Should a 1/2 power Pentode/Triode switch cause an amp to break up earlier even in full power mode? A friend just bought a 1966 Princeton Reverb that has a half power Pentode/Triode switch installed on the back of the chassis and it does lower the volume. But even when switched to full power, it breaks up much earlier, (about 3 on the volume) than my Princeton Reverb reissue. I have swapped tubes and checked all the voltages. The plate voltage in it seems low, about 399. My PRRI plate voltage is about 435. I think the lower plate voltage is causing the earlier break up. Could the Pentode/Triode switch cause the lower plate voltage?