page_title: Fleming valve
section_title: History
hierarchical_section_title: Fleming valve / History
caption_attribution_description: English: Full wave rectifiers: AZ1, 5Y3G, EZ3, 5C4S, EZ80, 6X4 Polski: Pełnookresowe duodiody prostownicze: AZ1, 5Y3G, EZ3, 5C4S, EZ80, 6X4
context_page_description: The Fleming valve, also called the Fleming oscillation valve, was a thermionic valve or vacuum tube invented in 1904 by English physicist John Ambrose Fleming as a detector for early radio receivers used in electromagnetic wireless telegraphy. It was the first practical vacuum tube and the first thermionic diode, a vacuum tube whose purpose is to conduct current in one direction and block current flowing in the opposite direction. The thermionic diode was later widely used as a rectifier — a device which converts alternating current into direct current — in the power supplies of a wide range of electronic devices, until beginning to be replaced by the selenium rectifier in the early 1930s and almost completely replaced by the semiconductor diode in the 1960s. The Fleming valve was the forerunner of all vacuum tubes, which dominated electronics for 50 years. The IEEE has described it as "one of the most important developments in the history of electronics", and it is on the List of IEEE Milestones for electrical engineering.
context_section_description: The Fleming valve was the first practical application of thermionic emission, discovered in 1873 by Frederick Guthrie.  As a result of his work on the incandescent light bulb, Thomas Edison made his own discovery of the phenomenon in 1880, which led to it being called the Edison effect.  Edison was granted a patent for this device as part of an electrical indicator in 1884, but did not find a practical use for it. Professor Fleming of University College London consulted for the Edison Electric Light Company from 1881-1891, and subsequently for the Marconi Wireless Telegraph Company. 
  In 1901 Fleming designed the transmitter used by Guglielmo Marconi in the first transmission of radio waves across the Atlantic from Poldhu, England, to Nova Scotia, Canada. The distance between the two points was about 3,500 kilometres (2,200 mi). Although the contact, reported November 12, 1901, was widely heralded as a great scientific advance at the time, there is also some skepticism about the claim, because the received signal, the three dots of the Morse code letter "S", was so weak the primitive receiver had difficulty distinguishing it from atmospheric radio noise caused by static discharges, leading later critics to suggest it may have been random noise.  Regardless, it was clear to Fleming that reliable transatlantic communication with the existing transmitter required more sensitive receiving apparatus.   
  The receiver for the transatlantic demonstration employed a coherer, which had poor sensitivity and degraded the tuning of the receiver. This led Fleming to look for a detector which was more sensitive and reliable while at the same time being better suited for use with tuned circuits. In 1904 Fleming tried an Edison effect bulb for this purpose, and found that it worked well to rectify high frequency oscillations and thus allow detection of the rectified signals by a galvanometer. On November 16, 1904, he applied for a US patent for what he termed an oscillation valve. This patent was subsequently issued as number 803,684 and found immediate utility in the detection of messages sent by Morse code.  The Fleming valve was used by the Marconi company in its shipboard receivers until around 1916, when it was replaced by the triode.
caption: Thermionic diode valves derived from the Fleming valve, from the 1930s (left) to the 1970s (right)
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