Triode were invented, Philipp Lenard used the principle of grid control while conducting photoelectric experiments in 1902. The first vacuum tube used in radio was the thermionic diode or Fleming valve, invented by John Ambrose Fleming in 1904 as a detector for radio receivers. It was an evacuated glass bulb containing two electrodes, a heated filament and a plate (anode). Triodes came about in 1906 when American engineer Lee De Forest and Austrian physicist Robert von Lieben independently patented tubes that added a third electrode, a grid, between the filament and plate to control current. Von Lieben's partially-evacuated three-element tube, patented
Charles Brown (engineer) Charles Brown (engineer) Charles Brown (1827–1905) was a British engineer. He was born at Uxbridge on 30 June 1827 and was apprenticed to Maudslay, Sons and Field. In 1851 he moved to Switzerland to join the Sulzer company. In 1871 he left Sulzer to set up Swiss Locomotive and Machine Works (SLM). While at SLM he invented the Brown valve gear, a radial valve gear for steam engines. He became involved in the development of electric locomotives in the 1880s. In 1885 he became manager of Maschinenfabrik Oerlikon and in 1890 he set up Charles Brown and Company at 91