Altons
Since you asked...
I have an Alton. It's 12 volt, I think they all are. This was fine by me because i planned to fit an electric start, for which I'd need 12 volts. My first three-phase one failed, as apparently all three-phase ones did eventually. It was replaced FOC by a new one which was single-phase like the original. They are widely used in place of dynamos, on Vincents obviously, but also for example on Velos. They are a straight swap for a dynamo. I've had no problems in 7000 miles with the single phase, which balances a 55/60 watt headlamp at about 45 mph. The new one has a finned block regulator. Mine is fixed to the flat top of the dynamo clamp. It puts out up to 150 watts. Unregulated it kicks out 31 volts ac at tick-over. (An unregulated 12 volt Lucas pancake dynamo kicks out about 18 volts dc.)
The conclusion of Know Thy Beast is that the Miller dynamo is a well made piece of kit, at least as good as the Lucas, but that the Miller regulator is a disaster. I think the story that the milliampere was a unit introduced to measure the output of a Miller dynamo is apocryphal.