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- ...... - " - , • Bottom view of 8072 amplifier. put tank is tuned for the center of the band by an indication of peak grid current when it is installed and needs no further adjustment. Varying the spacing of the coil turns simplified things in the amplifier shown. A variable condenser can also be used. Preliminary calculations showed that the amplifier input impedance would not match the usual 52 ohm exciter output impedance, Experimentally the excitation was tapped up from ground to a point where the SWR approached I :I , which worked out to be a center-tap on the coil. The grid tap on the input coil can also be calculated to equalize the grid and screen currents, but it provided only a starting p oint. The grid is closer to the cathode and when tied to ground with the screen, the grid current is much higher than the screen current and may exceed the plate currentl The calculated point for the grid tap where the grid and screen currents would be equal is about 8.3% of the way down the coil from the cathode. The grid current at this point was well below the 200 rna rating of the two tubes and the amplifier was hard to drive. The tap was placed at one turn from the cathode end which raised the single-tone grid current to a little over 200 rna and brought the drive down to the range of the 100 w exciter. I have heard that distortion checks have been made on grounded-grid amplifiers and no improvement was noted with a tuned input circuit installed, so it was left out. This has never been checked here, but the results would depend on the test set-up. I have always included a low impedance input tank in grounded-grid circuits after having had a pair of 8 13's "take off' in an amplifier a number of years ago and ending up having to neutralize them. The plate tank circuit is a little unconven- tional for ham equipment in that it is series fed rather than the parallel feed usuall y used. This eliminates the need of a high current plate blocking condenser and the rf choke is across the 52 ohm load, reducing the strain on it. The usual resistor-choke parasitic suppressor was not needed and the plate-to-tank lead is a 1"" wide flexible copper strap which really ties the two together. A pi-L tank circuit configuration was used as it reduced the size of the loading capacitor to an available capacity. Since a lead had to be connected to the pi section anyway it might as well be coiled up into enough inductance to attenuate the 2nd harmonic the 15 db that this configuration is supposed to give. The transfer relays need not be the rather expensive Jennings vacuum relays used. There are a number of small relays on the market that can be built into the linear amplifiers that would eliminate the expensive (count all the fittings too ) , bulky and clacking coaxial relays on the wall 01' on the back of the amp lifier. I never could quite understand why this was not done but then maybe everybody but me owns stock in a coaxial relay companyI There is nothing coaxial inside of the amp lifier so no discontinuities will occur. In this partieular application the extra contacts came ir; handy to apply a blocking bias. The static II is about 120 rna with 2300 v on the plates The - 40 v (no load ) bias in standby drops the II' to about 40 rna which lowers the static dissipation and helps with the cooling. The filament transformer used is the onI) one that could be found available. It is rate, at a higher current than required which mad. the filament voltage a volt too high. This re quired the series 25 ohm resistor in the pri mary which would not be needed if a 13.5 ' under load filament transformer can be found. The adjustment of this linear amplifier 0 any linear amplifier is quite simple with : 'scope and envelop detector to produce ; trapezoid pattern when a two-tone test signa is used. There are probably other methods 0 tuning up lineal'S, judging from the carrier and ''hello test" one hears on the air, but do not know of any good ones. A dummy loai is connected to the output and the load con denser is set near the high capacity enc Feed in enough two-tone signal to produc 200-250 rna of p late current. Tune the tan input condenser for resonance or maximur rf output as indicated on the 'scope or J meter on the dummy load. Now turn up th gain momentarily to 550 rna and see if ther are nice clean peaks on the 'scope patten 20 73 MAGAZI"
