automatic Sometimes, this means a change in the noise, hum on carrier, and cross talk. volume control systems to work inefficiently volume control circuit. Most likely the set B. Next comes the old faithful wave trap. on strong signals. The problem is to in- needs a new volume control anyway, so If one station is the cause of all the trouble, crease and conserve all the available volt- change it over to an antenna -bias circuit the very best solution is a wave trap, as this age. Increasing the voltage is best done and you will have a much better performing affects only the interfering station. How- by making sure the alignment of all trim- set. Again the trouble may be only the vol- ever, with modern types of aerials involv- mers is absolutely perfect. Frequently the ume control circuit. Much improvement ing transmission lines, the problem becomes distortion and cross talk disappear at the will frequently be had if the control cir- very complicated. In some cases, two traps same time. In rare cases the trouble is too cuit is merely changed a bit. The '24 tubes may be necessary, one in each side of the much AVC voltage, although this usually is and old control, if not noisy, may be left line. There are a great many types of only indirectly the cause of the trouble. right in. Such a circuit change is shown on wave traps appearing on the market, but Sometimes placing new tubes in a set or the next page (Figs. 5 and 6). Only a few usually only one will do the job. The prob - balancing up the set will cause distortion connections have to be changed. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 35

The value must be determined by experi- usually not furnished with all -wave aerial For example, suppose a station on 700 kc. is ment. Size is correct when you can cut kits, it is absolutely essential that one be modulated with a constant pitch of 6000 down the locals to zero volume and just a used for the first place of attachment or cycles. This will produce sidebands or vir- little to spare. Resistance will vary between trouble will always result. Impossible as it tual carrier frequencies of 706,000 cycles and a few thousand ohms and % megohm. is to understand, one may throw the lead-in 694,000 cycles. If there is another station C is the antenna section, if the control from the offending aerial out the window of approximately equal power on '710 kc. happens to be a dual. The only change de- and then, using another aerial, the noise will that we wish to receive, we will hear an in- sirable would be to shield the antenna lead be just as bad as with the defective one. terfering tone on the desired station of 4000 from the volume control to the primary coil. If the trouble is not due to the aerial in cycles. Whereas, if the modulation of the External Cross Modulations use, it has definitely been proven that ad- interfering station had been 4000 cycles, the For some years, servicemen have noted jacent aerials will produce the same result; tone on the desired station will be 6000 that certain peculiar cases of distortion or in fact, it behooves any serviceman who goes cycles. Obviously, in the first case, limiting cross modulation on local stations cleared to a roof to inspect his customer's aerial to the peak modulation frequencies to 5000 up when lead in strips were wiggled. The also inspect all other aerials on that roof, cycles would produce a 5000 cycle or higher answer is what some servicemen have long eliminating all shorts between them or pos- beat on the desired station, and if the re- suspected. In the presence of strong signals sibly cases of loose connection. Quite an ceiver audio system cut off abruptly at 5000 from locals, poor contact between portions undertaking, but absolutely necessary if you cycles, no interfering signal would be heard. of the aerial and ground or of other metal wish to be successful. But if the peak modulation of the trans- objects such as pipe, BX or house wiring Intermittent connections between metal mitter is not limited to 5000 cycles, beats of acts as a rectifier or detector of the strong objects of any sort, especially pipes and elec- less than 5000 cycles will be produced on radio signals flowing in them. Unfortu- trical conduit in cellars or walls of the build- the desired station and will be heard in the nately, detector action is such that if signals ing or even adjacent buildings, are fre- receiver. There is no solution to this prob- from two or more strong stations are pres- quently the cause of noise or cross modula- lem but to limit transmitter modulation to ent, their combined carriers and modulation tion. The cure may be effected by either 5000 cycles so long as channels are only are reradiated into the air on frequencies separating the offending conductors by an 10,000 cycles apart. See table below: other is similar insulator or by connecting them together. Carrier than their original. This Desired Station Interfering Station to the action of the first detector of any If, as occasionally happens, the cause can- 710,000 cycles (710 kc.) 700,000 cycles (700 kc.) superheterodyne. Thus, we will be able to not be located or is inaccessible, the installa- Modulation Carriers Monkey Chatter Monkey Chatter tune in these composite locals in numerous tion of one of the best types of shielded 714,000 706,000 706,000 694,000 places on the dial. If we assign frequencies lead-in aerial systems will materially reduce 4000 cycle Modulation 6000 cycle odulation to imaginary Stations A and B, we should this trouble. Transmission line types of It is apparent that 4000 cycle modulation be able to hear them as shown below in ad- aerial may be used if the line acts as a on 710 kc. produces a sideband which is iden- dition to their regular frequencies: true line and better if the set coupler has an electrostatic shield. tical with a 6000 cycle sideband on 700 kc. A= 600 kc. 2A+B=1900 kc. There is no cure for monkey chatter ex- B= '700 kc. 2A-B- 500 kc. C-Monkey Chatter cept as outlined. A high frequency tone A+B-1300 kc. 2B+A=2000 kc. With the advent of superpower stations control or trap in detector or speaker circuit A-B= 100 kc. 2B-A= 800 kc. operating on adjacent channels (the classic will reduce it somewhat, as will additional 2A=1200 kc. 3A=1800 kc. example is WOR, Newark, and WLW, Cin- tuned circuits ahead of the first detector, but 2B=1400 kc. 3B=2100 kc. cinnati), another form of cross modulation no permanent cure can be effected as long as If this is the result of a "cross" between has become apparent. Many have heard the the broadcasting stations modulate above only two locals, think of the confusion if unintelligible jibber-jabber in the background 5000 cycles with only 10 kc. separating their three or four strong carriers are present. when tuned to one of these stations. This carriers. May there somehow be 20 or at Such a cross may occur in any conductor. trouble can occur on any two stations oper- least 15 kc. channels soon. It is only necessary to have two alternating ating on adjacent channels provided they currents present such as 60 cycle a.c. on are fairly strong and their carriers are not Test Leads for the Experimenter open wire. The result is 60 cycle hum mod- greatly different in strength. For lack of a Split two 6 -inch penny pencils in half, the ulation on the carrier of your locals-one better name, the effect has been called long way, and remove the lead. Cut out the or more. This type of hum -on -carrier does "monkey chatter." The trouble is com- groove a little as shown in the drawing. This not respond to the usual cures because it monly thought to be due to lack of selectivity groove prevents the wire from pulling loose. enters the set through the aerial as a regu- in the set, but actually this is only partly Dig down in the old box and get some lar carrier. Distant stations are, of course, true because, theoretically at least, the ef- O. K. Do not confuse this with a similar fect would be impossible if stations stopped CUT OUT HALF SECTION OF PENCIL hum due to lack of line bypass condenser. all audio modulation above 5000 cycles, and As to cures-that old nemesis of the radio the audio system of all receivers cut of SOLDERED POINTED man, the lead-in strip, is the most frequent abruptly at the same place. 'FLATTEN W.I2WIRE cause of trouble. As we all know, copper This is not being done, nor is it likely to PLACE WIRE IN --FLEXABLE WIRE GROOVE OF PENCIL oxides make fine rectifiers; and wherever we be done in the future; the tendency is to let have copper exposed to the weather, this the higher frequencies modulate the trans- PHONE TIP oxide develops and sooner or later starts its mitter and build receivers that reproduce wire. Cut two 51/4 - dirty work. The best way is to remove the these high frequencies. There are a few number 12, hard copper inch lengths, sharpen points on one end, strip altogether and bring a new lead wire sets that have a trap in the speaker that limits Then solder four direct from the arrestor to the set. reproduction to those frequencies below 5000 flatten the other ends. of flexible wire to the flattened ends. Poor ground clamps, loose connections, or cycles, but this does not eliminate monkey feet as shown, and cement bad lead-in strips in the ground lead may chatter. The reason for this is: The overall Place into the pencil carter phone tips or spade be the cause of hum -on -carrier and cross selectivity of most sets is sufficient to ade- it together. Fix of the flexible wire and you talk. Leakage between the terminals of the quately separate the carriers of the adjacent tips to the end a pair of test leads. lightning arrestor has been a frequent cause stations. Most of this selectivity is in the I. have good of cross modulation and hum -on -carrier too, F. amplifier, but the selectivity of the pre- if the set and arrestor grounds are of the selection circuits is inadequate to prevent For Better Reception same wire. both signals from arriving at the first de- There are many sections of the country One of the most annoying cases of cross tector. where the soil contains very little moisture talk observed is that caused by a break in The result is that the sidebands of the in- with the result that the ground circuit for one or both wires of the transmission line. terfering station heterodyne with the car- a radio set is not very good. It can be This usually occurs under the insulation and rier of the desired station and said detector greatly improved by making up a salt and cannot be seen. Worst of all, one popu- does a fine job of extracting the beats. This water solution and using this solution to lar type of all -wave aerial, as previously beat varies with the modulation of the in- saturate the earth around the ground pipe. mentioned, has a line which normally shows terfering station, but is not understandable One part salt to three parts of water will open circuit. Although a screw eye is because it is an inversion of the original. do the trick. 36 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK How tu Advertise Your tiERVICI: SHOP

Dealer's Choice course, they attend to pick-ups, repairs, and to trace the media. Getting the work is the The pluggers I described have not revo- deliveries. important thing. Hew to the repair job- lutionized our business, nor have they led Here is some incidental information which let the quantitative data fall where they may! us to the end of the rainbow. They have, might provide you with a short cut or two: There is often a considerable period be- however, helped appreciably in forming a in apartment house mailboxes, 70% of the tween a customer's receipt of a card and background of much-needed customer con- cards are wasted-thrown on the lobby floor his 'phone call. Naturally a man's radio tact. Some of the card -calls are slow in immediately; the remaining 30% are pock- does not blow up just because he put your getting to the shop, but they're worth wait- eted. (Seems wasteful, but the average for name on file. We are getting calls from ing for. Get enough cards out, and it's other business cards is even higher than 7 persons who got some of our first copy; just like money in a trust fund-you'll get in 10. They would pay, I believe, if 9 in and some of these set owners have not had it, providing you don't change your address 10 were thrown away.) a repairman in the house for three or four too often. Two distinct responses follow their dis- years. These tardy customers are among We have, during the past three years, tribution. First, the immediate one, follow- our best; their lives are well -settled, they distributed 90,000 cards. That's a lot of ing a coincidental card and set failure; the usually own their homes, and their receivers, cards, but they have been looked upon only customer calls the number on the card be- although older, are higher -priced than those as an adjunct activity to service work; we cause he is too lazy to open a 'phone book. of the semi -transient kitchenetters. are radio men, not advertising experts. The There is an average of one call per thou- It is easier to give out cards in large apart- data we have collected as we gave out the sand cards that comes in immediately. A ment houses than in private homes, but the cards should be of interest to others in the apartment resident is sated by a continual same profession. Perhaps, with modifica- shower of mailbox advertising. The greatest tions befitting your location, budget, and response per thousand cards comes from Ours is a radio repair shop customers, you can evolve a card that is best smaller buildings. They find fewer pieces fitted exclusively for mainte- for your business. of advertising in their mailboxes, and give Specifications are as follows: nance. No frills- each piece more attention, for the same Size: 13/42t4 inches. The width was de- reason a child in a small family gets more NO DRAPERIES cided upon because it is the greatest which attention than a child who is one of many. permits entrée into mailbox slots. (If your -everything in the shop is Many persons, pretending they are dis- postmaster objects, slip 'em under doors. there for the single purpose of couraging a bothersome practice, make rules You know your postmaster better than I conditioning all radios quickly, which say they will never trade with any do; if you don't, you had better!) The properly, and at moderate cost. concern that uses door advertising. It has length forms a good proportion with the been my experience that such a person, width when lines run across the shorter di- Often it is some minor fault when he wants his set repaired in a hurry, mension. which keeps a set from playing forgets all principle and calls the repair Stock: White, weight that of a good -in that case, a repair is made shop which has put its 'phone number closest calling -card; heavy enough so the prospect's immediately, in your home. to his hand. Don't be frightened by any instinct prompts him to leave it flat instead thought of making ill -will with advertising of folding it. A good stock helps to dis- If a major repair is neces- of any type. If you do anything ninety tinguish your advertising from that of the sary, we have the largest stock thousand times, someone is going to be of- local fish market. of tubes and replacement parts fended. Type: 6 or 7 -point, light -face; Vogue. in the county. Once, following an especially weak mo- Allow 90 or 100 words of copy without ment, I distributed cards advertising free call squeezing. Only one line should be in bold- radio service in a six -block area. Then, to face; the words in the heavy line need not Lincoln 4321 compare results, I covered the same neigh- be pertinent to your business. Simply make Open until 10 p. m. borhood with cards announcing a dollar them conspicuous without disclosing the gist service charge. Although the cards were of the card to the person who gives it a SMITH RADIO nearly identical in size and makeup, the re- quick glance. 1234 N. 56 St. sults were very different. We got the ex- A person who comes across the card is pected response from the latter; the former, Bellwood more likely to drop it if he can understand however, provoked calls from the cheapest it immediately. If one line piques his curi- bunch of chiselers I ever came across in my osity, and if the remaining text is too small life. I learned then that, even though free to read at the time, chances are about 4 out customer in this class is like the man who service advertising resulted in more calls, of 5 he will pocket it. Hence the small type. gets a wife by writing to a matrimonial they were from customers I didn't want. Copy: Say whatever you wish, but keep agency-any matrimonial agency. He is If you are the type of person who is too it simple and innocuous. Business name, good picking, though, for, despite his con- proud, or too occupied with a rushing busi- address, and 'phone number are the essen- viction that all service men are alike he re- ness to distribute cards, you can hire some tials. Change the wording every month or signs himself to set breakdown as a trick kids to get rid of them for you. They will so-helps you later, when you become curi- of fate, and rarely questions price. His -down a sewer! ous concerning the most effective means of money is paid in the spirit of a man giv- distribution, and wish to co-ordinate results ing out alimony or taxes; he is reconciled with time of year or format. to the fact there is no appeal. He seldom, Speaker Troubles In our organization, the repairmen pass because of this cynical attitude, becomes Intermittent blasting of dynamic speakers out the cards; they carry them at all times, a staunch supporter of your shop. is very often traceable to the presence of afoot or awheel. They are left in mail- The delayed response is more difficult to minute metal particles. These particles gen- boxes; in cigar stores; in back of, and on check. Some customers dislike being asked erally collect in the air gap between the top of, consoles; with persons they meet; how they learned of you, or why they called moving coil and the field magnet and become and-heaven forgive them-even in beer your particular store. There will be, over magnetized. To remove the particles simply gardens. When business is slack, they are long periods, enough calls from sections disconnect the field supply and pass a thin distributed systematically during spare -time which have been carded to assure you it is piece of magnetized iron around the air gap. intervals; during our occasional rushes, of worth while, whether or not you manage RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 37

voltage regulator, reducer, or anything you What's the Line Voltage? think best, for your location. Even though the immediate response might be small, your More Power to You testing in the shop, and delivering the chassis, warning will be remembered later, if their set stops for any reason after the line voltage HAS the line voltage in your area been only to have the set fail as soon as it was has been increased. There is nothing which changed? If it hasn't, it will be; installed. The cause can usually be traced reconciles a customer to payment quicker there is a general trend under way to the presence of a lower voltage on the than a set failure you have prophesied. from 115 to 120 volts. The New York area repair bench outlet. has using 120 for some time; Chicago If you are in a 5%-4% area that has been Magnifying Meter Reading finished the final step of its 5 -volt boost been changed, remember that the 115 -volt last December. Nearly half of the country equipment, when being operated on 120 volts, It is sometimes desirable to detect minute a is yet to be moved upward. While I, as a can be subjected to an allowable maximum of fluctuations in the movement of meter repairman, do not hope for an increased 126. This is equivalent to a 13% overload, pointer to check surges in a circuit. It is meter number of set failures as a result, I am keep- and, although it be the operating policy of also necessary at times, to obtain ing myself apprized concerning conditions in your power company to keep well within the readings with the instrument placed at a To my territory, and am standing by to handle 5% margin of 120 volts, you should know position remote from the observer. obtain a folding any work which might be necessary. how wide this margin actually is. The mini- meet these requirements type magnifying mirror of the 25 and The method of change varies little between mum 4% below 120 volts is at 115-ex- old 50 -cent store variety. The mirror faces are power companies. Starting with the 115 - actly the rating of the equipment. In other words, no matter what range the power over five inches in diameter and when volt level, periodic boosts are made every in the back of meter, the image company allows, it is always above the rat- placed the month or two until 120 is reached. Con- of the meter is greatly magnified. sumers are usually notified of the change ing of a 115 -volt set. by means of a printed slip accompanying This is a condition worthy of note, espe- their light bill. It is probable that few of cially when repairing a cheap receiver. Some Cushioning Radio Equipment these notices are read. They are too easily of them, because of miserly engineering prac- Ordinary sponge rubber, such as kneeling mistaken for washing -machine ads to com- tice in choice or assembly of parts, contain pads which can be purchased for twenty mand attention during their quick trip from power transformers which, even at the 115 - cents in the "five-and-dime" stores, finds envelope to waste -paper basket. volt level, operate at a temperature just be- many applications around radio equipment. trouble in regenerative and The various State Commissions allow a low the point of conflagration. Microphone be eliminated certain excursion from the level in use. In In the better sets, where power trans- other receivers can oftentimes by placing the receiver on strips of this ma- one section, a 5% over -voltage and a 4% formers have a more generous tolerance, fail- terial, for instance. Microphonism in pre- under -voltage are specified as the limits. It ures might occur in the remaining apparatus amplifiers can usually be cured in the same is probable that your power company stays on account of increased voltages from the way as can hum pick-up resulting from within these limits as a matter of operating secondary windings. One distributor, han- using preamplifiers around amateur trans- policy, except when unusually severe load dling a very good line, reports that, while mitters where they are subject to mechan- or supply conditions are met. Regardless there has been no increase in the number ical vibrators from vibrating units. of range, it is important for the service- of power transformer replacements follow- the Possibly the greatest utility of this idea, man to know what maximum voltages he is ing the use of 120 volts, there has been an however, is found in fastening small pads, working with from day to day in his territory. increase in the number of filter condenser one or two inches square, on the bottoms of replacements. Another large sales -service Random voltmeter readings are of little oscillators, meters, oscillographs and other company, after replacing more than the usual value. In order to get a true picture of the instruments to keep them from scratching number of -out tubes in its "guaran- voltages at various points in, say, an area burned receiver cabinets, table tops or other surfaces tee" sets, now installs voltage reducers. of ten square miles, a recording voltmeter upon which they may be placed. Quite would have to be run continucusly in per- Although factual data is difficult to ob- frequently desks with polished tops are used tain, it is certain that more heat and volt- haps ten or more locations for long enough as "operating ' tables" in ham shacks. If in each location to get an average typical age failures will occur in a given number of equipment which normally belongs on the curve for the daily maximum in each sec- sets running hotter than in the same number operating table is so protected, much time tion. The instrument would have to be ac- running cooler. Heat and voltage failures and grief will be saved. curate, and have little operating inertia to walk hand -in -hand, and cannot be consid- A good plan is to cut small squares from record sharp rises or drops. When the ob- ered separately. a kneeling pad and attach them to the cor- servations were completed, the results would If the higher voltage level is in use in ners of the bottoms of small instruments. not have justified the bother and expense. your neighborhoods, change transformer taps Dope or DuPont's cement will fasten them The top daily voltages encountered are when the set is delivered; you will find many securely. Neat squares are cut by using a the important ones for the repairman to of them set for the old 115 -volt level. Sec- safety razor blade with a steel -edge rule to know. First, call your local power com- ondary overload is as important a heat factor guide it. pany, and ask what the line voltage is sup- as high primary voltage; check against this posed to be. (If you think this is a waste by noticing, with the proper primary volt- Homemade Banana Plugs of time, ask any five servicemen, in an area age across the power transformer, whether Cut a suitably size square of thin spring which has been raised, what line voltages he the socket voltages are the correct ones. An brass. The distance from the center to each comes across during a routine day. Few overloaded transformer-at any primary volt- corner should be slightly greater than the know for sure. In my case, the rise had age-can be detected by socket readings been made two months before I learned of which are too low when the power trans- BEND INTO y it. So check on it-a new level may have former is too hot. If resistors fail, use the THIS SHAPE sneaked in without your knowing it.) next higher wattage; condensers, the next After you know your rated voltage, make higher voltage. In properly designed sets, homes for comparison the easiest way to compensate for a raised checks in customer's SPRIG RASSBUT voltage is, of course, to bring down all sec- with those at the same time of day in your SOLDER'. shop. This can be done with little or no ondary voltages by use of the optimum pri- bother during your usual daily travel, and mary voltage. In the cheaply -designed sets, a few weeks' systematic data will soon show a little good judgment will be required, as BOLT you if any of your service sections are lower no two sets of conditions will be alike. The or higher than those in your shop. important fact to remember is that, regard- length of the intended plug. Spot the cen Watch out especially for sections which less of good or poor design, failures are a ter and draw a line to each corner. Then are higher than the reading in your store result of increased heat and voltage. draw in the legs approximately the shape location. Most of us have had the embar- If your town is planning a voltage boost, suggested. Cut out the cross with a pair rassing experience of making a replacement, notify all your customers, recommending a of tin shears. 38 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK AMYLIFIER SECTION

