Meh, I picked it up pretty well on my own (though under the slag I am still finding beads attached to only one piece of work :P ). I learn pretty quickly though.
For stick and TIG, you need an AC or DC output with current limiting. For MIG, you need an adjustable constant voltage output.
The first is done by either a series inductor or resistor, or more commonly, a transformer specifically designed to be lossy. The losses (mainly inductive) are adjustable by what's called a magnetic shunt, which effectively splits the transformer in two, magnetic field-wise.
The second, MIG, is done by taking a standard transformer (which has good regulation, meaning the voltage does not drop much when a load is applied - aka, constant voltage) and adding taps to it. So you might have 240V primary down to 15, 20, 25, 30, 35V taps on the secondary.
Looking at your transformer, it appears to have two windings, a small one on the bottom and a large one on top, seperated by laminated iron (the same construction as the main iron core) magnetic shunts. (Or are those wood blocks??) I'm guessing this is a ferroresonant transformer, and the oil can caps were the resonant part.
Meaning: primary is loosely coupled to the secondary, which has a certain value of inductance. Combined with the capacitance, it resonates at 60Hz. By constructing the transformer properly, it can be ran on the edge of saturation in the secondary (top) side - if primary voltage increases, it saturates more and stops working as well. (Saturation is where the iron core simply stops accepting a larger magnetic field, it maxes out.) If primary voltage drops (brownout), it comes out of saturation, efficiency goes up and secondary voltage remains constant.
That's my guess. Depending on the windings, your transformer may be welder ready right now!
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @