Comment by Animats

We had some early models which had two ordinary coax lines going in. Unplug either and the ring went down. They probably converted to something with one connector, and maybe a mechanism to close the loop if unplugged. That's a basic problem with token ring - anything removed must be jumpered out.

We just had two loaners for a demo, so we might have been given an old model. We were evaluating workstations, and had various devices for a few months at a time.

I saw quite a bit of rare early hardware over my career. Much of it was rare for a good reason.