PREVENTION OF OSCILLATION IN PUBLIC ADDRESS SYSTEMS

filters in the plate circuits of the amplifier tubes, is the simplest and most practical method of preventing oscillation as shown in Fig. 2. These filters are inserted in the plate supply lead to each amplifier tube, and effec- tively prevent alternating power supply volt- age variations from reaching the vacuum tubes. The size of the condenser and resistance that may be needed in any case may be de- termined mathematically. Results must al- ways be checked experimentally in order to evaluate factors that cannot be found analy- tically. To make the information available, The equipment used in checking P. A. Oscillation. computations and experimental work have been performed for a number of typical ONE of the difficult problems in- consider the skeleton diagram of Fig. 1, in amplifier circuits, and the results are pre- volved in the design of audio fre- which several tubes of an audio amplifier are sented here. While the tabulations given quency amplifiers is that of pre- connected to the same power pack. The in this article are not exhaustive by any venting oscillation. An amplifier which power supply has a certain amount of in- means, they are sufficiently complete to be seems to be perfectly well designed will be ternal impedance, determined by its design. of considerable assistance in the design of found, when constructed, to oscillate or Variations in the instantaneous plate cur- amplifiers. 1 various combinations, "motor -boat" so severely that the amplifier rent of any of the tubes will cause a varia- Table lists circuit is of no use. tion in the plate voltage of the power supply. and gives the "type number" of the filter Oscillation in an amplifier is almost in- Hence, the plate voltage of the first tubes to be used in each plate circuit. The "type where several variably the result of some kind of coupling of the amplifier will be found to vary, ex- numbers" are given in Table 2, and between input and output circuits termed actly as the plate currents of the last tubes. equivalent combinations of resistance feedback. To prevent instability, therefore, The variation in plate voltage of the early capacity are listed for each filter type. The which is to be made be- it is necessary to determine the possible tubes will be amplified, just as if it were a particular choice sources of this feedback, and to correct signal, and, if of sufficient amplitude and tween filters of the same type is determined drop them, Feedback can occur by: coupling of correct phase, a self -sustained oscillation by the direct -current plate voltage through the power supply, capacitative cou- will result. which can be permitted in the filter resistor, and by the allowable cost of condensers. In pling between the elements of the amplifier, If the phase relations are opposed, then Table 1, two choices of filter types are given, or inductive coupling between the elements. "degeneration" occurs, and the amplification Each of these will be discussed in turn. The one for a power supply of high resistance, over a certain frequency range is reduced. and the other for one of low resistance. effect of radio frequency currents which While oscillation does not take place, the A low resistance power pack is one em- may be present in the audio amplifier, when effect is undesirable, be elim- and should ploying a mercury vapor rectifier, with low it is connected to a radio tuner, due to in- inated. sufficient filtering or shielding, is not con- resistance chokes, and a transformer with sidered here. It will be noted that it is the first and excellent regulation. If the power pack em- last tubes of the amplifier that are principally The most common cause of instability is ploys a mercury vapor tube, but the chokes concerned with due to coupling through the power supply. the problem of stability due have higher resistance and the transformer to power supply coupling. Most amplifiers, with a voltage amplification poorer regulation, it should be classified as a greater than 500, will oscillate, if no pre- There are two methods by which coupling to coupling through the power supply may be minimized. IST TUBE AMPLIFIER TUBE cautions are taken prevent ADDITIONAL through the power supply. Feedback through The first is to employ a separate power sup- the power supply is caused as follows: ply for the last stages of the amplifier, gen- erally for the power output stage alone. A second method is to reduce the effective re-

I ST 2ND 3RD LAST sistance of the power supply, by alterations in its design. One such alteration is the sub- STAGE STAGE STAGE STAGE stitution of a mercury vapor rectifier tube GOOD ARRANGEMENT for a vacuum ti rectifier, if one has been used. IMPEDANCE OF FIG -I This improves the regulation of the power POWER SUPPLY

supply considerably, and tends to improve PLATE COUPLING the stability of the amplifier. Another im- '+-DEVICE-RESISTOR provement that can be made in the power TRANSFORMER _ OR CHORE supply is effected by increasing the size of BIASING the output filter condenser. In the mild RESISTOR cases of oscillation, doubling the size of the output condenser will cause some improve- _l FILTER POOR ARRANGEMENT ment, but this method is seldom the most -B FIG -2 +B economical one. Two types of circuits discussed above. Two types of P. A. stage arrangements. The application of resistance -capacity RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 39

high resistance supply. A power pack util- troublesome. Only one case in this category cuit elements. Leakage flux outside the izing a vacuum rectifier is always classed as is reported, that of a 79 twin triode. magnetic path of a transformer, or of an one of high resistance, insofar as the selec- To prevent coupling between the com- iron core choke, induces a voltage in other tion of filters is concerned. ponents of the amplifier, they should be so similar parts of the amplifier. If the induced If there is any doubt in a particular case, laid out that input and output circuits are voltages are of sufficient magnitude, and of into which class the power supply falls, the as widely separated as possible. Arrange the correct phase, instability results. This mag- columns given for a high resistance pack amplifier "in line," one stage after another, netic coupling can distort the frequency rather may be employed most safely. Numerically, than to fold it back upon itself. characteristics of the amplifier, and, if severe, the dividing point between high and low re- When the gain required is large, 50,000 cause oscillation. or more, shielding is sistance has been taken at 300 ohms, as employed to minimize Inductive coupling may be minimized by capacitative coupling. As determined by calculation and from the slope the desired gain employing magnetic shielding, or the trans- is increased, the better must be the shielding. of the regulation curve of the power supply former may be re -oriented so that the in- For voltage gains up to 100,000, it may be at its normal operating point. Allowance has duced voltage will be of smaller magnitude. sufficient to isolate the input and output cir- also been made for the shunting impedance Many types of cuits, and to shield the tubes in the amplifier, transformers are assembled in of the output condenser. iron boxes, make but when greater amplification is desired, excellent magnetic shields. The second cause of instability in an audio each stage should be isolated in an individual Additional shielding may be employed about frequency is amplifier capacitative coupling metal box. In a special amplifier that has entire amplifier stages, if needed. An iron between the input and output circuits of been constructed, with a gain of 5,000,000, or steel box surrounding a stage, making tubes in the amplifier. it was found necessary to employ separate good electrical and magnetic coupling at all Capacitative coupling may be inter - batteries for each stage, and to use multiple its edges, and connected to the common re, electrode, that is, within one of the tubes shielding, to the extent of shielding the bat- turn of the amplifier, serves a threefold pur- of the amplifier, or it may occur between teries from each other and from the tubes. pose. It eliminates electrostatic and magnetic the components of the amplifier external to In practice, such elaborate designs are rarely coupling between stages, and it prevents the tubes. Ordinarily, inter -electrode effects met, however. pick-up to the amplifier due to external mag- are small enough at audio frequencies to be The last cause of amplifier instability is netic fields, which might result in noise in negligible, although occasionally these are that due to inductive coupling between cir- the amplifier output.

TABLE 1 TABLE 2 Amplifier Description. Filter Required Filter 3 -Stage Amplifiers (including detector, if used.) (as given in Table 2) Number 1st Stage 2d Stage (Refers to 3rd Stage High Low High Low Table 1) C in mfds. R in ohms 1st Stage 2d Stage Input Tube Input Res. Res. Res. Res. I 2 10000 Tube Tube Coupling Coupling Supply Sup. Sup. Sup. 1 20000 57 56 Resis. 45 Resis. IV III II I .5 40000 57 56 Resis. 2.45s pp Trans. II I none none 57 56 Resis. 2.2A3 pp Trans. III II I none II 4 10000 57 56 Resis. 2A5 Trans. IV III II I 2 20000 57 56 Resis. 2-2A5 pp Trans. III II I none 1 40000 56 56 Resis. 45 Resis. III II I none 57 59 Resis. 2-59 Class B - IV - none III 8 10000 56 56 Trans. 45 Trans. IV III II I 4 20000 57 57 Resis. 2-2A5 pp Trans. IV III III II 2 40000 56 56 Trans. 2.2A3 pp Trans. III II I none 57 57 Resis. 56 Resis. IV III III II IV 16 10000 4 -Stage Amplifiers (including detector) 8 20000 2d & 3d 4 40000 2d Stage 3rd Stage 4th Stage 1st Stage Stages 2 80000 1st Input Tube Input Tube Input High Low High Low Stage Tube Cou- Cou- Coupling Res. Res. Res. Res. V 16 20000 Tube pling pling Sup. Sup. Sup. Sup. 8 40000 56 56 Resis. 56 Resis. 2.2A3 pp Trans. III II II I 4 80000 57 56 Resis. 56 Resis. 2-45 pp Trans. IV III III II 57 56 Resis. 56 Resis. 47 Trans. - V - IV The filter associated with any of the five 56 56 Trans. 56 Trans. 2-42 pp Trans. V IV IV III numbers may be made up of any of the Tubes with similar characteristics to those in the above table may be substituted directly. various combinations of R and C given For example, the type 76 may be substituted for the 56. above. A SCOTCHMAN'S SPECIAL AN economical, fool -proof amplifier advantages of the older types, and the simple operation so the simplest method was chosen which is capable of practically dis- construction which can be followed in mak- -a push-pull inter -stage transformer. For tortionless reproduction that can be ing amplifiers with it, plus the excellent phonograph operation or from a radio tuner built by any one is this "Scotchmen's Spe- results obtained, are certain to bring it into output, a 6C5 as shown in the diagram is cial." widespread popularity. plenty to overdrive the amplifier. But if The advent of television has brought this The type 6F8 dual triode is used as a microphone operation is desired, the 6F5 will particular circuit back into popularity as driver and also supplies bias for the 6ACS provide sufficient gain when used with the frequencies above 30,000 cycles per second push-pull output tubes. This tube was orig- types of microphones that have an output of are common in such applications. The power inally designed for use with the 76 as a minus 50 decibels or so. output of this particular circuit is 9.5 watts, driver, but the 6F8 has the same character, The type of power supply isn't very crit- absolutely undistorted and the latest report istics as the 76, only an added advantage is ical, no voltage divider is necessary and only shows that tubes which will have up to 40 gained by having both the tubes in the a double eight microfarad filter condenser is watts output per pair are in the last stages same envelope. needed due to the inherent characteristics of of experimentation. The new 6ACSG has The grids of the 6F8 have to be fed with triodes and their low power sensitivity. all of the advantages and none of the dis- an out -of -phase signal for correct push-pull Placement of the parts isn't critical as prac- 40 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK tically all of the connections between tubes 6C5 6AC5GS are merely wires. The power supply should 6F8 be able to deliver a maximum of 90 milli- amperes at 250 volts as the 6AC5's draw 32 milliamperes each and the 6F8 draws a total NVUT R1 SOKR. of 18 milliamperes, the 6C5 draws 8 milli- amperes. The filament supply should be able to deliver 2.0 amperes maximum. T3 No shielding is required on any of the tubes. e.3V.A.C. All in all, the "Scotchman's Special" will SW. CH -1 CH -2 provide the home constructor with an ampli- "s --f 00 00' 2501Lo.c. fier that is capable of reproducing faithfully 11lV.A.C. 00MA. the whole audio frequency spectrum at the c2 minimum of cost for parts. It can be built in the minimum construction time. It is pIp trouble -free from the standpoint of replace- l I'/ ment of parts, such as resistors and con- The circuit diagram of the "Scotchman's Special" P. A. System. densers, and is ideally suited for work with R1-500,000 ohm pot. Ti-Single plate to p.p. grids. the experimenter in trying out new micro- R2.-2000 ohm 2 w. T2-10,000 ohms p.p. plates to v.c. R3-25000 ohm 2 w. Ta-Power trans. to deliver 250 v. d.c. from filter. phone circuits, mixers, tone compensators, C1-25 mfd. 10 v. electro. CH1, CH2-Up to 30 hy. filter chokes. (15 hy. etc., where it is necessary to know that the C2-8 mfd. 450 v. electro. min.) C3-Same as C2. output stage is positively high-fidelity. AN A.C. - D. C. 4 -WATT AMPLIFIER

RECENTLY, when a d.c. amplifier was ing volume from the phonograph as well as needed by a ham in a location with only the gain from the crystal microphone input. that type of power available from A tone control consisting of a one-half the mains, none was found to be read- megohm rheostat in series with a .01 mfd. ily usable which would at once fill the bill condenser serves to control the high fre- with compactness and speech frequency re- quency output of the amplifier and to pro- quirements. After the present one was duce the effect of a greater low frequency designed it was thought to continue the de- response at lower volume levels. Most im- velopment and make a first-class a.c.-d.c. portant of all is the fact that this tone con- job of it as well, so that should the ham trol acts as an impedance shunted across the change location, the speech amplifier would output transformer, a condition necessary in not be outmoded. pentode as well as beam type tubes. Four watts of undistorted output were The 637 input is decoupled by use of a provided, together with the usual rugged resistor and condenser to avoid oscillation and feed-back. Because it is quite custom- construction required by the average ham The 4 -watt Amplifier. installation. The output was more than suffi- ary to ground one side of the a.c. line, and cient to drive a pair of class B tubes such because this amplifier was to be an a.c.-d.c. rect ground in a.c. application. By "float- as the 801 or T20. For that matter the unit, it was necessary to "float" the chassis. ing" the chassis it was possible to insulate amplifier made an excellent small pa. system This term is used in the industry to indi- the amplifier in such a manner that the pos- and also a driver for higher powered drivers cate that the "B" negative of the power sup- sibility of a shock to any person touching a should they be used. ply does not return to the chassis itself, which radiator or grounded object, and at the same is grounded to the circuit through .1 mfd. time The tube line-up consists of a 637 input touching the chassis, was eliminated. condenser. The chassis is a stage resistance coupled to a 6C5 which was standard one, measuring Actually, this last condenser acts as a di - in turn transformer coupled to a power of 5""x10"x3", finished in black crackle. 25L6's. The rectifiers were two 25Z5's. In adding all of the filament voltages together, a total voltage of 112.6 volts was required o to operate the filaments in series. Since the ti á line voltage available was 115 volts, and be- á cause tubes today are manufactured to with- a stand a 10% variation in filament voltage without shortening their life, no line cord resistor was used. The additional 25Z5 tube inserted mainly to eliminate the aforemen- l tioned resistor may also be used to supply field exciting current for a speaker. However, in the present circuit this was not done be- asas ZS cause a magnetic speaker, or the 500 ohm line to the modulators, was used. Sufficient gain was obtained from the 637 to permit operation directly from a crystal .G-.0 5000000Q_r microphone, and the overall gain of the en- tire amplifier was conservatively found to The circuit diagram of the A.C.-D.C. 4 -watt Audio Amplifier. be 89 db. Provision is also made for a high Tra sformer-Stancor 4-62-C single plate --pp R3-'4 megohm, ?ÿ w. grids R350,000 ohms, % w. impedance phonograph unit which works di- Ci, C2, C4-.1 mfd. 400 v. paper Re -3,000 ohms, 1 w. rectly into the 6C5. Fixed bias is supplied C3-.25 mfd. 400 v. paper R1-200 ohms, 2 w. C5, Cs-.01 mfd. 400 v. paper R4'4t megohm vol. control by a Mallory bias cell and the 6J7, pentode Cg, C7-10 mfd. 25 v. elect. Rs-',4 megohm tone control with switch connected, capacity coupled to the gain con- Cg, Clo-1S-15 mfd. 250 v. elect. SIC-Mallory cell trol of the 6C5 serves the purpose of mix- R1, R2-1 megohm, 1 w. CH -30 hy. Fil. choke (Stancor C-1002) RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 41 MAKING YOUR OWN RECORDS THERE are many times when the first switch of which mention was made, is without the amplifier to make records from serviceman will be asked "Can you used to throw in the speaker in place of the "air." This is a profitable source of make a record?" Invariably the an- the recording head. By throwing these income for servicemen living in small towns swer will be, "No, I'm sorry." There is switches first in the "up" position, a record and communities, which support a local not any reason why this situation should is made, and by reversing the switch posi- broadcast station. There are any number exist in the shop of any well equipped tion and putting the play-back head on the of artists both amateur and professional who serviceman. Especially, if he has an ampli- record, accurate reproduction is had of what would value a record of their broadcast per- fier, a few odds and ends lying around, and has been impressed upon the record blank. formance. if he will purchase a recorder. Never use more audio than is necessary The method of procedure is exactly like Briefly, a recorder is simply a loud speaker to get a full recording. The acetate upon making a record from the microphone, ex- from which audio signals have been used which the average recordings are made is cepting that the recording head transformer making a record instead of giving aural re- only a few thousandths of an inch in thick- is matched to the output transformer of the sponse. The output of the amplifier is ness. If too much audio is impressed on the radio receiver. It is well to make several hooked to the recording head, which in cutting head, the groove will be too deep tests before going ahead with the recording. turn places the audio response on a com- and sometimes even scratch into the alumi- This can be done by starting in a good position or acetate record. This is not to num disk beneath the acetate. This will half hour before the appointed time and be confused, of course, with the commercial cause distortion and other undesirable fea- obtaining a "level" and making a number wax recording outfits, which are far too tures in the record and at times even make of test records. Once the level has been involved for any serviceman to attempt. it unintelligible. The average groove, if cor- obtained through the same means used be- This article will confine itself solely to a rectly cut, will not exceed two ten thou- fore, the record may proceed as if the simplified method of recording which may sandths of an inch in depth. The easiest recording artist were in the studio or store be installed by any serviceman so as to way to judge whether or not you have too of the serviceman. One thing is sure, in realize on a market he has heretofore been much audio (without playing the record recorded radio programs be sure to include turning away from his door. back) is to test the thickness of the "scrap" the announcement of your customer's name Amplifier operates from 110 volts a.c. which will unfurl as the record is cut. This as made by the station announcer on the or d.c. and has two input channels, one for scrap should not be thicker than 3 human record; since without it will not have nearly a phonograph pickup (playback) and the hairs intertwined. Unfortunately the aver- the value as it would have with this little other for a high gain microphone such as age serviceman, with his desire to get the touch. crystal high impedance dynamic or high maximum recordings, will find that his scrap There are some recorders which use 331/3 impedance velocity types. The tube lineup is of the thickness of a horse's hair, which RPM and some which use 78 RPM and consists of one 6C8G double triode, two is far too deep and the recording will be there are still others which use both speeds. 25L6G's and one 25ZSG rectifier. Resist- entirely unsatisfactory. For those who are It will be found that the average 12" record ance or transformer coupling may be used more accurate -minded, the scrap should be will "take" a full fifteen minute program on between stages, although some weight and approximately the same size as No. 36 bare the 331/3 RPM speed. Whereas at the '78 have space can be saved with the former. The copper wire; and it is a good point to speed the record will take approximately 7 output of the amplifier is coupled to a DB a piece of that size wire on hand together minutes. The slower speed is very much meter, the use of which will later be ex- with a pair of cheap micrometers to meas- more difficult to record and a higher pow- plained, and through that to a double pole ure whether or not there is any great dif- ered motor must be used to turn the turn double throw switch; then to a matching ference between the scrap and the sample table. matches the Dispose of all scrap carefully as it is transformer which accurately wire. Also, the acetate must be very smoothly head to the inflammable. impedance of the recording put on the record and free of impurities. the service- output of the amplifier. An indispensable addition to These types of records are slightly more transformer of the average man's recording outfit is a cheap microscope The output expensive than the other types. With the amplifier system has output of 4, 8, 16 and such as can be purchased for approximately slower speed it is extremely important to 200 ohms, and the average recording head $1.00 in any novelty store. Dismount the watch the groove and the depth of the cut is 500 ohms. Some, however, have im- microscope from the stand and mount it since with the record turning so slowly any pedances of 5 ohms. In the particular am- upon the recording head, placing a 6 volt faults are greatly magnified. plifier used there was not a 500 ohm output pilot light so that it will throw its rays tap and so the matching transformer operat- directly upon that part of the record being In closing, it might not be amiss to state ing from S ohms input to 500 ohms output inspected. Inspection is made continuously that all business is best run with a "fine" was used to match the output of the am- during a recording. In looking through the front. If the serviceman will take the trouble plifier system to the recording head. microscope the depth and width of the to fit up a room with Celotex or other sound In order to play back the record after it groove both can be observed and the re- deadening material on the walls, rent a has been made, a second switch is used. cording head jumping the groove in any piano and set up a professional looking This throws the microphone out of the cir- overload peak can be avoided. recording studio, he will find himself hand- cuit and throws in the play-back head. The The recording machine can also be used somely repaid in dividends.

