Hi Steve,
What an interesting set- do you have a possibility to become it's new owner?
It made me think though. When I started school in 1978, the school set was a huge Thorn 1400 on a tall wheeled stand. I've a feeling it was branded 'Baird'
It had connections (PL259 and 1/4" jack) for video & audio in/ out. It also, consequently, had a hefty isolation transformer.
When not in use for a class, it was connected to a Sony CV2100 open reel B/W video recorder to record programs for future classes.
When I was 15 or so, I persuaded dad to buy a second hand CV2100 ACE (which I still have!!) I already had a 1400 chassis, so I traced out the in/ out PCB fitted to the school one and made a copy and modified my one accordingly.
No isolation transformer of course
.However, I did fit a relay between chassis and earth to disconnect the supply if the chassis became 'live'- quite safety conscious I thought!!
I had never come across RCD's then so connecting neutral and earth together via connected equipment never caused me any problems!
I took it into school for some reason and discover that when I connected it to the video recorder- the whole science block tripped out!! That was my introduction to RCD's
Sorry, just rambling, nothing much to do with the thread in question!!
All the best,
Nick