Here's the SPECTACULAR NEW ALL TRANSISTOR 5 B T- 3 55B TRANSCEIVER PRICED AT ONLYS299 "'5==O=--_- ,, ~ ._---..j SPEC if iCATIONS F,"'l. R~nl' _ 3780 40 10 KC. 7180-7320 IIC. 14 130 14 360 II C S.miconducto'l: 2- 9042 instan l hea t,n, tubes. 18 ' .ansi,lo•• , 2- ~ a " caps. I _len"., 9 d'odu Si••: 4 ~ H • I I % 1'1 .8%0. Weight 10 lb. " TRANS MITTER Po.... Input: 1651'1 pep Carrie' S"pp"euoon: _ 45 DB 5.8. Selli;lion: 80 . OM Iowoe. 20M uppt. u....",,1tCl 58: _ 40 08 ....., . I"' , l O·IOO ,*".. adj, P"",...e- mphon: .5 amps Reu.... 12:.15 . mps sse XMIT. 01-_'_:P , T. T. Holub. ' ..........1 on H'I •ee. R[CUVUl $ens,!,••,,; .S" v lot 1008 S + NIH SeleCti.i',: ] KC @ 6 DB Spurious: 'm,~ bell" 11'.... ec O• St.bilit,: l eu 100 cpI in a.,y I S min. period ul'lder no
Page 1 and 2: ~--.~ -- -- 50c (Not 75c, not even
Page 3 and 4: - - - 73 'IIagazine Nayne Green W2N
Page 6: ROHN • sets the ~ Standard Duty G
Page 9 and 10: CUST 1965 7 !I763 2El6 '---------+-
Page 11 and 12: Stronger Signals! Stronger Construc
Page 13 and 14: olt filament supply, make the follo
Page 15 and 16: '. . I I I '. I: :I I I. • '\. \
Page 17 and 18: ohms. One caution to be observed is
Page 19 and 20: a K ssb station only ~ cents per wa
Page 21: ,..... ~, & ~ , ~ ~ ,r .cc ' " . 'H
Page 25 and 26: for discriminating amateurs who are
Page 27 and 28: eing multiplied more than three tim
Page 29 and 30: • LLANC ~ . ® ~. Tenna-Rntor for
Page 31 and 32: 3 5 When a switch must be actuated
Page 33 and 34: send today for your 508-page IIIEO
Page 35 and 36: 1IJGUST 196'\ • I , I Bottom view
Page 37 and 38: IT'S A CLASSIC! With the 2·K LINEA
Page 39 and 40: AIIr.IIC:T l C)'::
Page 41 and 42: THINK SMALL••• C....I!IlIEII
Page 43 and 44: Herbert Cross KIAMN 59 Fla gler Ave
Page 45 and 46: AUGUST 1965 Curing Distorted RTTY P
Page 47 and 48: was paying much attention to receiv
Page 49 and 50: AU GUST 1965 db BELOW 0. 1 MICROVOL
Page 51 and 52: A llr.lI
Page 53 and 54: ., NEW! SPRAGUE SUPPRESSIKITS FOR V
Page 55 and 56: (and have about 28 db gain, but tha
Page 57 and 58: A UGUST 1965 55 TRANSCEIVER HIT PAR
Page 59 and 60: AUGUST 1965 51 RED HOT LOW, LOW PRI
Page 61 and 62: A I rr.l lCT ' 0.01:
Page 63 and 64: ~ c o e ~... - ~ ~ ---------_......
Page 65 and 66: SUBSCRIBE TO 73 Don't take a chance
Page 67 and 68: ••• BUILT-IN 12V DC AND 117V
Page 69 and 70: them I had promised some of the boy
Page 71 and 72: CRYSTALS are not all the same I .T
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insulation to ground, and I was not
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UCUST 1965 H Fig. 2 10 , • • --
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at any latitude and longitude. All
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PATENT PENDING MOBilE ANTENNA MOUNT
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UNIVAC WIRED MEMORY PLANES As shown
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?roblem . . . something not altoget
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TS 418A 400- 1000 meg signal genera
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ff P ack M onad nock M ountain (231
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~~I'.I.1~"'I'.II'.I.1.1.1.1.1.1.1.1
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member, organized pressure brings r
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}ONSET G-50 : 10 hours u se. $2 10
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More Letters THE BEST WAY TO BUY SU
Page 97 and 98:
"TAB" - TRANSISTORS - OIOOES II GTD
Page 99 and 100:
CAN BEAT OUR ANNIVERSARY SPECTACULA
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