Cathode bias

Cathode bias is a method used in vacuum tube amplifiers to set the operating point (bias) of the output tubes, usually power amplifying tubes. In this configuration, a resistor is connected between the cathode of the tube and ground. This resistor is referred to as the cathode resistor. The purpose of the cathode resistor is to provide a negative voltage relative to the cathode, which establishes the required bias for the tube.