Ron Johnson wrote:

It is possible (IME) for magnetrons to lose power over time, sometimes
the antenna cap gets eroded away and sometimes you find cracks in one
of the magnets.

Ron

Yes they do loose power over time ! It depends upon how fast the
filament/cathode looses the ability to produce electrons. Often
Thoriated Tungsten is used in the heater ! If it gets hammered it
rapidly looses emission.

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Best Regards:
Baron.