Re: [Harp-L] Low plate voltage on the preamp tubes?



I agree that reducing the plate voltage of Fender and similar amps warms up the sound and makes it less stiff and gainy. I have been happiest with 12AX7 voltages of 100 to 110V. It is not hard to do, but involves dealing with a portion of the circuit that has REAL HIGH voltage. A simple way to dial in the voltage and sound is to temporarily replace the power supply dropping resistor feeding the preamp tube plates with a potentiometer, adjust the pot to taste and/or voltage and then insert a fixed resistor of appropriate value. You might be able to find a tech that will do just this as you play and listen. It turns out that increasing the value of the last power supply dropping resistor has little effect on the upstream (power tube) voltages and power tube bias. Allen Amplification makes an guitar amp with switch selectable final resistance. Seems like one could also control this with a suitable control panel pot.

Heck, I'll do this for anyone who drags an amp to Augusta this year.

Jim R





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