[R-390] BFO Drift?

[ANTHONY CASORSO]

I have been listening to lots of CW lately and it seems that there is quite a bit of drifting going on in my 67 EAC R-390a. Even after its been on for more than an hour I can hear the signal slide up in pitch over a several minute period. I am pretty sure (but not absolutely sure) that it is the BFO. In my set I have replaced the 3TF7 with a 12BY7. I was listening to beacons using a waterfall display (Argo) and I could see the carriers slowly angle off over a long period and then, within a minute, come back down. The excursions are over 100Hz. The oven switch is off. Has anybody seen this sort of thing before? I have a counter, so I suppose I should put it on the PTO and confirm that it is OK. Just haven't gotten to the point of opening it up.
 
Thanks,
 
Tony
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