In Reply to: Question from the peanut gallery posted by Lew on August 9, 2012 at 14:31:18:
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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Follow Ups
- Answer from the peanut gallery - Ray Moth 17:09:23 08/11/12 (10)
- G2 , wide current changes ..... - drlowmu 09:18:18 08/15/12 (0)
- RE: Answer from the peanut gallery - tube wrangler 16:18:43 08/12/12 (5)
- RE: Answer from the peanut gallery - Ray Moth 17:02:33 08/12/12 (4)
- RE: Answer from the peanut gallery - drlowmu 11:14:05 08/14/12 (3)
- It was a goodpost. - gusser 11:35:47 08/14/12 (2)
- Partially good post. - drlowmu 14:17:19 08/14/12 (1)
- RE: Partially good post. - Ray Moth 03:52:31 08/22/12 (0)
- "CCS driving a resistor"... - Lew 13:41:21 08/12/12 (2)
- RE: "CCS driving a resistor"... - Ray Moth 16:49:01 08/12/12 (1)
- A belated thanks... - Lew 10:51:28 08/14/12 (0)