Biasing Tubes

[Boots]

I need to replace the EL34's in a Marshall JCM900. I know that every time the power tubes are replaced, they should be re-biased. Is that something I can do or should I take it to a professional?

I would really like to learn and do it myself. Has anyone done this themselves (the right way)?

 

[twist]

Unless you're already familiar with the circuitry of your amp, you'll need a schematic and a volt meter. The "bias" voltage on the grid of the tube is adjusted to produce the specified idle current through the plate/cathode circuit.

Twist

 

[Tom Hicks]

You need to have someone teach you but its not hard.The power tubes are biased in pairs,the outside pair and the inside pair.There is a nominal voltage range(adjustable by screwdriver on a little dodad wired into the tube sockets) for each pair.You want to have the voltage of the matched pairs as close to the same value as possible.Takes maybe ten minutes.

Tom