Vintage Amplifier Service Manual - MASCO model MA-75 13-tube 3-channel audio amplifier. Manufactured by Mark Simpson Manufacturing Company of Long Island City, NY. Dated 1947. 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.