MIKE PHONE JACKS MATCHING I XFMR

AMPLIFIER SYS-EM (5 TS) O D.B. D.P. D.T. METER --SWITCH SPEAKER et. .9

SWITCHES UP=RECORD' D. P. D.T. SWITCHES DOWN --°PLAYBACK" SWITCH --''

PLAYBACK

How fo hook up the home -recorder. '12 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK GENERAL & GADGET SECTION RADIO - EQUIPPED TREASURE LOCATOR phones, but if there is any metal present it will disturb the balance, there will be a 1,000 cycle modulation note heard in the phones, and the tube voltmeter will regis- ter the strength of the disturbance caused by the metal. If your transmitter and receiver are far apart you can increase the power in the transmitter very greatly, and locate large ob- jects at great depths. On the other hand, if you want to find small objects, you must bring your transmitter and receiver close together, and this requires a reduction in power if you want your set to balance accurately. The Fisher sets are a compromise between the extremes of theory. The Metallascope here described uses a frequency of 175 kc., The Treasure -Hunter, or M -Scope, is light in weight and can be easily carried about. and is especially adapted to finding small (The set cannot be used for the benefit of others objects relatively close to the surface, but a without violating the Fisher patents.) higher frequency can be used by changing the inductance and capacity values and the RADIO has supplanted the "doodle -bug" impedance of the choke coils, and this will in the search for oil, precious ores, enable the builder to detect large objects An M -Scope with separate transmitter and receiver. One man has the receiver, the and buried treasure. More than 150 such as gold deposits at great depths, if he other holds the transmitter at a distance. large corporations are now using the radio is careful to keep down the amount of metal equipment invented by Dr. Gerhard Fisher he puts into the equipment. difference in the result. The Chokes are of Palo Alto, California, in their every- In looking at the diagram, you will see labelled "2" in the drawings. day work of locating oil and metal beneath that we have indicated conventional type -30 Now we jump down to the loop frames the surface of the earth. Hundreds of tubes for the receiver, and type -31 tubes for which are wound with 80 turns of No. 33 individuals who have tried the Fisher sets the transmitter. These weigh less than D.C.C. copper wire, center -tapped, and here in prospecting and treasure -hunting have shielded -grid or pentode tubes which some again we must caution against using any- reported successful finds. Now you can make experimenters prefer, require less plate volt- thing outside of the specifications if you your own set at home for a small sum, by ages, and are less noisy in operation than the want to have a perfect balance on the com- following the simple and easy directions heavier tubes. pletion of your set. which RADIO NEWS is authorized by Dr. Construction of Apparatus In the diagram, R-1 is a 10 ohm filament Fisher to release for amateur use only. You can duplicate the M -Scope, the larg- resistor; R-2 is a 5 ohm for 1 tube, and 2.5 Diagrams for making treasure -locating est of the Fisher sets, for your own use, but ohms for 4 tubes, and R-6 is 2 ohms. You radio equipment are presented here with not for sale, or for use by you as an employee can make up these resistors yourself with Dr. Fisher's permission. The first, called of another person, since sale or rental of the 30 Nichrome wire, which you wind on a the Metallascope, or M -Scope, was devel- device, or using it for hire would subject you fibre strip. In figuring resistance, allow 1 oped in 1929, and is protected by U. S. to prosecution for violation of the patent. ohm resistance for each 1.6 inches of length Patent No. 2066561. Perhaps the best things to make first are of wire. At this rate, R-1 will have 16 The principle of the M -Scope is that of the handles. These are of oak. There are inches; R-2 will have 8 inches for the one the Radio Balance, which requires a radio two, each 34" long, 1%2" wide, and %g" type -31 tube; 4 inches for four type -30 tube, transmitter tuned to any frequency between thick. These should be planed and sand- and 31/2 inches of wire for five type -30 tube. 50 and 5,000 kc.; with wavelengths between papered and the holes should be drilled in If you have assembled your equipment 5,996 and 59.9 meters; and a modulation of accordance with the drawing. Use no paint correctly, you now stand between the han- 1,000 cycles. The transmitter output is on them; a simple stain is sufficient to pro- dles, with the receiver in front of you in a coupled to a balance loop antenna. tect them from the elements. horizontal position, and the transmitter in The receiver has an impedance coupled Next, you will want the r.f. Chokes, each a vertical plane, behind you, and the phones radio amplifier, audio -amplifier, detector, and with 1500 turns, of No. 34 copper wire, on your head. Turn on the power. If the a sensitive tube voltmeter. Like the trans- enamel covered. Be sure to get No. 34, apparatus is in balance there should be no mitter, the receiver is also coupled to a enamel covered, for another gauge or differ- sound in the phones, and no dial indication balanced loop antenna. ent covering may throw out the balance of unless you are standing over buried metal. If the set is in balance, and there is no this design. The windings can be either However, failure to follow the specifications metal present, there will be no sound in the "Random" or "Duo -lateral"; this makes no we have given you may mean that your set

^ DETAIL OF á I 163-,1Al TRANSMITTER MOUNT- !r a ,,/ ING^ 15 ,d( 15 /XIA d 16k." bi 15 ye l6á-. 13 LOOP a' a FRAME Irta 1 SHELF FOR -LOOP -- BOX FRAME 9 LEADS (TWO REQUIRED) - a TUBES AND (TWO REQUIRED) 5" CHASSIS METER`) a 41> 5 1\ a BAss BOLT.*'x2- b= WASHER 4_ V4' TWO( -TRANSMITTER- C. HANDLE PLYWOOD -RECEIVER- d FIBER WASHERS (SIDE PANELS) e BRASS NUT 34" -5 "1- 11-4" MECHANICAL WORK -- OAK HANDLES (TWO REQUIRED) f. BOX FRAME Constructional details for the loop frames, transmitter and receiver boxes, and the handles for the Fisher Treasure -Hunter. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 43

TUBE AND CHASSIS STRIPS

ALL HOLES I} DIA.

SIN TE VOLTAGES IN STEPS AS DESIRED Circuit of the 2 -unit M -Scope. 1-Milliammeter 7-.001 mid., 1 w., fixed 2-R. F. Choke, 1500 turns, No. 34 enamel copper 8-O to .0005 mfd. trimmer adjuster 3-1 meg. resistor 8A-.00025 mfd., 1 w., fixed 34-3 meg. resistor 9-push-pull switches meg. resistor 10-Tip jacks for phones 5-.0005 mid., 1 w., fixed R2-5 ohms, 1 w. 6-.006 mfd., l -w., fixed Re -2 ohms, 1 w.

is in balance when the transmitter is inclined Next, make your frames. These are of at a slight angle from the vertical. Try it oak, too, but you must not use any nails, in different localities free from electrical dis- bolts, or screws of iron or steel. Use wooden turbances and buried metal until you have dowels and glue as much as possible, and located your neutral position of the trans- when you do find it necessary to use metal, mitter, and then mark this with a line select brass bolts and nuts. Where you em- scratched on the box for future use. ploy glue and dowels, reinforcing blocks can With your equipment assembled and ad- he placed inside the corners. These are not justed, you are now ready to prepare for essential, and they are not shown in the The author using the locator. field work. The simplest way to gain ex- drawing, but they do add strength to your perience in operating the set is to follow a frames. Plywood is used for the side panels. curately estimated, but you can obtain good buried pipe line. Strangely enough, a pipe Having made the handles and frames, we approximate estimates by noting the angle of line lying on the surface of the ground, or are ready for the actual radio equipment. the transmitter at which you get maximum one that has been laid very recently will not If you do not have one already, buy a milli - readings on your meter. By taking several suit your purpose. The reason is that the ammeter (d.c.) with enough shunt resist- readings for these angles, at different points, ground itself is a conductor. A pipeline ance to permit about 3/4 full scales deflection and plotting them on paper you can then which has been buried for some time will with the receiver switch ON, and the trans- figure the depth by either simple proportion enable the transmitter to set up eddy cur- mitter switch OFF. The case of the meter or trigonometry. rents which re -radiate and create disturb- should be of bakelite. The equipment which we have described ance in the matrix around the pipe. A newly To search for buried treasure, oil, or min- is the M -Scope, which sells for about two laid surrounded by loosely packed earth, or erals, first go over the suspected ground, hundred dollars. The simpler set, which is a pipe lying on the ground gives little dis- plotting accurately on a map of the area the sold for ninety-five dollars, is the MT turbance and you will have tronble following points where you get maximum meter read- Scope, which is also covered by a patent, it with your set. ings, as well as the spots where you get low but can be copied by readers of this maga- To test yourself, follow the estimated readings, recording in each case the exact zine by permission of the patent -owner. course of the pipe line you have chosen, such reading of your meter. When you have a Internal parts of MT -Scope are fewer as a city water line, and plot it on a rough large number of readings, connect those of in number, and better adapted to the be- map. When you have followed this for the same degree and you will have located ginner who is content with a set of medium several hundred feet, take your map to the the outlines a n d office of the water company and compare it center of your me- 30 30 30 with their actual surveys of their pipe system tallic substance. for that neighborhood. This will serve as a Depth of the ob- RCA L00P check on your readings for direction. ject can not be ac -

A -B 3VA+ I5V.B++

I2VA+ . B

A small M -Scope with both rmir. & rcvr. combined. A more elaborate M -Scope using "in -front -in -back loops." C1-.00025 mfd., I w. RI -1 meg. R-5 ohms, l w. 5-.0005 mfd., fixed C2.00005 mfd., 1 u. Li -9 turns Rr-2 ohms, l w. 6-.006 mid., fixed C3-.O mfd., 1 w. L2-7 turns 1-Milliammeter (0-1) 7-.001 mid., fixed C4-.001 mfd., 1 w. L3-15 turns, 1" form 2-R. F. Choke, 1500 turns No. 34ECC 8-O to .0005 mid., trimmer adjuster C5-,001 mfd., I w. L4-25 turns, I" form .3-I megohm 8.A-.00025 mfd., fixed (:r-.0001 variable, 1 w. 3-1-3 megohms 9-Push-pull switches 4-.I megohm 10-Phone tip jacks 44 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK sensitivity. This has six type -30 tubes in the voltmeter to adjust the depth range of the is a third Fisher circuit, which has never Receiver, and one type -31 tube in the trans- transmitter; this gives a depth range of over been placed on the market commercially. mitter. It has a filament voltmeter; filament 20 feet which is sufficient for locating most This uses only three tubes, and employs rheostat; a balanced loop antenna which buried treasure. Operating the batteries four only the one double -loop, instead of separate eliminates body and ground capacity; a hours a day, they should last three to four loops for the transmitter and receiver. portable type 45 -volt B battery, and two type months, which shows that this set is de- Whichever set you build, you can be con- "Little Six" filament batteries. signed for economy in use. fident that efficient operation will locate any In the transmitter, the MT -Scope, has, in For the experimenter who wants to try buried metal, whether you are looking for addition to the transmitter tube, a filament something extremely simple to build, there a lost pipe-line or Captain Kidd's treasure.

DUAL - DIVERSITY COUPLER

MOST fading is due to the arrival of be leveled down to desired volume by the a single desired signal over not one receiver's a.v.c. system. atmospheric path, but its simulta- This not only increases average signal vol- neous arrival over two or more paths due to ume through eliminating the volume decrease absorption and reflection of the signal by the on the downward fade, but erases all the Heavyside layer of the atmosphere. As a noise which afflicts the weak signal in its rule transmitted signals are radiated over a downward fade. Given a signal the maxi- general direction in a circle around a trans- mum volume of which on a good receiver mitting antenna, or in a beam. Either way provides relatively or completely noise -free some of the signal travels up towards the reception, the Diversity Coupler eliminates Heavyside layer, while the other bounces the noise which invariably accompanies fad- along the ground. There may be several sig- ing by replacing the downward fade with nals propagated sky -wise. Thus two or more, a strong signal. The change -over relay is at rear. -instead of only one,-identical signals A practical operating form of the Diver- reach the receiving antenna, because the un- TOA.vc. won SISTpR 2A4G 20,22 300V sity Coupler is illustrated and diagrammed equal path lengths cause the signal to arrive GUARDIAN herewith. It is contained in a grey enameled 0-100 before, with and after itself. RLT. steel case 8" x 4" x S%2". Operating -wise, it This phase shift, or lag and lead, causes has two binding post strips, one for a con- what was originally one signal to appear at nection to the receiver's antenna binding the receiver as two or more identical signals post and two for connection, one to the ex- of slight time difference. These signals are isting antenna and the second for connection identical as to audio modulation, but lead to a second antenna anywhere from 20' to and lag each other as to carrier frequency. 50' long. The only requirement for this sec- When all arrive exactly simultaneously, they 25V ond antenna is that it be at right angles, or add, and this is the "top" of a fading cycle. as close to this as possible, to the existing When they lag or lead one another, they are SPSTI VVr MC8I antenna. out of phase and tend to cancel out. The usVAC. If the existing antenna is horizontal, the extreme "bottom" of a cycle, corresponding second or new antenna should preferably be IF ND DETECTOR Ci 61-i6 to a completely faded out signal, is when TPICAL ncvtii vertical, or at least at right angles to it. The the phase difference is such as to result in second binding -post strip has two terminals cancellation. for connection to the two ends of the re- The means of eliminating fading lies in ceiver's a.v.c. load resistor. The one knob the fact that it does not occur for a given 75v C BATT on the front panel turns on a.c. power and signal simultaneously in direction in two dif- then regulates the volume level at which au- ferent antennae. Thus, two antennae act NOISE SILENCER CIRCUIT tomatic selection between the two antennae like a see -saw, for when the signal has faded TAr = I occurs. Backing this knob "off" mutes the down in one, it has faded up in the other. Diagram of the diversity coupler. Diversity Coupler, but keeps it ready to be Obviously, the answer is to combine the cut into circuit whenever a signal starts to same signal as received in two different an- needs only an antenna selector switch oper- fade by simple advancement of the knob. If tennae so as always to listen to the strong ated by the fading signal. As the signal in it is turned up too far, the automatic switch signal. This cannot be done by simple inter- one antenna fades down to what may be will "chatter," for it is essential that the connection of the two antennae, because the considered one-half its maximum volume, antenna be switched out as its signal begins phase shift which causes the fading prevents the decreasing a.v.c. voltage generated in the to fade; down should at the instant of the additive combination of the signals at receiver by the signal is caused to operate switching, be a little weaker than the second radio -frequency. Thus a dual -diversity re- the antenna switch to shift over to the second antenna signal, in order that the signal in ceiver must be very complicated in that it antenna in which the signal will be rising. the second antenna may be just enough must be two complete receivers with a com- A casual reading of the above will sug- stronger to hold the switch closed after the mon audio amplifier only. A common a.v.c. gest that this coupling system provides only shift is automatically made. This difference, system must be used to squelch the weak - one-half average signal volume. The reverse a matter of 1 to S microvolts, is controlled signal receiver so that it may not contribute is true, for it provides a constant signal vol- by single knob. noise when its signal fades. ume equal to the maximum volume obtained The circuit diagram shows that the Diver- The new system devised by the author. on the same receiver without it. This is sity Coupler is an extremely sensitive voltage - instead of requiring two receivers, can be because the full cycle of fading is not actu- operated S.P.D.T. switch used to select either added to the existing set to accomplish the ally heard on any receiver equipped with a one of two antennae. Its sensitivity and ad- same results. In this new diversity coupling good a.v.c. system-only the downward fade justability to different strengths of signals is system no attempt is made to combine the is actually heard. When the signal fades up, what allows it to be operated by a receiver's same out -of-phase signal from two different the a.v.c. levels it off to average volume, but a.v.c. voltage, which varies in accordance antennae, since the weak one will be of no when it fades down, the a.v.c. cannot release with signal strength, and is the "power" used practical value anyhow, but rather to cause enough receiver sensitivity to bring in a sig- to switch from the weak signal to the the fading signal automatically to select for nal which has faded out. strong signal antenna automatically. In the the receiver that one of two antennae in The new Diversity Coupling System op- illustration are seen the three contacts mak- which a desired signal is fading upward at erates to erase the downward fade by replac- ing up the S.P.D.T. switch, together with any given instant. The addition to any good ing it with an upward fading signal, and so the circuits and components which cause a receiver to obtain dual diversity reception hold volume consistently strong enough to fading signal to operate it. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 45

Although simple in the extreme in prin- the 2A4G, tube. Still further to the left is plate switch contacts and switch coil. The ciple and in operation, the delicacy of the a vertical partition, on the right of which are 1/2 mfd. condenser and 150 ohm resistor pre- operation to be performed, involving the mounted the MC81 transformer at bottom vent sparking at the plate circuit switch con- translating of a volt or less into eight to and the MC80 at top. tacts, while the 400 ohm rheostat and 12 ten watts of power to operate the switch, Before turning to the illustration showing mfd: condenser across the coil serve two pur- involved extensive research and experiment this partition assembly, the Guardian D100 poses. The condenser stores energy from over a long period. magnetic switch may be profitably studied the short duration pulse due to instantaneous Examining the illustration, and neglecting with a magnifying glass. At its left can be plate circuit make and break so as to cause the switch contacts marked for antenna con- seen a black rectangle, which is the magnet the switch arm to complete its stroke, and nections the left hand pair of binding posts operating bar, which, when the magnet pulls, also to filter the current so as to prevent noise are for connection across the receiver's a.v.c. breaks the contact between the two extreme introduction through d.c. circuit make and load resistor to provide signal controlled ac- left contact blades (silver studded) and so break so physically close to the antenna. tuating voltage. In effect, the signal gener- breaks the 2A4G plate circuit. To their In operation, no consciousness of the ated a.v.c. voltage is used to add to the right are a group of four blades. The ex- operation of the Diversity Coupler is had ex- negative grid bias for the 2A4G gas triode treme right one is the antenna switch actu- cept a "click" every time the signal fades Thyratron control tube provided by the 25 ating blade, raised and lowered by the clover- down. This is due to the antenna circuit volt filament secondary (for 25Z6 dual rec- leaf cam seen at the top right of the switch. switching, and is a very small price to pay tifier tube) of transformer MC81. Turning to the other illustration the ratchet for the elimination of fading and its steady, This negative grid bias is obtained by and pawl operating this cam from the switch long duration noise on downward fades. It using one diode of the 25Z6 rectifier, a 12 magnet can be clearly seen, together with can be eliminated completely by a simple mfd. dry electrolytic condenser, a 3000 ohm, the auxiliary pawl which locks the switch noise silencer consisting of a 6H6 double 1/2 watt resistor and a 2000 ohm potenti- in correct position, preventing over- or diode with its diodes connected in parallel ometer. These provide about 12 volts d.c. under-travel. across the receiver's second detector, plate across the 2000 ohm potentiometer, which The only trick about this switch is to to cathode and cathode to plate. A biasing is applied to the 2A4G grid in amount just make sure its contact blades are so bent battery and potentiometer are the only other insufficient to prevent this tube igniting, or that before the arm, or center blade, of the accessories needed for this noise squelcher, provide a high -current path from cathode to antenna switch has left one contact, it has to adjust bias so the added diode cannot con- plate. closed the other. It is essential that this duct, and so shunt the signal diode tem- In this way, any a.v.c. signal voltage adds switch "make before break." Likewise, it porarily, until a noise voltage louder than to it to prevent ignition, but when the signal is essential that the plate circuit breaking the signal appears. fades downward, the grid bias drops, the switch should not open its contacts until the For code reception, where a continuous Thyratron ignites or conducts, and pulls the movement of the magnet arm has almost carrier is not present to hold the Diversity switch over from antenna No. 1 to antenna fully completely its downward stroke or ap- Coupler to antenna No. 1 or No. 2, and No. 2. Transformer MC81 also lights the plication of current. it would tend to switch antennae in follow- 2A4G filament, and could not be combined Interior illustration shows clearly the three ing code carriers, the remedy is a delay cir- with plate transformer MC80 because of antenna binding posts, the 400 ohm rheo- cuit. Put a % megohm, % watt resistor in regulation problems-when the 2A4G ignites stat and 150 ohm, % watt resistor, and the series with the 2A4G grid lead, and a % it suddenly draws, not zero plate current, %2 mfd. and 12 mfd. condensers across the mfd. condenser from its grid to filament. but about 85 ma., which drops the plate voltage from MC80 and, were MC80 and MC81 combined, would drop the bias volt- age for an instant so that the switch would "chatter" instead of going cleanly from posi- tion No. 1 to No. 2. Hence, separate, though l//7// small and inexpensive, transformers are es- ANTENNA GROUNDS, AIR CORE R.F. R CHOKE FILTER A.F OR POWER sential for grid -filament and plate voltage. INDUCTANCE TRANSFORMER CHOKE TRANSFORMER Once the fading signal has caused the bias on the 2A4G to drop below ignition poten- tial, the tube passes a high plate current, and the grid loses control until the plate circuit is broken. So a second switch is mechanically built into the Guardian D100 magnetic T TI switch so that when it operates, the plate +Aü f circuit is broken for the instant AUTC VARIABLE I.F TRANSFORMER QUARTZ FIXED VARIABLE SPLIT necessary to TRANS INDUCTANCE CRYSTALS STATORI cut off plate current, to be reclosed as soon FORMER CONDENSERS as antennae have been changed to provide a more negative a.v.c. voltage so that the circuit will be ready to operate again when the signal in the selected antenna has begun to fade. MC80 provides 150 volts a.c. for 2A4G plate power, through the second diode of FIXED VARIABLE CENTER SINGLE COND- CRYSTAL HEADPHONES CLOSED OPEN the 25Z6 rectifier and a 12 mfd., 250 volt TAPPED[I BUTTON ENSEP CKT CKT dry electrolytic condenser. It will be noted 1 --RE S I STOR S MICROPHONES JACKS- that both grid and plate rectifiers have no -T- filter chokes, for they are not needed, since A MA TC a.c. hum is not a problem at all, these cir- -4r4".- - r cuits having nothing directly to do with the O O O MULTIPL 1 t } } VOLT SPST. I / receiver, and so being incapable of causing AMMETER S?DT hum in its output. MILL [AMMETER CONNECTION I DPST. I LOUD THERMOCOUPLE NO CONNECTION ()PDT. SPEAKERS The internal assembly of the Diversity METERS SWITCHES Coupler is clearly illustrated. On the panel at the right is mounted the 2000 ohm grid, PLAT SUPPRESSOR or "sensitivity," potentiometer with its a.c. NJECTOR GRID KEY SCREEN GRID on -off switch. Directly below it, mounted FILAMENT CONTROL GRID NEON LINK AC on tie -lug strips, are the grid and plate filter GENERATOR condensers with the 3000 ohm grid voltage TEST LAMPS CATHODE _ dropping resistor on its leads about them. M=THOUSAND To their left is the 25Z6, with behind it II= OHMS FILAMENT OR HEATER 46 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

