Disclaimer:
I am not an expert, do not try this unless you are comfortable around high dc voltages! Do not take what I have written as correct unless it is confirmed by those who actually know whats going on
Right so I've been wanting to learn how to do this for a while, read up a whole ton and apart from the danger factor it seems fairly simple, heres my first go at it.
I removed the amp from the chassis and had a peak (with my eyes not my hands) at the EL34 sockets from the top. Firstly I spotted

The red plate B+ voltage wire isnt looking too healthy and if that touched something else Im sure there would be some fireworks. Cut it short, tinned it and resoldered it properly.
Set your multi-meter to DVC, in my case I used 1000 (as your plate voltage should be 400-500 odd). Connect the ground terminal to a lug on the amps chassis itself and the red wire to pin 3 of your EL34 socket.

Basically 3rd pin counting clockwise just after the locator tab. Make sure the amp has a speaker load, connect power to the amp and turn it on (leaving it on standby). Let it warm up for about 10 minutes or so on standby before switching the standby switch off and you should get

A reading of 488VDC, it was bouncing between 487 and 488 the whole time. Now you use the following formula:
Bias = (Wattage of tube / plate voltage) x 70%
so
Bias = (25w / 488 ) x 70% = 0.0358V or 35mV
Now this is the part I dont understand from the online instructions..
Set your meter to lowest DCV setting (200mV or less) and touch the ground lead to the ground side of the 1 ohm resistor and the positive lead to the pin 1 side. Do this on all power tubes and adjust the tube with the highest value to your desired bias voltage from step 4.

Theres the adjuster, but can someone explain the 1ohm resistor bit?
I am not an expert, do not try this unless you are comfortable around high dc voltages! Do not take what I have written as correct unless it is confirmed by those who actually know whats going on
Right so I've been wanting to learn how to do this for a while, read up a whole ton and apart from the danger factor it seems fairly simple, heres my first go at it.
I removed the amp from the chassis and had a peak (with my eyes not my hands) at the EL34 sockets from the top. Firstly I spotted

The red plate B+ voltage wire isnt looking too healthy and if that touched something else Im sure there would be some fireworks. Cut it short, tinned it and resoldered it properly.
Set your multi-meter to DVC, in my case I used 1000 (as your plate voltage should be 400-500 odd). Connect the ground terminal to a lug on the amps chassis itself and the red wire to pin 3 of your EL34 socket.

Basically 3rd pin counting clockwise just after the locator tab. Make sure the amp has a speaker load, connect power to the amp and turn it on (leaving it on standby). Let it warm up for about 10 minutes or so on standby before switching the standby switch off and you should get

A reading of 488VDC, it was bouncing between 487 and 488 the whole time. Now you use the following formula:
Bias = (Wattage of tube / plate voltage) x 70%
so
Bias = (25w / 488 ) x 70% = 0.0358V or 35mV
Now this is the part I dont understand from the online instructions..
Set your meter to lowest DCV setting (200mV or less) and touch the ground lead to the ground side of the 1 ohm resistor and the positive lead to the pin 1 side. Do this on all power tubes and adjust the tube with the highest value to your desired bias voltage from step 4.

Theres the adjuster, but can someone explain the 1ohm resistor bit?