Marconi Radio Valve Type QX, by Marconi Company, London, c. 1921

Marconi Radio Valve Type QX, in a thin glass envelope with caps at either ends. With grid and anode connections as envelope side pips and a single strand tungsten filament running the entire length, with a spring for tensioning. Construction was co-axial with helical wire grid surrounding the filament and the fitting within cylindrical anode. In this valve, a 'U' shaped glass support held two stout wire rods that attached to the anode and grid respectively. Thus electrodes were only supported at one end. Type QX valves were identical to Type V24 valves but with a tighter grid pitch. Previously catalogued with assorted other valves.