Homemade Pilot Light Socket only to have its characteristics altered due and 600 volts should meet all requirements. The accompanying drawing shows how a to surrounding objects when raised into Connect as shown in Figure 2. In calculat- socket for the radio pilot light or a flash- position. ing multiplier resistances, you must know light bulb may be made easily from an ordi- maximum meter current and the meter re- nary screen -grid tube clip, a few pieces of Chart of Tap and Clearance Drills sistance; then add resistance in series un- insulated wire and a couple of insulating In radio construction work experimenters til the sum (multiplier plus meter re- washers. A drop of solder on the end of are often confronted with the problem of sistance) equals the desired voltage range the bottom lead makes a good contact for selecting the correct size drill for tapping, divided by decimal fraction of an ampere. or the positive terminal of the bulb. The for drilling a clearance hole to take a As shown in Figure 2 the meter is al- socket can be mounted by soldering directly certain size machine screw. This chart gives ways set for the highest voltage-pro- to the chassis or by means of a soldering the drill sizes required for average use. If tected against mistakes. Lower voltages are lug as shown in the drawing the machine screw must pass readily through read by holding down the proper key, the hole, then the size drill is selected under temporarily shunting out part of the multi- GRID CLIP the column headed "Clearance." plier resistance. A cheap a.c. voltmeter can Screw Threads Drill Number be extended in same a l. Number Per Inch Per Tap Clearance the manner with 2 48 50 44 top range of '700 or 800 volts. DROP OF SOLDER CLIP MAY BE SOLDERED ON END OF WIRE TO CHASSIS OR TO A LUG 2 56 50 44 2 64 50 44 PRESS FOR 300V T PRESS FOR v.. 3 40 49 39 -p ., 3 48 45 38 3 56 44 38 600 300V. 30V. 4 32 43 31 FROM CLIP INSULATING WASHERS INSULATE WIRE 4 36 42 31 PROD _4CLIP 4 40 41 31 Figure 2. 5 30, 32 40 29 Antenna Impedance Matching Simplified 5 36 38 29 The ham is often faced with a difficult 5 40 37 29 6 30, 32 35 26 Handy Continuity Tester it problem when comes to matching the 6 36 33 26 This pencil -tester should find a wide vari feeders to an antenna. Normally the antenna 6 40 32 26 7 30 31 21 ety of applications in every experimenter's is operated in an elevated position where 7 32 30 21 and serviceman's workshop in tracing con- it is not accessible, so the matching is done 8 24, 30 30 17 8 32 29 17 tinuity and shorts. It is especially useful in on the ground, with a prayer that when 9 24 29 13 checking from point to point, testing coils, raised to position the match will still be sat- 9 28 28 13 9 30 27 13 switch contacts, and other applications where isfactory. Where the feeders are of the 9 32 25 13 very low resistance is found. tuned variety this of course does not apply. 10 24 25 8 10 30 22 8 The sensitivity of the indicator can be It is in the case of non -resonant feeders so 10 32 21 8 controlled by lamps of 12 20 19 2 substituting different commonly employed on the five -and -ten - 12 24 16 2 current drain. A dial -lamp of high current meter bands that it does apply, and is one of 12 28 14 2 consumption is useful where it is desired to the reasons that standing waves are so often 14 20 10 T/a 14 24 7 % limit the resistance indication to a few ohms present on such systems. such as in coils and switches, while the Where the antenna is a type that employs Meter Kinks special low current dial -lamps used in bat- a matching section, such as the "J", the Presented herewith are simple methods tery operated receivers can be used to indi- "half -waves in phase" and various other ar- whereby two separate meters are employed cate continuity in circuits up to approximately be rays this problem can sometimes over- to obtain multiple current, voltage and re- 50 ohms. Another useful application of this come by making the matching section more sistance measurements. unit is its employment as a small torch for than one half wave or quarter wave long. An 0.15 milliammeter of 295 ohms resist- working in dark corners of receivers, etc. a Under conditions where half -wave match- ance can be purchased for about 60 cents For use in this capacity it is only necessary ing section is specified, it can just as well and one with zero adjustment for about to fasten the alligator clip to the test prod. be two or more half waves long and can $1.00. A meter of this type will take care to a BAKELITE TUBING DIAL LAMPSHOLDER thus be extended down point within of all current measuring requirements with TEST PROD reach a the roof, and the proper of ladder or sufficient accuracy. A shunt equal to one - I Zei point for attaching the feeders determined of will ninth the meter resistance increase RETAINING PLUG 'SCREW SPRING PENCIL TYPE with the antenna in its normal elevated the range ten times, measuring current up BATTS. position. Or when a quarter -wave match- to 150 mas. Connected as in Figure 1, the ALLIGATOR CLIP ing section is specified, it can be lengthened meter is always prepared for the highest -""--TEST CORD to any odd number of quarter waves. reading and is a safeguard against burn -out. Suppose the problem involves a 5 -meter To read 0-15 ma. press down the key, this Fuses Save Dollars vertical "J" antenna with spaced feeders, will momentarily disconnect the shunt. A good guess is that burned out trans- the "J" to be mounted on a mast with its To measure resist- formers represent one of the largest single bottom 30 feet above the roof. Normally ance use your more items of replacement cost in the radio game. a quarter -wave matching section would be sensitive voltmeter Yet we radio experimenters go right on employed and the point where the feeders in the substitution building receivers, transmitters and other connect to it would be about 27 feet above method a with equipment without fuses or other protective the roof, with the shorting bar a foot or 100,000 ohm cali- equipment to protect the relatively expensive so below that. If the mast is husky enough to brated adjustable re- power supply parts when, at a cost of only a support a long ladder, all well and good. It sistor. The range few we could gain such protection. is more simple, however, to make the match- can be extended by cents, ing section five quarter waves long, thus connecting known An automobile fuse rated at 1 ampere, bringing its lower end down to about 10 values in series and connected between the line and the power Figure I. feet off the roof where it can be reached adding so much to transformer primary, will do the trick for comfortably from an ordinary step ladder. the reading. This method avoids meter medium and small receivers. For larger re- The shorting bar position near the bottom error and voltage drop. Simply adjust to ceivers and small transmitters the same kind end can then be determined in exactly the the same voltmeter reading, whatever it may of fuses but rated at 2 amperes will do the same way as with a quarter -wave section, be and the resistance is the same as the un- trick and for larger transmitters the fuses and the correct connection point for the known resistor which produced that same should be proportionately larger in current feeders also. The only difference would be deflection. No ohms scale is required on rating. These fuses cost five cents each and that the match would be a permanent one the voltmeter. the mountings about a dime. Certainly because the antenna would be in its normal For the voltmeter, an instrument of 1000 safety is cheap at these prices. position during the adjustment and there- ohms per volt is good, one of 2000 ohms The proper place for the fuse is in the fore not subject to changes encountered per volt very good and 5000 per volt excel- line input as mentioned. Then if a short when an antenna is matched on the ground, lent. Three d.c. voltage ranges of 30, 300, circuit occurs anywhere in the filament or RADIO NEWS 19-10 RADIO & TELEVISION DATA BOOK 47 plate circuits of the receiver the fuse will Increasing Voltmeter Utility the junk drawer and assembled on a small go before the transformer can be damaged. Everyone who experiments with radio or board alongside or attached to a B eliminator In equipment which employs more than electricity is equipped with a voltmeter of of reasonable power. one power supply, as in transmitters where some type but many are not fortunate MAGNETIC SPEAKER the exciter, modulator and final stage may enough to own milliammeters-or at least each have its own power supply, the line so they believe. If you are one of this latter supply to each power transformer should be class you are due for a surprise because your separately fused. Not only does this provide voltmeter is a milliammeter as well. If you MICROPHONE4 TO protection but when a fuse goes it will show open it up and look inside you will find IOOMIL TRANSCEIVER the portion of the rig in which the trouble the meter mechanism and a resistor. Short V v uSV. TO exists. FIGI circuit this resistor KEY 250V.DC The best plan in selecting fuses for a C and the instrument given job is to figure the actual power becomes a straight drawn from the transformer, including all milliammeter. Its filaments, plates, pilot lights, etc. under range will be O to 1 Connect the output to an old magnetic conditions of maximum operating load. The milliammeter if the speaker, turn on the power and press the power on the primary side will be somewhat voltmeter is one with key. The neon bulb will oscillate and pro- higher than this, due to transformer losses. a 1000 ohms -per -volt duce a tone in the speaker. Its strength can You will be safe to double this figure, con, rating. If a 100 ohms - be controlled by the variable resistance while vert it into terms of primary current by per -volt rating the the pitch can be varied from a low note of dividing this value (in watts) into the line current range will be 0 to 10 ma., etc. Instead only a few cycles to one of the highest audible voltage. Then use a fuse having a current of short-circuiting the resistor, you can bring frequency by means of the tuning condenser. rating nearest to this value. Doubling the out a lead from between one side of the The note can be transferred to the trans- power value as suggested avoids blowing the mechanism and the resistor and mount ceiver by placing the mike close to the fuse as a result of normal surges that may another binding post on the meter case to speaker and will not interfere with voice occur. which to connect this third lead. Then you unless the key is depressed. can use the instrument either as a current meter or a voltmeter, depending on which Plug-in Resistors Tips on Radio Noises of its terminals you employ. All of this For experimental purposes where resistors The basic cause for the interference from is illustrated in Figure 1. (A) and (B) are have to be changed often as in biasing vari- small motors is due to dirt on the commu- the original voltmeter terminals while (C) is ous types of tubes, control networks, etc., tator, which in turn prevents the brushes the added one. Terminals (A) and (B) are a plug-in arrangement is very desirable. The from making correct contact, resulting in used for voltage measurements; terminals following idea has worked out very success- sparking. The first job to do is to clean (A) and (C) for current. The range of fully. the motor. If the frame of the motor is either meter may be increased in the usual The shells of several old tube bases were ungrounded make this connection, it helps manner. Shunting suitable resistors across sawed off close to the bottom with two of greatly in minimizing this type of noise. If (A)(C) will increase the current range. the prongs left intact, except for cleaning there is still some interference marring your Inserting suitable resistors between (B) and out the wire and solder. Next the resistor reception, traceable to the motor, connect a the voltage to be measured will increase the was mounted as shown in the drawing with 2 mfd.-1000 v. condenser across the voltage range. the leads crimped so that when said leads were pressed into the prong they made a brushes. For very small motors, such as are Fish Pole Antenna used in hair driers, vacuum cleaners, and good connection and support for the resistor. The manufacturers, quick to take ad- Sockets were then fitted to the receiver or soda mixers, 0.5 mfd. condenser will do the vantage of the increasing interest in auto, trick. were then fitted to mobile radios, have introduced several new PIG -TAIL RESISTOR In the case of a refrigerator or furnace the receiver or bread- types of aerials for roof, door and bumper board layout a n d control, try connecting an 0.25 or 0.5 mfd. mounting. One of the simpler types that From hard wired into the resist- condenser across the input. the experimenter can make for himself is the of these de- ance circuit. usage the thermostat contacts bumper rod antenna. Purchase a cheap one vices often become mechanically defective, It is a simple mat- piece metal fishing rod, one that has a ter to pull out these resulting in sparking and considerable radio wooden or some kind of an insulated handle. noise. plug-in resistors from You are not interested in its properties as a the socket to substi- LEADS CRIMPED IN fishing pole and therefore a cheap rod will TUBE BA SE PRONG tute a resistance of a answer a lead-in the Homemade Scratch Filter the purpose. Solder to different value. For bottom end of the metal rod and then fasten permanent use the resistor leads could be A scratch filter generally consists of a the pole to the rear bumper by means of an soldered into the tube base prongs and the choke, condenser and a resistance connected improvised iron strap and two long stove latter inserted into the socket for good in a series -resonant circuit. It is connected bolts. For this job it will be necessary to or until the resistor burned out and required directly across the input transformer of the prepare two holes in the handle to take replacement. pick-up and is employed to attenuate the the bolts. hissing frequencies caused by the needle Several ways will present themselves for Selecting Antenna Wire scratch. The choke can be a 1500 turn supporting the antenna. On some cars it In selecting wire for antennas it is too can be fastened on the bumper rod, on other often the practice to simply go into a radio makes can be on it mounted the bumper store and ask for so many feet of antenna CHOKE is the rod be support. It suggested that wire, taking pretty much whatever the dealer given a coat of aluminum paint to prevent PICK TO offers. Where the wire is to be used for an UP .002 TO.0IMFD. AMP rust. ordinary "L" type antenna for broadcast Variable Tone Modulator reception there is little harm in this pro- 2,000n The majority of manufactured or home- cedure because the exact length of the an- made 5 meter transceivers are not equipped tenna is not critical, nor the strain on the with tone modulation for c.w. work. It is wire great. honeycomb coil or a standard 125 or 85 a simple matter to add this feature without Where the antenna is to be used for trans- millihenry choke. All three units are ob- molesting the transceivers in any way. As- mission, or for a self -resonant receiving an- tainable from any radio store but if the semble a % to %2 watt neon bulb, a .001 tenna greater care is needed. Here the an- reader wants to roll his own, wind approxi- mfd. variable condenser, a 100,000 ohm vari- tenna length is critical and usually the an- mately 1800 turns of No. 28 d.c.c. wire on able resistor and a key as shown. A 1/4 mfd. tenna must be stretched taut under a con- a form 2 inches in diameter by 11/2 inches condenser should also be connected across siderable amount of tension. Moreover, if long. the key. All this material can be taken from a tree is used as a support the wire may be 48 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK under tremendous strain during storms. For and DX listener will find a small card file cuit are loose and the cause of considerable such uses, solid wire is usually employed system unbelievably helpful in pursuit of radio interference. Look for corroded con- and is generally available in hard -drawn and their hobby. Using a file in an amateur nections responsible for high -resistance con- soft -drawn forms. station, for instance, you can tell in a few tacts. Check the line cord-the handling Hard -drawn wire is recommended for such seconds whether you have ever worked a that this part has to undergo is considerable critical service. The reason is that it has station. On each card you can record in- and quite often it is hanging by a single close to twice the strength of the soft -drawn formation on the station, equipment used, strand of wire. Replace the line cord plug variety; and what is more important, soft- signal strength, reports on previous con- with the new tight -grip plug. Inspect the drawn wire under strain will stretch as much tacts, the "ham's" name and location, type volume control, this part can be replaced as 25 per cent as against less than 1 per cent of antenna he uses, etc. On subsequent hook- very often with a big improvement in re- for hard -drawn wire of the same size and ups with stations worked before, you will sults. Clean the contacts on the tube sock- subjected to the same strain. Actual tests have all pertinent data at your finger tips. ets; also check these contacts for proper made on No. 12 wire showed the soft wire In DX work, another such file could con- grip on the tube prongs. Brush or blow broke at 150 pounds pull whereas the hard - tain cards for each station heard, together out the dust particles on the variable con- drawn broke at almost exactly 300 pounds. with notations of information concerning densers, etc. There are numerous other in- Just before breaking, the soft wire had these stations. When requesting a verifica- spections and jobs that can be made on any stretched from 5' to 5', 11", whereas when tion from a station, you can make up a re- piece of radio equipment that will pay divi- subjected to the same strain of 150 pounds port based on this information, covering a dends in better all around results. the hard -drawn wire showed no appreciable period of a week, month or a year, as the stretch. At just short of 300 pounds pull case may be. A Practical Speaker Repair the hard -drawn wire showed elongation of A file of this kind will be found very Dynamic Speakers with rusty, nonremov- approximately %g inch. handy in experimental work, for making able field pole pieces that the cone's voice - To avoid sag, and for the antenna length notes of each experiment for future refer- coil fits over, may be easily repaired. to remain fixed, use hard -drawn wire. If the ence. It is surprising how often you will First cut out the cone carefully with a strain is likely to be greater than 300 pounds refer to these records. On these same cards sharp knife so that an empire -cloth disc may use copper -clad steel wire which is still note any articles or books that you may be cemented between steel shell and cone. stronger. have read covering the same subject and CLOTH REPAIR DISC GLUED ON this file will therefore a A Sharply Tuned Wavetneter represent not only record of experimental findings Despite monitors and frequency meters but a fairly comprehensive bibliography of technical in- the old style absorption type wavemeter still formation. has its place in amateur equipment. Har- For most purposes a small metal file box monics have no effect on its operation and with hinged cover capable of holding sev- with intelligent use it will give a definite eral hundred cards can be purchased com- check on frequency to a limited degree. In plete with an alphabetical index and cards the past its chief handicap has been broad After cone is removed the No. 243 pole for a total of about 35 cents. These are tuning and it was difficult to obtain a true piece may be cleaned with a piece of emery standard 3 x 5 inch file cards. As the cards reading. Presented herewith is a simple paper. Turn the speaker upside down and accumulate and outgrow the small file they method for overcoming this objection. tap it lightly to remove small particles of can be transferred to a drawer type file Instead of connecting the indicating lamp rust and other debris. which will accommodate something over a in series with the tuning coil and condenser Place cone back on speaker by applying thousand cards, and which can be obtained as in the usual manner, shunt the lamp rubber cement to its outer top edge and strip for around a dollar. across the circuit as shown in the drawing. it on the steel shell. Before the cement is A little work is involved in jotting the Connecting the de- (VOLT DIAL LAMP dry, put the empire -cloth disc in place and data down on the cards, but this is as noth- vice in this way us- press it firmly in position with a pencil eraser ing compared with the value of always hav- ing a 6 volt dial end. ing the desired information available when lamp the tuning will When the cement is dry the cone is cen- you need it. be unusually sharp tered, finishing the repair. and when carefully tuned the instru- Fix It Now Low Cost Tester ment will be able to The experimenter and the DX listener Here is a condenser and continuity indicate the transmitted frequency to within should check over his equipment every so checker that one can build and use for a narrow percentage of the true frequency. often, so as to eliminate the small troubles, many tests that are commonly employed by Employ busbar for the leads as they can which if neglected, may become serious a radio serviceman. The device uses a half - also serve as supports for the lamp socket. problems. In many cases the DX listener wave rectifier to change the current from a.c. can improve both the sensitivity and selec- to d.c. A resistance cord drops the line Increasing Efficiency of Detector Tube tivity of his set, simply by replacing a single voltage to 12 volts for the required filament A five -prong cathode type triode will os- defective tube, by lining up the tuning coils, voltage to the 12Z3 tube. A simple filter cillate more readily if the grid prong is iso- is a etc. It puzzling fact, how often a fan 12Z3 54000151W lated from the composition base, especially will tolerate distorted reception, due per- so when used in a super -regenerative circuit haps to an open resistor or some other part as a self -quenching detector. which could be found easily by a simple con- This isolation may be easily accomplished tinuity check or the use of an ohmmeter. with a highspeed hand grinder, using pref- The doctor and the dentist find it good busi- erably a small saw in the chuck rather than ness and good psychology to sell their pa- yY CONTINUITY TEST an abrasive wheel. tient the idea of a periodic examination. Hold the tube with the base upward and Many radio servicemen are applying this system comprises a 50,000 ohm 1 watt cut away a section around the prong, simi- same idea with equal success. The Radio resistor and a 200 volt, 8 mfd. condenser lar to cutting a piece of pie. away Cut Gadgeteer who makes his own equipment The neon lamp can be either the %2 or 1 enough of the composition base to leave can use a little of this psychology, and the watt size. When testing the condition of room for a small screwdriver or matchstick advantage will be that his apparatus will condensers a pair of test prods should be to be used to push the prong in place when operate as originally designed and con- plugged into the jacks marked "condenser the tube is inserted in the socket. Care structed. test." For testing resistors or other parts should be exercised not to cut the wire con- After a piece of radio apparatus has been for continuity the test prods should be necting the grid to the prong. in use for a period of time an inspection plugged into the jacks marked "continuity will often disclose that the screws used for test" as shown in the diagram. Handy File System fastening the condenser or other parts to It will be noted that the condenser under The experimenter, serviceman, amateur, the chassis and completing the ground cir- test is in series with the neon lamp and the RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 49 power source and following the general hole prepared for it in the side of the tube in a conventional pentode amplifier procedure employed in this method of testing cabinet. and half -wave rectifier arrangement. A 350 it will be possible to determine if the con- Exact focal distance can only be found denser is normal, leaky, or short-circuited. by experimenting with the lens and the When one wishes to check the presence screen. A shadow box is necessary in order 1257 of voltage, or the polarity of the line, he to observe image detail. must first turn off the power supply of the tester, then connect the test prods into the Twin -Triodes in Cascade c, proper terminals as indicated on the drawing. Twin -triode tubes such as the 53, 6A6, LIST Or PUTS. M- J/NG1(dV770NMIR( One set of plugs are marked for voltages up 6N7, and 79 are well known and popular T 000P0221 7PM7lO1ME1 %1.áár mesa MIMI to 400 volts, the other jacks are marked for when used with the two triode sections ¢I - 300 0'IN LINI CORO 113/341 R. 1100 (NM, INRT7 voltages to 120 volts. The size of the re- in parallel or in push-pull, but are not gen- C L OMiA [t[CI'POLYIrc ad.d s- I uGvcnc arcAra sistor "R" depends upon the neon bulb. A erally used with the two sections in cas- C¡=rM.7O. 500 rWli resistor of about 40,000 ohms will answer cade as shown in the drawing, because of this purpose. The neon lamp can be cali- the tendency toward motor-boating. This ohm line -cord resistance is used to obtain brated by the eye. is unfortunate because with the two sections the correct filament voltage. As only fair Although there have been a number of cascaded in a resistance coupled circuit, quality response covering the voice fre- these neon checkers described in the past voltage gains of from 700 to 2000 can be quencies is desired any inexpensive single- the experimenter will appreciate the low obtained with the single tube; or in terms button carbon microphone may be used. cost and simple design of this instrument. of decibels, from 57 to 66 db. Sufficient power is provided to drive a small loud speaker with plenty of volume Changing the Crystal Frequency for the job. If you wish to raise the frequency of your crystal, the procedure is not so diffi- Measuring Power Output cult as you might imagine. Ordinary kitchen The standard equipment required for lin- cleanser, such as Old Dutch or Bon -Ami ing up a receiver generally comprises a powder, will act as an excellent grinding modulated oscillator and an output meter. material. Place a small amount of the An experimenter may have the first instru- reason for the tendency toward powder on a piece of plate glass and use The ment or can borrow one, but very often his is all of these tubes un- just enough water to make a thin paste. motor -boating that measuring apparatus does not include the a common cathode. That Then simply polish down the crystal by fortunately have second device; that is, the output meter. has its own grid and plate, rotating it in the paste solution, pressing is, each section As a simple substitution for the output meter both. This down firmly in order to obtain an equal but there is only one cathode for you can use a Mazda flashlight bulb or a where cathode bias is used, that there amount of pressure over the entire surface means, 110 -volt, 8 -watt pilot lamp to provide visual first and second of the crystal. Do not attempt to grind is coupling between the indication of power. Using the flashlight regardless of the size of the too much, but after a minute or so, wash plate circuits, bulb, it is necessary to disconnect the voice the crystal and test it in the oscillator. cathode by-pass condenser. coil of the speaker and connect the lamp is avoid this com- To lower the crystal frequency, apply The simple remedy to across the secondary side of the output individual bias volt- India drawing ink to both surfaces with a mon coupling by using transformer. Keep the input voltage down; Only two to three small brush or mark them evenly with a lead ages on the two grids. that is, the applied signal from the oscillator, is for each and the pencil. Frequency response can usually be volts of bias required so as to prevent burning out the lamp. The may, therefore, conveniently lowered from 10 to 30 KC. The lead pencil biasing source 10 -watt lamp can be connected in series with smallest type method has the advantage that one can be either flash -light cells (the a 2 mfd. condenser, ahead of the output still the Mallory bias cells. merely erase a few kilocycles when this is will do), or better transformer. The voice coil circuit should because they never desired! The latter are preferred be open for this test. required replacement and are extremely small. in the one en- Projection Device for C.R. 913 Tube The two sections enclosed Improving Quality velope are shown in the conventional cas- Amateurs, experimenters, and servicemen Even with the best of ordinary baffling, cade form for simplicity. The coupling are familiar with the CR913 tube, because the range, both in quality and volume, of condensers and resistors are of the usual of its application, low-cost, and adaptability small dynamic speakers is rather limited. values and C1 is necessary only when the to compact design in cathode ray oscillo- By adapting a discarded exponential horn microphone or other input is of a type which scopes. Here is a kink whereby the image as a baffle the ability of the speaker may be constitutes a closed circuit, and avoids short- of this tube can be enlarged to at least improved considerably. These horns-gen- ing the bias battery or cells. The bias cells 3 inches in diameter with good detail. erally made of fibre-may be obtained quite are shown at B1 and B2. If the Mallory bias Obtain, from an old camera or second- cheaply from any obsolete orthophonic used they do not require by-passing hand shop, a piano -convex lens with a speed cells are victrola. flash -light cells should be by-passed with of about f 6.3. Next secure a mirror about but The throat of the horn should be cut 25 mfd. condensers. 9" square. Then purchase from a camera off at a point where the cross-sectional shop a ground - of its shape, is approxi- Phone QRM area, regardless glass screen, 4x5 mately equal to the cone of the speaker. Many an amateur who has had no QRM inches. With this It may then be attached to the speaker difficulties whatever while operating on cw, material at hand, with small brackets. A small section of the finds that when he tries phone interference install and mount original baffling should be retained, however, is caused in nearby broadcast receivers. Such the parts as shown to prevent distortion. t 4 VIEWING many instances, from MIRROR \ SHADE in the drawing. complaints come, in xi LENS GROUND the owners of up-to-date modern receivers, GLASS The tube should Soldering Iron Tip be placed in a ver- and therefore, according to regulations, it By mixing a little powdered graphite with tical position. The behooves the amateur to aid in removing a drop of oil and applying it on the screw LONG lens is mounted 1" the interference. In most instances, a wave BOLT threads of the soldering iron tip it will pre- 2" above the trap or other complicated tuning device is ia to vent the tip from sticking. The graphite tube by means of unnecessary and a simple method for elimin- also helps to prevent corrosion. two long bolts. ating this trouble is to place a 2.5 millihenry The mirror is mounted on the wall of the RF choke in series with the antenna lead to cabinet by a wedge-shaped piece of wood. the broadcast receiver. Neon Lamp Substitute This mirror should be placed at a 45 degree Neon test lamps cost from 50c up, but angle and it is mounted approximately 4" Single Tube Announcer if you will search around the five and ten above the tube. Place the groundglass screen Designed for simplicity and economy, cent store you may be able to pick up one 4" to 5" from the mirror and over the 3" this announcing system employs a 12A7 type or more of the little carbon filament lamps 50 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK that sell for 10c. These lamps are even more mfd. condenser as shown in the drawing. sponge to the halyard, as shown. Soak the sensitive to r.f. current than a neon bulb. One side of the condenser also connects to sponge in oil and then pull it up to the For use in a wave one side of a telegraph key, the other side pulley by the halyard. Slapping it against meter the filament of the key then connects to the minus side the pulley will squeeze some of the oil out can be used either in- of a 90 volt B battery or eliminator. Then onto the pulley and thus thoroughly lubri- tact or "blown." With a 0 to S megohm variable grid leak is con- cate it. a whole filament the nected between the plus side of the power Finally, lower the antenna and go over it BLOWN usual glow is pro- source and the remaining side of the con- carefully for bad joints and contacts. Where FILAMENT duced just as with a denser. corrosion or broken soldering is evident, re- neon. With a blown make the joint and resolder. The electrical filament the tuning is connection must be perfect or efficiency is sharper. Operating in lost. It is very important that all electri- series will produce a cal resistance must be overcome in soldered broader glow point than if the lamp is joints and time given to this will be well re- shunted across the circuit. The filament can paid in increased signal transmission and be blown by shooting about WO volts reception. through it. If your antenna system employs a light- ning switch, see to it that snow and ice A.C.-D.C. Receiver Tube Tester cannot collect in the winter and short signals To quickly locate an open circuit in to ground. The best way is to build a sim- a.c.-d.c. receivers, a handy tester is a small Pressing the key completes the circuit be- ple shed roof shelter for it as indicated in neon light with two rubber covered electric tween lamp, phones and resistor and causes the sketch. Bring the feeder or feeders wire probes soldered to the base and side of the lamp to oscillate. For normal use set down to long stand-off insulators. From the bulb base. the resistor at about 11/2 megohms. Lower- there the leads pass inside the shelter to the Method of Testing ing or raising the resistance will alter the switch and to their proper connections with- Placing one probe to negative, which is pitch of the signal. out fear of weather conditions. usually the chassis, move the other as Look other points Winterizing the Antenna over all for weaknesses follows: such as cracked or chipped insulators, loose Whether your antenna is used for receiv- To the high side of the line cord, then halyard cleats, stay connections to ground, ing, transmitting, or both, it should to the filament resistor that is wound in the be given and mast base supports. When winter gales a good "once sets cord. (If a ballast tube is used, move probe over" before winter in. blow and temperatures drop into the zero Much of the pleasure and efficiency of good to each live prong on the ballast tube.) The region a strong mast and efficient antenna radio depends upon the antenna system. So cord and filament resistor are checked this will add to your radio pleasure and not be a way for continuity. give every joint the benefit of the doubt. constant source of worry. employ Placing one probe to negative, move the If you a mast, look it over for weak other probe to each filament prong of the points in construction and remedy them. If possible, slap on a heavy coat of Handles for Phone Cord Tips tubes, starting at the rectifier, and then on The tips of phone cords can be more easily through all the other tubes. paint. An unpainted mast will deteriorate rapidly. withdrawn from the pin jack if a %Z' This step checks the tube continuity. knurled a post is Look over is nut from battery binding Placing one probe to the high side of the the stays. Any stay that kinked or line cord, and the other probe to each con- badly rusted should be replaced with a new one. A broken stay during a tact of the dial lights, if they are 6 -volt mile lights and are insulated from the chassis (or 60 winter gale will probably mean dis- aster. Better fix it now. to the live side of the bulbs if they are 110 - volt lights) check the continuity of the bulb A rope halyard, supporting any strain, is filaments. good for about a year. Any that appear suspiciously weak must be removed and The a.c.-d.c. cord should be plugged in new rope reeved and the switch turned on for all tests. through the pulleys. No need to climb mast Whenever the neon bulb does not glow, the or lower it to do this. Just butt the ends of the new and old rope there is the open tube, light or resistance, as the case may be. together and spiral a piece of wire along the joint from one to the other. Then care- Replacing the Magnetic Speaker fully haul the joint up and through its soldered to the tip. The knurled nut should There are a great many radio beginners pulley until the new rope is in place. be drilled out so that it can be passed over who would like to replace their magnetic the phone tip and soldered to the end, as speaker with an electro-dynamic type. They illustrated. The knurled edge makes removal hesitate because they think it is and insertion of the tips, extremely simple. an involved OIL SOAKEDDER procedure. Purchase an output choke SPONGE LEAD or IN transformer of suitable impedance for the Mark the Resistors and Save Time dynamic speaker. Connect this in series If you will mark each carbon resistor with with the field supply which in turn is its ohmage value, using quick drying lacquer shunted by a 4 mfd. condenser. Connect and a small brush, much time will be saved this field in turn in series with the plate terminal of the output tube. The circuit then will run from the place of the output TO GNU tube to the matching output transformer, Before reeving in arty new halyard it will from the matching output transformer to be wise to weatherproof it as follows. Fill the field circuit just described, and from a bucket with boiled linseed oil and coil the the field circuit to the positive lead of the rope into the bucket. Leave it there over- power supply of the receiver. night. Then stretch it between posts and wipe off all extra oil, catching this in a A Few Cents Builds This C. P. Oscillator bucket as you work along. Such treatment The search for a simple code practice makes the rope pliable and just about dou oscillator still continues and here is one that bles its life. anyone can build in a few minutes. It em- Metal pulleys will rust in time making when selecting the correct resistor in set ploys the fewest posible parts and costs but them hard or impossible to turn. To cure a building or in repairing. Condensers, r.f. little to construct. A quarter watt neon hard turning pulley without taking down chokes, etc., too, can also be labeled with test lamp is connected in series with a .001 the mast is a simple matter. Tie a small their capacities. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 51

