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[[Image:Triode tube 1906.jpg|thumb|[[Triode]] Audion [[vacuum tube]] from 1908. The [[Hot_cathode#Cathode_heater|filament]] (which was also the cathode) was at the lower left inside the tube, but has burned out and is no longer present. The filament's connecting and supporting wires are visible. The plate is at the middle top, and the grid is the serpentine electrode below it. The plate and grid connections leave the tube at the right.]]
The '''Audion''' was an electronic detecting or amplifying [[vacuum tube]]<ref name="Okamura" /> invented by American electrical engineer [[Lee de Forest]] as a [[diode]] in 1906.<ref name="Patent">De Forest patented a number of variations of his detector tubes starting in 1906. The patent that most clearly covers the Audion is {{US patent|879532}}, ''[
| last = de Forest
| first = Lee
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| isbn = 9780313296369
| url = https://books.google.com/books?id=4l_2kkv5aeMC&q=%22Audion&pg=PA28
| access-date = January 7, 2013}}</ref><ref name="IA-SA-reprint">{{cite journal |last1=de Forest |first1=Lee |title=The Audion - A new receiver for wireless telegraphy |journal=Scientific American |date=30 Nov 1907 |volume=64 |issue=1665 |pages=348-352 |url=https://archive.org/details/sim_scientific-american-supplement_1907-11-30_64_1665/page/348/mode/1up |access-date=21 October 2023}} Non-paywalled reprint of the DeForest presentation at the October 26, 1906 New York meeting of the AIEE. Text version available at the [https://www.earlyradiohistory.us/1907aud.htm Early Radio History] site.</ref> Improved, it was patented as the first [[triode]] in 1908,<ref name="Okamura">{{cite book
| last = Okamura
| first = Sōgo
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|url=http://www.ieee.org/documents/00573757.pdf
|pages=685–697
|doi=10.1109/jproc.1997.573757}}</ref> The many practical applications for amplification motivated its rapid development, and the original Audion was superseded within a few years by improved versions with a higher vacuum.<ref name="Lee" /><ref name="Nebeker" />
== History ==
[[Image:Audion receiver.jpg|thumb|An Audion [[radio receiver]] by [[Lee de Forest|de Forest]]. The Audion tubes were mounted upside down to prevent the delicate filaments from sagging and touching the grids. This receiver provided the ability to choose operation of either one of the two provided detector tubes
It had been known since the middle of the 19th century that gas flames were [[Electrical conduction|electrically conductive]], and early wireless experimenters had noticed that this conductivity was affected by the presence of [[Radio frequency|radio waves]]. De Forest found that gas in a partial [[vacuum]] heated by a conventional lamp filament behaved much the same way, and that if a wire were wrapped around the glass housing, the device could serve as a detector of radio signals. In his original design, a small metal plate was sealed into the lamp housing, and this was connected to the positive terminal of a 22–volt battery via a pair of headphones, the negative terminal being connected to one side of the lamp filament. When wireless signals were applied to the wire wrapped around the outside of the glass, they caused disturbances in the current which produced sounds in the headphones.
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===Kenotron and Pliotron===
[[Image:
<ul>
<li>''Second row (B):'' triodes developed at [[Western Electric]] which bought the rights from de Forest in 1913
<li>''Top row (A):'' French triodes. The French government gained the right to manufacture Audions in 1912 when de Forest failed to renew his French patents for lack of $125.
</ul>]]
Langmuir had long suspected that certain assumed limitations on the performance of various low-pressure and vacuum electrical devices, might not be fundamental physical limitations at all, but simply due to contamination and impurities in the manufacturing process. His first success was in demonstrating that, contrary to what Edison and others had long asserted, incandescent lamps could function more efficiently and with longer life if the glass envelope was filled with low-pressure inert gas rather than a complete vacuum. However, this only worked if the gas used was meticulously 'scrubbed" of all traces of oxygen and water vapor.
He then applied the same approach to producing a rectifier for the newly developed "Coolidge" X-ray tubes. Again contrary to what had been widely believed to be possible, by virtue of meticulous cleanliness and attention to detail, he was able to produce versions of the Fleming Diode that could rectify hundreds of thousands of volts. His rectifiers were called "Kenotrons" from the Greek ''keno'' (empty, contains nothing, as in a vacuum) and ''tron'' (device, instrument).
