You are aware that the SOHC4 does not employ a permanent magnet, right?
Ours varies the alternator output strength by varying the magnetic strength of the field coil.
That is not to say the circuit you referred to wouldn't "work" with ours. But you would have to wire the field coil direct to +12V. And then let this design short out phases of the alternator output to keep from over charging the battery with the zener reference, rather than actually sensing the battery voltage ( and temperature) to make decisions about alternator output strength. While the stator windings are robust enough to take routine shorting, I fear for the field coil being run at 100% input power all the time. I suspect wire insulation will break down with the constant heat. I already have a field coil that fried, from adding extra power drain on the bike (radio and lights back in the 80s). This forced the regulator to drive the field coil more than usual to keep the battery up. The 550 is supposed to have about 5 ohms for the field coil. And mine now has just under 4, with the resultant weak mag field strength and corresponding poor charging effort. Good thing that bike has a light switch, as I can't run all the time with lighting on in city traffic. Someday I'll put in the replacement field coil I acquired. ...when my spare time is ever more copious. And I don't have other bikes to ride. :-)
Out of all the SOHC4s I've had, only one Vreg didn't work like it was supposed to. That was a bike where a PO tweaked it to try and compensate for corroded wiring terminals, worn switch contacts, and an oxidized fuse block. After proper re-adjustment, it worked like it should. In theory, the internal contacts should wear eventually. But, the shop manual explains how to restore that portion back to spec. Seems a pretty robust unit, to me.
One thing I see in the stock regulator, that I have never seen in a combo unit, is temperature comp for battery state of charge. See, a lead acid battery will display a lower voltage when cold even at full charge. If you try and charge it, as it were a hot battery, you can overcharge it and boil off water in the electrolyte. The stock regulator compensates for that, as well as some battery chargers/maintainers, but it is not very common, as it requires a bit of extra engineering cost that 90% of customers simply won't pay extra to have. I assume it is ignored, that battery replacement is more frequent than it should be.
FWIW
Cheers,
