[Collins] 75A-4 Loud Audio Resolution

Tue, 14 Jan 2003 21:35:16 -0800

Roger,
Thank you for taking the time to share the final results of your efforts
to cure the audio problem.  This will go into many archives and will
most certainly help one or more of us solve this or a similar problem in
the future. 
Chris

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Roger Shultz
Sent: Tuesday, January 14, 2003 6:16 PM
To: Collins QTH; Collins CCA
Subject: [Collins] 75A-4 Loud Audio Resolution

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

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