Examples, if you use thicker wire and less of it you will get higher current but lower voltage, if you use thick wire (not as thick) and a few more turns of it you will get high current and slightly higher voltage. or if you keep the original windings you will get one to two thousand volts at one to two amps.
Now to jump right in here's what you will need!
1) A microwave oven transformer
2) An angle grinder or if you don't one and your very keen.. a hacksaw.
3) 1-5 Gauge insulated copper wire.
4) A grounded 3 pin wall plug
Onto the next step!
Step 1: Removing the secondary windings
Step 1) Take you microwave oven transformer and secure it tightly into a vice or onto a solid bench with clamps. Then plug in your angle grinder or pick up your hacksaw (with proper safety gear of course)
Step 2) Cut away the secondary windings, the large amount of thinner wire. and use whatever means necessary to just remove all of the secondary windings.
Step 3) there will be a small length of usually red wire in the middle below where the primary was this is the filament windings, remove these as well. then there is the magnetic shunts, you can also remove these, just tapping them out with a flat head screw driver will work. once all this is removed leaving only the primary left,continue to the next page!
also pictured below is what you should have, but in the pictures I have not yet removed the shunts. (the primary connections are on the opposite side.)