[R-390] Gain drift
dog
agfa at hughes.net
Sat Oct 20 09:10:26 EDT 2018
OK, this morning, checked the grid of V504. After a few minutes RF is
dropping along with TB102-3 -DCV so I'm going to let it cool off. Since
the plate of V504 didn't show any dropping, it looks like it could be in
T502. I don't really see any other stuff in that path. I don't think I
replaced C523 and I have a bunch of 4700pf I got for those. I doubt it's
that or R551 since that plate circuit is good. Could be something inside
the T502. Sure acts like a tube though as quick as it happens and fast
as it drops. But it does eventually come back to 'normal' after a while.
It's a bugger. I should try another V504 tube just for drill, but I've
tried all the tubes before. It could be in that cathode follower V509B,
I could just pull it and see what happens to the RF through V504. I'd
loose the AGC voltage but so what.
I'm writing this to help me understand what I'm doing. Otherwise I loose
track.
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