Yes, this is a transformer machine, but it is also a square wave machine, as far as I know. It is what I learned on in college, but it is far different from my transformer machine.
Transformer vs. inverter is not nearly as important as the waveform. Most people ignore the waveform.
This is a sinewave transformer machine. Notice the lack of all the fancy dials?
Yeah....it only needs up to 104 amps at 230 volts single phase input, but it will put out 460 amps on the other end.
For steel and stainless, I use thoriated. I got a bunch of it for free, from my neighbor. Pure for aluminum is how I started, but then I tried 2% lanth and I like it better. It seems to work fine for steel, but it is a waste when I have boxes and boxes of thoriated for that.
I'm pretty sure we used thoriated on ac for welding aluminum, at the college, with the syncrowave. It worked better than pure on a sinewave machine because it held a better point, but it did like to split. The 2% lanthanated seems to hold a better point than pure and it will handle more amperage. It isn't hard to roast an 1/8" tungsten with that Miller 330.