Marshall 50 Watt 800 2 Channel 6550 Amps Gold Pin Option

These are all adjustable bias amps and all you need to check and adjust the bias is a bias probe and a Multimeter, or our all-in-one Eurotubes "Pro One" bias probe that reads both the plate current and the plate voltage simultaneously. You can find all these under the Related Products Tab. 

You can use the "Generic Bias Video" we made using a Marshall 800 for reference. 

The video below explains the difference between bias probe types.