A BTH (British Thompson-Houston) wireless crystal receiver, type C-Form A, in a walnut case with instructions to the inner lid and company trade plaque, the exterior with BBC/GPO approved log, 29cm long, 13cm wide, 21cm high This is a type C- Form A radiolar form circa 1923, the BBC/PMG stamp GPO number 106, crystal change over switch permit to select one of two independent crystals. It is broadcast only (medium wave) model. The British Thompson-Houston Company Ltd. was based at Crown House, Aldwych, London, WZ2 and produce crystal sets, valve radios, loud speakers and valves. In 1928 BTH amalgamated with Metrovick and Edison Swan to form Associated Electrical Industries Ltd (AEI)