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
Xiaodong Wang (electrical engineer) Xiaodong Wang (electrical engineer) Xiaodong Wang () is an information theorist and professor of Electrical Engineering at Columbia University. He earned a BS degree in electrical engineering and applied mathematics from Shanghai Jiaotong University, an MS degree in electrical and computer engineering from Purdue University, and a PhD from Princeton University in electrical engineering. He formerly served as assistant professor of Electrical Engineering at Texas A&M University before he joined Columbia as an assistant professor in January 2002. He is a Fellow of IEEE and an ISI Highly Cited author. He has won numerous prestigious awards, among them the National