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) 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