Vacuum tube

The vacuum tube is a device that controls the flow of electrons in a vacuum and were initially used to amplify signals for audio and other devices. This allowed broadcast radio to reach the masses in the 1920s. Vacuum tubes steadily spread into other devices, and the first tube was used as a switch in calculating machines in 1939. Its impact was to launch the electronics industry.

In 1883 Thomas Edison noticed that electrical current could “jump” from a hot filament to a metal plate in an experimental incandescent light bulb. John Ambrose Fleming invented the first vacuum tube, the diode, in 1904. This eventually led to Lee De Forest’s 1906 creation of the triode, which not only forces current in a single direction but can be used as an amplifier for signals such as audio and radio signals. Bell Labs was able to make use of this feature in its “coast to coast” phone system, and the tubes were soon used in other devices, such as radios, television sets and amplifiers. Vacuum tubes can also convert AC to DC current and generate oscillating radio-frequency power for radar systems.

Early computers used tubes. For example, ENIAC, the first electronic, reprogrammable, digital computer that could be used to solve a large range of computing problems, was unveiled in 1946 and contained over 17,000 vacuum tubes. Since tube failures were more likely to occur during warm-up periods, the machine was rarely turned off, reducing tube failures to one tube every two days.

Transistors were invented in 1947, and in the following decade assumed most of the amplifying applications of tubes at much lower cost and reliability.