Hi there–i just sold one like that–maybe a bit earlier than ’77 as had 17V DC- unless of course you’re gonna tell me they didn’t make them before then lol– for £103– around $170 –probably a decent buy for someone at that price–plugged it in and was sounding amazingly good- but as i only paid £25 for it ,can’t complain. They’re only worth as much as someone is prepared to pay!