Yes it looks like the JC Whitney regulator is for alts. But with the addition of a high current diode to block the battery from discharging through the coils, that regulator will control a generator. I did that on my bike. I took an extra regulator from a Delco 10 SI alternator I had lying around, added a heavy rectifier and used them to regulate the two-brush twelve volt generator on my Harley, at least until the bike's constant vibrations broke the diode off. I posted a picture of that voltage regulator at the web site link I posted above.
I have a schematic that I found on the web of the Delco regulator. Very simple in principle. I don't have that link, but here is another link to a voltage regulator design for a beemer... it has a different polarity, so to make it work for GM you would have to flip all the transistor polarities. And you would have to add a diode at the armature to make it work with a generator, as I mentioned
http://homepage.sunrise.ch/mysunrise/joerg.hau/mot/voltreg.htm One thing I have found out about building electronic stuff like that at home, it is extremely time consuming. To make a worthwhile product you would have to go through a development process of prototyping and troubleshooting, then fabbing circuit boards, if you have the experience, or sending out to have them made. I got a little taste of the amateur product development headache with an electronic ignition I make, which I sell in very small volume (like about one unit every two months) through a motorcycle discussion board. It takes all afternoon just to make one or two units, and these is a very simple circuit with just two transistors. But the final result is a beatiful unit sealed inside a piece of seamless square aluminum tubing about the size of a cigarette lighter. For potting compound I use ordinary black silicone rubber door and window sealant in a tube from the hardware store. I tried epoxy, but it caused the circuit to malfunction. You can see a photo of it at the webshots.com link.
Back to voltage regulators... the transistorized version of the 12 volt Harley regulators that are sold by Accel and other vendors would probably work on a GM truck (although it would cost less to use the JCWhitney regulator and a hefty diode). I've never worked on an old GM generator but I think the setup is the same as Harley: the generator has an armature terminal and a field terminal. The charging current comes out of the armature terminal. The regulator determines the armature output by the amount of current it allows to go from the field terminal to ground. This sets up a stronger or weaker magnetic field, allowing for a greater or lesser output power from the armature depending on how much voltage the regulator senses at the battery wire.
One significant difference between the mechanical and solid state regulators: while the mechanical regulators have current limiting, the solid-state ones do not, at least the ones I have seen. So if you have a dying battery that will not hold a charge the generator will put out maximum current in an effort to keep the battery voltage up. Older motorcycle gurus will tell you that a generator can burn out under those conditions.
But it is easy to limit current on a solid state regulator by putting a resistor of a few ohms in the wire that connects the field terminal to the regulator. How big a resistor would have to be determined emprically, but it would be somewhere in the 1 to 10 ohm range.
I'd be interested in collaborating or at least discussing this stuff more, since it looks like there are some EE's on this board. Myself, I'm an engineering school dropout (2 years of mechanical engineering).
