Vintage Amplifier Service Manual - OPERADIO model 530, 531 & 1335 Soundcaster 4-channel audio amplifier with phonograph record player. Manufactured by Operadio Manufacturing Company, of St. Charles, IL. Dated 1948. 6 pages. Original old Sams Photofact manual includes schematic, layout, voltage & resistance test chart, repair parts list and description. This manual would make a sensational accompaniment to your retro phono equipment.