Marconi general-purpose valve, type L2/B, B4 base, pinch marked L642 (RMW/C53 - McVitie Weston number), by Marconi Company Limited, 1931.
Marconi general-purpose valve, type L2/B, B4 base, pinch marked L642 (RMW/C53 - McVitie Weston number), by Marconi Company Limited, 1931.