[R-390] R-390A Audio hiss

[Bill Smith]

Hi, Joe

Hope I didn't sound curt, wasn't my intention.  From your description, your
noise might have been originating in the audio module (after the volume
control).  In that case, my first thought was a gassy or shorted tube.  But
from your description below, your noise appears to be originating from
stages in front of the volume control, and that does change things a bit.

First of all, I'd step back, and analyze the reciever.  You should read the
archives and web pages regarding rebuilding R-390A's.  I am not suggesting
you are in for a major project, but you should find out if (1) your set has
capacitors that may need replacement (2) identifiy if someone fiddled with
the set before you obtained it (3) if it has been modified (hope not!).

Then, I would make a general sensitivity test.  This can be done without any
test equipment.  It consists of observing strength of the crystal calibrator
on the carrier level meter for each band.  The procedure is in the manual.

As John Page suggested, check the IF gain control.  If the IF gain is turned
up too high, it will generate all sorts of subtile, undesireable effects.
The receiver was designed with quite a bit of excess gain reserve.

Hope that gets you started!  These sets are well built, very reliable and
easy to tame, but they do fall in to the "high maintenance" equipment of the
'50's and '60's.  After all they are now at least 36 years old!  :-)

73 de Bill, AB6MT
billsmith@ispwest.com


----- Original Message -----
From: Jhowings@aol.com
To: billsmith@ispwest.com
Sent: Saturday, August 30, 2003 12:37 PM
Subject: Re: [R-390] R-390A Audio hiss


You might be right, sounds like it's an amp running
with excessive gain, but this level doesn't change
other than proportionately as volume is increased.  I
was kinda cheating, looking for an answer w/o a lot
of trouble shooting,  I always ask so I don't re-invent a horse.   Thanks,
Joe