Output Tube Bias Bias of the output tubes in an amplifier is very important both from an operational point of view, and from a longevity point of view. The bias determines the class of operation of a tube amplifier. Of course this depends on the tube type and plate voltage. This affects the sound of the amp. It also affects output tube life.
Confusion reigns for the term bias as it applies to tube amps and solid state ones.
Tube and solid state amplifiers use the term bias in completely opposite ways. Unfortunately, this adds to the confusion in an area which is already misunderstood. The term bias refers to a negative voltage in tubes, whereas in transistors it is a positive voltage. This is the source of the confusion. Bias voltage controls current flow by applying a voltage across a grid.