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In Reply to: Bias setting posted by Ray Moth on April 5, 2007 at 15:03:09:
With multiple parallel pairs, you need to be sure one tube isn't hogging the current. So adjust each one carefully to spec, and re-check when you're done.
Follow Ups:
Hey guys,Sorry for the delay. The tubes are not single bias, they get biased via one adjustment on the back.
and you expect it to be stable? looks like your amps should have been a bit more expensive.
Whatever.....
you have 3 tubes hanging off each grid resistor. These resistors are evidently connected to a single pot. There's be no circuit penalty for using a pot per side of the PP pair( just cost ). If you treat all 6 tubes the same and they're not, what do you expect to happen?Building a driver stage that can drive a 3x parallel set of grid circuits(needed for proper idividual adjustment ) is not going to be as easy, or cheap. You get what you pay for.
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