[Amps] Microwave Transformers?

[KB0NLY]

I've seen a few websites mentioning the use of Microwave transformers for the plate supply in amps.  I have access to a couple microwaves with good transformers but other problems. 

Question is, since they are not labeled on the transformer, what is the average specs on these?  Voltage and Amperage?

Is there other problems in trying to use one?  I'm assuming it must be a so-so adventure otherwise everyone would be doing it as a cheap source of transformers.

73,

Scott