Service info is in Sams Photofact folder 750-7, which is 1965. Don't have anything that recent myself...
Schematic is online here:
http://techpreservation.dyndns.org/s...RC4671_55.djvu
(you need the free DjVu viewer from Lizardtech.com)
If it's like the others in the series, there are RCA jacks for extending the speakers. When attached. the speaker connects through the hinges.