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
European Triode Festival European Triode Festival Since 2000 each year the "European Triode Festival" (ETF) has been held in various venues in Europe (the first three events were called "Aarhus Triode Festival" aka "ATF"). The ETF focuses on do-it-yourself audio valve amplifiers using triode vacuum tubes, and brings together high end vacuum tube audiophiles from all over the world (from as far away as Finland and New Zealand). At the festival, participants demonstrate their (all home-built) equipment (analogue/digital/amplifiers/speakers/etc.) and discuss aspects of high-quality vacuum tube sound reproduction. The event is a private venture of in total 300 audio lovers, of which some 120