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
Harold Rosen (electrical engineer) Harold Rosen (electrical engineer) Harold A. Rosen (March 20, 1926 – January 30, 2017) was an American electrical engineer, known as "the father of the geostationary satellite", and "father of the communications satellite". He formed and led the team that designed and built the first geosynchronous communications satellite, Syncom, for Hughes Aircraft Company. Rosen served in the US Navy as a radio communication and radar technician during World War II. He graduated from Tulane University in 1947 with a Bachelor of Engineering degree in electrical engineering. He received his M.S. (1948) and Ph.D. (1951) in electrical engineering from the California