[R-390] Problem solved - Raspy BFO

[Bill Cotter]

Well, my wild guesses of C535 and C530 were just that - wild guesses.

I had a thought about the 12BA6/12BA6 series combo in the BFO and 
PTO, thinking the string may have an issue. I had tested/swapped 
the BFO tube to no avail, but not the PTO tube. Sure enough the 
12BA6 in the PTO had a F/K/G short, according to the Hickok-6000A. 
I swapped out the shorted RCA and dropped in a Dumont 12BA6, and 
the raspyness went away.

Lessons learned:

1) I had jumped to the wrong conclusion about the BFO because I 
could not hear the 120Hz modulation on the PTO in AM mode. I 
suppose the PTO modulation was below the audio output response 
range. When beating the incoming signal against the BFO, the raspy 
tone was apparent.

2) For a problem that just suddenly crops up, check tubes. If you 
don't find a bad one, check more tubes until you checked them all!

Thanks es 73 Bill N4LG




Greetings everyone,

I have a BFO problem with my EAC R-390A (completely recapped & 
restored) that has eluded me after doing all the usual easy stuff 
(test/swap tubes, measure voltages, etc). While listening to an AM 
station, strong or weak, or turning on the calibrator, and I flip 
on the BFO, the note is raspy and harsh. Otherwise the receiver 
works great. I have checked for fil/cath shorts in the tubes, dirty 
DC, AVC, etc and have not found the culprit.

It's time to bring out the Tek-475 and snoop around. My first 
suspicion is a leaky 12pf C535 or 100pf C530.

Any thoughts/suggestions/experiences? It's time for me to step up 
to "level-2" troubleshooting.

73 Bill N4LG