jOe wrote:What I was driving at is, can a 6v be modified to work on a 12v system
Why would you? You can buy a NOS one on eBay right now. There are two: one is $99, the other is $85. It is Delco # 1119614 and Harley # 74510-64 Search for "Delco-Remy 1119614"
A NOS regulator is a very worthwhile investment. Regulators wear out from hours of operation, not from calendar age. A NOS regulator has 0 hours. A used regulator has unknown hours. The NOS regulator will last your lifetime - and much more. The used one? Guess your best. There are new reproduction ones sold for half the price, but you'll have to guess your best on the quality of those.
Could you? Perhaps. Assuming the one you are speaking of has the same internal construction. Since the 12v system carries half the amperage of a 6v, the wires in a 6v regulator would not burn up from application of 12 volts. However, it is very doubtful that anything would work correctly. Even if the coils in the voltage and current sections worked passably at double the voltage (doubtful), the voltage section would need to be adjusted to operate at twice the voltage, and the current section would need to be adjusted to half* the current. I doubt that there would be that much adjustment range. Also, there are one or two resistors in there that might be the wrong value. Remember, Delco-Remy spent a lot of money on engineering to make a product that worked correctly and last a long time.
-----
Many regulators (of the same voltage and polarity) have the same internal construction, and the only differences are the factory adjustment of voltage and regulator settings. A regulator for a 1968 Cadillac, which has a lot more electrical requirements than a 1968 Harley, operates at voltage X and current Y, while the Harley will have lower settings. Getting these adjustments correct is a tedious, time-consuming process, and is best done on a test bench rather than on a vehicle. Instead, Delco factory adjusted a regulator for a 1968 Cadillac, and gave it part number 1119abc, and they factory adjusted one for a 1968 Harley and gave it part number 1119614. That way, the mechanic can look it up in the catalog, and just slap it on the vehicle- instead of spending considerably time trying to adjust a generic one.
But you can't judge a book by its cover - regulators which look the same from the outside can be way different inside. Even inside, you may not be able to see a difference, and by that, I don't mean just the adjustments. 20 years from now, people will have to get pretty creative to replace a failed regulator. But today, you can still buy a brand-new one for a reasonable price - so do it!
* not exactly. In general, later motorcycles had more electrical equipment, larger batteries (for electric start) and needed a higher charge rate than older bikes.