Lee de Forest

Lee de Forest was an American inventor whose three-element Audion, patented in 1906 and 1907, was the first practical device able to amplify a weak electrical signal, and became a foundation of electronic radio, telephony and sound film. He built the Audion by adding a control grid to the two-element vacuum tube John Ambrose Fleming had already patented, but for years did not fully understand why his own device amplified a signal. Edwin Armstrong worked out and patented the regenerative feedback circuit that explained and dramatically improved that amplification, filing in late 1913; de Forest then filed a competing claim based on an August 1912 laboratory notebook entry, and the priority fight reached the US Supreme Court twice, which ruled for de Forest in 1928 and again in 1934. De Forest titled his own 1950 autobiography Father of Radio, a title he used for the rest of his life, though most working engineers of his own era, and most historians since, have credited the regenerative circuit itself to Armstrong; the dissent recorded on this page sets out that disagreement. De Forest also pursued sound film: his Phonofilm process, publicly demonstrated from 1923, was one of the first successful sound-on-film systems. He held more than 300 patents over his career.