Vintage Amplifier Service Manual - BELL SOUND model 3750 12-tube 4-channel public address audio amplifier. Original old Sams Photofact manual includes schematic, layout, voltage & resistance test chart, repair parts list and description. Manufactured by Bell Sound Systems, Inc., of Columbus, OH. Dated 1948. 6 pages. Original old Sams Photofact manual includes schematic, layout, alignment instructions, voltage & resistance test chart, repair parts list and description.  This manual would make a sensational accompaniment to your retro audio equipment.