McVitie Weston valve collection, STC valve, type 33A/100A
STC valve, type 33A/100A, domed envelope with two horns, (RMW/Y560 - McVitie Weston number), by Standard Telephones and Cables Limited.
STC valve, type 33A/100A, domed envelope with two horns, (RMW/Y560 - McVitie Weston number), by Standard Telephones and Cables Limited.