The Fleming valve is a diode which was used as a radio signal detector in the early 1900s. It is considered to be one of the most important developments in electronics. It paved the way for the advancement in wireless telegraphy and telephony.
Also called the thermionic valve, vacuum diode, kenotron or thermionic tube, the Fleming valve was invented by John Ambrose Fleming, a British scientist and professor at the University College in London, in 1904. It was the first practical application of the thermionic emission which was discovered by Frederick Guthrie in 1873. Thomas Edison made a separate discovery in 1880 while working on the incandescent light bulb. It was called the “Edison effect”. Edison acquired a patent for the thermionic tube in 1884, but he did not come up with any practical use for it.
While working for the British Marconi Company in 1899, Fleming was trying to rectify a weak wireless signal. He tried to use the Edison effect and it worked. In 1904, Fleming acquired a patent which he originally named it “oscillation valve”. The Fleming valve had an immediate practical use as detector of messages sent by Morse code.
The development of the Fleming valve was a major breakthrough in electronics. It led to the development of the Audion, a three-element vacuum tube, which was the first electronic amplifying device. The Audion, which was refined into the triode, was used in the earliest development of radio communications, radars and long-distance telephone systems.
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