[R-390] R-390A IF deck caps in T501 or T502

[Larry H]

Hi Dave,  Yes, I changed the caps with the T501 still installed.  It was
easy since my IF xformer does not have the thick coating Jacques was
referring to.  I replaced both caps on the one failing coil because I
wanted to be sure it was a cap problem.  I temporarily installed a 240 pf
without  trimming the leads as a test.  Once determined, I was going on the
assumption the bad cap was the 200 pf mica and installed a new one of
those, and reinstalled the original 39 pf.  As it turned out, I guessed
right.  A person could go the other route and leave the original 39 pf in
and replace the 200 pf as a test.  Good luck.

Regards, Larry

On Sat, Jan 26, 2019 at 10:07 AM Dog T <agfa at hughes.net> wrote:

>
> I was working on this issue last spring/summer. It took me quite a while
> and it was all described in my thread 'Gain Drift'. I used a Boonton
> (really a Moto) millivolt meter to start measuring gains along the IF tubes
> and found that between T502 the input was good, but the output changed.
> Could find no problems with tubes or voltages, although I did not check all
> the voltages, but I did narrow it down to T502. I just got sorta burned out
> at that point and let it go for a while. Then I see Larry's post. So I
> happen to have some 500V dipped SM 200pf Caps (4 of them) and I'll put them
> in T502 and report back when I get motivated.
> It was a bear to troubleshoot because it only happens when leaving the RX
> off for quite a while and then the gain changes within a few minutes of
> turn on. It's very noticeable though.
> Larry, did you change the caps in situ? It would be a real pain to take
> out T502, and maybe that's why you changed both of them. How would one know
> which one was bad?
> Some of my messages to the list are still not going through, I can't
> figure it out.
> Dave N3DT
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