TBC's used to cost a packet, (the one we had was
worth around $20kAU at
late 70's prices and was the size of a big desktop pc.)
Oooh, that's a small, cheap TBC! :-) Ours took up the better part
of a 19-inch rack, and was priced commensurately. And that was in
1982, although the unit was probably 2-3 years old at the time. I'd
be surprised if there really was a TBC with a full frame buffer the
size of a big PC before 1980; the necessary memory alone would have been
bigger than a PC, not to mention the logic and the analog signal
processing.