Audiovisual introductions in 1906

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).

thumb|A McIntosh Laboratory|McIntosh stereo audio amplifier with output power of 50 watts per channel used in home component audio systems in the 1970s.

thumb|Triode Audion [[vacuum tube from 1908. The filament (which was also the cathode) was at the lower left inside the tube, but has burned out and is no longer present. The filament's connecting and supporting wires are visible. The plate is at the middle top, and the grid is the serpentine electrode below it. The plate and grid connections leave the tube at the right.]]