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In Reply to: Re: cascade driver stage posted by Lew on December 10, 2001 at 07:15:33:
While not really pratical for the average DIYer, you might want to consider
the ingenious biasing approach used by Henry Wolcott in his novel Presence amplifier. Henry uses one CF with a high negative bias on its grid to drive multiple 4.7K resistors, one to each output tube grid. Then a micro-controlled biasing circuit selectively pulls current in a positive going direction at the tube grid point to decrese the initially high negative bias to a value that sets the plate current of each tube to the
desired value. His approach requires only one normally-sized coupling cap per phase but allows for individual adjustment of each output tube. In the Presence, the micro sets the bias automatically at turn on, after which it shuts down and has no further effect on the bias unless the bias button is pressed. Pretty nifty!
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Follow Ups
- Re: cascade driver stage - Kevin 14:17:34 12/10/01 (2)
- bias scheme - Lew 10:33:53 12/11/01 (1)
- Re: bias scheme - Kevin 14:38:26 12/11/01 (0)
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