Re: magnetrons as diodes

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Frosty <frosty90@xxxxxxxxx>

Thanks for all the replies...i set it up and try 
some measurements tomorrow and tell you what happed...
Thanks,
 Jesse

On 1/3/07, Tesla list <<mailto:tesla@xxxxxxxxxx> tesla@xxxxxxxxxx> wrote:
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


----------
From: Tesla list [ mailto:tesla@xxxxxxxxxx]
Sent: Tuesday, January 02, 2007 8:26 PM
To: <mailto:tesla@xxxxxxxxxx>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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Frosty