Thanks for that.
There were certainly no brushes or slip rings.
The laminations on the stator and rotor are only about 4 cm (1.5 inches) long. The rotor is about 10 cm (4 inches) diameter and the stator about twice that.
There is no separate exciter part. The only thing that changed along the short length of the rotor was the magnet about 1 cm square embedded in the laminations at one end. I can follow TCMtech's description, but on other alternators where I have seen an exciter generator and rotating rectifiers, the exciter was completely separate. On this machine I can't see any exciter.
(I'll admit, the larger machine was 6000 times the power of this, so efficiency becomes more important, and size, weight and manufacturing cost less so.)
I think TCMtech is right in that the voltage was set by the RPM, and when we tried it on a hairdryer that tried to take too much power, the speed would hunt, slowing and speeding up in about 2 - 3 seconds, but not doing any damage. It was stable at lower loads.
It seems to be 3000 rpm, 50 Hz. It is 2 pole, and it is a tiny 4 stroke single cylinder Honda engine, so 1500 rpm would be too slow.