total resistance is 150 X 1000 = 150,000 All -Wave Tuned Antenna HIGH -RESISTANCE ohms. The current from the circuit just In many places it is impossible to prop- VOLTMETER considered would be: erly erect the doublet type antenna with E a center lead-in. Also, this type is not The function of a voltmeter is to measure I = -= 100 _ (20,000 + 150,000) _ satisfactory on the 200-500 meter band, the difference of potential existing between R without prohibitive length or complicated two points in a circuit. It should not influ- .0006 amperes, or .6 milliamperes. transformers. ence in any way the circuit or device across and the I X R drop across the circuit re- The old reliable inverted "L" antenna, which the difference of potential exists. Since sistor is, which can be erected almost anywhere, is every voltmeter will draw some current from E = I X R= .0006 X 20,000 = 12 volts excellent on the broadcast band and very the circuit across which it is connected, this and the voltage read at A B would be good on short -waves. However, the end current really puts a load on the circuit or 100 -.12 = 88 volts. connection makes it voltage -operated on device being measured. If the circuit or de- This shows that the high resistance volt- short -waves; hence an electrostatic shield vice has quite some resistance, the meter meter gives a reading of 88 volts which is between primary and secondary of the re- current flowing through it may produce much nearer the true open -circuit or no- ceiver transformer would cause great loss. an additional appreciable fall of potential load voltage of 100 volts than before. The circuit illustrated herewith relies through it. In this case, the voltage indi- Since a voltmeter having a high resist- ANT. cated by the meter is really lower than the ance takes very little current from the line, actual voltage which exists across the cir- the meter itself must be very sensitive, that cuit normally when the meter is not con- is, it must require very little current to move nected to it. its coil and pointer over full scale deflection. Thus in (A), suppose we are to measure This means that either the permanent mag- the output voltage across the B battery elimi- net must be stronger than in the usual meter, nator circuit at A B. An e.m.f. of say 100 or else more turns of wire must be wound volts is applied to the circuit by the rectifier to obtain the same am- on the moving coil GND. CROSS SPREAD + pere -turn effect at a smaller value of am- peres. The latter method is used in the more upon boosting the desired signal than construction of high resistance voltmeters 20.000 suppressing lead-in pickup. This is accom- used in radio work. The moving coil has OHMS plished by tuning the antenna circuit to several layers of exceedingly thin copper the desired wave -length. No impedance- wire in order to produce the necessary mag- iobv. matching transformers are needed. The netic field strength. Such meters have a antenna proper may be anything from 25 resistance high as 1000 ohms -per -volt. as to 75 feet long. The lead-in, doubled upon The ohms -per -volt may be understood term itself, is made practically non -inductive, specific of a 1000 by considering the case and its capacity minimized, by the spacing, ohms -per -volt meter having three ranges, 7.5, a 11/2 inches. Transpose every four feet 150, volts. resistance in (A) and 750 Then the with 2 inch square spacers, which can be High -resistance Voltmeter. series with the '7.5 -volt terminal is 7.5 X threaded on and worked along to position. with 1000 or 7,500 ohms; that in series the The antenna is a quarter -wave, or Mar- 150 is 150 1000 150,000 tube, and a resistor of 20,000 ohms is in series -volt terminal X = coni, for broadcast, and a Zeppelin for with the voltage tap we are connecting the ohms; that in series with the 750 -volt ter- short waves, receiving the latter best from voltmeter across. Suppose the voltmeter has minal is 750 X 1000 = 750,000 ohms. either side. Two inverted L's, at 90 de- a range of 150 volts and a total resistance of The "ohms -per -volt" value of RDA is equal grees angle, converging on a common lead- 1,000 ohms. The current actually flowing to the total resistance Rt of the meter di- in, will receive from all directions-but this through the resistor and the voltmeter may vided by the maximum voltage Et marked calls for a highly selective receiver! be found by Ohm's law. Since the 20,000 upon the scale considered, or Some experimentation will be necessary ohm resistor and the voltmeter resistance are Rt to find proper size of coils. Old style sets now in series we have: RDv = with low -impedance input may require the E Et variable condenser in series with the wire Voltmeters having a resistance of 1000 I = -= 100 ± (20,000 + 1,000) = that goes to antenna post, and loading coil R ohms -per -volt are used extensively for volt- in wire to ground post of the receiver. (It .0048 amperes, or 4.8 milliamperes. age measurements in radio receiver power is important that these two wires be marked packs. Voltmeters having an ohms -per -volt for identification so that they will not be This current flowing through the 20,000 value as low as 100 are used in ordinary elec- connected to the wrong posts.) ohm resistance causes a voltage drop across trical work, since the few milliamperes of The secondary of an r.f. transformer, it of E I X R .0048 X 20,000 = 96 = = current taken by the meter is not objection- designed for a .00035 condenser, will be volts. able here. about right for the broadcast coil Ll. Short- The voltage actually recorded on the meter It should be remembered that it is not pos- wave coils 2, 3, and 4 consist of 45, 25, then, is the difference between the applied sible to make a high -resistance voltmeter of and 15 turns respectively, wound on 1 -inch circuit voltage and the drop across the 20,000 the same range from a low -resistance V. M. tubes. ohm resistor or, Voltage atAB=E - (I X R) 100 - 96 = 4 volts. R. M. A. COLOR CODE Thus the meter is not indicating the true For Fixed Condensers, Unit: Micro- voltage of the circuit, since it is drawing Microfarads For Resistors, Unit: Ohms so much current from the circuit that the circuit voltage drops when it is connected. First Dot Second Dot Third Dot Body Color End Color Dot Color The meter reads 4 volts, whereas the volt- age of this circuit when the meter is not Black 0 Black 0 Black 0 Black 0 connected, is 100 volts. Of course this is Brown 1 Brown 1 Brown 0 Brown 1 Brown 1 Brown 0 an exaggerated case. Red 2 Red 2 Red 00 Red 2 Red 2 Red 00 Orange 3 Orange 3 Orange 000 Orange 3 Orange 3 Orange 000 is to use The remedy for this condition Yellow 4 Yellow 4 Yellow 0000 Yellow 4 Yellow 4 Yellow 0000 a high -resistance voltmeter, that is, one hav- Green 5 Green 5 Green 00000 Green 5 Green 5 Green 00000 ing a high resistance connected in series with Blue 6 Blue 6 Blue 000000 Blue 6 Blue 6 Blue 000000 its moving coil. Suppose the meter has a Purple 7 Purple 7 Purple 0000000 Purple 7 Purple 7 Purple 0000000 resistance of 1,000 ohms for each volt range Gray 8 Gray 8 Gray 00000000 Gray 8 Gray 8 Gray 00000000 of its scale (1000 ohms -per -volt), then its White 9 White 9 White 000000000 White 9 White 9 White 000000000 62 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK PORTABLE P. A. SYSTEM In order to reproduce the excellent fidel- provide a means of setting the meter to a ity of the amplifier, the selection of the out- certain audio level, a 200,000 ohm poten- put transformer and speakers must be con- tiometer may be used as a series resistor sidered. The use of a Universal type of and connected as shown on the schematic. output to line transformer permits a proper This will not provide any accurate reading impedance match to be made to meet vari- to be had, but is used simply to limit the ous loads at changes in plate voltage. The maximum deflection of the needle to read selection of the taps shown are correct for zero on the scale at the peak volume re- the average watts output as is had when quired for a given application. using the 2nd position on the voltage switch. The complete amplifier is contained in By using a 500 ohm secondary the change a metal cabinet measuring 12 inches wide, of plate load offers far less mismatch to 500 12 inches high and only 71/2" deep. A ohms line than it would if a low voice coil durable leather carrying handle is bolted impedance were used, with a net result that securely to the top of the cabinet. the audio watts output may be changed by Many P.A. installations that are set up in choosing various positions on the switch and connection with stage presentations use two the change in voltage applied to the 6L6 or more microphones, not only to permit plates will not materially effect the response greater range of pickup, but also to allow Easy to operate is this P.A. rig. of the amplifier. One to four speakers may the gain to be reduced to the individual THE use of high -impedance microphones be used. When using all four speakers at mikes in order to reduce the possibility of such as crystal, velocity, etc., as stand one time, the 2000 ohm taps are used all in feedback from the speakers. The use of a and equipment for most public address parallel, or a total impedance of 500 ohms. pair of head phones to monitor the amplifier applications is now almost universally The frequency response of the amplifier is highly recommended as it permits the adapted. Likewise, the modern Permanent may further be enhanced by adding a sim- operator to concentrate on the pickup from Magnet type of speaker having a Uni- ple network in order to provide stabilized the various microphones where unbalanced versal line transformer makes for a rapid feed-back. The values of R16 and R17, condition might easily be corrected. Pro- installation. The amplifier shown and de- together with C8 and R19, control the vision is made for the operator's head -set scribed in this article was designed to have amount of signal output voltage that may and a choice of jack position may be had four individual high gain input channels be fed back to the control grids. for either high or low level. to accommodate four microphones at one A standard D.B. meter may be used in In setting up the amplifier, the master time. These may be any of the high im- place of the 0.25 ma. This meter has its gain should be adjusted so that the top pedance types designed to work directly to scale marked from -10 to +6 D.B. and is level of volume on all the inputs can not grid, or may be low impedance types with a calibrated for 500 ohm lines. In order to be exceeded. line transformer to grid. A master gain is used, permitting general volume control or for pre-setting of the audio gain. And a means of adjusting the audio watts output from eight watts to approximately thirty watts by means of a special tapped plate supply transformer which supplies various potentials to the rectifier is incorporated. The use of p.m. speakers with Universal line inputs of 500.1000-.1500 and 2000 ohms makes it convenient to use a 500 ohm out- put at the amplifier. The use of 500 ohms permits standard characteristics in the speaker line and a db. meter may be used to indicate various output levels. T The use of phase inversion is becoming TO ruLS very popular in amplifier design, as its use CH -1 in conjunction with resistors eleminates an- - CH -2 Mi other source of hum -pickup, namely, the rfÖr on ` input transformer. Certain precautions are needed if proper drive ratio to the ampli- 110 V. A.c. fier stage grids is to be obtained. The phase =Co =Cio inverter tube type 6C8G contains two high cw mu triodes with separate cathodes. Co The control grid of the first section re- 9 ceives the input voltage, from the mixer tubes and by means of the coupling con- input P.A. denser in the first plate circuit, feeds the The hook-up of the 4 channel portable system. No. 2 control grid with voltage of identical Ri S megohms 3/4 w. R22-25,000 ohms 1/2 w. R2-4000 ohms ',4 w. R23-100,000 ohms 1 w. amplitude, but opposite in phase to the No. 83-250,000 ohms 1 w. R24 -X95,000 ohms 1 w. 1 grid. The setting of the correct propor- R4-500,000 ohms C1-10 mid. 25o. elctro. 85-20,000 ohms 1 w. C4-.05 mid. 400v. paper tion between the two No. 1 plate resistors 11g-10,000 ohms 1 w. C3-25 mid. 25v. electro. determines the amplitude voltage and may R7-400 ohms 1 w. C4-4 mid. 25v. electro. 14 -200,000 ohms C5-10 mid. 25v. electro. be adjusted by means of a vacuum tube R5-1500 ohms 1 w. Cg-.1 mid. 400v. paper voltmeter if one is available. The 6L6 am- Rio-50,000 ohms 3¢ w. C7-8 mid. 450r. electro. plifier are resistance coupled to the Ru -100,000 ohms 3¢ w. Cg-.1 mid. 4000. paper tubes Ri2-10,000 ohms 1 w. Cg ---8 mid. 450r. electro. inverter and the quality of the audio is ex- R13-10,000 ohms 1/2 w. Cao -8 mid. 450v. electro. tremely free from distortion at the grids of R14-100,000 ohms 1 w. T1-pl. & fa. irons. R15-10,000 ohms 1,4 w. T2-unlversal Cl. A Output the 6L6's. No grid driving power is required Rig -100,000 ohms 1/2 w. CRi-Swgg. ch. 200 M.A. amplifier stage due to the use of R17-5,000 ohms 1 to. CI12-Fitt. ch. 200 M.A. in the Ris -200 ohms 10 w., Utah CC 200 C113-Fl1t. ch. 100 M.A. "Class A" amplification. This adds to the R15-50,000 ohms j/g w. M1-0.25 D.C. milliammeter economy of the unit, as self bias may be used R:o-,200,000 ohms Utah RC 200 M M2-0-200 D.C. milliammeter R215,000 or 10,000 ohms y... M3- -10+6 DR Meter with only 2% total harmonic distortion. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK K3

eY M QS1 a - YE de WZAFS

THAT'S the news about C -Ds. And it's news too big to hold. Cornell-Dubilier has combined Super Performance with New Economy to bring you a capacitor HIGH in quality, HIGH in efficiency, voltage and dielectric strength, yet down-to-earth in price. Take the shortest route to your jobber today. Ask for C-D-the capacitor with more abundant life at no extra cost. here are two of the popular amateur ca- pacitors in the complete C -I) line.

