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) Central Electricity Board was established, the national grid created and the supply of electricity standardised. He was made GBE in 1925. In 1928 he began introducing major new electricity power systems in the West of England with his friend and then colleague, Dr John A. Purves. He was awarded the Faraday Medal for 1938 by the Institution of Electrical Engineers (now the Institution of Engineering and Technology). He died after an operation at the London Clinic in 1938. He had married Annie Glendenning Quick of Biscovey, Cornwall, with whom he had at least one son. John Snell (electrical engineer) Sir