In a grounded grid amplifier using a triode vacuum tube, the cathode is connected to a radio frequency choke. The other end of the radio frequency choke connects to the:

In a grounded grid amplifier, the grid is directly connected to DC ground. To properly bias the tube (set its resting operating current), the cathode must be made positive relative to the grid. This is achieved by connecting the B- (the negative return of the high voltage supply, or a specific bias supply) to the cathode circuit. Because the RF input signal (drive) is also fed into the cathode in a grounded grid configuration, an RF choke is placed between the cathode and the B- supply. This choke prevents the incoming RF drive signal from taking a short circuit path through the DC bias supply, ensuring all the RF energy goes into driving the tube.