[R-390] r-390a chirping CW

[Jim Brannigan]

I had a problem with a 75S-3B that drove me crazy.
On CW and SSB there was distortion on the signals, AM was OK.  It almost
sounded like VHF aurora distortion.  I checked everything.....a scope on all
the oscillators..the whole works....I tore apart the product detector
circuits and no luck.....I put a CV-591 in the IF chain and it was still
there!!!!
Finally I changed all the tubes, AGAIN.....and it was gone....
Backtracking through the tube substitutions I discovered that the PTO was
FM'ing.  This did not show up on the scope because I was using a signal
generator, and not an SSB or CW signal.
In the end, I replaced all the components in the PTO, except the coil.

So far so good....

Jim

> Hello,
>  I have a capehart r-390 a sn 557 that is working quite well except for a
> couple of problems. All bands and all filters work. There are a couple of
> problems though and I'm asking the learned group on this list for any
quick
> information or ideas.
>  Problem #1:
>   Good clean CW signals chirp when heard on the 390a. It sounds like the
BFO
> changes frequency with AGC levels. Checking the voltage at the audio
module
> and it's a steady 150.1 volts. Haven't checked farther into it.
>