[R-390] R-390 NON A Problem

[David Faria]

GE List.  I'm playing with one of the nicest 390's I've seen in a long time
and its got a rather irritating problem.  It has what I would call a static
crash ever so often and I was curious if anyone else has had this problem.
I think its a leaky cap. on the RF Deck.  I have by-passed the tube stages
one at a time on the deck using a tube extender with a filament resistor to
to maintain the remaining tubes on the deck.  The filaments r in series.  I
seem to have narrowed it down to the last mixer in the series(V205) using a
scope and bypassing.  I am seeing fluxuations in both the grid and plate
voltage when the crash occurs(Pins 1 and 6).  My guess is c-325 off the
plate circuit of that tube.  Any speculation would be appreciated.  Is it
typically the plate cap. leaking to ground that would do this?  Would a
capacitor checker be able to determine if this cap is bad?  What is the
reason the cap will just not fail?

I've checked all the tubes on a TV2 and thumped em trying to create the
problem.  I have replaced all the modules except the RF deck and the problem
is still there.  Sometimes it will run for 30 minutes without a problem and
then start.  This is a very nice unit and I don't want to recap. unless its
necessary.

Thanks for ur responses
Dave Faria