Audion amplifier tube

The Audion was an electronic amplifying vacuum tube invented by American electrical engineer Lee De Forest in 1906. It was the first triode, consisting of a partially evacuated glass tube containing three electrodes; a heated filament, a grid, and a plate. It is important in the history of technology because it was the first widely used electrical device which could amplify; a small electrical signal applied to the grid could control a larger current flowing from the filament to plate.