Vintage Radio Service Manual - OPERADIO model 1A35 4-tube 2-channel public address audio amplifier. Manufactured by Operadio Manufacturing Company, of St. Charles, IL. Dated 1948. 4 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 audio equipment.