Back in the old days many of the higher quality welders, both Ac line powered and engine drive, had a large variable inductor built right into them so all you had to do was turn a big knob right on the front of the machine to fine tune your weld.
I have been watching the scrap yards and industrial equipment auctions for some time now for machines that have that big variable reactance system still intact to the point of being rebuildable and usable so I can set one up as an external system to use with the modern welders. The new machines seem to never have the correct range of inductance built in to them.
The good ones now have at best a low, medium, or high internal connection that can be changed if you take the machine apart but many dont even have that option now.
The so called welding experts seem to think that its not needed but for anyone who has ever welded with one of the old school machines that had that feature the weld characteristics are so much smoother and nicer than what is typical of todays best machines.