I use a 720/730 on 10 m. I feed the 720 on 40m. using a digital vfo. There
are no substantial mods to the 720, other than PTT and replacement of a
burnt-out power transformer.
I made the following modifications to the 730:
(1) I removed the clipper stage and its associated components.
(2) I installed a 40 hy 120 mill modulation reactor and mounted it in the
space where the clipper tube used to be.
(3) I disassembled the modulation transformer and restacked the laminations
like a power transformer, eliminating the gap in the core.
(4) I changed the values of some coupling capacitors, and I recall removing
a bypass cap across the mod tranformer (I think).
After the mods, it shows flat response from 20 to over 11,000 cps with no
visible distortion on the o'scope. I feed audio from the 500 ohm line in my
audio rack thru a step attenuator to the "phone patch" input on the back of
the modulator, bypassing the low level mic preamp. I changed the mod
transformer turns ratio tap to give the least amount of stepdown, therefore
improving the positive peak capability. I wired up a PTT circuit that works
off the same 28 vdc relay line that controls the rest of the station.
I always get good reports on the signal quality when the band is open. I use
a simple quarter wave ground plane with 3 drooping radials.
Don K4KYV
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