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However, some large transmitting tubes are designed to operate with their anodes at red, orange, or in rare cases, white heat.

This two-grid tube is called a tetrodemeaning four active electrodes, and was common by Arcing between tube elements can destroy the tube.

Hydrogen thyratrons have long been used in radar transmitters. This complex tubf causes barium and strontium atoms to diffuse to the surface of the cathode and emit electrons when heated to about degrees Celsius. Some thyratrons can carry large currents for their physical size. The highest-power tube currently available is the Eimac 4CMKG, a forced water-cooled power tetrode capable of dissipating 2.

The magnetron is the type of tube used in all microwave ovens. The only time it was switched off was for conversion to Mk2, which added more tubes. Although some applications had used earlier technologies such as the spark gap transmitter for radio or mechanical computers for computing, it was the ekectron of the thermionic vacuum tube that made these technologies widespread and practical, and created the discipline of electronics.

However, reliability was compromised, and production costs for the tube were much greater. To avoid the warm-up delay, “instant on” television receivers passed a small heating current through their tubes even when the set was nominally off.


When held negative with respect to the cathode, the control grid creates an electrob field which repels electrons emitted by the cathode, thus reducing or even stopping the current between cathode and anode. Skip to main content.

Vacuum tube

Originally, the only use for tubes in radio circuits was for rectificationnot amplification. Learn more – opens in a electronn window or tab.

This in turn improved tube gain, since the gain of a triode is inversely proportional to the spacing between grid and cathode. A device with two active elements is a diodeusually used for rectification.

The valve was electgon service from until and had a recorded life ofhours. Despite great advances in solid-state photodetectors, the single-photon detection capability of photomultiplier tubes makes this vacuum tube device excel in certain applications.

Retrieved 21 August It was sometimes known as the ‘sheet beam’ tube, and was used in some color TV sets for color demodulation.

Vacuum tube – Wikipedia

The two grids are positioned so that the control grid creates “sheets” of electrons which pass between the screen-grid wires. Nuclear medicine imaging equipment and liquid scintillation counters use photomultiplier tube arrays to detect low-intensity scintillation due to ionizing radiation.

A tube with an unusually high level of internal gas may exhibit a visible blue glow when plate voltage is applied. Sometimes emission can be restored for a time by raising heater voltage, either for a short time or a permanent increase of a few percent. The triode and its derivatives tetrodes and pentodes are transconductance devices, in which the controlling signal applied to the grid is a voltageand the resulting amplified signal appearing at the anode is a current.


Please enter 5 or 9 numbers for the ZIP Code. To combat the stability problems and limited voltage gain due to the Miller effectthe physicist Walter H. The earliest vacuum tubes evolved from incandescent light bulbscontaining a filament sealed in an evacuated glass envelope. Mouse over to Zoom – Click to enlarge. The New Audio Cyclopedia 1st ed. Elimination of silicon from the heater wire alloy and more frequent replacement of the wire drawing dies allowed production of tubes that were reliable enough for the Whirlwind project.

By placing an additional electrode between the filament cathode and plate anodehe discovered the ability of the resulting device to amplify signals.

Making tubes smaller reduced tubbe voltage where they could safely operate, and also reduced the power dissipation of the filament.

The continuous dynode was resistive, and its ends were connected to enough voltage to create repeated cascades of electrons. These are housed in an oil-filled aluminium housing to provide cooling.

Usually oxygen in the air reacts chemically with the hot filament or cathode, quickly ruining it.

Potentiometer digital Variable capacitor Varicap. See terms – opens in a new window or tab. This three-grid tube is called a pentodemeaning five electrodes. Tube heaters may also fail without warning, especially if exposed to over voltage or as a result of manufacturing defects.