Vintage Radio Service Manual - SENTINEL model 309-I 309-N 309-R 309-W 5-tube Superheterodyne AM radio receiver. Manufactured by Sentinel Radio Corp., of Evanston, IL. Dated 1947. 4 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.