[R-390] Wandering IF gain

[quartz55]

Been messing around with this thing for about 3 days now.  Problem seems to be between the plate of V501 and V502 plate circuit, but can't pinpoint it.  Only thing I can think of doing now is replacing all the 5000 pf caps in that area.  All the voltages seem stable and the resistors check out well in spec.  It did help a bit to resolder the area around the input of the filters, and I replaced the fixed cap for the 4K filter, it was a bit too much, reduced it to 75 pf and now its right in there with the tuning.  After about an hour it does settle down and work 'normally' as far as I can tell.  Just for info, I seem to get about 20uV input for -7V out at diode load max gain and about 350uV input at min gain.  Around 150uV mid range on R519 which seems to agree with book.

Only ceramic disk ones I find reasonable are from Mouser, $.44 for .005 3KV.  The 1KV one is about $1.50.  Might as well get enough for the whole thing.  I'd never get the ODs in there.