Sounds like a better regulator is the solution

My regulator is an ordinary machine-sensed automotive one in the
alternator, which is why I was asking about proper regs with which to
replace it.

A kind offer of the tape drive motors, but I am in the UK. However, I have
a faulty Quantum DLT drive under my desk - is that the kind that the
motors come from or are we talking about one of the big, vertical
open-reel ones that so impressed us in old films?

Regards,
Jerry