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Re: Hey, Mark..

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Posted by Al Sekela on November 20, 2003 at 18:59:57

In Reply to: Hey, Mark.. posted by Lew on November 20, 2003 at 11:49:37:

Lew,

You seem to be thinking about the MP-1 circuit. The power amps have a dual triode driver tube with cathodes connected to the output stage grids, and the DC offset and bias (quiescent grid voltages) are set in the cathode legs feeding this tube. I'm not familiar with the Mark 1 circuit, but I believe the driver is the 12AU7. Excessive mismatch of the two triodes in the driver tube would make it impossible to achieve zero offset. The tube may be called "good" under loose tolerances on section matching, but still cause the observed amplifier problem.

-Al

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