Generators, 'A' or 'B' Circuit?

I thought I'd throw in a little information about auto and tractor generators this week.  Please consider this information as general in nature.  You should find an experienced electrical technician for proper identification and testing.

The main difference in the various generators that were produced in older vehicles and tractors is that there were either 'A' circuit or 'B' circuit units.  What this means is how the units output, is controlled by the regulator, regulating the field current (to the 'F' terminal on the generator).  In the 'A' circuit generators, which were mainly Delco units, were controlled by the regulator varying the ground to the field.  In 'B' circuit generators, the regulator applied current to the field, which was internally grounded.

Most 'A' circuit units were on GM products and many farm and industrial tractors.  'B' circuit units were mainly found on Ford products and possibly industrial units, but there were a few 'A' circuit Ford tractor units produced.   Later generators on Ford tractors were all Lucas brand 'B' circuit generators.  Other manufacturers like Autolite and Prestolite made generators also, and they could be either 'A' or 'B' circuit.  Delco may have made a 'B' circuit generator, but I've never came across one!

I will offer a little testing and advice for generators in the next post!