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
John Snell (electrical engineer) John Snell (electrical engineer) Sir John Francis Cleverton Snell, GBE (15 December 1859 – 6 July 1938) was a British electrical engineer and administrator. He was born in Saltash, Cornwall, the only son of Commander John Skinner Snell, RN and his wife Harriet Cleverton and educated at Plymouth Grammar School, Finsbury Technical College and King's College, London. After working for four years from 1885 with Messrs. Woodhouse and Rawson he was appointed in 1889 a resident engineer at Messrs. Crompton and Co., where he worked on electrical supply projects in London and Stockholm. From 1892 he worked as assistant to