Re: Source of free toroids(?)

Subject:   Re: Source of free toroids(?)
  Date:    Tue, 29 Apr 1997 17:47:09 -0700 (PDT)
  From:    "Edward V. Phillips" <ed-at-alumni.caltech.edu>
    To:    tesla-at-pupman-dot-com

"The magnetron of a microwave oven has ring magnets made of ferrite (or
some sort of ceramic like stuff).  Any thoughts about this source?  I
don't see why the magnets wouldn't work, but that's why I'm asking."
        They are absolutely NG for this purpose, but (if large enough)
would be great for Levitron base magnets.  Wrong kind of ferrite, 
magnetized so that the permeability is very low.  I personally think
that air core solenoids of 10 mH and greater are the way to go, as
they have to voltage breakdown problems and no core saturation.