[Amps] LF oscillation caused by defective plate choke?

[N1BUG]

I would like to thank Peter, Jim, Carl, and others in addition to 
Manfred for input on my amplifier issues. I now have a plan to 
improve the by-passing.

I wish it were reasonably possible to add the second choke and 
by-pass in the plate circuit. Unfortunately with the somewhat 
crowded layout of this amp there is no place to put it without a lot 
of metal work and another ugly kludge. Hopefully, since things seem 
stable for the moment with the new plate choke, improved by-passing 
will help ensure it stays that way.

Thanks again, everyone.

73,
Paul N1BUG