Bias is an important factor in setting the operating point of a tube amplifier. Too much bias and the tubes will overheat, potentially causing damage. Too little bias and the amplifier will not be able to produce enough power. The best way to set the bias on a tube amplifier is with a multimeter. First, turn off the amplifier and allow it to cool down for at least 15 minutes. Then, remove the cover of the amplifier so you can access the tubes. Next, locate the grid resistor for each tube. This is typically a large resistor located near the base of each tube (it may also be labeled on the circuit board). Using your multimeter, measure the resistance between each grid resistor and ground. The resistance should be between 0.5 and 1.5 ohms for most tubes. If the resistance is outside of this range, you will need to adjust the bias potentiometer until the correct resistance is achieved. Once the bias has been set, replace the amplifier cover and turn on the power. Allow the amplifier to warm up for at least 15 minutes before playing any music. Follow these steps and you'll have your tube amplifier biased correctly in no time!