Radio receiver crude triode, was invented in 1906 by Lee De Forest as a more sensitive detector for radio receivers, by adding a third electrode to the thermionic diode detector, the Fleming valve. It was not widely used until its amplifying ability was recognized around 1912. The first tube receivers, invented by De Forest and built by hobbyists until the mid 1920s, used a single Audion which functioned as a grid-leak detector which both rectified and amplified the radio signal. There was uncertainty about the operating principle of the Audion until Edwin Armstrong explained both its amplifying and demodulating functions in a
William Petrie (electrical engineer) William Petrie (electrical engineer) William Petrie (1821–1908) was an English electrical engineer, known for the development of the arc lamp. Born at King's Langley, Hertfordshire, on 21 January 1821, he was eldest of four sons of William Petrie (born 1784), a War Office official, and his wife Margaret Mitton, daughter of the banker Henry Mitton, of the Chase, Enfield. In 1829 his father was sent to the Cape of Good Hope, where he acted until 1837 as deputy commissary-general, with as neighbour Sir John Herschel, the astronomer, who was a significant influence on the younger William Petrie's interest in science.