All transformers are not created equal.  Neon Sign transfromers and Oil Burner
ignition transformers are designed for arc/spark duty (quasi short circuit).

Microwave oven transformers are not.  I have not had the oppotunity to tinker,
but, basedon the design, I suspect they would have a short life in a tesla coil
application, with some risk of the end of life being marked by the great
ceremony known as "letting out the smoke".

	(In case anyone is unfamiliar: all electronics run, really, on smoke.
	If you don't believe me, let the smoke out and see what happens...
	This is PARTICULARLY true of the branch called power electronics...)

If i had some appropriately rated tubes, the microwave transformers might be
good to work with.  (The magnetron freq ia set internally.  Can't recallibrate.)

Microwave oven transformerss could be used, but would take care in handling,
and likely lose in efficiency.