TYPE liv

TYPE rr-

TQ

DYKANIOL TRANSMITTING CAPACITORS are genuine Dykanol, FIREPROOF transmitting filter capacitors that can be mounted vertically or inverted by means of the mounting ring supplied. Equipped DYKANOL with neat porcelain terminals. Available in a com- TRANSMITTING CAPACITORS plete range from 2 mike 600 to 2 mike 2000 v, at Type TJU Dykanol capacitors are the most new low prices. Type TO is specified in the new Thordarson dependable units offered to the radio trade 100 watt x-mitter. Be sure to seed for new Catalog No. 161 today. -amateur, broadcast and commercial. Beautifully designed, compact, light -weight, safely rated, furnished with universal mount- ing clamp, well -insulated terminals, fire -proof CORNELL-DUBILIER and attractively priced. Fully guaranteed.From half mike,600to 2 mike 5000volts (capacitors ELECTRIC CORPORATION up to 25,000 v. d.c. supplied on request.) 1042 Hamilton Blvd., So. Plainfield, N. J. Cable Addresr: "CORDU" 64 RADIO NEWS 1940 IIADLO & TELEVISION DATA BOOK

A Silent Microphone Ring ASIX inch embroidery hoop and eight INTERNATIONAL "Q" SIGS small rubber bands can be made into a very serviceable microphone ring. Abbre- Question Answer First, form four hooks by straightening viation office paper clips out and cutting into 11/2 RA What is the name of your station? 1'he name of my stations is inch lengths and bending with round nosed QRB How far approximately are you from The approximate distance between our pliers. my station? stations is nautical miles The hooks are inserted into the holes in- (or kilometres). tended for them in the mike and then two QRC What company (or Government Ad- The accounts for my station are settled small rubber bands looped into each hook. ministration) settles the accounts for by the company (or by Set the mike on the table, hold the smallest your station? the Government Administration of hoop in the hand, and run the rubber band from one hook over the rim, around under QRD Where are you bound and where are I am bound for from and back into the hook again. Do the same you from? with the other three. Move the mike into QRG Will you tell me my exact frequency Your exact frequency (wave -length) is the exact center and then place the other (wave -length) in kc/s (or m)? kc/s (or m). hoop over the smaller one. This will keep QRH Does my frequency (wave -length) vary? Your frequency (wave -length) varies. the bands from slipping from the weight QRI Is my note good? Your note varies. of the mike. QRJ Do you receive me badly? Are my sig- I cannot receive you. Your signals are The mike may be mounted anyway de- nals weak? too weak. Do me Are my sig- well. Your signals are sired; the suspension method is excellent. QRK you receive well? I receive you In an apartment on the main street of nals good? good. Are I I with town with street cars going by every few QRL you busy? am busy (or am busy minutes, the rubber bands absorb more shock Please do not interfere. Are with. than the usual springs. QRM you being interferred with? I am being interfered QRN Are you troubled by atmospherics? I am troubled by atmospherics. Holder for Test Leads QRO Shall I increase power? Increase power. AN efficient means of avoiding tangled QRP Shall I decrease power? Decrease power. Shall I send faster? Send faster ( words per minute). messes of test leads is by the use of a QRQ ( words piece of fibre tubing for holding the leads QRS Shall I send more slowly? Send more slowly in the manner of the old-fashioned napkin per minute). holder. QRT Shall I stop sending? Stop sending. QRU Have you anything for me? I have nothing for you. An old cartridge fuse of a larger size, 60 - Are you ready? I am ready. amp. or 100 -amp., which are often discarded QRV QRW Shall I tell that you are Please tell that I am calling by factories and power companies, is good calling him on kc/s (or him on kc/s (or m). enough for this purpose, although new fibre m)? tubing may, of course, be used. The inner QRX Shall I wait? When will you call me Wait (or wait until I have finished corners should be rounded away to permit again? communicating with ) I easy insertion of the folded leads. will call you at o'clock (or Low -Cost Field Strength Meter immediately). is my Your is No. (or accord AFIELD strength meter for the amateur QRY What turn? turn ing to any other method of arrang- need not be a complicated affair par- ing ticularly for noting field patterns near the it). Who is calling me? You are being called by antenna system or plotting strength of QRZ What is the strength of my signals (1 The strength of your signals is field from directional systems. A fixed crys- QSA to 5)? (1 to 5). tal, milliammeter and tunable tank are the QSB Does the strength of my signals vary? The strength of your signals varies. essentials and can be put together quickly Is my keying correct; are my signals Your keying is incorrect; your signals by any radio builder. QSD distinct? are bad. The outfit can be made breadboard style QSG Shall I send telegrams (or Send telegrams (or one tele but more stable readings be by can obtained one telegram) at a time? gram) at a time. enclosing the hook-up in a can or metal box. QSJ What is the charge per word for The charge per word for is Mount the 0 to 1 milliammeter and the con- including your internal telegraph francs, including my in- denser on the panel. Then fit a four prong charge? ternal telegraph charge. socket on the top of the box for the tuning coils. The crystal is mounted within the QSK Shall I continue with the transmission Continue with the transmission of all box. The tuning condenser and tank coil of all my traffic, I can hear you your traffic, I will interrupt you if my should be of a size to suit the frequency through signals? necessary. being tested. A .00025 mfd. condenser will QSI. Can you give me acknowledgement of I give you acknowledgment of receipt. suit most anything down to 20 meters. Wind receipt? both the tank coil and absorption coil on QSM Shall I repeat the last telegram I sent Repeat the last telegram you have sent the same form. you? me. In testing the field strength and pattern QSO Can you communicate with I can communicate with di- of an antenna system it is only necessary to direct (or through the medium of rect (or through the medium of insert the coil to suit the transmitted fre- )? quency and note the various readings of the QSP Will you retransmit to free I will retransmit to free of milliammeter in different locations with ref- of charge? charge. erence to the antenna after carefully tuning QSR Has the distress call received from The distress call received from meter the for maximum readings. The read been cleared? has been cleared by ings can then be plotted on a suitable chart. QSU Shall I send (or reply) on Send (or reply) on kc/s (or Tubing Antenna kc/s (or m) and/or on waves of m) and/or on waves of THE use of metal tubing rather than Type Al, A2, A3 or B? Type Al, A2, A3, or B. wire offers a number of advantages for QSV Shall I send a series of VVV 9 Send a series of VVV antennas designed for use in the ultra -high QSW Will you send on kc/s (or I am going to send (or I will send) on frequency ranges. There is the larger sure m) and/or on waves of kc/s (or m) and/ face area and the resulting reduction in r.f. Type Al, A2, A3 or B? or on waves of Type Al, A2, A3 resistance. or B. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK Sfi I WILL TRAIN YOU TO START A SPARE TIME OR FULL TIME

RADIO SERVICE BUSINESS

J. E. SMITH President National Radio Institute Established 1914 WITHOUT CAPITAL The man who has directed the home study training of more men for the Radio Industry The world-wide use of Radio has made many op- inspectors, foremen, engineers, servicemen, and than any other man in America. portunities for you to have a spare time or full pay up to $6,000 a year. Automobile, police, avia- time Radio service business of your own. Four out tion, commercial Radio, loud speaker systems are of every five homes in the United States have Ra- newer fields offering good opportunities now and dio sets which regularly need repairs, new tubes, for the future. Television promises to open many HERE ARE A FEW EXAMPLES etc. Servicemen can earn good commissions too, good jolis soon. Men I trained have good jobs in selling new sets to owners of old models. Even if these branches of Radio. Read how they got their OF THE KIND OF MONEY you have no knowledge of Radio or electricity, I jobs. Mail coupon. will train you at home in your spare time to sell, install, fix, all types of Radio sets; to start your I ALSO GIVE YOU I TRAIN MY MEN TO MAKE own Radio business and build it tip on money you THIS PROFESSIONAL snake in your spare time while learning. Mail cou- SERVICING pon for my 64 -page book. It's Free-it shows what INSTRUMENT $200 TO $300 A MONTH I have done for others-what I am ready to do for Here is the instrument. every IN OWN BUSINESS you. Radio expert needs and wants - an All -Wave. All- "For the last 18 months I have been in l'urpose, business for myself, making between Many Make $5, $10, $15 a Week Extra Set Servicing In- $200 strument. It contains every- and $300 a month. I have N.R.I. to thank in Spare Time While Learning for my start in this field."-ARLIE J. thing necessary to measure FROEHNER, 224 W. Texas Ave., Goose The day you enroll I start sending Extra Money A.C. and D.C. voltages and Creek, Texas. Job Sheets; shows you bow to do Radio repair current; to test tubes. re- sistance; adjust and align any set, old or new. It satisfies jobs. Throughout your training I send plans asid $10 TO $25 A WEEK IN SPARE TIME your needs for professional servicing after you graduate directions that made good spare time money-$200 -can help you snake extra money fixing sets while training. "I am making from $10 to $25 a week in to $500-for hundreds, while learning. I send you spare time while still holding my regular special Radio equipment to conduct experiments Save Money- Learn At Home job as a machinist. I owe my success to N.R.I."-WM. F. RUPP, 203 W. Front and build circuits. This 50-50 method of training Money Back Agreement Protects You St., West Conshohocken, Pa. makes learning at home interesting, fascinating, I ant so sure I can train you to your satisfaction practical. penny you CHIEF OPERATOR BROADCASTING that I agree in writing to refund every STATION Why Many Radio Experts Make pay me if you are not satisfied with my Lessons A copy "When I completed 20 lessons, I ob- $30, $50, $75 a Week and Instruction Service when you finish. tained my Radio Broadcast Operator's of this agreement conies with soy Free book. License and immediately joined Station Radio is young-yet it's one of our large indus- WItII'C, where I ans now Chief Operator." tries. More than 28,000,000 homes have one or Find Out What Radio Offers You -HOLLIS F. HAYES, 85 Madison St.. more Radios. There are more Radios than tele- Mail the coupon now for Sample Les- Lapeer, Mich. phones. year Radios out of Act Today. Every millions of get son and 64 -page book. They're free to any fellow date and are replaced. Millions more need new EARNINGS TRIPLED BY over 16 years old. They point out Radio's spare spent N.R.I. TRAINING tubes, repairs. Over $50,000,000 are every time and opportunities and those coining "I have been doing nicely, thanks to year for Radio repairs alone. Over 5,000,000 auto full time Training. are in Television; tell about my training in Radio and N.R.I. My present earnings Radios are in use; more are being sold every day, about three times what trey were be- ; from men I trained opportunities for Radio Television show you letters fore I took the Course. I consider N.R.I. offering more profit -making what they are doing and earning. Find out Training the finest in the world."-BER- YOUNG, telling experts. And RADIO IS STILL Radio COUPON in an NARD COSTA, 952 Manhattan Ave., GROWING, expanding into new fields. The few what offers YOU! MAIL Brooklyn, N. Y. envelope, or paste on a postcard-NOW ! hundred $30, $50, $75 a week jobs of 20 years ago OVER $1,000 BEFORE GRADUATING have grown to thousands. Yes, Radio offers oppor- J. E. SMITH, President "Before completing half the N.R.I. Course tunities-now and for the future! National Radio Institute, I was servicing sets. and I made $1,000 Dept. 9BJ9 lo $1,200 before graduating. I ara doing Get Ready Now for Your Own Radio Radio service work for myself now."- Business and for Jobs Like These Washington, D. C. ASHLEY G. ALDRIDGE, 1220 Shepherd THIS St., Petersburg, Va. Radio broadcasting stations employ engineers, op- BOOK erators, station managers and pay up to $5,000 a FREEHELPED LESSON year. Fixing Radio sets in spare tinte pays many NAS Get My on Radio $200 to $500 a year-full time jobs with Radio OF ;1 Servicing Tips FREE jobbers, manufacturers and dealers as much as $30, $50, $75 a week. Many Radio Experts open L,NDREDS I want to prove my Training gives practical, full or part time Radio sales and repair businesses. MEN MAKE money -making information, that it is easy to un- _!: Radio manufacturers and jobbers employ testers, derstand-what you need to master Radio. My MORE sample lesson text, "Radio Receiver Troubles- MONEY Their Cause and Remedy," covers a long list of Radio receiver troubles in A.C., D.C., battery, uni- versal ; auto, T. R. F., superheterodyne, all -wave, and other types of sets. And a cross reference GOOD FOR BOTH SAMPLEELE SON system gives you the probable cause and a quick FREE.( g way to locate and remedy these set troubles. A special section is de- J. E. SMITH, President National Radio Institute, voted to receiver Dept. 9BJ9, Washington, D. C. check-up, alignment, Without obligating me, send your Lesson "Radio Receiver Troubles- 44..e.«," Their Cause and Remedy" and free book bout spare time and full time balancing, nectraliz- Radio opportunities and how I can train for them at home in my spare ing, testing. You can time-about the N.R.I. Set Servicing Instrument. I am particularly Inter- ested ln the branch get this lessor_ Free of Radio checked below. D Radio Service Business of My Own Loud Speaker Systems, Installations and Service by mailing the cou- D Spare Time Radio Repair Work D Auto Radio Installation and Service pon. O Retail Sales of Radio Sets and Equipment Television Station Operator Service Expert for Retail Stores 'ervice Expert with Radio Factory Broadcasting Station Operator Commercial Radio Station Oper t.., Aviation Radio Operator All-around Servicing Expert ¡If you have not decided which branch you prefer-mall coupon now, for Information In b,ie y,u de, l,b.t

sait: AGI'

Anitltr-9F 14X1 56 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

Feverish Activity. A recent experience with a Fada 25 dem- INTERNATIONAL "Q" SIGS onstrated the close relation between heat and Abbre- Question Answer voltage failures. The owner reported that his viation set cut off in the middle of his favorite pro- listening for (call sign) grams, and that it would not resume opera- QSX Will you listen for (call sign) I am m)? on kc/s (or m). tion until the following day. Our "outside on kc/s (or to transmission on Change to transmission on man" called at his home during various times QSY Shall I change m) with- kc/s (or m) without in the day when he happened to be in the kc/s (or the type of wave? or changing the type of wave or neighborhood, and reported each time that out changing Shall I change to transmission on an- Change to transmission on another the set was normal. other wave? wave. We finally explained to the customer the Shall I send each word or group twice? Send each word or group twice. only way we could find the phantom fault QSZ Shall I cancel telegram No. Cancel telegram No. as if it would be to live with the set. We did not QTA as if it had not been sent? had not been sent. want to pick it up because of our previ- QTB Do you agree with my number of words? I do not agree with your number of ous experience with mysterious faults in words; I will repeat the first letter of other sets we picked up and tested in the each word and the first figure of shop; usually, after wasting our time, we each number a neglected found the trouble to be in feature QTC How many telegrams have you to send? I have telegrams for you (or in the set owner's house. for ) He suggested, because the receiver failed QTE What is my true bearing in relation to Your true bearing in relation to me is most frequently between 8:00 and 9:00 p.m., you? or degrees or that we come to his apartment to play cards What is my true bearing in relation to Your true bearing in relation to with him every night until the music stopped. (call sign)? or (call sign) is degrees at He hoped, he told us good-naturedly, that (time) or we were better pinochle players than service- What is the true bearing of The true bearing of (call men. We called at his home after we closed (call sign) in relation to sign) in relation to (call up one night, carrying an analyzer and a (call sign)? sign) is degrees at copy of Hoyle. We laid the power pack (time). over on its side so that we could make tests, QTF Will you give me the position of my The position of your station according after the set stopped, with a minimum of station according to the bearings to the bearings taken by the direc- chassis disturbance. taken by the direction -finding sta- tion -finding stations which I control The Fada quit the first night. I laid down tions which you control? is latitude longitude. one of the highest melds I ever held in my QTG Will you send your call sign for fifty I will send my call sign for fifty seconds life to follow the others to the front room. seconds followed by a dash of ten followed by a dash of ten seconds on A filter condenser section was shorted; we seconds on kc/s (or kc/s (or m) in unbolted the chassis and took it to the shop. m) in order that I may order that you may take my bearing. The next day we hooked up the set on take your bearing? the floor. It not only played, but continued QTH What is your position in latitude and My position is latitude way of (or by any other way of to play without interruption during a four - longitude (or by any other longitude day stalemate. We did not want to de- showing it)? showing it). liver the set without making sure we would QTI What is your true course? My true course is degrees. is knots (or not be installing a rather expensive filter QTJ What is your speed? My speed block unnecessarily; the customer did not kilometers) per hour. subma- signals and sub- want to accept it until after we had given QTM Send radioelectric signals and I will send radioelectric me to sound signals to enable you to our unqualified okay. Luckily, he was one rine sound signals to enable marine my distance. fix your bearing and your distance. of those rare persons who realized how tricky fix my bearing and Have you left dock (or port)? I have just left dock (or port). a set can be at times, and did not require QTO Are you going to enter dock (or port)? I am going to enter dock (or port). his repairman to be a cross between Stein- QTP Can you communicate with my station I am going to communicate with your metz and a Hindu mystic. QTQ by means of the International Code station by means of the International was we wrapped the power It only after of Signals? Code of Signals. chassis in newspapers that the music was cut QTR What is the exact time? The exact time is off. The filter was but block defective, the QTU What are the hours during which your My station is open from to trouble did not appear until it had reached station is open? a certain operating temperature. We had, QUA Have you news of (call sign Here is news of (call sign of by reducing heat dissipation, simulated the of the mobile station)? the mobile station). operating conditions in the closed console, QUB Can you give me in this order, informa- Here is the information requested where the heat from the rectifier tube, as- tion concerning: visibility, height of sisted by the heat from the tuning tubes be- clouds, ground wind for low, brought the block to a temperature (place of observation)? which probably provided a shorting path QUC What is the last message received by The last message received by me from when the pitch softened. you from (call sign of the (call sign of the mobile sta- A higher voltage in the customer's house mobile station)? tion) is could have caused a similar occurrence, pro- QUD Have you received the urgency signal I have received the urgency signal sent viding the shorting path did not burn badly sent by (call sign of the by (call sign of the mobile enough to short out all lower voltages. In mobile station)? station) at (time). this particular case, the voltages were the QUF Have you received the distress signal I have received the distress signal sent same in both locations, but the breakdown sent by (call sign of the by (call sign of the mobile voltage decreased as the temperature rose. mobile station)? station) at (time). Pet vs. Pest QUG Are you being forced to alight in the I am forced to alight (or land) at A shop underling, after reading about sea (or to land)? (place). the mouse -in -chassis incident, offers a QUH Will you indicate the present baro - The present barometric pressure at sea suggestion to set manufacturers. While it metric pressure at sea level? level is (units). would not be wise to become too enthusiastic, QUJ Will you indicate the true course for The true course for you to follow, with the recommendation is passed quietly along me to follow, with no wind, to make no wind, to make for me is to the trade for what it is worth: chassis for you? degrees at (time). holes should be made either too small for When the signal is followed by a question mark, su ch as QTR?, it refers to the first column, mice, or large enough for cats! and when no question mark is used, becomes the answer (column two). RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK b7

HO `MUSTS' .qo tJL uaL RECEIVER

1. Crystal Filter 2. Electric Bandspread 3. R.F. on All Bands 4. Ceramic Coil Forms All Contained in Model 438

In a relatively short time Howard has risen to a dominating position in the communications field! Howard values in quality amateur receivers are made possible because Howard is also a large manufacturer of household receivers, with con- sequent savings in manufacturing and material costs to the amateur division.

MODEL 450-A MODEL 438 With the advent of the world 12 Tubes -6 Bands-Frequency Coy- famous 430, many have asked erage .54 to 65 MC . . Ceramic for a larger receiver here . . . - Coil Forms Dual I.F. Channels Two S.L.F. Ceramic Insulated Tuning it is! embodies professional Condensers . . 47 inches of electric Model 438 before associated with bandspread . . Crystal Filter . . Cali- features never in this price class . . real brated "R" Meter . . Accurately equipment R-9 reception: Ceramic calibrated direct reading dial . "DX" with Price, with Tubes, less Coil Forms .. R.F. Stage on all Bands .. Band Xtal Speaker, Less Crystal V I Netet Separate Coils for each Filter .. Complete Coverage 540 KC - 43 MC . . Electric Bandspread with vernier control . . (2 -stage Iron Core I.F. amplifier) . . Accurately Calibrated MODEL 430 Slide RLle Dial .. 8 Tubes . . Provision for a 6 -volt Power Supply . , Band -in - 6 Tubes-4 Bands-Frequency Coverage use Indicator . . B.F.O. with Pitch 54 to 43 MC . . Ceramic Coil forms . , . 2 Watts Power Output . . B.F.O. with pitch control .. Iron Core I.F. Control Built-in 6" Dynamic Speaker , . Head transformers . . Electric bandspread . Phone Jack . . Dounlet or Marconi Built-in Dynamic Speaker . . Headphone Antennae Connections , . Provision for jack , . Accurate direct reading slide rule External Speaker . Provisions for dial . . Provision for Howard tune type tube type Meter. "R" meter. Howard "R" Price, complete with % 9Q95 Tubes and Speaker i7Net / v 3 For Complete Technical Details see Your Jobber or Send- this- -ra--rCoupon MODEL 440 --N - NMat 9 Tubes -5 Bands-Continuous cover- Howard Radio Company age .54 MC to 43 MC .. Ceramic Coil 1731-35 West Belmont Ave., Chicago, III. Forms . . S.L.F. Ceramic Insulated Tun- Please send me more information on ilg Condensers, Electric Bandspread, R.F. Model 438 Mode1.430 . . Core I.F. Trans- on all bands Iron Model 450-A Model 440 formers . . Electric bandspread .. Cali- Cable Address: "Howardco" brated "R" Meter . . Crystal Filter . . Name Price with Tubes, less speaker, less Crystal 66eiNei Address Exaort and Pacific Coast Prices Slightly Higher City State Ccmen.ica1 Oldeet !?adio Alanu f actune4 58 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK

New Application for the 6E5 value making the shadow angle change or audio frequency measurements such as THE 6E5 or 2E5 tuning indicator tube with voltage exactly as if there were d.c. an output indicator, detection of grid cur- can be used as a voltage. It differs applied to the terminals. The .1 mfd. con- rent or positive peaks on grids of a.f. ampli- from the conventional circuit as it does not denser from plate to ground is very im- fiers or measurements of impedance of choke employ a diode rectifier but is actually a portant as values less than this will cause coils, condensers and resistors at low fre- vacuum tube voltmeter measuring a.c. or the line of the shadow to be fuzzy on fre- quencies. As the capacity of the test leads d.c. voltage without placing a load on the quencies as low as 60 cycles, and a con- cause too much loss for r.f. measurements, circuit to be measured. denser with higher capacity will make the an adapter is used. It consists of a six The operation of the voltmeter is as change of the shadow angle too sluggish prong male and female plug wired together follows: The cathode tap on the voltage for abrupt changes in voltage. with a 5 wire cable, all connections being divider is permanently adjusted so that the The diagram as shown is fine for all d.c. made straight through except the grid cir- shadow angle of the 6E5 tube is zero. When cuit which is left vacant. One plug of the d.c. is applied to the terminals (negative to adapter is inserted in the tube socket, the ground) the shadow angle will increase other receives the 6E5 tube. with an increase in voltage to a maximum A short length of stiff wire is wrapped of 90° with approximately 8 volts applied. around the grid prong of the tube and ex- For voltages over 8 volts the 10 megohm, tended outward at the junction of the tube uniform tapered potentiometer may be set and plug as pictured in the drawing. A to calibrated points thereby multiplying the 5 or 10 megohm resistor should be con- range indefinitely. nected from grid to ground if the circuit When an a.c. voltage is applied, a pul- to be measured does not provide a d.c. sating d.c. voltage appears in the plate cir- path. cuit, because the tube is biased to nearly As no means are provided to insure cut-off. The condenser from the plate to permanent calibration, indication of abso- ground holds these pulses to the peak lute values of voltage may be inaccurate.

