In 1906 American inventor Lee de Forest introduced a third electrode called the grid into the vacuum tube. The resulting triode could be used both as an amplifier and a switch. de Forest marketed his triode under the name Audion.
"The audion consisted 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 extra residual gas limited the dynamic range and gave the Audion non-linear characteristics and erratic performance.
Originally developed as a radio receiver detector
by adding a grid electrode to the Fleming valve
, it found little use until its amplifying ability was recognized around 1912 by several researchers,
who used it to build the first amplifying radio receivers
and electronic oscillators
The many practical applications for amplification motivated its rapid development, and the original Audion was superseded within a few years by improved versions with higher vacuum."(Wikpedia article on Audion, accessed 9-2020).