36 watt, EL34 master volume question...

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hughesp
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36 watt, EL34 master volume question...

Post by hughesp »

I've been looking at the Phat Ass rev. 3 schematic and got thinking...

The master volume (1Meg) + the 270k grid resistors would create approximately 212.6k grid leak resistance.

Would there be any harm in doing a dual 1 meg pot with 1 meg gird leaks (giving 500k grid leaks)? I know el34 tubes are spec'd at maximum grid leak resistance of 700k in cathode bias, so it wouldn't be exceeding that, even after including grid stops....

Or, and this may be flawed logic... thinking that since, in the regular 18 watt, we use 470k grid leaks (and el84 grid leak max in cathode bias is 1Meg), we should be shooting perhaps for something around half of the max Rg1 value - so around 350k for el34s... 538k would be the value, but that isn't a standard resistor value... maybe 520k resistors along side the 1meg master?

I haven't done any experimenting, but I'm curious as to what might give the most 18watt like response...
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Post by sub »

I think it won't harm anything, but in my opinion 500K grid leaks is too much for EL34... I have tried it....(1meg dual pot + 1meg resistors) Sound was different than with EL84.
About 220K sound good IMHO.
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Post by hughesp »

Right on - that makes sense. I was just running stuff over in my mind and was curious what sort of rational might be there for that...
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