Guys I have the stock original 66 62 amp alt inn my car with an extrnal regualtor all new wiring ............ground straps etcet5c but I keep blowing the reg I have had the points type and the electronic type .....dont tell me to switch to the newer style alt......... when it works iot works great chaging is controlled well but a couple of times a year I get in and start the car and the volt guage shows discharge ...change reg and its fine again for a month or two ?? I do have kill switch on cat htat when parked I shut off all the power

You might take a VOM and check the resistance from the case of the regulator to the alternator (they should be at or near the same potential). I had to remove some bolts and shine up the metal on the radiator surround on my '69 to get it reliable.

The regulator turns the field coil on and off, if the resistance of the field coil is too low because a few of the winding have shorted it will cause the current to go up. The regulator was designed to handle a given load say 3 amps, if the regulator now has to handle 5 amps it will fail over and over until you fix the actual problem; a bad rotor.
Have either a local alternator shop check it or look up the specs and then check it with an ohmeter.

Thanks guys .........some good points here I never checked