Daily Herald Photograph: Flat valves for hearing aids

One photograph of two flat radio valves held beside a 3 pence piece for scale titled 'Britain Shows Her Radio Brains Electronic Private Show'. Caption on back reads: 'Engineers and industry experts from 18 countries were expected at Grosvenor House, London today (Monday) when Sir Robert Renwick opened a three day exhibition organised by the Radio and Component Manufacturers Federation, of which he is president. The radio, TV and electronic devices seen at this private showing were, during the war only shown in strictest secrecy. Countries sending representatives included Austrail, Poland, Czechoslovakia, and the U.S. Photo shows:- on of the valves developed for hearing aids is so small that three will fit into a thimble. Here seen are two of the valves compared with a threepenny piece.'