When asking questions always give us the year of car that you are working on. Anyway, a voltage requlator was not used on the generator. The item that sits on top of the generator is a cut-out relay and it is just basically an off-on switch for the generator. When the points on the cut-out are open it prevents the battery voltage from running back through the generator. When the points are closed (car running) that allows the generator voltage to go to the battery.
From what you describe, it sounds like possibly the points on the generator cut-out are stuck closed. If so, and with the car not running, that will allow the battery voltage to run back to the generator. Having no place to go the battery voltage will make the generator and the cut-out hot, and it will tend to melt the solder on the armature in the generator. Pull the cover off of the cut-out on top of the generator and look at the points. If the points are closed you found your problem. If that is the issue then you will need another cut-out or you will need to convert your cut-out to solid state by installing a diode.
If the points are not closed then, as a test, you can replace the cut-out and see if that cures the problem. If it does fix the issue then you have a defective cut-out.
Also, check the cover on the cut-out to make sure that it is not touching either the battery terminal or the generator terminal on the cut-out. If it is touching either terminal that would cause a direct short.
