Round Radio Valve Type CA, by Ediswan, London, c. 1915
Inventory Number: 13117
Date: c. 1915
Maker Details: Attributed to Ediswan.
Inscription: "MARCONI'S W.T. CO. LTD / PAT. APPN. NO. 28413-18. / 2V-PF-50 / 3F" stamped on exterior surface of bulb.
Size: 170 mm in overall length
Other Given Number(s): Christie's 205.
Round Triode Radio Valve Type CA (production model), with three oxide coated platinum filaments, as indicated by the PF (Platinum Filament) and 3F (Three Filaments) printed on the exterior surface of the glas bulb. This receiver valve, a variant of Type N, was completely surrounded by a coarse mesh grid and cylindrical anode. The three filament version had a moulded base with four side contacts - one for each filament and one common contact. The tubulation at the top of the valve contained a piece of asbestos that could be heated to release a small amount of gas into the valve to optimise its operation. With brass and ebonite base.