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In Reply to: Re: Question for Ralph on MP1 posted by Legendre on August 14, 2005 at 16:32:37:
The problem is current; all high Gm tubes need a lot of current. (Want high Gm, because in a cascode, gain = Gm*RL, where Gm is the transconductance of the bottom tube section, as you know but maybe others don't.) I came to the conclusion that the Atma-sphere solution in the context of the MP1, to use a pair of 12AT7s in parallel to form the "bottom" part of the dual-differential cascode is a pretty good one, because 12AT7s will give pretty good Gm without needing such large amounts of current. To do better than that, one would probably need a separate supply. (You tell me; I doubt that the tranny in the MP1 can produce the current needed at 250 to 300V, but maybe I am wrong.) So, the tubes I had in mind for the bottom of the dual-diff amp might include the 5842 or the ECC99 or 5687, if there were more current available. There are other more esoteric ones too.
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Follow Ups
- Re: Question for Ralph on MP1 - Lew 06:39:20 08/15/05 (5)
- Re: cascode current - Ralph 13:37:30 08/15/05 (4)
- Re: cascode current - Lew 07:14:18 08/16/05 (0)
- Re: cascode current - Lew 15:10:39 08/15/05 (2)
- Re: cascode current - Tom Dawson 15:31:50 08/18/05 (1)
- Re: cascode current - Lew 06:54:46 08/19/05 (0)
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