If the Weller Irons discussed are those I used ages ago, the technology is based on the Curie point which is the temperature at which an alloy loses magnetic properties. So by placing an alloy with a curie point of x degrees at the end of the tip and having a magnetic switch close by, you get a temperature controlled soldering iron.

Erik

Anyhow, Oren has a problem which is not his soldering iron, he need (to answer that he has) install the capacitors. I use an old router for noisse test, if a circuit will keep running next to my old router (sparky) running it is sufficiently noise protected.