[AMRadio] DX60 modulator chassis ready to go


John Lyles jtml at losalamos.com
Sat Mar 18 17:55:51 EST 2006


This modulator is not exactly like the 1952 nor the 1959 ARRL HB 807 modulators. It appears to be a class B modulator, not AB1 or AB2. It has 5 tubes, three are 12AU7 and two are 807. The input audio is conventional mike preamp and audio stage, using both halves of first 12AU7 with a gain pot to the grid of the the second 12AU7. It appears to be connected with both triodes in parallel, driving a UTC S2 single ended to push pull 2:1 driver transformer. The ends of the secondary each drive a grid of the third 12AU7. Plates are hard connected to B+ and they are configured as cathode followers. These drive the grid and screen of triode connected 807s. There is no bias supply at all, the 807s being direct coupled to the cathodes of 12AU7 triode sections, and the grids of those are through the S2 secondary to ground. I suppose some self bias might develop on the 807 grids. Output transformer is a Stancor A3892 30 Watt polypedance. There is an octal socket to bring all the power in
(filament and B+1 and B+2) and a mike connector, and a volume control. Entire chassis is 9.5 inches long, 4 inches wide, and about 7.5 inches tall to the plate caps on the 807s. It is dirty but there are only a few caps that might need replacing if they are leaky. 

Has anyone seen this particular design commercially made years ago, or in any articles? It appears quite compact, and with the cathode followers to the 807s, reminds me of the audio lineup of a Gates BC1G, with 807s driving 833s that way. 

I am asking $80 plus S/H for this thing with all tubes in it. 






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