Sound recording and reproduction 1920s when several radio-related developments in electronics converged to revolutionize the recording process. These included improved microphones and auxiliary devices such as electronic filters, all dependent on electronic amplification to be of practical use in recording. In 1906, Lee De Forest invented the Audion triode vacuum tube, an electronic valve that could amplify weak electrical signals. By 1915, it was in use in long-distance telephone circuits that made conversations between New York and San Francisco practical. Refined versions of this tube were the basis of all electronic sound systems until the commercial introduction of the first transistor-based audio devices in
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.