Elliott, check the paperwork that came with your Cayin and see if it states that it has "automatic biasing" or something to that effect. If not, there should be a procedure on how to do it. Are there any test points on the top or back of the chassis?
If it must be adjusted and the measurements are internal flip the amp on it's back and use the spring loaded hook type test leads with the power off. Make sure there is a load (speakers) on the outputs unless stated otherwise. You want nothing connected on the inputs. They should have a setting (usually in millivolts) that you adjust a pot to. That will set the current flowing through the tube. Some amps have an individual pot for each tube and some share a pot between both tubes in a push pull type amp. If I recall, yours is a push pull design.
I suspect that it's auto biasing or more than likely you would have red plated a tube if your swapping tubes. Uneven current matching on the tubes can lead to a runaway current situation that results in red plating.
Don't rely on your tube tester to match tubes, they don't test the current at full operating voltages.
There is a Fisher forum on AK, lots of information over there on adjusting those amps.
BillWojo
If it must be adjusted and the measurements are internal flip the amp on it's back and use the spring loaded hook type test leads with the power off. Make sure there is a load (speakers) on the outputs unless stated otherwise. You want nothing connected on the inputs. They should have a setting (usually in millivolts) that you adjust a pot to. That will set the current flowing through the tube. Some amps have an individual pot for each tube and some share a pot between both tubes in a push pull type amp. If I recall, yours is a push pull design.
I suspect that it's auto biasing or more than likely you would have red plated a tube if your swapping tubes. Uneven current matching on the tubes can lead to a runaway current situation that results in red plating.
Don't rely on your tube tester to match tubes, they don't test the current at full operating voltages.
There is a Fisher forum on AK, lots of information over there on adjusting those amps.
BillWojo
