How to characterise unknown transformer

[pixpop]

I have some old equipment to pull apart for parts, which includes a power transformer. How do I measure the transformer to determine it's characteristics so I can decide what to use it for? In circuit, it generates 45-0-45 VDC, but how do I figure out how much current it can supply? Do I apply an increasing load until it gets hot, or look for a certain amount of ripple.. what's the best method?

[pinkmouse]

An easy way to estimate is to look at the enclosure it came in. It should have a required wattage label somewhere on it, usually near the power inlet. Other than that, look at the on board fuses, they are usually 25% to 50% over rated for the normal running load.