[Collins] Kwm-2a no SSB audio drive

[Dr. Gerald N. Johnson]

On Mon, 2007-11-26 at 18:04 -0500, walnutcreek at appstate.net wrote:
> Hi all,
> I recently moved and have been working on one rig after another as I unpack.  I hooked this 2a up and it tested fine for output and receive.  It works fine in CW, but when I switched to USB and LSB I have no audio driving the RF amplifier.  I'm going to have to get out my manual and dig through it, but if anyone can shoot me an e-mail telling me which tube is the likely culprit I'd love to hear from you.
> Thanks,
> Cam
> WA4JKW
> 
Depends on the vintage of the radio. Some generate CW with the BFO fed
around the balanced modulator, some generate CW with an audio tone.

Those that generate CW with the audio tone use almost all the same
circuits for SSB as for CW and so only the first audio tube is suspect
(along with mode switch contacts).

The later rigs bypass the audio and the balanced modulator for CW and so
that leaves the audio, maybe the BFO (or at least the USB and LSB
crystals), and the balanced modulator as suspect.

Lots of ALC indication could be the ALC zero, a leaky capacitor in the
ALC detector, or a bad ALC rectifier. And the ALC rectifier has varied
over the KWM-2 production lifetime.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer