Vacuum tube
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The vacuum tube, also called a triode, was invented in 1906 by American inventor Lee de Forest. The triode resulted from the introduction of a third electrode (called a grid) into the diode (an earlier form of vacuum tube similar to an incandescent light bulb).
The triode could be used both as an amplifier and a switch. Many of the early radio transmitters were built by de Forest using triodes, which revolutionized the field of broadcasting at the time. Radio transmission used vacuum tubes as analog devices, to modify (but not stop and stop) an electrical current. The ability of triode vacuum tubes to act as switches (on/off devices that stop or start) would later be important in the building of the first electronic computers.