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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
grandetech OP
73 posts
 
Both Rodman9999 and Newbee understand exactly what my problem correctly, yes the image shift to one side 10-15%. Thanks for answering all my question precisely and confirmed. Now I have faith to speak with the seller and he sounds pretty responsible, I will post what the outcome is for future case reference to other members.
reb1208
518 posts
 
The tubes could be matched for triode balance and trans-conductance but not for gain. In this case, one tube appears to have higher gain than the other. Just use the balance trim to center the image and enjoy the tubes. That is why its there. On my Cary SLP-2002, I have to adjust the filament voltage on the circuit board with a meter, fidling with a small blue pot. Be glad the SLP-05 has the convenience of just turning a knob on the faceplate.
rodman99999
6,206 posts
 
"Transconductance" IS how you measure the "gain" of an electronic device(tube, op-amp or transistor). You'll note that it is determined by finding the difference between the voltage at the input and the current at the output of the device in question: (http://en.wikipedia.org/wiki/Transconductance) Tube pairs with matched transconductance are sought out to avoid system imbalances. If the tubes in question were matched as to triode balance and to one another: there should be no imbalance from channel to channel as a result of installing them. That's providing there is no imbalance elsewhere in the system that the installation of properly matched tubes happened to reveal.
grandetech OP
73 posts
 
Thanks for rodman99999 info, I further confirm one of the pair has problem because that one started producing noise after couple of days trial.
rodman99999
6,206 posts
 
The tube becoming noisy that quickly also confirms Mr N's response regarding it's being about to expire.
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