TRIAC AC regulator for welding transformer

An old welding transformed once had a AC regulator, that frequently burned the potentiometer. Regulator, possibly TRIAC had disappeared, and the transformer primary was connected mains. Thin iron plate would be much more convinient to weld with small current, so AC regulator is a must.

TRIAC phase angle controller is cheap and siple, it only requires few external components. This circuit is straght from my vocational training book, Sähkötekniikan perusoppi 5, Elektroniikka II (Pentti Salo). I used TIC246M TRIAC:a and 2,6mm welding rod burned nicely, while the heat sink only got slightly warm.

Here are the circuit board- and component placement diagram. Circuit board can house different size of components, depending holes that you drill. The pictures show the other components and the potentiometer that I placed on a connector. I placed the TRIAC to the bottom side of PCB for easy heat sink placement. TRIAC TO-220 case back side is connected to high voltage, so use insulator between TIRAC case and heat sink and allso the screws.