You will need a voltmeter (Radio Shack has them for about $15). The rectifier and all tubes stay in. Let it warm up but have no music playing. Set the voltmeter to DC volts and insert the red lead on the voltmeter into the left tube socket on the front panel that reads "Bias Set 1.56V" and touch the black lead anywhere to the chasis. Turn the left screw at the back of the top circuit board (it comes through the top of the chasis) until the voltmeter reads 1.56V. Repeat with the right tube socket input and the right screw. You will have to go back and forth between the two screws because as you increase one the other decreases. You only have to do this with new tubes and periodically (every few months as the tubes age. Good luck. Rick
