I built a stick welder using two microwave transformers and a DC bridge rectifier. To control the heat, I created a triac current regulator attached to the AC input of the transformers. I have used this specific circuit for a long time with these transformers however I got an overheat blow out of my BTA41-600B triac last time (the triac physically caught fire). I ordered 4 new ones, and they seem to be instantly failing with the load terminals stuck open. If I allow full current to pass through the triac, it doesnt break, however when I try to regulate the current, it instantly stops regulation and stays shorted. Is there something wrong with my design? And if so, why are these the only triacs being affected?