Fred wrote:

I would have thought the AVR would have terminals for a battery for the
initial excitation? Given that this is a 1980's alternator I doubt the
electronics at the time would have stretched to supplying 71V and 18A. I
may well be wrong but I would have thought a mechanical vibrating regulator
would be more likely.

Back in the 1980s we had these things called "computers" which were
sometimes the size of a small car, and ate 10s of kW at 5V. And we had
these other things called "Radars" which sometimes ate megawatts - at a
somewhat higher voltage.

So I wouldn't be at all surprised to find an electronic one in equipment
of that vintage.

Andy