Amplifier by their physical placement in the signal chain; a preamplifier may precede other signal processing stages, for example. The first practical electrical device which could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. Today most amplifiers use transistors. The first practical device that could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. Vacuum tubes were used in almost all amplifiers until the 1960s–1970s when the transistor, invented in 1947, replaced them. Today, most amplifiers
John Snell (electrical engineer) General Charles Edmund Webber on electrical supply projects in Kensington and a number of country houses, before entering municipal service in London in 1893 as assistant electrical engineer in St Pancras during the construction of the Kings Road power station. In 1896 he transferred to Sunderland as Borough Electrical Engineer, additionally becoming Borough Tramways Engineer in 1896 after which he converted the tramway system to electric power. In 1906 he set up in business as a consulting engineer in Westminster, amalgamating with Preece and Cardew to form Preece, Cardew and Snell. During that time he served as an expert witness