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STC valve, type V.T.13.C, pinch marked BS37, marked AM 5 Science Museum Group © The Board of Trustees of the Science Musuem
STC valve, type V.T.13.C, pinch marked BS37, marked AM 5.6-30, Ref. No. 10A/7510, black moulded square 4-pin base, (RMW/J63 - McVitie Weston number), by Standard Telephones and Cables Limited.