PRACTICAL REMOTE AMPLIFIER THE radio station where a great num- The front panel and chassis is constructed ber of outside pick-ups form a large from 14 and 16 gauge aluminum, resp. The part of the daily operations schedule, front panel is cut 19" long and 9" high. must be equipped with not only a sufficient The chassis is bent from one piece as shown quantity, but also quality type, of amplifiers. in Fig. 4, the top of chassis is 6" and bent Commercial amplifiers meet practically every down for 4". The sides of chassis are then demand of a broadcaster, however to be cut in the shape shown in sketch, being 6" equipped with an adequate number is rather wide with the sides parallel to 4" and tapered costly. to the 9" mark to fit behind the front panel. The circuit shown was used in the ampli- All these parts are then fastened together fier illustrated here. The first two stages with angle brackets. As shown in sketch, 8 using 6J7's as pentodes with a 6F6 work- such angle brackets will be necessary. Ready ing as a triode in the output. The input made 1/2" tapped 6-32 brackets will solve this channels are 250 ohms and the output is problem perfectly. 500 ohms working into a 5 DB pad to cut Obviously it is much easier to drill all panel controls enable easy operation. down line reflection. The main gain varies Front necessary holes in panel and chassis as shown in steps of 2 DB from 0 P to 40 DB. The overall gain including mixers and output pad in sketch and then assemble the parts. After volume indicator can be attenuated from is about 105 DB. The hum level is down chassis has been assembled the tube sockets minus 10 DB to plus 6 DB, also in 2 DB 50 DB at zero level, loaded. The filament are mounted in a piece of aluminum 2" wide steps. The frequency response is plus or drain is .9 amps and the B battery drain and 6" long, which can be cut from the minus 1 DB from 40 to 10,000 cycles. The is 25 mils.

637 C4 8J7 e 6F6

13

TO MIXERS

EXTERNAL'S. CONNECTION 90V. SOV. 1111111+ INTERNALW BATT'S. -11 I I I I I Rear view shows ease of servicing the unit.

1

nat. re ' OPTIONAL SWITCHING CIRCUIT 6ea s OUTLET PLUG J ee,lc.,. TO BATT. 131111, C sr 1,.... AMP eoar ce Circuit of the remote amplifier. Br: ... s.ns C1-20 mid. 25v. Ri-.5 meg. Ris-25 meg. R17-649 ohms C2-10 mfd. 50v. R2-.5 meg. Ru-.25 meg. Ris -817 ohms C3-8 mid. 200v. R3-1,250 ohms R13-1,000 ohms Rre-1,028 ohms ',F "-- - C4-.1 mid. 400v. R4-10,000 ohms R14-2,000 ohms R20-1,249 ohms ' C5-20 mid. 25v. R5-50,000 ohm° ohms R21-1,630 Rn-.25 meg. Cg -10 mfd. 50v. AU Weston Precision ohms C7-8 mid. 200v. R7-.5 meg. Pot. wire wound R22-2,052 C8-.1 mid. 400v. RD -2,000 ohms Ti-i1TC 4.10 Cg -20 mid. 25v. RD-I0,000 ohms RID-410 ohms T2-3,000 ohm choke C10-1 mid. 400v. Rio -50,000 ohms Rie 515 ohms T UTC A-24 Construction details of chassis. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 59 waste from the chassis. This cradle like ele- Reducing Drift in Receivers great reduction in frequency drift will be ment is then fastened to chassis directly below When constructing a communication the result. Many of the communication sys- the holes cut in chassis to allow tubes to receiver it is desirable that the filament tems leave the receivers in constant opera- pass. The cradle is mounted with 1" 6-32 tion, including the plate as well as the transformer have a large safety factor to machine screws which are inserted in sponge filament supply. It is a decided advantage prevent excessive heat within the cabinet. rubber washers on either side of the cradle to be able to come home with the inten- and on the top of the chassis. By going a bit farther, it is good practice tion of "looking over the band" as the Ham The tubes will then be free from mechani- to allow the tube filaments or heaters to would say, and find the receiver ready and cal jars that may cause undesirable micro - remain turned on at all times which will willing to remain as originally calibrated phonics in the first stages. With the trans- then maintain a fairly constant temperature at the factory. The life of a vacuum tube formers mounted in positions shown in Fig. around the various parts in the set and a operated under the above conditions is in - 3, the microphone receptacle and battery plugs are mounted on the back of chassis as also shown in same picture. Wiring is conventional, with care taken to shield all the grid leads and the plate leads from the coupling con- denser. The placement of the parts in the under chassis is largely a matter of choice, keeping in mind that the shorter the leads the less trouble to be encountered. After wiring has been com- L pleted the gains can be mounted and connected to proper channels, running temporary battery leads the PRESENTS... amplifier can be checked for «dean operation with a pair of phones. Now that everything is OK the batteries can be two new McMURDO SILVER engineering triumphs mounted on either side by the use of a large U clamp made PRECISION FREQUENCY METER from a piece of the 14 gauge DUAL DIVERSITY FOR EVERYONE aluminum or, if you are more Diversity reception is the only effective the law requires that every amateur station ambitious, a piece of iron. It means known of eliminating fading and its shall regularly check and measure transmitter Frequency measuring apparatus is drilled to pass a 10-32 ma- accompanying noise in reception. Heretofore frequency. is required to be external to transmitter fre- chine screw and with bat- the very cheapest of diversity receivers has quency control. For precise frequency meas- be cost many hundreds of dollars. teries in position it can urement a stable and dependable frequency fastened to side of amplifier. Now, through a new invention of McMurdo meter -monitor is indicated. the The amplifier can then be Silver, GUTHMAN exclusively offers GUTHMAN is proud to offer the precision checked with an open micro- new McMurdo Silver Diversity Coupler. frequency meter and amplified monitor illus- phone in the circuit and the Simply and easily connected to any good trated above, and parts for its construction. communication or broadcast receiver, and output compared to other This instrument provides features hereto- requiring nothing more than a second standard amplifiers. fore available only in precision laboratory antenna at right angles to the regular If an audio is at equipment. Designed for precise measure- oscillator receiving antenna, it automatically and ment, it offers 73/4", 324 degree dial accur- hand with an output indicator, noiselessly eliminates fading. a low level in the order of ately calibrated for 5 to 160 meter bands, zero can be applied to the Available as a kit for only $16.80 net to zero adjuster for use with 22 precision cali- input, making sure the out- amateurs, or $22.20 factory wired and tested bration frequencies regularly available, A.C. or D.C. operation, stabilization of electron put transformer has a load re- with tubes, the Diversity Coupler has been as radio coupled oscillator, and monitor detector -am- sistor connected across it, and described by RADIO NEWS "THE invention of 1938." For an insignificant cost plifier. the frequency characteristic it turns any good set into a dual diversity re- It is styled to "dress up" any station, found with the comparison of ceiver ... such as only the commercials could priced extraordinarily low, designed for pre- the two Indicators, that is the afford up to now. cision work. one at the input of the am- plifier and the output V. I. ordinarily used. WA I T . . WAT C H ! Something new in communication receivers will be offered by Guth- The case for the amplifier man soon. Designed and built by McMurdo Silver to commercial construction standards, giving an of efficiency quite extraordinary, and boasting features and performance worthy of $100.00 to was custom built by a cabinet order $200.00 receivers, it's worth waiting for. Style and appearance to make your mouth water price maker. It is made of ply wood ... will delight you. Don't buy a new receiver until you see the Silver Super at your jobber, or write Dept. covered with a tough leather 408 for full details. and varnished. The amplifier See your jobber or write for can be constructed for a cost full details on these and an slightly over $80.00. For the outstanding line of quality ham or P. A. man, who would r.f. and i.f. transformers, fixed have need for a high gain am- and variable condensers and plifier and not necessarily other parts. need the mixers or V. I. it could be constructed for about $40 since these two compo- nents cost about half the total amount. The unit will make a superb EDWIN I &CO.,INC. preamplifier for recordings or 402 S.PEORIA S CHICAGO, U. S. A. broadcasting. ' 60 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK creased as the heating and cooling effect sired. Here is a little adapter that has is reduced when a constant temperature is proven an excellent aid for trying turns be- WHAT IS maintained. fore making the final solder connection. Using this adapter, wind on more turns ELECTRICITY? Tinning the Soldering Iron than are called for, and solder all leads to Many servicemen do not know how to their respective prongs except one lead of Final Analysis tin an iron with rosin -core solder after the the secondary coil as shown in the sketch. iron has become hot and has been in use. Interesting to reflect that, while electricity The adapter consists of a thin wafer socket. is utilized so in If the iron is too hot to take hold, the cord expertly our profession, Push the prongs of the coil form into this there is yet much difference of opinion con- should be removed for a minute or so to socket as far as they will go, then tempor- reduce this heat. As the iron cools off it cerning its nature. Four sources are drawn arily connect the loose lead of the coil to upon in getting information as to its nature: will reach a temperature where solder will the proper adapter connector. To Funk C+1 Wagnalls, electricity is readily take hold, providing, of course, the Now push the coil into the regular socket "a material agency, which, when in motion, tip of the iron is clean. Filing of the tip so that the prongs of the coil -form just make will improve matters in any case. contact. In this way you will have freedom exhibits magnetic, chemical, and thermal ef- for working along the "cut and try" method fects; and which, when at rest, is accom- Reaming with Tools Made of Soft Steel without removing the coil from the socket. panied by stress." Much trouble can be caused by using Remove one turn at a time then check for To Croft, in Practical Electricity: "Elec- handles of pliers, etc., as a reamer when band width until the correct number is tricity is the stuff of which everything tangi- enlarging holes in chassis and panels. The reached for the desired frequency. When ble is made." friction may magnetize the tool and then this is determined, remove the adapter and To Morecroft, in his Principles of Radio when it is further used near small parts will run the lead down through the prong and Communication: "The electron is nothing pick these up and cause no end of grief. solder in place. but electricity." Heating the afflicted tool over the gas burner will usually restore the tool to good Cure for Noisy Volume Control To the power company: 7%Zc per kilo- condition. When the resistance strip of a volume watt-hour. control becomes worn or broken it will cause Concerning Doublet Antennae noisy operation and will ruin reception. Many an experimenter and serviceman Here is a stunt that will enable the user has installed the most expensive type of to continue using the set without any servic- AUTOMATIC commercial doublet in an effort to reduce ing expense. the noise level, and to increase the signal Take out the volume control and remove FREQUENCY input. Sometimes they have even made up the resistance strip. Locate the break and, elaborately double spaced double -doublets cleaning the ends of the wire, solder them CONTROL only to find that after they were hooked up together. Then gently bend the strip until to work as well the set, that they did not what was the back side becomes the front MEASUREMENTS as a single wire. or convex side. Put it back on the form. The fault lies not with the doublet, but TOMATIC frequency control, as This will present a fresh side over which the with the match between the antenna and applied to modern receivers, is easily contact will slide or roll without interfer- the set. A serviced when once it is understood. ence or break and it will be as quiet as when The first is to what As with other special circuits, (automatic thing determine the new. input -to -the -receiver impedance is. Next a volume control was an example), automatic frequency control was sprung upon many doublet must be used that will match that Home -Made Antenna Tuning Condenser servicemen who were not in a position to input. We know of at least one receiver An efficient antenna tuning condenser can that has an impedance of only 200 ohms. understand it well enough to be able to be made for ultra high frequency receivers meet service problems. It is wholly useless to match a 600 ohm from material found in the parts box. Use Basically each automatic frequency con- doublet to it, since there will not be the a piece of %Z" brass or copper tubing about trol system consists of a discriminator and maximum transfer of energy. 2" long. Solder a small mounting bracket an oscillator control circuit. The so-called Always match the doublet to the set, and to one end and mount the tube horizontally discriminator is a selective rectifier -filter sys- make the doublet so that it will match. on a baseboard. A binding -post and screw tem which supplies a d.c. voltage, which Formulae are available in most handbooks. can be used to attach the bracket as shown. varies with the exciting frequency, to the a of Fashion tight fitting plug bakelite oscillator control tube. Oscillator frequency Adapter for Determining Coil Frequency or fiber for the opposite end of the tube. control is brought about through regula- In winding plug-in coils it is general ex- Drill and tap the center of the plug for a perience to find that the prescribed number tion of the gain (amplification) of the con- piece of standard threaded brass rod. Then trol tube by means of the voltage supplied of turns in theory is not the number needed find a brass nut to thread on the rod and by the discriminator. in practice. After the coil had been assem- solder a bracket to this nut and mount it Figure illustrates a typical discriminator vertically in front of the plugged end of the la circuit. Consider the transformer T to be COIL FORM tube as shown. loosely coupled and tuned to the frequency THREADED BRASS ROO THREADED FIBER PLUG of the receiver. The situation at resonant '_------BRASS OR CU. TUBING-, --rte ...,,NUT frequency is as follows. TO ANT. ^e,renze KNOB As the voltage Vt builds up across the K -SOLDER L.-` SOLDER primary a current in phase with Vt is in- BRACKETS - duced into the secondary. Because the BINDING POST TO RC5 R. current lags voltage by 90 electrical de- Attach a bakelite binding post knob to grees in an inductance, the voltage Vs one end of the threaded rod. Run the rod induced into the secondary by this current through the brass nut and threaded plug as is 90° ahead of VI at resonance. At the shown. The antenna lead-in is connected same time a current through C induces a to the binding post and the wire to the re- voltage V', in the secondary. Because these ceiver grid circuit to the brass nut. Screw- voltages induced in the secondary are in ing the thread in the tube increases the ca- phase they alternate in step and hence pacity; threading it out decreases it. If cause equal currents to flow through the WAFER there is any tendency for the rod to touch diodes. (The induced voltages reach similar SOCKET the inside of the tube, line it with paper. values simultaneously.) The total voltage bled with the leads soldered in the prongs, You will find that this condenser will make is equal to Vs plus V" and is arbitrarily :he tuning range is, unfortunately, either possible fine tuning of the antenna circuit called Vs. above or below the frequency coverage de- to gain the maximum of signal strength. Under off resonance conditions either in- RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 61 ductive or capacitive reactance predominates a pentode is used to control the oscillator and hence causes the plate current of the and the phase of the voltage V. changes frequency. Screen grid, suppressor and tube to lag its plate voltage by approxi- accordingly. At frequencies greater than cathode connections are made in the stand- mately 90°. The result is apparent shunt resonance, inductive reactance is predomi- ard manner. The gain of the tube is con- inductance across the oscillator tank. There- nant in the tuned circuits and V. leads Vi trolled by means of the additional bias fore, frequency change is readily accom- by less than 90°. Conversely, for frequen- supplied by the discriminator. plished by varying the gain of the tube and cies less than resonance, capacitive reactance A small amount of the voltage developed hence the amplitude of its output. is the greater and V. leads Vi by more across the oscillator tank is fed into the Essentially these are the basic principles than 90°. Since Vb is unchanged in phase, control grid of the pentode (this same grid underlying automatic frequency control. the alternations of V and Vu no longer is biased by the control voltage) and am- And now that they are understood, let's go coincide and the rectifier currents become plified. This exciting signal voltage under- looking for trouble. unbalanced because a greater voltage results goes a 90° phase shift across condenser C, Probably the first thing to be done is in one side of the secondary than the other. At higher frequencies than resonance diode 1 will have the great- er current flow and vice versa for lower frequencies. In Figure lb we see just how the control voltage is developed. From this illus- tration it becomes evident that this control voltage may be either positive or negative and of various amplitudes. Electrons move from negative to positive so that all one must do to determine the polarity of the voltages Et and Es is to In every state of the union, and on every conti- visualize the electron flow. nent of the globe, Skyrider receivers are providing Since these are in series Ec, dependable communications reception for ama- the control voltage, equals teur and commercial radio stations. The many Et plus Es added algebra- testimonials received from far of: lands are evi- ically. dence that the Hallicrafters are achieving their re- When suitably filtered, purpose-to provide reliable communications ceivers with a high standard of performance, the control voltage is de- built to suit every amateur need. livered to the control tube Because this performance so generally exceeds where the actual frequency expectations, a world-wide preference for the control is accomplished. Hallicrafter Skyriders has been created, and fur- Two methods of utilizing thered by the generous praise of their owners. vacuum tubes for fre- A 13 -Tube Super witt 2 stages of Pre -Selec- Your Hallicrafters dealer will gladly show you quency control are shown tion, a built-in Noise Limiter, and complete the Skyrider receivers, or complete description coverage from 62 MC to 545 KC on 6 bands. forwarded upon direct request to the in Figures 2a and 2b. Fig- 1000° of Bard Spread. Maximum useable will be ure 2a illustrates a typical sensitivity and... selectivity. Also available Hallicrafters Laboratories. with single stage of Pre-Selection and without type involving variation of Noise Limiter. effective capacity to change frequency, while Figure 2b depicts the inductance va- riation type. A triode with a choke in its plate circuit reflects ca- pacity into its grid circuit. Degeneration resulting from the condenser CI in- creases this effect. The ac- tual amount of reflected "capacity" depends upon the gain of the tube and it A 9 -Tube Super with a tuning range from is this fact which is used to 38 MC. to 545 KC (includes 10 meter band), An 8 -Tube Super that offers exceptional performance for Image affect frequency control by 1000° Spiral Band Spread and Infinite its modest cost. Provides full coverage from 44 MC to Rejector for the elimination of image inter- 545 KC (includes 10 meter band) with good sensitivity varying the effective bias ference. and selectivity on all bands. Built-in speaker and sep- on the grid of the tube. arate Band Spread Dial. R and C are filter com- Sk BddY ponents. In actual practice Tbe this circuit is not commonly used because it has several disadvantages. The tube acts as a poor condenser and hence introduces losses 2611 Indiana Ave., Chicago, U. S. A. into the oscillator tank. Cable Address: Hallicraft, Chicago The amount control of All Hallicrafters Receivers sold varies considerably with A junior communication receiver with full ' coverage from 18.5 MC to 545 KC, and all on Iiberal Time Payments. frequency and is unsym- the essent-atcontrols '.or amateur reception. metrical about resonance. Built-in Speaker, Separate Band Spread Write for cotnpis.r- re, Svyri der A receiver at an un- Dial. real amateur Skyrider 5-I U, Skyrider Marine. A better system involves usually low price. Diversity, inductive control as shown ORLD'S LARGEST BUILDERS OF AMATEUR COMMUNICATIONS EQUIPMENT in Figure 2b. In this circuit 62 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK to conduct careful tests of the tubes in- volved. Unbalanced diode currents can cause mistuning or even station rejection so a tester which checks both diodes is essen- tial. Of course the control tube must be able to amplify evenly and well or it should be discarded. A power output or mutual conductance tester is preferable for these tests. An open in the condenser C (Figure la) 250M I MEGI will result in neglible response of the dis- criminator. The effects of a shorted con- 300 denser should be evident. MMF Incorrect use, although not a defect, is 250M11 also a responsibility of the serviceman. In MIDWEST MODEL VT -20 order to be able to help his customers he FIG.3 must know how to use it himself. A set using A.F.C. will select the station (from two or three on adjacent channels) which junction of the output resistors and tune A.F.C. amplifier, a 6K7, which serves to has the greatest carrier voltage in the re - the primary for maximum output. Then, isolate the A.F.C. circuit and provide more with the meter across both resistors (from positive action. Such amplifiers are now cathode to cathode), tune the secondary for quite common. minimum output. A vacuum tube voltmeter The Arvin 1237 and 1247 circuit, Figure is by far the better instrument to use. Check 4, is very like the one in Figure 3 but the these adjustments with an output meter. whole set is interesting because it employs During these alignment operations the set the double superheterodyne system. A sec- should be tuned to the center of the band, ond oscillator converts the if. into another 1000 kc. for the broadcast band. of a different frequency. A.F.C. applied to FIG. IA Testing the A.F.C. is quite important and the second oscillator in the conventional is easily done if this method is used. Tune manner results in very smooth and uniform ceiver's antenna, hence do set up push not in and zero -beat a signal from a signal gen- control. button A.F.C. so that a stronger station may over -ride the desired one. If the sta- IOOMMF 6J7G TOIF.STAGE 6J7G 6H6 tions involved have equal carriers the set ¿SC. will select the one with the highest percent- -NW age of modulation. Such a set is liable to swing from one to another if their modula- tion percentages differ enough. Swinging or shifting from one station to another is sometimes troublesome on short waves 500MMF where fading is quite severe. Situations such as this must be carefully explained to the customer. Naturally the question of suitable test 05 MF equipment comes up. Several types of equipment may be used, depending upon the connection used for measurement. ARVIN 1237-1247 A conventional output meter may be FIG.4 used across the output stage. If such an The Arvin 1237-1247 set discussed in the article. indicator is used the A.F.C. can be tuned in this manner. After aligning the r.f. and erator set to 1000 kc., with the A.F.C. off. Philco has an interesting setup in their i.f. stages in the conventional way, tune the Then, with the A.F.C. on, the output should model 38-2, illustrated in Figure 5. The set to zero -beat with the signal generator not change. After this test try several sta- discriminator output is balanced above which should be set tions and listen for a change in quality ground. Two "lines" supply bias to the at 1000 kc. Detune (which should not occur). Try tuning con- two grids of the 6N7G used as the control the discriminator siderably off resonance. The station should tube. A small amount of voltage from the secondary winding snap in. oscillator is introduced into both control a bit and tune the Commercial versions of the basic circuits grids simultaneously. The control grids are primary for mini- previously discussed are presented in Figures effectively in parallel for r.f. and so the mum output. Then 3, 4 and 5. voltages on the grids are in phase. How- adjust the secondary Figure 3, the Midwest model VT -20, is ever, the plates are in push pull and hence winding for maxi- nearly standard except for the separate the output voltages are 180° out of phase. mum output. If the output reading does Osc FIG.5 not change when the SERIES PHI LCO 36-2 A.F.C. is switched COMP. 250 off and on the ad - MMF [c. justment is correct. g FIG 2A 6ABG P 10M n 6H A high resistance TUNNING \**1 TOIF.STAGE COND. - Two ci cuits de- voltmeter may be T ON-OFF / scribed by author. used across the out- A.F.C. put of the discrim- 49M IL I MEG inator is but not , OGF70- G reliable because it draws current and -1115 MF hence does not show 110MMF zero voltage accu- 49MIL ---"-- rately. Connect the .05MF voltmeter from OSC COMP. /FIG.2B = ground to the The A. F. C. System of the Philco 38-2, which is explained. RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK 63

