several voltage regulator burn

Fyi

If you can get the transistor number you can replace it. And replace it with a higher current version.

This is my thoughts, no particular order...

1. The regulator might not be able to handle the field current the alternator is needing.
2. There might be an intermittent short in the field wire between the alternator and the regulator.
3. Perhaps there is something (electric choke?) on the field wire.

A way to test for #2 and #3 is run a dedicated wire from the VR to the field terminal on the alternator.

As for the regulator not handling the field current, turn off everything in the car, (radio, lights etc. ) remove the field terminal and run a jumper with an amp meter in series from battery to the field terminal. This will full field the alternator resulting in high voltage charging (18v?) note the amperage. And disconnect the field wire. DO NOT LEAVE IT FULL FIELDING FOR MORE THAN A FEW SECONDS!!!!

Then look at the specs of the VR. Can it handle that?

If not look for a Heavy duty VR that can.