[R-390] bfo problems

[Jim Brannigan]

I had a similar problem with a 75S-3B.  It drove me crazy trying to find
it......

It turned out to be a bad tube in the PTO.........

Jim
> My r-390a has a slight hum when the bfo is on. Cw and ssb signals have a
> slight "vibrato" sound. Cw notes are not clean and crisp with any setting
of
> the mgc level. I suspected one of the filter caps, but they are ok. The
> decoupling cap on the bfo 150v b+ is ok , there is no cathode to filiment
> short. I turned off the bfo switch, and injected a 455 khz carrier from my
> urm-26d signal generator to pin 5 (plate)of the tube socket. I still had
the
> hum with the signal generator acting as the bfo. The radio sounds fine
> listening to a m broadcast. Any ideas ???  Thanks
> .......Steve.....KJ8L