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) him with hands-on experience with radio communications and the then-new field of radars. In 1949, Rosen married Rosetta, and they had two sons, Robert (born 1950) and Rocky (born 1966). Rosetta died in 1969. In 1984 he married Deborah Castleman, a satellite systems engineer also working at Hughes Aircraft Company. Rosen died on January 30, 2017 due to complications from a stroke, aged 90. Rosen has more than 80 patents. He was a Fellow of the IEEE and the AIAA, and a member of the National Academy of Engineering. Rosen has received numerous awards which include: Harold Rosen (electrical engineer)