Marconi Radio Valve Type DEV, by Marconi Company, English, c. 1923

Marconi Radio Valve Type DEV (Dull Emitter V), with grid and anode connections as side pips on envelope, and single strand tungsten filament running entire length with spring for tensioning. Construction was co-axial with helical wire grid surrounding filament and fitting within cylindrical anode. In thin glass envelope half painted red, with envelope caps at either ends. Previously catalogued with five other valves: Marconi Type Q Valve (Inv. Num. 33191), Marconi Type V24 Valve (Inv. Num. 35245), Marconi DEQ Valve (Inv. Num. 74920), Mullard ORA/B Valve (Inv. Num. 18833), Marconi FE2 Valve (Inv. Num. 92775).