Looking at the rack, since a Straight-8 has huge
backplanes that fill
the top of the rack, there are no upper doors - I'm wondering if
that's an -8/S cabinet.
Hmm you are right, It can't be a PDP-8
http://www.oldcomputers.arcula.co.uk/files/images/pdp8101.jpg
I then thought It might be a PDP-5, but that is probably not so:
http://www.mcmanis.com/chuck/computers/images/pdp5-rescue.jpg
Perhaps it is for a peripheral for one of the above?
mvh,
Pontus.