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
David Davies (electrical engineer) David Davies (electrical engineer) Sir David Evan Naunton Davies , known as Den Davies or David "DEN" Davies, (born 1935) is a British electrical engineer and educator. He was knighted for services to science in 1994. 1985-1988: Head of the Department of Electronic and Electrical Engineering at University College London (UCL), and holder of the Pender Chair, having already been lecturing there, in "Communications Systems", for many years prior to that. 1986-1988: Vice-Provost of University College London 1988-1993: Vice Chancellor of Loughborough University 1993–1999: Chief Scientific Adviser for the Ministry of Defence 1994-1995: President of the Institution of Electrical Engineers