"As always, it ain't that simple..."
As a die-hard (but untrained) DIYer I earlier found info on the 'net on how to bias the EL-34 power tubes in my Rivera M60 amp, which has bias pots. The link has disappeared meanwwhile, and I moved house and misplaced the info. In addition to the usual warnings about lethal voltages, it consisted of where to connect the test leads and roughly what voltage to aim for. Could anyone tell me this?
Couldn't find a schematic for the M60 with a quick google. Saw some circuits for older Rivera amps that show no easy provisions for quick biasing. Maybe your amp is different.
First off, you have to measure the plate voltage on the output tubes. Stating a specific bias reading without knowing the plate voltage is like describing the length of a fish with only one hand - it's meaningless! Even different amps of the same model might show a bit of a plate voltage difference and this affects the bias "sweet spot".
has some great stuff about biasing and also you can google up Randy's "Tone Lizard" site which also has some great info.
You don't likely have a bias test point built in so you'll either have to add a couple of resistors to the circuitry or use what's called the shunt method, where you measure the DC resistance of each side of the output trannie winding with the amp turned OFF and then measure the voltage drop across each winding with the amp idling with no signal. Ohm's Law will give you the plate current. You can then adjust the bias control if you need to change it.
It's a little more ticklish with the high voltages involved but the nice thing about the shunt method is that you don't need to install bias test points.
You absolutely should read Mr. Aiken's FAQ.