If you are getting no bias reading even with a good tube in place, the first thing to check is the B+ fuse located inside the amplifier.
If you remove the bottom cover, you will see a fuse on one of the relay boards, this is the B+ fuse. It should be a 1A Slow Blow. There is a good chance a bad tube took out this fuse to protect the rest of the circuit.
If you replace this use and still having the problem, you may have taken out a cathode or screen grid resistor. These are not always easy to spot by eye unless they are burnt.
As other have mentioned, be carefull inside these amps as there are leathal voltages present.
If you remove the bottom cover, you will see a fuse on one of the relay boards, this is the B+ fuse. It should be a 1A Slow Blow. There is a good chance a bad tube took out this fuse to protect the rest of the circuit.
If you replace this use and still having the problem, you may have taken out a cathode or screen grid resistor. These are not always easy to spot by eye unless they are burnt.
As other have mentioned, be carefull inside these amps as there are leathal voltages present.