The way to use Microwave Iron in your power supply is to take 2 units that are electically similar (easier to do since most of the innards are made by a few suppliers so you can use the part numbers right off the trannie) and bolt them together. The frames of the single ended transformers then become your center tap. and keeps the winding to frame voltages at the recomended levels to prevent breakdowns.
You also have to remove the magnetic shunts, else your regulation will be really bad. The Filament windings can be pulled out or left in place (I'd remove them).
To be really sure of a good electrical connection, I take the two frame connections and move them to a common point on one frame and clean the mating surfaces abit on the frames, pull the center tap wire direct from the common point. You can leave it open though it looks ugly as sin, or put it in a small box and bring out your wires.
Since most MOT's are 1-1.5kv you can get 2-3kv out at around 0.2-0.5 Amps depending on the trannies. Use Variac to power them up to a known LOW voltage and you can figure the final outpoot pretty close.
They are also very easy to rewind as low voltage-High current filament transformers. Just remove the secondary(unfortunately you have to use a wood chisel or similar, I don't know how you could unwind it to save the copper
) That leaves plenty of room for a few turns of thick wire for filaments on bigger tubes like 4-250s and 4-400's.
I get mine from the Appliance reclaim at the dump, always free, and with some patients you can get some good Iron plus HV diodes, interlock switches, etc. the Caps are very low uf values (aournd 1) so their usefullness in a HV supply is limited, but they are HV oil caps so they could be handy for other stuff....
