Alterator charging voltage

Finally got my 318 running this morning. I checked the voltage at the battery (at idle) and it read over 15 volts. I assume the voltage regulator is going bad. On this engine, is the regulator internal to the alternator or externally regulated? If it's internal do I need a new alternator or can it be fixed? My '65 chevy was externally regulated.
Ron
Author: 1970ccc