HQ-170 AVC "pulls" freq - update

[Doug Hall]

Hi all,
   A few days ago I posted an inquiry about problems with the HQ-170 pulling
the frequency when the AVC was on. With the AVC off, signals are stable.
I've received over a dozen replies, and out of those replies, 8 people have
reported the same problem, either with a 170 or 180 receiver. So I'm led to
believe that this is a common problem with Hammarlund receivers. After
checking the tubes and replacing the questionable ones and verifying proper
DC voltages, the problem persists.
   Basically it comes down to the question of what is being "pulled." It
seems that it has to be either the HF oscillator (6C4) or the BFO. I'm going
to pull the 6C4 and feed a signal in directly from a signal generator and
see if the problem persists - if it does, the BFO is suspect. My gut feel is
that the problem lies in the HF oscillator, although I can't see why AVC
voltage would have an effect there.
   So come on, guys and gals, dig out your VTVMs and sig gens and let's
figure out what's going on here. There are a lot of HQ-1XX owners that could
benefit from a solution to this problem.
73,
Doug Hall, KF4KL