For example: 150 to 170 Amps, what is the upper limit on material thinkness? I would like to join up to 1/4" material (steel) for example. Looking at the instructions for the Lincoln 175+ it said "Caution" - 'using this machine to weld thicker than suggested material may result in cold or insufficient welds' - more or less. I would think that 2 or 3 passes would help alleviate that but there does have to be enough heat to penetrate the base metal sufficiently.
Changing the gas merely increases the theshhold of the machine being welded with, ie, it drops the amount of power required to perform the same task with a lesser gas like C-25 or straight argon, kind of adding Nitrous to your old car, still goes from a-b but somewhat faster and does't hurt anything along the way.
Building you own is a little crazy, I've been at this for 20 years, I would'nt even bother attempting that one....
Mr Bill, I have used a Beta Mig 200 for 20 years with no problems. I have heard that the 250 version was not that great. Speaking of building your own, I also use a 24 volt battery charger to power some wire feeders. I have a couple of 200 amp transformers in the junk box. I may build another power supply. The name Mr Bill brings back memories from Saturday Night Live.