Audio power amplifier inside the chassis of the main product. The audio amplifier was invented around 1912 by Lee De Forest, made possible by his invention of the first practical amplifying electrical component, the triode vacuum tube (or "valve" in British English) in 1907. The triode was a three terminal device with a control grid that can modulate the flow of electrons from the filament to the plate. The triode vacuum amplifier was used to make the first AM radio. Early audio power amplifiers were based on vacuum tubes and some of these achieved notably high audio quality (e.g., the Williamson amplifier of
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,