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In Reply to: better detailed driver tubes for M-60 posted by chosenhandle on September 6, 2005 at 10:53:33:
Yes, it's been discussed before.Changing the "driver tube" (the cathode-follower that drives the output tubes) is not likely to have a very important effect on retrieval of detail, as the driver tube supplies no gain to the circuit. That said, I have been very happy with 12SX7s as driver tubes vs other 6SN7s. You have to re-wire the circuit to obtain 12V filament voltage, but it can be done.
There is more qualitative effect to be gained by changing the input voltage amplifier tubes. The topology is a dual-differential cascode, and that's why two tubes are necessary. Unfortunately, the HV supply (and the existing octal socket) limits your possibilities for changing to another tube type vs the 6SN7, so you are pretty much limited to tube rolling (see others' suggestions; it's a matter of taste and serendipity what sounds best). One tweak that works to give better sound is to double the current through the input circuit, which can be achieved by halving the value of the cathode resistor on the CCS that subserves the input stage. The tubes run a little harder, but the amp is very conservatively designed to begin with, so no problems are likely. IMO, the amp sounds better in every way with a tad more current thru the input stage.
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- Re: better detailed driver tubes for M-60 - Lew 13:10:57 09/21/05 (0)
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