Docc This is a pretty good site for sorting out valve amp issues For info on biasing, click on the link to tube amp FAQ in this link You'll need to make up a tool to check the bias on your amp and any others that aren't fixed bias.
BEFORE doing any work at all inside a valve amp, make sure the electrolytic capacitors have been drained as they can hold lethal voltages. You can make up a tool to drain them using a wooden chopstick (do not use a graphite pencil under any circumstances), a short length of wire, crocodile clip and a 220k 1w resistor. Solder one end of the resistor to the wire with a crocodile clip on the end. tape or heatshrink the resistor/wire assembly to the chopstick so the end of the resistor not connected to the wire is at the sharp end of the chopstick. without touching any bare wiring on your tool (you shouldn't have any), connect the croc clip to earth and hold the chopstick end against the positive side of the first electrolytic capacitor on the power supply circuit (it'll be the one nearest to the mains transformer/rectifier. measure the dc voltage across the cap. Fully charged, it'll be in the 300-450v range. once it gets below 10, you're ok to work on the amp.
You'll obviously have to have the power connected and the amp switched on to check the bias, but most amps with adjustable bias have a socket to do it and don't require the amp to expose any live wiring. Have a good read of the articles in the above links. All interesting reading.
edited to add links.