Hivac valve, type XD, gauze anode, (RMW/D83B - McVitie Weston number), made by Hivac Limited, aka the High Vacuum Valve Company, London.

Hivac “midget” range of valves were initially developed for hearing aids but by 1936 they were also being sold “for constructing pocket radios and truly portable sets.” By 1938, Hivac were advertising the use of these miniature radio valves “allow compactness in assembly of components" and were suitable for HF/VHF receivers. Some Hivac midget valves were used in German and British clandestine radios during the Second World War.