vacuum tube

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(n.) An electron tube in which most of the air has been removed, permitting electrons to move freely. The first tube was a two-element diode, invented and patented by Ambrose Fleming in 1904. Three years later, Lee De Forest developed the first triode (known as the “Audion”) by adding a grid between the cathode emitter and the anode collector, creating the first amplifier. A change of voltage at the grid produced a corresponding greater change of voltage at the anode. Transistors in integrated circuits perform the same functions that tubes were designed to perform at a fraction of the size and power consumption.