Editing Triode (section)

===Precursor devices===
[[File:Triode tube 1906.jpg|thumb|upright=1.05|De Forest Audion tube from 1908, the first triode. The flat plate is visible on the top, with the zigzag wire grid under it. The filament was originally present under the grid but was burnt out.]]
[[File:Lieben-Reisz vacuum tube.jpg|thumb|upright=0.4|Lieben-Reisz tube, another primitive triode developed the same time as the Audion by Robert v. Lieben]]

Before thermionic valves were invented, [[Philipp Lenard]] used the principle of grid control while conducting photoelectric experiments in 1902.<ref name="Burns">{{cite book
 | last1  = Burns
 | first1 = Russell W. 
 | title  = Communications: An International History of the Formative Years
 | publisher = Institute of Electrical Engineers
 | date   = 2004
 | location = London
 | pages  = 339
 | url    = https://books.google.com/books?id=7eUUy8-VvwoC&q=Lenard+%22Grid+Control%22&pg=PA339
 | isbn   = 0863413277
 }}</ref>

The first [[vacuum tube]] used in radio<ref name="Aitken2">{{cite book
 | last1  = Aitken
 | first1 = Hugh G.J. 
 | title  = The Continuous Wave: Technology and American Radio, 1900-1932
 | publisher = Princeton University Press
 | date   = 2014
 | pages  = 195
 | url    = https://books.google.com/books?id=ebr_AwAAQBAJ&q=Fleming+valve&pg=PA195
 | isbn   = 978-1400854608
 }}</ref><ref name="Fisher">{{cite book
 | last1  = Fisher
 | first1 = David E.
 | last2  = Fisher
 | first2 = Marshall
 | title  = Tube: The Invention of Television
 | publisher = Counterpoint
 | date   = 1996
 | pages  = 54
 | url    = https://books.google.com/books?id=eApTAAAAMAAJ&q=%22first+vacuum+tube%22+fleming+valve&pg=PA54
 | isbn   = 1887178171
 }}</ref> was the [[thermionic diode]] or [[Fleming valve]], invented by [[John Ambrose Fleming]] in 1904 as a [[Detector (radio)|detector]] for [[radio receiver]]s. It was an evacuated glass bulb  containing two electrodes, a heated filament (cathode) and a plate (anode).