Triode Triode A triode is an electronic amplifying vacuum tube (or "thermionic valve" in British English) consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode). Developed from Lee De Forest's 1906 Audion, a partial vacuum tube that added a grid electrode to the thermionic diode (Fleming valve), the triode was the first practical electronic amplifier and the ancestor of other types of vacuum tubes such as the tetrode and pentode. Its invention founded the electronics age, making possible amplified radio technology and long-distance telephony. Triodes were widely used in consumer
Valve audio amplifier technical specification it is referred to as the "phase inverter") to drive the power section. As an alternate to the long-tail pair, the "concertina" uses a single triode as a variable resistance within a potential divider formed by Ra and Rk either side of the valve. The result is that the voltage at the anode swings exactly and opposite to the voltage at the cathode, giving a perfectly balanced phase split. the disadvantage of this stage (cf the differential long-tail pair) is that it does not give any gain. Using a double triode (typically octal or noval) to form a SET input