A zillion years ago when I was a grad student, our lab was given an old key-to-tape machine and my task was to get it running. I did, but can't recall that we ever made any use of it. It worked like a paper tape punch except putting characters one at a time onto a reel of 9-track mag tape. I can't recall but it must have inserted an IRG (inter-record gap) akin to feeding a new card in an 026 card punch.