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Question on NOS tubes bias doubt

I just put a New pair of NOS KEN RAD VT-231 in my CARY SLP-05 pre buffer stage, one for left and one for right, it sounds bias to the left for around say 10-15%, so I turn it off and swap them to confirm if it is not my room acoustic nature, as expected, it now bias to right for same amount. My question is, is it so called BIAS and that is why most tube gear has bias adjustment function? And should this be happening when seller says it is a matched pair NOS? I can compensate it with the balance feature on Cary SLP-05, but I doubt this pair is not matched. The testing figure in fact being declared slightly different while most of them are.
grandetech

Showing 1 response by newbee

newbee
4,751 posts
 
If you are saying that the center image of your stereo systems drifts substantially with these two tubes that they must not be matched, despite what you have been told, I agree.

In fact I would suggest that not only were they not matched, but that the weak tube is close to dying. IME, other than an onset of noise or dullness, drifting is the hallmark of a tube which is about to die. IME, perhaps there are other reasons of which I'm not aware. I do not use this tube type.
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