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D&A 12 TUBER PROBLEM

That is a bias adjustment. Unless it is bad (arcing internally) it should not cause the problem you are having or at least I would think. Tune it for max output on high power and then back it down 10% or so. I really don't think that tuning is the problem that you have. Something else is going on...........not sure what. It is hard sometimes to understand what is going on without being there in person to see it first hand.

BC
 
Sounds like more than 1 tube is weak or bad in the final section. Need to replace all your caps too, if not already been done.

My .02
SR
 
Without the equipment to do it with, and with out knowing how to do it, your best bet is to take the thing to someone who has that equipment and does know what they are doing. You just can't 'freehand' it, it don't work that way. Who ever sold/gave that thing to you was not doing you any favors.
- 'Doc
 
I'm wondering if maybe one of the tubes has a "saggin" grid causing this? I know it mostly happens on tubes mounted horizontal but could explain this noise. Just enough slack in it to produce a small arc while transmitting. When testing tubes and doing a short test I always thump the tube to make sure something like this is not there.
I agree that an amplifier with HV in it (or any other one) is not for someone to work on that does not have the ability or experience in them. They can leave a lasting and permanent impact on you. It is best to carry it to someone that is qualified.
It hurts less this way too..............the pocketbook is better than the body in my mind.

BC
 

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