The first electronic amplification device. Invented in 1907 by Lee de Forest who called it the audion, the triode is a diode with an extra perforated electrode, the grid, whose function is to vary the amount of current flowing from anode to cathode.
A multi-grid radio valve (or tube) with three electrode s (an anode, cathode, and a control grid), commonly used in audio and radio amplifier s, and oscillator circuits.
A triode is a type of 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 electrical amplification device. The principle of its operation is that, like in a vacuum tube based diode, the heated filament causes a flow of electrons that hit the plate and create an electric charge to it.