Igranic ‘Pentrovol’ transverse current microphone, serial number 478, patent number 301441, mounted on stand, made by the Igranic Electric Company Limited, England, 1920-1932. From amateur wireless transmitting and receiving station (G5FK), built by F. Briggs Esq., as exhibited at the Radio Exhibition of 1932. Igranic 'Pentrovol' microphone with stand, 1920-1932 Radio Communication 1920-1932