[R-390] Noise when warm ('390A)

[Jim Miller]

Here is what happened to me Stewart Warner 390a few years ago.  I would get 
snap/crackle after warming up just like you said.  And it tended to go away 
when no signals were present (such as antenna disconnected, hence no AGC). 
I discovered that as the AGC voltage increased when a signal was present, 
the noise would start up.  No AGC voltage (no signals) and the noise went 
away.  I tried everything, it drove me crazy.  Then someone on the list 
(forgot who) said this could be caused by a breakdown of the center 
dielectric in the miniature coax cables that carry the diode load voltage 
from the IF strip to the AF deck and some of the front panel controls.  Even 
with the low voltages there (7-10 volts) the little coax cables would start 
to break down causing the popping.  Sure enough, I replaced the mini-ax 
cable from IF deck to the terminals on the back, to the front panel, etc. 
and cured it.  You can verify this by temporarily running a good cable from 
the IF deck to the AF deck or an external audio amp, isolating all other 
cable runs.  Replacing the cables can be a pain if you are a purist and want 
to pull the old cable from the wiring harnesses, or you can just run the new 
cables along side the harness.

Jim N4BE

----- Original Message ----- 
From: "Dennis Wade" <sacramento.cyclist at gmail.com>
To: <r-390 at mailman.qth.net>
Sent: Sunday, September 11, 2005 11:50 PM
Subject: Re: [R-390] Noise when warm ('390A)


Update.

First thing I did was start unplugging modules to try and see when it went 
away.

Guess what.

It goes away when the antenna is unplugged  (sigh).  Sorry guys.
Should have checked that first, although it still doesn't sound like
its from the antenna.

Is there any failure mode anyone can think of that would only be
apparent when the antenna is connected?  Haven't changed the antenna
configuration here by the way.  Its a 120' dipole fed with open wire
line to a balun.  Coax to the balanced antenna jack fed according to
Rippel's instructions.

      Thanks for all the suggestions from all.

               Dennis

On 9/11/05, llgpt at aol.com <llgpt at aol.com> wrote:
> The voltage regulator tube OA2 has been known to have those symptoms.
>
> Les Locklear
> Gulfport, MS.
>
> -----Original Message-----
> From: Dennis Wade <sacramento.cyclist at gmail.com>
> To: R-390 HF Receiver List <r-390 at mailman.qth.net>
> Sent: Sun, 11 Sep 2005 15:07:08 -0700
> Subject: [R-390] Noise when warm ('390A)
>
> Hi everyone,
>
>       I've noticed lately that after a few hours of operation, a
> "frying bacon" or "snap-crackle-pop" noise begins to occur, slowly
> increasing as time goes on.  No real difference in band or mode.
>
>       Any quick troubleshooting hints to isolate to a stage?
>
>       What is the consensus...more likely a cap or a tube?
>
>             Thanks for the advice,
>
>            Dennis
> --
> Dennis L. Wade
> KG6ZI
> Carmichael, CA
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-- 
Dennis L. Wade
KG6ZI
Carmichael, CA
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