Vintage NATIONAL model "Horizon 5"  4 channel audio preamplifier. Control unit designed to be used in conjunction with National Horizon 20 or National Criterion tuner.  Original old Sams Photofact manual includes schematics, layouts, voltage & resistance readings, parts list. 4 pages. Dated 1955.  National Company Inc.  of Malden, MA.  This manual would make a sensational accompaniment to your vintage audio equipment.