RE: magnetrons as diodes

["Tesla list" <tesla@xxxxxxxxxx>]

Chris,
 
Magnetrons are a special case of high voltage vacuum tube diodes.  As you point out, because of the strong magnets, the electron path is bent into a many-turn spiral.  As the electrons speed by the slots going into the multiple cavities, they cause a resonant oscillation to build up in the phase-locked cavities.  Take away the magnets, and the electron path goes straight between the cathode and anode, like any other diode, with the added advantage of having a built-on heat sink.  There will be zero microwave production.
 
A good experiment would be to remove the magnets, hook it up to your MOT powered by a variac, feed the rectified output to a load, such as a few feet of water-filled hose with electrodes at each end, and measure the output voltage and drop across the magnetron.  But BE CAREFUL ? the voltage and current combination is LETHAL.
--Steve Young
 

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From: Tesla list
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mailto:tesla@xxxxxxxxxx] 
Sent: Tuesday, January 02, 2007 8:26 PM
To: tesla@xxxxxxxxxx
Subject: RE: magnetrons as diodes
 
I know relatively little about tube technology, so I may well be wrong,
but I don't see why not.  If you use the original microwave oven
transformer, you can use the filament winding to heat the cathode like in
the original configuration, and the case would be the anode of the
diode.  If the magnets were removed, I don't think the cavities
inside would resonate, so I don't think microwaves would be
produced.  Always good to check though.  I don't know what the
working voltages would be though.  As I said, I know very little
about tube technology, so I'm not sure what the minimum forward bias
would be, but I think the maximum voltage across it would be limited only
by internal arcing between the cathode and case.  This could be
measured by applying increasing voltages from the cathode to case until
it started conducting (ie, an arc forms).  This might damage the
magnetron tube though if there's some insulating material in the
path.  If I'm not conclusively proven wrong by someone else here, I
plan to try this soon.  I just finished disassembling a microwave
oven and (with some difficulty, as I only had some small pliers) the
magnetron.  If I try it before you do, I'll let you know how it
works.

Chris



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