Control grid Control grid The control grid is an electrode used in amplifying thermionic valves (vacuum tubes) such as the triode, tetrode and pentode, used to control the flow of electrons from the cathode to the anode (plate) electrode. The control grid usually consists of a cylindrical screen or helix of fine wire surrounding the cathode, and is surrounded in turn by the anode. The control grid was invented by Lee De Forest, who in 1906 added a grid to the Fleming valve (thermionic diode) to create the first amplifying vacuum tube, the Audion (triode). In a valve, the hot cathode emits
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