Fender DRRI Bias

[ajeffcote]

I have a DRRI with all new transformers.Before I installed the power tranny,the plate voltage was 420v.Now it is running 454v.I'm running JJ 6V6S power tubes.I tried adjusting the bias.Should be set to about 23 milliamps,right?Turning the pot all the way up gives me 16.5 milliamps max.What do I need to do?Do I reduce the plate voltage or change the bias circuit to accommodate the higher voltage?Probably reduce the plate voltage?And how do I do that,whichever that may be?Please,any help will be most appreciated.Thanks.

[PRNDL]

I show 16-19 mA for 6V6's with 454 volts on the anode to run at 12 watts and 60-70% dissipation. Higher bias will shorten the tube life.

[MWJB]

Increase the value of the resistor grounded fom the bias pot (r59). 19K would look to be good. As you increase plate current, the voltage will drop slightly. 22/23mA on the JJs will be fine.

[ajeffcote]

Thank you for the direction.I tried replacing the 22ohm resister at(R69) by the bias diode to a lower value,from a 22 to a 10.That didn't work,but it sounded logical to me.I then replaced R59 like you told me and that did the trick,But I decreased the value.There was a 22K in that spot( the schematic said it would be a 10K).I had a 2.2K so I tried that.Now I have plenty of adjustment available.All the way from 2ma to about 45ma.Thank you,again.

[MWJB]

Indeed, my bad - decreasing R59 was the way to go!