[cwc]

Hi Charlie,
I'd keep an eye on the voltage on the second grid of he 6A8 (osc plate) to make sure it's not changing much. A volt or is fine 20 or 30 not so good.
Also if you have a 110mmf mica (6) I'd swap it with the one that is in there.
I see there are a few ground connections if they are done with rivets they are suspect.

Merry Christmas!
Terry

Thanks.  I'll look at those things.  

Unless I'm missing something (always a possibility) maybe I can just monitor the B+ supply and look for a change there since there is just 3.5 ohms between the supply and the 2nd grid??