Editing Plate electrode

{{Short description|Type of electrode used in vacuum tubes}}
[[Image:Triode-english-text.svg|thumb|Cutaway diagram of a triode vacuum tube, showing the plate (anode)]]
[[Image:Roehre anode el84.jpg|thumb|The plate from an [[EL84]] [[pentode]] tube widely used in audio amplifiers in 1960s era radios and televisions, and still used in guitar amplifiers]]  
[[File:Triode schematic labeled.svg|thumb|[[Schematic symbol]] used in [[circuit diagram]]s for vacuum tube, showing plate]]

A '''plate''', usually called '''anode''' in Britain,  is a type of [[electrode]] that forms part of a [[vacuum tube]].<ref>Thomas A. Edison {{US patent|307031}} "Electrical Indicator", Issue date: 1884</ref> It is usually made of sheet metal, connected to a wire which passes through the glass envelope of the tube to a terminal in the base of the tube, where it is connected to the external circuit.  The plate is given a positive [[electric potential|potential]], and its function is to attract and capture the electrons emitted by the [[cathode]].  Although it is sometimes a flat plate, it is more often in the shape of a cylinder or flat open-ended box surrounding the other electrodes.

==Construction==
The plate must dissipate heat created when the electrons hit it with a high velocity after being accelerated by the voltage between the plate and cathode.   Most of the waste power used in a vacuum tube is dissipated as heat by the plate.  In low power tubes it is usually given a black coating, and often has "fins" to help it radiate heat.  In power vacuum tubes used in radio transmitters, it is often made of a [[refractory metal]] like [[molybdenum]]. and is part of a large [[heat sink]] that projects through the glass or ceramic tube envelope and is cooled by [[Glowing anode|radiation cooling]], forced air or water.<ref>C H Gardner (1965) [http://www.r-type.org/static/story.htm The Story of the Valve], Radio Constructor (See particularly the section "Glass Base Construction")</ref><ref>Robert B. Tomer, ''Getting the most out of vacuum tubes'', Howard W. Sams, Indianapolis, USA 1960, Library of Congress card no. 60-13843, available on the Internet Archive.  Chapter 1</ref>

==Secondary emission==
A problem in early vacuum tubes was ''[[secondary emission]]''; electrons striking the plate could knock other electrons out of the metal surface.  In some tubes such as [[tetrode]]s these ''secondary electrons'' could be absorbed by other electrodes such as grids in the tube, resulting in a current out of the plate.  This current could cause the plate circuit to have [[negative resistance]], which could cause unwanted [[parasitic oscillation]]s.  To prevent this most plates in modern tubes are given a chemical coating which reduces secondary emission.

==See also==
* [[Anode]]

==External links==
*https://web.archive.org/web/20101007201649/http://pentalabs.com/tubeworks.html – The history of vacuum tubes
*[https://books.google.com/books?id=KSkDAAAAMBAJ&dq=van+der+Bijl+Thermionic+valve&pg=PA132 The Thermionic Detector – HJ van der Bijl (October 1919)]
*[http://www.john-a-harper.com/tubes201/ How vacuum tubes really work] – Thermionic emission and vacuum tube theory, using introductory college-level mathematics.
*[http://www.ken-gilbert.com/techstuff/vtf.html The Vacuum Tube FAQ] – FAQ from rec.audio
* [http://www.marconicalling.com/museum/html/events/events-i=39-s=0.html The invention of the thermionic valve]. Fleming discovers the thermionic (or oscillation) valve, or 'diode'.

==References==
{{Reflist|30em}}
*Shiers, George, "The First Electron Tube", Scientific American, March 1969, p.&nbsp;104.
*Tyne, Gerald,  ''Saga of the Vacuum Tube'', Ziff Publishing, 1943,  (reprint 1994 Prompt Publications), p.&nbsp;30–83.
*RCA ''[[Radiotron Designer's Handbook]]'', 1953 (4th Edition). Contains chapters on the design and application of receiving tubes.

{{Electronic components}}
{{Thermionic valves}}

{{DEFAULTSORT:Plate Electrode}}
[[Category:Vacuum tubes]]
[[Category:Electrodes]]


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