Wow. That 780 model was the one I bought - in late 1978 !! In fact my parents are still running the thing, it looks 'near new' and still sounds fine (the FM tuner is no slouch). Certainly a bargain when you consider how it has been used. And the lights are still all working !
I ran it with a Dual direct-drive turntable, Mission speakers and a JVC cassette deck. It was the 'dogs bollox' at the time. A 'massive' 35 watts into 4 ohms, if I remember right..
The only thing I still use from that set-up is the Zerostat (although still have the speakers) !