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'''Application images'''
<gallery>
[[Image:General electric pliotron pp schenectady 3.jpg|thumb|upright|General Electric Company Pliotron]]
▲''Bottom row (D):'' De Forest Audions<br />
▲''Third row (C):'' Pliotrons, developed at [[General Electric]] by Langmuir<br />
▲''Second row (B):'' triodes developed at [[Western Electric]] which bought the rights from de Forest in 1913. These were used in telephone [[repeater]]s which made possible the first transcontinental telephone line in 1915.<br />
▲''Top row (A):'' French triodes. The French government gained the right to manufacture Audions in 1912 when de Forest failed to renew his French patents for lack of $125.]]
Image:First vacuum tube AM radio transmitter.jpg|The first Audion AM [[radio transmitter]], built by [[Lee de Forest]] and announced April, 1914
Image:De Forest Audion AM radio transmitters.jpg|Some of the earliest Audion [[AM radio]] transmitters, built by de Forest around 1916. The invention of the Audion [[oscillator]] in 1912 made inexpensive sound radio transmission possible, and was responsible for the advent of [[radio broadcasting]] around 1920.
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{{Commons category|Audion}}
{{Wikisource|QST/March 1916/Practical Pointers on the Audion|Practical Pointers on the Audion}}
* [https://web.archive.org/web/20121010212743/http://digitalgallery.nypl.org/nypldigital/dgkeysearchdetail.cfm?trg=1&strucID=51420&imageID=99555&total=7075&num=20&word=col_id%3A187&s=1¬word=&d=&c=&f=&k=0&lWord=&lField=&sScope=images&sLevel=&sLabel=%26quot%3BThe%20Pageant%20of%20America%26quot%3B%20Photograph%20Archive&imgs=20&pos=34&e=w 1906 photograph of the original Audion tube, from New York Public Library Digital Gallery]
* {{Cite web |last=Lewis |first=Tom |date=1991 |title=Telephone History - Empire of The Air: The Men Who Made Radio |url=http://www.privateline.com/TelephoneHistory3/empireoftheair.html |url-status=dead |archive-url=https://web.archive.org/web/20140511182508/http://www.privateline.com/TelephoneHistory3/empireoftheair.html |archive-date=May 11, 2014 |website=Privateline.com}}
* http://www.britannica.com/EBchecked/topic/1262240/radio-technology/25131/The-Fleming-diode-and-De-Forest-Audion
* {{citation |url=http://www.ieee.org/publications_standards/publications/proceedings/langmuir.pdf |title=The Pure Electron Discharge and Its Applications in Radio Telegraphy and Telephony |journal=Proceedings of the IEEE |volume=85 |issue=9 |pages=1496–1508 |date=September 1997 |orig-year=1915 |first=Irving |last=Langmuir |author1-link=Irving Langmuir |doi=10.1109/jproc.1997.628726 |s2cid=47501618 |ref=none}}{{dead link|date=July 2024|bot=medic}}{{cbignore|bot=medic}}. Reprint of {{citation |first=Irving |last=Langmuir |author1-link=Irving Langmuir |title=The Pure Electron Discharge and Its Applications in Radio Telegraphy and Telephony |journal=Proceedings of the IRE |volume=3 |issue=3 |pages=261–293 |date=September 1915 |url=https://books.google.com/books?id=AF0AAAAAMAAJ&pg=PA261 |ref=none |doi=10.1109/jrproc.1915.216680}}. (Includes comments from de Forest.)
* [https://babel.hathitrust.org/cgi/pt?id=uiug.30112089533605&view=1up&seq=356 The Audion: A new Receiver for Wireless Telegraphy], Lee de Forest, Scientific American Supplement No. 1665, November 30, 1907, pages 348-350, Scientific American Supplement No. 1666, December 7, 1907, page 354–356.
* [http://120years.net/wordpress/the-audion-pianolee-de-forestusa1915/ Lee de Forest's Audion Piano on '120 years Of Electronic Music']
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