Princeton Reverb too high idle current

[glebert]

Working on an all-original 1965 Princeton Reverb. Came in with one power tube not conducting and one alternating between no conduction and high current. Put in a new set of JJ 6V6S tubes and amp is working but tubes are pulling 35mA of current with 425V plate voltage, so over 100% of the 14 watt rating. Grid voltage is -35V, so in line with the schematic. Is this current to be expected with these voltages? Other than trying to order a special "cold" set of tubes is there anything I should be looking at other than adjusting resistor values to get a more negative bias voltage?

TIA,
Greg

[Chuck H]

Any pair of tubes will be different. And high plate voltages are more of a problem than ever because AC outlets are higher than they use to be. Just adjust the bias voltage for a safe operating range. eg: 70% ish. The older amps weren't designed to manage todays conditions with higher AC and more variable tubes. That's the short answer. So we have to adjust the amps now accordingly. The cooler bias will actually increase plate voltage a little. But it will probably be ok.

[g1]

The supposed '65 PR re-ish shows -40V, so maybe they did some tweaking. See attached.

[Jon Snell]

Depends on the HT.
If 420volts then around -35 is correct. If 450v then -40 is correct.
If the voltage is not as your service manual describes, (model dependant) I would check for DC volts leaking from the junction of C42 and R14, through C42.