On the top plate in front of each 845 tube there's a bias pot and bias switch, all you need to do is let amp warm up about 10 mins, flip bias switch on for one tube , use small screw driver , turn bias down to zero and then up to 75 - meter is on front of amp, flip switch back off, do same for 2nd tube and all done - all down. Takes very little time . .LM recommends checking every 150 hours.
CAmp also as a hum pot in the event an 845 hums you can control it. Haven't has that issue in 18 months of having the amp and using it fairly regularly