[R-390] Local & Line potentiometers

[Craig Heaton]

Good Morning Drew,

The three section plug-in electrolytic cap is located in the AF module. The
Motorola AF module works fine, audio normal, in the Motorola. When it is
placed in the Amelco, the volume is still loud. Taking the IF section from
the Motorola and placing it in the Amelco, the volume is still loud. 

Volume is still loud with MGC mode, but with distortion if the RF gain is
set too high. 

Today, for grins & giggles resistance will be added to the Line & Local
inputs. It will be interesting to see what it takes to calm the beast.

Regards,
Craig
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-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Drew P.
Sent: Wednesday, January 01, 2014 8:29 AM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Local & Line potentiometers

Craig wrote:

"A little time was spent on the beast this evening.
1: No ground problems at the end of the pots, even added a jumper once
again. No change
2: Checking the audio at the CCW ends, less than 5 millivolts with the
O'scope.

Going to check a few more items tomorrow; swap IF's between the Motorola and
Amelco again. This should rule out AGC issues there. Then on to the RF
section."

I'm not convinced that it could be an AGC problem.  In the couple of
R-390A's I've operated, the audio gain pots work normally even in MGC mode
(which disables AGC), and with RF gain all the way up and the receiver
overloading on a strong signal.

My vote goes for one section of the three section plug-in electrolytic cap
being open with resultant loss of decoupling.

Drew
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