3-2-29a-3 Electromechanical

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3-2-29a-4 Vacuum Tube Computers - My Background


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"Explains the six basic functions of electronic tubes and shows how each type of tube is used in industrial and military applications."

Public domain film from the Library of Congress Prelinger Archive, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization.


In electronics, a vacuum tube, electron tube (in North America), or thermionic valve (elsewhere, especially in Britain), reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum. Vacuum tubes may be used for rectification, amplification, switching, or similar processing or creation of electrical signals. Vacuum tubes rely on thermionic emission of electrons from a hot filament or hot cathode, that then travel through a vacuum toward the anode (commonly called the plate), which is held at a positive voltage relative to the cathode. Additional electrodes interposed between the cathode and anode can alter the current, giving the tube the ability to amplify and switch.

Vacuum tubes were critical to the development of electronic technology...

In most applications, vacuum tubes have been replaced by solid-state devices such as transistors and other semiconductor devices... However, tubes still find particular uses where solid-state devices have not been developed or are not practical, or where the tube device is regarded as having superior performance over the solid-state equivalent, as can be the case with some devices used in professional audio. Tubes are still produced for such applications and to replace those used in existing equipment such as high-power radio transmitters...


Vacuum tubes with two active elements ("diodes") are used for rectification. Ones with 3 or more elements ("triodes", "tetrodes", etc.) are used for amplification, functions which rely on amplification such as oscillators, and switching...

The 19th century saw increasing research with evacuated tubes, such as the Geissler and Crookes tubes. Famous scientists who experimented with such tubes included Thomas Edison, Eugen Goldstein, Nikola Tesla, and Johann Wilhelm Hittorf among many others. With the exception of early light bulbs, such tubes were only used in scientific research or as novelties. The groundwork laid by these scientists and inventors, however, was critical to the development of subsequent vacuum tube technology.

Although thermionic emission was originally reported in 1873 by Frederick Guthrie, it was Thomas Edison's 1884 investigation that spurred future research, the phenomenon thus becoming known as the "Edison Effect." Edison patented what he found, but he did not understand the underlying physics, nor did he have an inkling of the potential value of the discovery. It wasn't until the early 20th century that the rectifying property of such a device was utilized, most notably by John Ambrose Fleming who used the diode tube to detect (demodulate) radio signals. Lee De Forest's 1906 "audion" was also developed as a radio detector, and soon led to the development of the triode tube. This was essentially the first electronic amplifier, leading to great improvements in telephony (such as the first coast-to-coast telephone line in the US) and revolutionizing the technology used in radio transmitters and receivers. The electronics revolution of the 20th century arguably began with the invention of the triode vacuum tube...

...it was Lee De Forest who in 1907 is credited with inventing the triode tube while continuing experiments to improve his original Audion tube, a crude forerunner of the triode. By placing an additional electrode in between the filament (cathode) and plate (anode), he discovered the ability of the resulting device to amplify signals of all frequencies. As the voltage applied to the so-called control grid (or simply "grid") was lowered from the cathode's voltage to somewhat more negative voltages, the amount of current flowing from the filament to the plate would be reduced. The negative electrostatic field created by the grid in the vicinity of the cathode would inhibit thermionic emission and reduce the current to the plate. Thus a few volts difference at the grid would make a large change in the plate current and could lead to a much larger voltage change at the plate, resulting in voltage and power amplification. In 1907, De Forest filed for a patent[3] for such a three-electrode version of his original Audion tube for use as an electronic amplifier in radio communications. This eventually became known as the triode....