Listed as Brimar brand (STC) in first three rinformation sources. Grid from top cap.
Literatur
History of the British Radio Valve to 1940 p. 144 & 199
Babani, International Radio Tube Encyclopaedia 20 & 21
Universal Vade-Mecum, Electron Valves and Semiconductor Devices
Taschenbuch zum Röhren-Codex 1948/49
20A1: Brimar Valve Manual 1938-9
Adrian Riesen
20A1: Telefunken Werkstattbuch
Wolfgang Bauer
Mehr...
Just Qvigstad
20A1: Brimar Valve Manual 1938-9
Adrian Riesen
Mehr...