excitation anode

Typically, a two or three phase supply of a few amperes passes through small excitation anodes.

The Ignitron dispenses with excitation anodes by igniting the arc each time conduction is required to start.

The Excitron is similar to other types of valve described above but depends critically on the existence of an excitation anode to maintain an arc discharge during the half-cycle when the valve is not conducting current.