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In Reply to: Gain adjustment for MP1 posted by MVA on September 13, 2008 at 13:49:27:
I think you are referring to the two small-diameter trim pots that flank the larger central volume control. The answer is no, those controls do not act on the grid bias or plate voltage per se. They set balance between the two halves of the dual-differential amplifier that constitutes the input amplifier stage of the linestage. The bias on the two grids of the dual-diff amp is determined by the fixed plate voltage and the current that flows thru each half of the circuit. The current is controlled by the constant current source that is attached to the cathode(s). So, if you want to change tubes from the 6SN7 to either of the others you mention, you would have to change the value of the resistor that connects the CCS to the B minus supply, and you may also have to change the two plate resistors along with. Since the 6SN7 is already one of the best sounding of all IDHTs, I don't think it's worth the effort, but that's only my $.02.
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- RE: Gain adjustment for MP1 - Lew 14:21:50 09/14/08 (0)
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