Marshall 6100 bias circuit

[strato56]

Fwiw, I have had a 6101 with a faulty LowPowerSwitch. Even closed, that switch had resistance, so the outer EL34's didn't pull as much current as the inner EL34.
Inner tubes had 30mA idle current and the outer 10mA.
Also, when in Low Power Mode, plate voltage rises, so you may want to check bias also in that mode ( If the guitar player ever uses that switch )

[Randall]

I finally got my new set of 5581WXTs. This set runs about 74mA with instructed -41v of bias voltage. Crazy! I don't think much of this method of biasing. I'm going to dial it down to 30mA @ 483v, which is -55v bias voltage.

[alexradium]

-41v was probably referred to el34,on 5881 marshalls it was around -55