Plate electrode

<h2 id="construction">Construction</h2>
<p>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 <a href="/facts/Refractory_metal/WtGXfsVQ">refractory metal</a> like <a href="/facts/Molybdenum/RX6vp2bF">molybdenum</a>. and is part of a large <a href="/facts/Heat_sink/ccIEdHnq">heat sink</a> that projects through the glass or ceramic tube envelope and is cooled by <a href="/facts/Glowing_anode/NN0TInbJ">radiation cooling</a>, forced air or water.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
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<h2 id="secondary-emission">Secondary emission</h2>
<p>A problem in early vacuum tubes was <i><a href="/facts/Secondary_emission/ssI9RAtE">secondary emission</a></i>; electrons striking the plate could knock other electrons out of the metal surface.  In some tubes such as <a href="/facts/Tetrode/WnYG1oVT">tetrodes</a> these <i>secondary electrons</i> 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 <a href="/facts/Negative_resistance/QgkR8esF">negative resistance</a>, which could cause unwanted <a href="/facts/Parasitic_oscillation/Cj84g9dJ">parasitic oscillations</a>.  To prevent this most plates in modern tubes are given a chemical coating which reduces secondary emission.
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<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Anode/TjYt95zG">Anode</a></li></ul>
<h2 id="external-links">External links</h2>
<ul><li><a href="https://web.archive.org/web/20101007201649/http://pentalabs.com/tubeworks.html">https://web.archive.org/web/20101007201649/http://pentalabs.com/tubeworks.html</a> – The history of vacuum tubes</li>
<li><a href="https://books.google.com/books?id=KSkDAAAAMBAJ&dq=van+der+Bijl+Thermionic+valve&pg=PA132">The Thermionic Detector – HJ van der Bijl (October 1919)</a></li>
<li><a href="http://www.john-a-harper.com/tubes201/">How vacuum tubes really work</a> – Thermionic emission and vacuum tube theory, using introductory college-level mathematics.</li>
<li><a href="http://www.ken-gilbert.com/techstuff/vtf.html">The Vacuum Tube FAQ</a> – FAQ from rec.audio</li>
<li><a href="http://www.marconicalling.com/museum/html/events/events-i=39-s=0.html">The invention of the thermionic valve</a>. Fleming discovers the thermionic (or oscillation) valve, or 'diode'.</li></ul>

<ul><li>Shiers, George, "The First Electron Tube", Scientific American, March 1969, p. 104.</li>
<li>Tyne, Gerald,  <i>Saga of the Vacuum Tube</i>, Ziff Publishing, 1943,  (reprint 1994 Prompt Publications), p. 30–83.</li>
<li>RCA <i><a href="/facts/Radiotron_Designer%27s_Handbook/lUAwMmXS">Radiotron Designer's Handbook</a></i>, 1953 (4th Edition). Contains chapters on the design and application of receiving tubes.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Thomas A. Edison U.S. patent 307,031 "Electrical Indicator", Issue date: 1884 <a href="https://patents.google.com/patent/US307031" target="_blank">https://patents.google.com/patent/US307031</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>C H Gardner (1965) The Story of the Valve, Radio Constructor (See particularly the section "Glass Base Construction") <a href="http://www.r-type.org/static/story.htm" target="_blank">http://www.r-type.org/static/story.htm</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>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 <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
</ol>

Plate electrode open-in-new

Plate electrode