Heathkit Stuff, as the name implies, available in Kit form for assembly by enthusiasts if I remember correctly. Their Schematics and assembly manuals should be freely available Can't search too much as I'm at work.
Thanks greenhorn. Yes I am as well aware that these are kits that enthusiasts used to build back in those days. This one is from the US. Infact I have got all the build documentation used for this amp. I plan to put this up for give away shortly.
A monthly DIY magazine called Electronics Illustrated used to feature the Heathkit range of offerings. The magazine was brought out by the publishers of the equally well known Mechanix Illustrated, Fawcett Publications.
Your amplifier seems to be from the 1960s and well assembled.