[Collins] 75A-4 Loud Audio Resolution

[Roger Shultz]

A couple of weeks ago I asked the question of the group and received many
excellent suggestions.

This is what I learned and what resolved the problem.

The problem about why I still had audio bleed through at minimum audio gain
is clearly a result of 50 ohms residual resistance on the pot. Several pots
I tested had residual resistance but this one had the most. Finding a proper
audio taper pot with lower than 50 ohms or zero resistance at the stop will
solve that problem which I verified by simply grounding the center arm of
the pot.

The problem of too much audio was because the AVC circuit was completely out
of alignment. When I re-tuned both top and bottom slugs on T-4, not only did
the receiver virtually "come alive", the audio level became regulated or
controlled. I was apparently operating with AVC nearly "off"! Now I have
nominal listening volume at a "2" on the audio level control which seems to
be normal from others experience as well. I think that also contributing to
the mix was that I have almost all new capacitors and the radio is well
peaked at this time exceeding factory spec's. I have a 10 db S/N on 10
meters of below a -124 dbm as mesured on my HP 8640B. It sure does hear well
now!

Thanks again to all who helped with their suggestions.

73, Roger NJ2R