Triode

A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube (or valve in British English) with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device, which propelled the electronics age forward, by enabling amplified radio technology and long-distance telephony. Triodes were widely used in consumer electronics until the 1950s, when bipolar junction transistors replaced them. The word is derived from the Greek τρίοδος, tríodos, from tri- (three) and hodós (road, way), originally meaning the place where three roads meet.