1993 kubota B6200 tractor?

I'm trying to fix the charging system on a 1993 kubota tractor. The voltage regulator is external to the alternator/generator. Does the tractor have a generator or an alternator? There are two wires coming out of the alt/gen. When the engine RPM's come up off of idle, the output voltage of the alt/gen reads between 16 and 17 volts a/c. The regulator does not put out a charging voltage, ie. the battery voltage does not increase...it reads 12.8 to 13.2 volts DC. Is the regulator bad, or is it something else?