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Answer from the peanut gallery

Lew,

G2 needs a low impedance supply, as well as a fixed voltage supply. That's especially true for Class AB1 PP pentodes, because G2 current demand can vary greatly from quiet to loud music passages - as much as 500%. That's why either very low DCR supplies or series regulation supplies have often been used for G2 (shunt regulation is not really practical with such great variation of current demand).

I personally favor a MOSFET source follower regulator with a voltage reference on the gate. This approach is "modern", using modern technology, is very simple, provides adequate regulation for the purpose, doesn't use NFB and isn't noisy. The voltage reference can be a high voltage zener, a string of gas tubes or, best of all IMHO, a CCS driving a resistor. (If using a zener, it's best to "suppress" it with a high value cap. to deal with the noise, although the tendency for such zeners to drift is a potential problem too.)



Edits: 08/11/12 08/11/12

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