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Triode Audion vacuum tube from 1908. The filament (which was also the cathode) was at the lower left inside the tube, but has burned out and is no longer present. The filament's connecting and supporting wires are visible. The plate is at the middle top, and the grid is the serpentine electrode below it.
De Forest Audion tube from 1908, the first triode. The flat plate is visible on the top, with the zigzag wire grid under it. The filament was originally present under the grid but was burnt out. Lieben-Reisz tube, another primitive triode developed the same time as the Audion by Robert v. Lieben
Lee de Forest (August 26, 1873 – June 30, 1961) was an American inventor, electrical engineer and an early pioneer in electronics of fundamental importance. He invented the first practical electronic amplifier, the three-element "Audion" triode vacuum tube in 1906.
The triode and its derivatives (tetrodes and pentodes) are transconductance devices, in which the controlling signal applied to the grid is a voltage, and the resulting amplified signal appearing at the anode is a current. [31] By comparison the later bipolar junction transistor uses a small current to control a larger current.
In 1906 Lee De Forest added a third electrode and invented the first electronic amplifying device, the triode, which he named the Audion. This additional control grid modulates the current that flows between cathode and anode. The relationship between current flow and plate and grid voltage is often represented as a series of "characteristic ...
Armstrong began working on his first major invention while still an undergraduate at Columbia. In late 1906, Lee de Forest had invented the three-element (triode) "grid Audion" vacuum-tube. How vacuum tubes worked was not understood at the time.
The first amplifying vacuum tube, the Audion, a crude triode, was invented in 1906 by Lee De Forest as a more sensitive detector for radio receivers, by adding a third electrode to the thermionic diode detector, the Fleming valve. [38] [59] [91] [92] It was not widely used until its amplifying ability was recognized around 1912. [38]
In 1915 Cunningham started the Audio Tron Sales Company in San Francisco. Based on the West Coast, he was in direct competition with Lee de Forest, a leading manufacturer of triodes sold under the Audion brand. Before 1915, triode vacuum tubes were spherical or shaped like an incandescent light bulb. Cunningham took a different route.