Lee de Forest
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Lee de Forest was an American inventor and a fundamentally important early pioneer in electronics. He invented the first practical electronic amplifier,
the three-element "Audion" triode vacuum tube in 1906. This helped start the Electronic Age, and enabled the development of the electronic oscillator. These made radio broadcasting and long distance telephone lines possible, and led to the development of talking motion pictures, among countless other applications.
De Forest, some time between 1914 and 1922, with two of his Audions, a small 1 watt receiving tube (left), and a later 250-watt transmitting power tube (right), which he called an "oscillion".
American DeForest Wireless Telegraph Company's observation tower, 1904 Louisiana Purchase Exposition at Saint Louis, Missouri
Ohio Historical Marker. On July 18, 1907 Lee de Forest transmitted the first ship-to-shore messages that were sent by radiotelephone
Vacuum tube
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A vacuum tube, electron tube, valve, or tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
Later thermionic vacuum tubes, mostly miniature style, some with top cap connections for higher voltages
Hot tubes in an audio power amplifier, emitting their distinctive red-orange glow
Illustration representing a primitive triode vacuum tube and the polarities of the typical DC operating potentials. Not shown are the impedances (resistors or inductors) that would be included in series with the C and B voltage sources.
Radio station signal generator with vacuum tubes