[R-390] More On Low Audio Problem

[Cecil Acuff]

Fred,

    I have been studying the schematic since we swapped some emails and went 
back and read your original post this morning to see what I had missed.

Here is what I see....

If you can trace a signal from pin 1 through the switch, which would be out 
pin 3 to pin 9 then out pin 7 which goes to pin 7 on V601B then through R608 
at a lower level (about half I would expect) then back to pin 4 which is 
connected to pin 6 within the switch and out to both the Line gain and Local 
gain pots.  It should work.  The only thing in that signal path the switch 
and R608.  You might check R608 and make sure it's not broken or way out of 
spec.  By jumpering pin 1 to 6 you are bypassing the switch and R608.

Just some additional thoughts...

I have to leave to go to a church function but will be back in a few hours 
and I'll check on the groups input and your progress!

Cecil....
----- Original Message ----- 
From: "Frederick Bray" <fwbray at mminternet.com>
To: <r-390 at mailman.qth.net>
Sent: Saturday, December 17, 2005 11:40 AM
Subject: [R-390] More On Low Audio Problem


> First, let me thank everyone who has replied -- both on and off list.
>
> I think I have narrowed the problem down to the first AF amp/cathode 
> follower.  I would appreciate it if those who are more experienced that I 
> with the 390A can confirm that I am on the right track.
>
> I used an audio signal generator to ascertain that a signal injected at 
> the local and line level controls seems to produce a normal audio output.
>
> Using a VTVM, I confirmed that on there is an AC voltage on terminal 1 of 
> the wide/sharp switch and that I can trace this voltage through the 
> switch.  Jumpering this voltage to terminal 6 on the switch seems to 
> restore the audio level to approximately normal, or at least much closer 
> to normal.
>
> From looking at the schematic, I think that what I am doing is bypassing 
> the first AF/cathode follower and going directly to the local and line AF 
> amps.
>
> Does this make sense?
>
> Thanks,
>
> Fred Bray
> KE6CD
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