DUO-TRAC "Cell-o-Phone" sound recorder by British Ozaphone Ltd, console model 381, serial number 0800, using an optical sound reproduction system and cellophane tapes, complete with eight boxed 1/8" tapes and technical literature; made in England c1936. Duo-Trac 'Cell-o-Phone' optical tape player, c 1936. 1936-1938