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Old 23rd February 2011, 09:35 PM   #1
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Join Date: Apr 2007
Default does tube bias drift like silicon devices

Considering using 10 output tubes per channel in an amp build I was wondering if the bias drifts in a tube like it does in a solid state device.
With a bias pot per pair of output tubes the adjustment should be pretty close to where you want it for each two tubes in the output if things do not drift too terribly bad. I know that solid state transistors sometimes need to achieve temperature equilibrium to get an accurate bias setting. Do the tubes act the same way or can you expect the bias to stay put.
I really do not wish to install a servo bias adjustment circuit. However, if needed then so be it.


Last edited by tryonziess; 23rd February 2011 at 09:35 PM. Reason: spelling
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Old 23rd February 2011, 09:49 PM   #2
jcx is offline jcx  United States
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tubes don't just do the long warm up offset/operating point drift with temperature - they also "age"/wearout

where Si devices mostly do the same thing for decades once packaging/constrution stresses stabilize after a number of thermal cycles

depending on power level, derating, tubes may need rebiasing several times a year and eventually can't be made to work at all

Last edited by jcx; 23rd February 2011 at 09:52 PM.
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