[Hallicrafters] S-19R AVC problem

[Wayne Light]

Well folks...I'm stumped.
 
I have the version of the S-19R that uses the 6SK7 and the 6SQ7.  It works fine until I turn on the AVC switch. I then get a loud hum and some loud whistles when that switch is turned on... when turned off, every thing is back to normal.  I've replaced about every part in the AVC circuit and exchanged a couple of known to be good tubes.
 
Any ideas?
 
Wayne


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