Not that they weren't stable. They were powered with unfilterd DC,
which caused a wideband output. They are operated as a self excited
oscllator when used in a microwave, and as long as the thing is in
band, the frequency or bandwitch doesn't really matter.

Wasn't that an Eagles song? "Bandwitchy Woman"?


Isn't the frequency determined by the dimensions of the cavity
the energy is dumped into? Or does that tune it too broadly?

If I understand your misunderstanding... "Wideband" refers to the "spuriae"
generated by the unfiltered 60 Hz and its harmonics.