Cancellation in the plate circuit governs the P1 R2E12 RII12 can be used to compare any power level with amplitude of the output. an arbitrary standard power level. As a As in other inductive control circuits the P2 R1E22 R2I22 reference level or "zero" level, 6 milliwatts grid voltage undergoes a 90° shift across This can then be substituted in the first is one of the most commonly used. Employ- the coupling condenser and hence the plate equation and one gets an expression giving ing this zero level, a power of 6 milliwatts current lags the plate voltage by 90 elec- the number of db. to be found from voltage would be called "zero db."; 6 watts would trical degrees, again appearing as inductance. ratios direct, if RI = R2. But this amounts be plus 30 db.; and .6 milliwatt would be This apparent inductance is then reflected to figuring out the power in each case and -10 db. In all cases the zero level must be into the oscillator tank circuit. The ampli- still the decibel expresses the power ratio, not known before the statement can have any tude of this shunt inductance is directly the voltage ratio. meaning! The use of 6 milliwatts as a level, proportional to the amount of cancellation Since the decibel represents a ratio and however, is by no means universal; some of in the plate circuit of the control tube. not a number of watts, it cannot be used to the largest broadcasting chains use a differ- From the foregoing discussion it may be refer to a given power level, directly, but it ent level. One milliwatt, 10 milliwatts, 12 seen that only the method of using the discriminator output is different from the ordinary. Here's YOUR Practical WHAT TRAI N ING for RADIO IS All in ONE Mandy Volume! A HER- E AT LAST is a quick, easy, inexpensive way to get the practical radio training you need to qualify for a radio job. Condensed into this one great book, Ghirardi'a "Radio Physics Course", you will find the equivalent of THIRTY-SIX easy -to -understand reading courses covering all the essentials of radio, electricity and sound. Here is practical self -instruction that will fit you for many different DB? kinds of jobs. The Opportunity of a Lifetime! MOST of the mis- No longer need you be deprived of the advantage of radio training because of its cost, or the time it usually requires. Think of getting conceptions in in ONE CONCISE AND COMPACT VOLUME a complete rating the merits course in ELECTRICITY, a complete course in RADIO, a com- plete course in SOUND, and in addition thorough instruction in and performance of am- Television, Talkies, Photoelectric Cells and Cathode -Ray Tubes, plifiers, microphones and Testing and Servicing, Automobile, Aircraft and Marine Radio, Short -Wave Reception, and many other special subjects that all go receivers occur in the use to make up a complete education in the field of radio. And all for of the decibel and the the phenomenally low price of $4.001 This is only a fraction of what you would expect to pay for a course in just one of these lack of a single standard essential subjects. zero level as a reference point. Short -Cut Courses of Self -Instruction It is not necessary, here, Prepared by that World -Famous Authority, to go into the derivation ALFRED A. GHIRARDI of the decibel, but it would Every one of the 36 big sections of "Radio Physics Course" is an be best to restate its defini- expertly prepared home -study course. Each is brief and simplified tion. The decibel is a unit for time -saving and easy to understand -yet each is so thorough and practical that every minute spent with the book rapidly pushes which expresses the ratio ahead your preparation for a good -paying radio job. Self -testing of one power level to an- review questions and problems for each section make it simple not only to understand everything but also to check your own progress. other. The power may be No previous training or knowledge of mathematics are required. electrical power represent- Ghirardi's "Radio Physics Course' is the book that leading radio schools have chosen as the most thorough, instructive and interesting ing sound, or acoustic radio book ever written. Because it makes learning radio so very power (power of sound simple, it is used as the basic text in the courses of more radio waves). To be exact, the schools than any other radio book in the world! number of decibels gain -972 Pages - 36 Volumes in One. - or loss is equal to ten times Radio, Electricity and Sound Complete the logarithm of the power Plus Many Other Valuable Special Features 508 Schematic Diagrams, Charts and Photos Fit Yourself for a Radio Job Quickly, ratio. 856 Review Questions 1. Radio Rroadusting I8. Vacuum Tube Char- Easily, at Little Cost Pl System. acteristics. DB = 10 logio 2. Sound, Speech and 19. Construction Features Do it the easy "Ghirardi way" at home with "Radio Physics Course". Music an Related to of Vacuum Tubes. A few minutes of your spare time daily will give you all the knowledge P2 B roadcasting. 20. Vacuum Tube Detector and training you need to have. Even if you know some of these 3. Electron Theory, Elec- and Amplifier Action. subjects, tric Current. 21. Radio Frequency Am- you need the book to fill in the gaps of your radio education It should be particularly 4. Electrical Units, Ohm's plification. and bring you up to date. Law, Resistance. 22. Superheterodyne Re- noted here that the decibel 5. Electrical Circuits, ceivers. B atteries. 23. Design of R.F. Ampli- TRY IT FOR IO DAYS AT OUR EXPENSE refers to a ratio and to 8. Magnetism. fiers and Tuning Coils. Electromagnetism. Fill out the coupon below and mall it at once. "Radio Physics 7. 24. Audio Amplification. Course" will be /lent you by return mall. See for yourself its won- power. It is not an abso- 8. Electromagnetic In- 25. Loud Speakers. derful completeness and simplicity. Keep and read the book for ten duction. 26. The Battery Operated days. -Then, it you are not satisfied in every way, return the book lute unit of power level 9. Inductance and In- Receiver. undamaged and every penny of your money will be Inetantiy re- ductors. 27. The Power Supply funded. With this Money -Back Guarantee. you caa't lose) So don't and not a expressing 10. Capacitance and Con- Unit. delay one moment. Thte le your big opportunity to get comp unit densers. 28. Electric Receivers. training in radio at the amazing pelee of $4. Fill out the coupon NOW! 11. Alternating Current 29. Automobile and Air- voltage ratios. Sometimes, Circuits. craft Receivers. 12. Electric Filters. 30. Phonograph Pickups MAIL THIS COUPON TODAY! when the impedance of the 13. Electrical Measuring and Sound Amplifier Instruments. Systems. RADIO 6 TECHNICAL PUBLISHING CO., circuits is the same, the 14. iEleetromuctromagnetie Radi- 31. Short Wave Reception. ations. 4S Astor Place, Dept. TEL Nºw York, N. Y. 32. Vacuum Tube Appli- Enclosed find $4 for my copy of Ghtrardl's "RADIO 15. Rtthe cations and Photo- PHYSICS Pl Brrdio adcasting Sys- electric Cells. COURSE", with your 10 -day money -back guarantee. tem. 33. Television. ratio can be expressed 16. The Receiving Station. 34. The Antenna and NAME Detection w,th Crys- Ground. ADDRESS P2 tals. 35. Testing and Servicing. 17. Elementary Study of 38. Sound Motion Pictures. CITY STATE in terms of voltage or cur- the Vacuum Tube. Appendices. free descriptive literature about "RADIO rent, because: O Ple 8 Cend me leht 84 RADIO NEWS 1940 RADIO & TELEVISION DATA BOOK milliwatts, are also being used as reference in decibels is the input delivers 100 volts across the out- levels. So it is necessary to make sure of the E2 Z1 put, and the gain is reference level before comparing such ratings DB _ 20 log -± 10 log - 100 5,000,000 given by different sources. As an example, E1 Z2 DB=20 log -+ 10 log suppose an amplifier has an output of 30 One should never forget to include the .01 500 watts. When the zero level is 1 milliwatt, last term. When Zi equals Z2, then the term 20 X 4 + 10 X 4 = 120 db. the output would be called 45 db., while a can be omitted, for it will be equal to zero. Obviously, the type of rating should be 10-milliwatt zero level would reduce it to 35. This will happen when measuring amplifiers different, and this as a good thing to remem- Measurements of sound intensities in the with transformer input and output if both ber when comparing the merits of resistance - air are also referred to various "zero" levels. are of the same impedance (both 500 ohms, coupled amplifiers. A suggested remedy is At present, there seem to be two different or both 200 ohms, etc.). to agree on a standard value of grid resistor levels in use: one starts at 1 millibar sound There is an additional difficulty with re- for measurement purposes. (Some firms are pressure (equivalent to 24.4 X 10-16 watts sistance -coupled amplifiers. According to doing this and use 150,000 ohms.) An al- per square centimeter), and the other, which the definition, it is required to measure the ternative way would be to rate amplifiers in will presumably become the standard, starts input power, but on a resistance -coupled terms of power sensitivity like power tubes. at 1 X 10-18 watts per square centimeter amplifier it would amount only to the power Finally, there is the great bugaboo, rating (equivalent to .207 millibar). Any level of dissipated in the grid leak, for the tube itself microphones. Many manufacturers are rating sound energy when measured in the second does not draw any power. The result is that their microphones as "so many db. down." scale will be 14 decibels higher than in the that rating depends on the size of the grid Trusting amateurs and P.A. men construct first scale. Again, it is important to know leak. The same amplifier, made by manu- their amplifiers figuring that they need the the zero level before the level in db. has any facturer A, can be made by manufacturer B, difference between that figure and the de- meaning. but changing the input grid leak from V2 sired output in db. (6-milliwatt zero level). There are all sorts of opportunities for megohm, to 5 megohms, he is justified to Of course, that doesn't work. Such a rating misunderstanding when measuring the gain rate the gain 10 db. higher. Yet, for all of microphones does not mean anything of amplifiers. The gain of an amplifier, in practical purposes, the gain remains the same. until it is known what zero level is employed decibels, is simply "10 times the logarithm The trouble is with the system of rating. and how loud a sound must be made to of P2/Pi; where P2 is the output power and Let us take an example: an amplifier has a get the stated output. P1 is the input power. Since it is often cus- resistance -coupled input and a transformer All that was originally taken care of be- tomary to measure voltages only, one should output. The grid leak is % megohm and cause the zero level was defined as "output not forget to take into account any difference the transformer output impedance is 500 of 1 volt at open circuit with a sound pres- in impedance. For example, taking an ampli- ohms. During a test it was found that .01 sure of 1 bar." This zero level does not fier with transformer input and output; sup- volt across the grid leak resulted in 100 volts mean very much to the average user, for he pose the input impedance is 200 ohms, while across the 500 -ohm load. Now the gain is: does not know how loud one bar is and the the output impedance is 8 ohms (for a voice 100 500,000 1 volt across open circuit will become con- coil). Under measurement the voice coil DB = 20 log + 10 log siderably less when the microphone is con- will be replaced by an 8 -ohm resistor, with .01 500 nected to a load. As a matter of informa- a voltmeter across it. Similarly, the input DB = 20 log 10,000 + 10 log 1000 tion, 1 bar is +74 db. in the scale with zero circuit will be connected to the proper im- DB=20X4+10X3=110db. level at 10-16 watts per square centimeter. pedance network, again using a voltmeter. But if the grid leak is changed to 5 meg According to Dr. E. E. Free, it is equal to After the measurements are taken, the gain ohms, the result will still be: .01 volt across "average conversation." SOME INTERNATIONAL PREFIXES AR SYRIA FR8 REUNION OK CZECHOSLOVAKIA CE CHILE FT4 TUNIS OM GUAM CM CUBA FU8 NEW HEBRIDES ON BELGIUM CN MOROCCO FY8 .FRENCH GUIANA OQ5 BELGIAN CONGO CO CUBA (fones) G GREAT BRITAIN OX GREENLAND CP BOLIVIA GI (see G) NORTHERN ISLAND OY FAROE ISLANDS CR4 CAPE VERDE GM (see G) ....SCOTLAND OZ DENMARK CR5 PORTUGUESE GUINEA GW (see G)....WALES PA NETHERLANDS CR6 ANGOLA HA HUNGARY PI NETHERLANDS (schools) CR7 MOZAMBIQUE HB SWITZERLAND PJ CURACAO CR8 PORTUGUESE INDIA HC ECUADOR PK NETH. INDIES CR9 MACAO HH HAITI PX ANDORRA CR10 TIMOR HI DOMINICAN REPUBLIC PY BRAZIL CT1 PORTUGAL HJ, HK COLOMBIAN REPUBLIC PZ SURINAM CT2 AZORES HP PANAMA SM SWEDEN CT3 MADEIRA HR HONDURAS SP POLAND CX URUGUAY HS SIAM ST SUDAN D GERMANY HZ HEDJAZ SU EGYPT EA SPAIN I ITALY SV GREECE EA8 CANARY ISLANDS J JAPAN TA TURKEY EI IRISH FREE STATE K4 PORTO RICO, VIRGIN TF ICELAND EL LIBERIA ISLANDS TG GUATEMALA EP, EQ IRAN (ex -Persia) KS CANAL ZONE TI COSTA RICA ES ESTONIA K6 GUAM, HAWAII, MIDWAY U, UE, UK, UX U.S.S.R. F3 FRANCE ISLAND, SAMOA (U. S.) VE CANADA F8 FRANCE VK AUSTRALIA FA ALGERIA K7...... ALASKA VO NEWFOUNDLAND FB8 MADAGASCAR KA PHILIPPINE ISLANDS VP1 BRITISH HONDURAS FD8 TOGOLAND (French) LA NORWAY VP2 DOMINICA, GRENADA, ST. FE8 CAMEROONS (French) LU ARGENTINA LUCIA, ANTIGUA, ST. FF8 FRENCH WEST AFRICA LX LUXEMBOURG KITTS -NEVIS FG8 GUADELOUPE LY LITHUANIA VP3 BRITISH GUIANA FI8 FRENCH INDO -CHINA LZ BULGARIA VP4 TRINIDAD & TOBAGO FK8 NEW CALEDONIA MX MANCHUKUO VP5 CAYMAN ISLANDS, JAMAI- FL8 SOMALI COAST N U S NAVAL COMMUNICA CA, TURKS & CAICOS FM8 MARTINIQUE TIONS RESERVE ISLANDS FN8 FRENCH INDIA NY CANAL ZONE VP6 BARBADOS F08 FRENCH OCEANIA,TAHITI OA PERU VP7 BAHAMAS FP8 ST. PIERRE MIQUELON OE AUSTRIA VP8 FALKLAND ISLANDS, FQ8 FR. EQUATORIAL AFRICA OH FINLAND SOUTH GEORGIA RADIO NEWS 1940 .RADIO & TELEVISION DATA ROOK ÓJ

VP9 BERMUDA ZC5 PALESTINE ¿E1 SOUTHERN RHODESIA VQ1 (*VR3) FANNING ISLAND ZD1 SIERRA LEONE ZKI COOK ISLANDS VQ2 NORTHERN RHODESIA ZD2 NIGERIA, CAMEROONS ZK2 NIUE VQ3 TANGANYIKA (British) ZL NEW ZEALAND VQ4 KENYA ZD3 GAMBIA ZM WESTERN SAMOA VQ5 UGANDA ZD4 GOLD COAST, TOGOLAND ZP PARAGUAY VQ6 BRITISH SOMALILAND (British) ZS, ZT, ZU SOUTH AFRICA VQ8 MAURITIUS ZD6 NYASALAND *ZU9 TRISTAN DA CUNHA VQ9 SEYCHELLES ZD7 SAINT HELENA *Suggested by the British Empire Radio Union. VRl GILBERT & ELLICE ISLANDS ZD8 ASCENSION **Official, by French Govt. VR2 FIJI ISLANDS VR3 FANNING ISLAND VR4 BR. SOLOMON ISLANDS VR5 TONGA ISLANDS VR6 PITCAIRN ISLAND SCIENTIFICALLY CONSTRUCTED VS1, VS2, VS3. . MALAYA VS4 BORNEO VS5 500 WATT RADIO -FREQUENCY AMPLIFIER SARAWAK VS6 HONG KONG VS7 CEYLON VS8 BAHRAIN ISLAND VS9 MALDIVE ISLANDS VU INDIA W, K, N UNITED STATES XE MEXICO A NEW INNOVATION IN AMPLIFIER DESIGN XT, XU CHINA A radically new type of construction in this unit completely ELIMINATES ALL CLOSED METALLIC LOOPS. With this outstanding design feature, plus other layout refinements, XZ the beginner and advanced amateur can readily construct a push-pull amplifier with very BURMA high efficiency and unusually good circuit stability on frequences as high as 60 megacycles. YA Note these additional features:- AFGHANISTAN Designed for 40, 20, 10 and 5 meters Perfect circuit symetry throughout YI Panel and metal parts completely drilled All metal parts bright cadmium plated Accommodates any pair of medium - IRAQ power triodes Ceramic insulation used throughout YJ (**FU8) Bated at 1750 volts and 500 watts input Unusually neat appearance NEW HEBRIDES $24.00 YL BPA-500 Kit complete (less tubes, meters, and coils)-Amateur Ne+ LATVIA You must SEE it at your BUD jobber to appreciate it !II YM DANZIG YN AIR -WOUND TANK COILS TINY -MITE CONDENSERS NICARAGUA 500 Rating YR Watt ROUMANIA YS SALVADOR 5 to 160 METERS YT, YU JUGOSLAVIA INCLUSIVE YV VENEZUELA ZA Coil supports of fire-resistant plastic are A new line of small condensers for all ALBANIA firmly cemented to turns. Ceramic Insu- applications where such units are required. lation is Alsimag 196. Designed for cor- The various types include: Single and ZB1 rect L -O ratio for phone as well as C.W. Dual units in Single, Double, and Triple MALTA Coils have individual links. spacing; also Coil Padders and Balancing Priced from $1.65 to $2.70 Net Condensers. All units reasonably priced. ZB2 GIBRALTAR Write for free descriptive literature or send IOc for 60 page Station log and complete ZC1 ham catalog #DB 39 TRANSJORDANIA ZC2 COCOS ISLANDS ZC3 BUD RADIO, INC. CHRISTMAS ISLAND ZC4 CLEVELAND, CYPRUS OHIO f;G IIADiO NEWS 194e RADIO & TELEVISION DATA BOOK STANCOR OFFERS YOU THESE OUTSTANDING VALUES 'FOR THE HAM: 20P TRANSMITTER KIT

Designed to meet the demand for an eccn mi2al unit, this complete Shone and C.W. traismit.er includes A.C. power supply in a cabinet 1x12"x 8s/.". It operates or any frequency front 1.6 to 60MC and is crystal zontrolled. The R.F. 6F6 -G crystal oscillator drives an 807 amplifier Split- stator condensers in oscillator and ampl l r cir- cuits insure proper L -C ratio. The speech ai plifier and modulator: 6J7 input, 6C5 voltage amplifier, 6N7 driver (Class "A"), and 6N7 modulator (Class "B"). Sufficient gair for any crystal micrephcne or high impedance input. Complete kit it ay be bought with tubes, crystal, 50 holder, meter and cabinet for approximately Au NET

FOR THE HAM AND SERVICEMAN: 415 UNIVERSAL SPEECH AMPLIFIER KIT

Designed as a universal amplifier for rack and panel or table type mounting. It can be used with any high impedance low level input. Standard out- put impedances of 4, 8, 15 and 500 ohms. Output transformer is replaceable with driver or modula- tion transformer so that the amplifier can be used to drive a high powered modulator; or, become low power modulator delivering 15 watts. Tube lineup: 6J7 input, 6C5 voltage amplifier, 6N7 driver (Class "A"), and P.P. 2A3's (Class "AB"). A 5Z3 full - wave rectifier is used plus an 80 as a half -wave bias rectifier, supplying fixed bias for the P.P. 2A3's. Complete kit with F415 chassis and tubes-approxi$30- 00 mately NET WRITE FOR CATALOGS DESCRIBING STANCOR COMPLETE TRANSFORMER LINE

STANDARD TRANSFORMER CORPORATION 1500 NORTH HALSTED STREET CHICAGO, ILLINOIS 1 J14

., l nE.` r+ .`n'f -. s,l' .!'.. - ir .:'-

+ ,

L

Pf4'. 'm;

I

f+.

r. r .a.,.}'{ , ` 44:

r U:

hfi

4i. À!`.t

liJ

4 '1"f". r, ,

e

kt

'f sL,,, S^ xi-FIG