How many of you have had an easy time biasing the power tubes of your push pull amps? In my limited experience, they always use one turn pots with a hair trigger sensitivity, and the screw in the pot must be filled with tar because it is hard to turn and sticks. There is never an easy and definite approach and land exactly on the setting, it is always turn back a lot, then turn it forward again, let it snap from the sticking, and see where it lands, repeat. Granted, we are adjusting a $5 part to .001VDC, but it could be better. It seems to me a 10 turn pot would deliver same range of adjustment, but with more sensitivity.
Then god forbid you check it again a week later or at a diferent time of day. Ideally the tubes will have moved bias readings together and both will show same error so you could leave it alone. But I hate it when they change in relation to each other for no apparent reason, other than the obvious - welcome to tubes sucker.
I guess this is most prevalent during tube break in, they will change a lot, then finally settle down and remain kinda stable. New Sensor tubes hold tight bias, IME.
I have read that PP zero crossing distortion will increase when the PP pair is not equally biased. Can anyone confirm that's true?
On some amps, the bias is critical, it's easy to hear when they are a slight bit off. With others it doesn't seem to be noticable. What's been your experiences with biasing tube amps?