Music technology (electric) remained so until the 1920s, when several recent 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
Alexander Russell (electrical engineer) Alexander Russell (electrical engineer) Alexander Russell, FRS (15 July 1861 – 14 January 1943) was a Scottish electrical engineer and educator. He was born in Ayr, Scotland and educated at Glasgow University (gaining an MA in Mathematics and Physics) and Caius College, Cambridge. He was later (in 1924) awarded a doctorate. After teaching mathematics at Cheltenham College and the Oxford Military College, he took a post at Faraday House, in Southampton Row, London, which had been newly founded to train electrical engineers. In 1909 he became the Principal, a position he held until 1939. There he pioneered the sandwich course,