Cavity magnetron - A cavity magnetron is a high-powered vacuum tube that generates coherent microwaves. They are commonly found in microwave ovens, as well as various radar ...
http://en.wikipedia.org/wiki/Magnetron

i always tell my buddies about this, and they are amazed.

it is hard to get to, it looks like they set the Magnetron on the table, and built the microwave around it.

but most under cabinet /range hood microwaves are a few hundred dollars.

so it makes sense to pay $50 for a new magnetron, and spend a few evenings monkeying with it.

here's where i have bought them in the past:
http://mcmelectronics.com/search.aspx?C=&K=magnetron
http://mcmelectronics.com/

be aware, a magnetron from your local store maybe 3 times as much.

 

there is also a fuse on most microwaves that protect the magnetron. check it first and maybe get away with a $.50 fuse over a $50 magnetron.

 

Or a $50 microwave

 

paid $109 at Sam's for my stainless steel interior microwave.

 

A magtube failure isn't very common anymore and most people assume no heat = magtube when most likely it's a failed Primary or Secondary door latch switch.

Watch out for that Capacitor too...2100V discharge doesn't feel nice, I know.

OEM magtube's will fetch 125-200, but an aftermarket, even through an appliance repair shop shouldn't be more than 75.00.

P.S. Take apart your old Magtube for the magnets, they come in handy for many things...Extremely strong, but brittle, so be careful.

Oh, one more thing...

Magtube, Magnetron = same thing.

Magmatrometer = laughter after you leave the store, or maybe ridicule while you're still there.