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In Reply to: Re: What PP amp to build? posted by sorenj07 on April 3, 2007 at 18:26:57:
I like the Williamson too, but being a cathode biased triode
design, it should need closer to a 10K OPT, right? Triode connection
is quite forgiving as compared to pentode or ultralinear mode, but
going from 10k to 5k would seem like a distortion introducing stretch,
UNLESS he paralelled a pair of EL34 tubes --then he'd be spot-on
with about 24-26 watts of tride output power, COOL! His stated OPT
should easilly handle the current, and the williamson driver should
drive the additional input capacitance of a second pair of EL34's
no prob. I would, however delete the feedback line, and bypass the
first stage cathode resistors with about 16V 470uF caps too. For that
matter, once the feedback loop is cut, the first 6SN7 stage becomes
superfluous (loop gain now higher) and I'd delete it and just use
the uneeded half of the 6SN7 as the other channels input stage --
still bypassing the second (now 1st stage after mod) stage's
cathode resistor with the 470uf cap. Should have plenty of gain to
be driven to full output with normal input levels. REMEMBER to
triode connect the EL34s.This is definitley a strong possibility.
Follow Ups:
I forgot the second stage of williamson was the split-load inverter!
What was I thinking???Anyhow, keep the driver circuit unchanged (don't delete the first
stage) except for the before mentioned elimination of the feedback
line connection, and the addition of a 470uf cap to the first stage
cathode resistor *Which you will now have to recalculate for a
single resistor OR simply parallel a 1.2K with a 470 Ohm and this
would be your cathode resistor. (Sorry, too lazy to calculate at
the moment for single R!)-T.M.
..you'll have a ridiculous amount of gain - no?
And one would have to build it carefully to avoid hum and excess
noise due to the gain as well --all doable. On the flip side:
You'd never need a separate preamp to drive it.
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