William Sommerwerck wrote:
It appears that our microwave oven has lost cooking/heating power over
the
years. Is that possible: Can the magnetron put out less power as it ages?
How can one test the heating power of a microwave oven: Perhaps by
heating
a known quantity of water to a desired rise in temperature over a
prescribed
time period? Are there any such measures for a microwave oven of a known
original/rated power?

It's not a magnetron, it's a klystron. It's a tube and tubes get weak.
But more likely, one of the power sources has become weak.

I don't know where you get your information, but microwave ovens use
magentrons. A klystron is a rather different sort of microwave device. For
one thing, it's an amplifier, not an oscillator (unless you misalign it,
especially the B cavity).

I know about these things, because I used to install and align klystrons. I
could tell you a few "Jedi tricks".



.....Just remembering a few years of tweaking 1kw klys'es at 0-dark-30 in
the military and watching the beam current like a hawk.....


ISTR some commercial process heating chambers that used multiple
klystrons for outputs.