Abstract: In a microwave oven system comprising at least one magnetron of a given operating frequency and a mains unit for the at least one magnetron, the at least one magnetron of a given operating frequency is replaceable by a magnetron of another operating frequency. The magnetrons of the different operating frequencies have at least approximately the same mechanical dimensions so that they can be easily replaced quickly. The mains unit can be used for the different magnetrons in unchanged form or in a form involving minor modifications, without any change in the electrical parameters or with a slight change therein, thereby affording interchangeability of the various magnetrons.

Abstract: An apparatus for concentrating and solidifying a salt solution includes a vessel for containing the salt solution having an exposed surface, the vessel having a generally open upper portion, a cover for sealing the generally open upper portion of the vessel and having a generally hood shaped portion, the cover including at least one inlet conduit for admitting the salt solution to the vessel and a discharge conduit for vapor, and a magnetron for generating microwaves for heating the solution in the vessel. A microwave waveguide is disposed between the magnetron and the vessel and incorporates the cover, for directing microwaves from the magnetron into the vessel, the waveguide transitioning within the cover from the generally hood shaped portion into a horn having a variable cross-section and/or variable vertical spacing with respect to the vessel. This structure enables microwaves to be radiated directly onto the exposed surface of the salt solution in the vessel.