Vintage MASCO models AC-12,  AC24, ACL, ACS and ACS-6 24-channel intercommunication system.  Original old Sams Photofact manual includes schematic, layout, alignment instructions, voltage & resistance test chart, repair parts list. 4 pages. Dated 1953.  Mark Simpson Manufacturing Company, Inc. of Long Island City, NY. This manual would make a sensational accompaniment to your classic electronics equipment.