[R-390] Cosmos Drift

[ToddRoberts2001 at aol.com]

I have seen some R-390A PTOs with long term drift that were cured by plugging 
in a new 6BA6 tube. A weak 6BA6 could be the cause, might be worth a try 
replacing it.  After 3 days does it continue to drift or does it ever settle down? 
I would think after 3 days all the components would heat soak to an even 
temperature. Could be a bad cap or other component somewhere. Not sure if it is 
possible to replace the negative temp coefficient caps in there. Maybe at some 
point it is just not worth it to spend more time on that PTO and find a nice 
Collins or Motorola PTO with the good old corrector stack. 73 Todd WD4NGG