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In Reply to: 6SL7 tube CCS in V3 socket posted by Paul Speltz on April 16, 2002 at 10:34:23:
How much current is now passing thru your 6SL7 CCS? If you are still running your "doubled current" mode, with 50K plate resistors, I am guessing about 4mA. Does the 6SL7 bias properly with that much current? Also, in the M60, are you using the 6SL7 in triode mode as a CCS or in cascode configuration? There's probably not enough voltage available to make the 6SL7 work as a CCS in cascode mode, I guess. I noticed reading the Valley and Wollman book, where they show nicely how a CCS linearizes the output of a cathode-follower, that they compare a pentode (I think) CCS to a 1Meg resistor(!) The output is noticeably more linear with the CCS, even when compared to such a high cathode resistance. They don't specify the impedance of the CCS, but it must have been very much higher than 1 Megohm. Unfortunately, it's hard to do a lot better than 1 Megohm impedance with a triode CCS alone. A triode in cascode mode is akin to a pentode, however. It just needs a lot of voltage to operate well. I wonder whether a pentode would work well with less voltage and sound even better than a 6SL7 CCS in an M60, is what I am getting at. I know this is a heresy. I expect to receive a dead fish wrapped in a newspaper any day now.
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Follow Ups
- Re: 6SL7 tube CCS in V3 socket - Lew 13:36:19 04/16/02 (2)
- Re: 6SL7 tube CCS in V3 socket - Paul Speltz 15:03:56 04/17/02 (1)
- Re: 6SL7 tube CCS in V3 socket - Lew 07:21:21 04/18/02 (0)
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