I would build a modulator using a pair of KT88 or KT90 tubes, multi match mod transformer, drive the grids of the KT88 tubes with a HIFI amp.
The KT90 pair is good for about 140 watts of audio in AB1 (no driving power). 809's or 811's in class b would also work. Build a nice modulator with a multi match mod trans and you can modulate anything with it. A thordarson 300 watt multi match would do well... You could have fun with this project, make it mike input (D104 or a low Z mike) with tone controls, or the easy way of the line level equipment (berrenger ultra voice) and a power amp. A while ago, I found a 25 watt dual channel power amp made by symetrix for under $100.00 at a trading post place, its 1 inch high rack mount, along with the 1 inch high berrenger, it makes for a very small clean audio setup. 25 watts is way more then enough to drive all the modulator grids I have, the 4x150a's, the 811a's, etc. You get eq, compression, noise gate, line or mike level input, and with the twist of a few knobs, can restrict the audio down on the low and/or high end, or open it up to full fidelity. Brett N2DTS > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of John Lyles > Sent: Saturday, March 18, 2006 5:56 PM > To: amradio@mailman.qth.net > Subject: [AMRadio] DX60 modulator chassis ready to go > > 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. > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
