A
triode is an electronic
amplifying vacuum tube (or
valve in British English) consisting of three
electrodes inside an evacuated glass envelope: a heated
filament or
cathode, a
grid, and a
plate (
anode). Invented in 1906 by
Lee De Forest by adding a grid to the
Fleming valve, the triode was the first
electronic amplification device 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 electronics devices such as radios and televisions until the 1970s, when
transistors replaced them. Today, their main remaining use is in high-power
RF amplifiers in
radio transmitters and industrial RF heating devices. The word is derived from the
Greek τρίοδος,
tríodos, from
tri- (three) and
hodós (road, way), originally meaning the place where three roads meet.