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.
[4] 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.
[4][5]"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.
[1][7] Originally developed as a radio receiver
detector[3] by adding a grid electrode to the
Fleming valve, it found little use until its amplifying ability was recognized around 1912 by several researchers,
[7][9] who used it to build the first amplifying
radio receivers and
electronic oscillators.
[8][10] The many practical applications for amplification motivated its rapid development, and the original Audion was superseded within a few years by improved versions with higher vacuum."(Wikpedia article on Audion, accessed 9-2020).
Jeremy Norman’s
