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In Reply to: RE: Magnavox Rebuilds and Fultons (longish) posted by Eli Duttman on April 5, 2014 at 16:04:39:
Eli,
As I understand it, the shared bias resistor PP pair requires reasonable tube matching, at least for idle current, so there should not be a big difference to begin with. Perhaps you mean that it helps average over differences in transconductance?
I think a lot of the benefit of sharing the bias resistor and cathode bypass cap between tubes is that you don't really hear the cap most of the time, as long as the class AB channel is running effectively as in class A, since then the current through the resistor is essentially constant (DC) and the cap is not doing much. It only charges and discharges on peaks, where the current has a large audio frequency component. With four separate caps, you would hear them more. OTOH there is little argument for using only a single cap and resistor for both channels, except as an extreme economy measure.
regards,
JJ
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