solid state replacement for relais type voltage regulator

[fritz]

Dear All,

I own a Kawasaki Z650B1, build 1976 with an old
generator, stator field controlled by a nippondenso relais
type voltage regulator.
Its the same system they used in cars up to the early 80ties
where one end of the stator coil is tied to ground - the other
end is switched directly on 12V, via 10Ohm Resistor or shortened.
(depending on load voltage)

There is no OU with the Kawa so far - but starting the big DIY on that
is probably inventing the wheel over and over.
So if there is someone who knows about a nice solution for that -
this would be quite helpful.
Normally, this things end up with a dirty oscilloscope and a box of dead
MOSFETs - I want spare that.