[R-390] SSB mod

[Cecil Acuff]

Have you set the IF gain as per spec on AM?

Cecil...
----- Original Message ----- 
From: "Bill Wilson" <we509w at yahoo.com>
To: <R-390 at mailman.qth.net>
Sent: Thursday, March 17, 2011 9:21 AM
Subject: [R-390] SSB mod


> Greetings to the list,
>
>  Currently I'm restoring a Collins R-390A that a friend of mine salvaged 
> from
> the landfill.  The AGC circuit has the SSB mod that works great for SSB 
> with no
> distortion or complaints.  The issue I am having is that on regular AM 
> listening
> the volume is very low and sometimes the audio on some stations is only 
> heard by
> turning up the local gain fully clockwise.  This particular mod was done 
> by
> removing R545 (100K) and removing R546 (180K).  Instead of R546 a diode 
> was
> installed going to pins 1 & 2 of V509A (AGC rectifier).  R547 (220K) was 
> reduced
> to 10K.  Spot checking some resistances indicated a 1 meg+ resistance on 
> pin 2
> of V504 which should be about 280K with the AGC in the "on" position.
>
>
>  Any hints on getting the AM audio (AGC on) back up a few notches short of
> scrapping the entire SSB mod would be welcome.
>
> Thanks in advance,
>
> Bill
>
>
>
>
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