Are there any downsides to the slower speed 4 pole heads in the ST class?
Yes, these heads have a very high rotor mass, and the diameter is larger than the modern turbine type rotors. High RPMs generate considerable centrifugal force that could deform the windings, and even throw a bobin (winding) off the rotor! When the RPM goes far above the rated speed, the voltage and thus the current go higher in the harmonic winding, and the field. I have not tested these heads to see where they come flying apart, and I don’t know if the current and voltage get high enough to smoke the harmonic or field winding, but it is possible. If the throttle rack sticks on your engine, and RPMs get real high, it may not be economical to fix the head id it scatters parts or smokes. One could calculate the amperage in the field. and put a fuse in series with the AC side of the rectifier, this would offer some protection in over speed, and if the generator has a load on it, the field fuse might pop before the appliances and generator head does. Experience from the field is helpful i
