[R-390] R-390A A Silver Mica cap bit me again, 2nd crystal osc.

[Larry H]

Well, I was happily listening to a station on the AM low band and it
started getting weak.  I thought it might have been band fade, but that was
not it.  Then it got a little stronger and then it went low again. This
fluctuation alerted me to a possible SM migration problem - well we will
see.

First, I checked the alignment of the RF section.  No luck there.  Then I
measured the 2nd crystal osc output for that band and it was low at -3.7
vdc.  Bands 1 through 6 were -6 to -7 vdc.   I then tried a different tube
and reseating the coax connector,  No luck there, either.  So, that leaves
you know what - the trimmer, the switch and the small pf tuning cap
across it.  It wasn't the switch, so time to face reality and remove the
osc deck.  I cleaned the trimmer, but that was not it.  Luckily I had
the right value new SM cap in the parts box, so replaced it, and that was
it.  Band 0 voltage now -6.5 vdc.  I monitored it for a while and it held
steady.  Before replacing the osc deck, I monitored it for a few more
hours.  It held, so installed it back into the rx and all is well.  One day
passed and still good.

Another bad SM cap subdued.

FYI - This osc deck is a 1959 contract Stewart Warner.

Regards, Larry