"glennpm"- Thanks for posting that link; I think I'm going to dig my "Stitch-Welder" out tomorrow. As I remember, the instructions that came with it were not nearly as detailed as the ones in the article. They certainly didn't go into the theory, diodes and solenoids, etc.)
To further muddy the water, a year or so ago I purchased an "Everlast" 140 amp stick welder. It is the next generation of welders, using what is called "inverter" technology, rather than transformer. I bought it because it is very small and light and has the option to run on 110 volts (though it is primarily a 220 volt unit). I was initially only going to use it for off-site use where there was no 220 power, but find myself using it in the shop more and more often. I bring this up only because the referenced article said that regular arc welders can not be set to a low enough amperage for sheet metal. This thing will go down to 10 amps reliably. The only sheet metal work I have had an opportunity to do during the time I've had it was to shorten up a battery hold down for my '51 (It was about 1/2" to long for the aftermarket case I bought to house my Optima). The Everlast was all hooked up, so rather than unlimbering my MIG, I decided to try the Everlast. It worked perfectly, uniform bead and no burn through. When I had my 225 Miller stick welder, I usually used 1/8" 6013 electrodes on heavier stock; I usually ran them at around 125 amps. I find I can run them just as well on theis machine, although they seem to like a slightly lower amperage setting. I have been thoroughly impressed with all aspects of this machine.
Another thing about it is that it is a DC welder, not AC which is preferred by a lot of folks. AND, it comes with a TIG torch; all you have to do is buy a bottle and a regulator and you have a TIG welder (albeit "scratch-start"). I have not sprung for a bottle of Argon yet. The apparent downside is that Everlast welders are made in China, but if mine is any indication, the apparent quality and warranty make that on non-issue. Everlast makes a lot of different units from this all the way up to large TIG units, and all are highly rated.