Amps will not hold bias.


I have a pair of Cary Audio 300B monos that will not hold bias, it is not the tubes as I have several to choose from and the amp's have the issue regardless of the tubes installed. I am sure that you guys probably know what the problem is so I thought I would ask before sending them to Cary.
clshaw57
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Thanks Jim
And this is why I am so confused. It would seem that the tubes are clearly the issue but 3 pairs of 300B tubes? And of course I did not want to buy another pair in the hopes all would be well.  I was hoping that there was an obvious technical issue that would explain the problem. But? They did bias and hold steady prior to displaying this problem. This issue has occured in 2 seperate homes, I just moved. Plugged directly into wall or conditioner, with 3 different set of 300B tubes and of course every other OCD audiofool thing I can think of. And the bias problem is strange as it is actually difficult to get it to set to target 83mva but can get close then will drift drastically up or down depending on which way the bias was being adjusted.
Make sure you have speaker wires hooked up.

Make sure no signal is going in. Like, no music if pre amp is on.
You mentioned, "83 mA", but- not how much drift and/or over what period on time. "Drastically" can be quite the subjective term.