[R-390] R-390A 800 cps tone in cal below 8mh bfo off

[Larry H]

Roy - Thanks for more additional info.  I was able to do some additional testing without pulling the RF deck - perhaps a little mickey-mouse, but I think it gets me there.  I was able to add a bypass cap to the 17 mh osc screen grid pin 6 - no help.  I was not able to do the plate supply, C328.  I was able to add bypass to the cal cathode follower plate and B+ supply - unfortunately no help there either.  After thinking about why the extender had an affect on the tone, I tried adding cap to the cal osc plate cap, 150 pfd C312.  I added 100 pfd to it and the tone was gone.  I am not clear at all how this did it, but will do the trick til I can pull the deck and do more testing.  It does not negatively affect the markers that I can tell.  Might be a while, but I will report back.
Regards, Larry