Audion Audion The Audion was an electronic detecting or amplifying vacuum tube invented by American electrical engineer Lee de Forest in 1906. It was the first triode, consisting of an 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 electronic device which could amplify; a small electrical signal applied to the grid could control a larger current flowing from the filament to plate. The original triode Audion had more residual gas in the tube than later versions and vacuum tubes; the
Alan Blumlein is effectively connected as a triode, and if the tap was at the supply end, as a pure pentode. Blumlein discovered that if the tap was placed at a distance 15–20% down from the supply end of the output transformer, the tube or valve would combine the positive features of both the triode and the pentode design. Blumlein may or may not have invented the long-tailed pair, but his name is on the first patent (1936). The long-tailed pair is a form of differential amplifier that has been popular since the days of the vacuum tube (valve). It is now