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RE: magnetrons as diodes

Original poster: "Breneman, Chris" <brenemanc@xxxxxxxxxxxxxx>

I got everything removed from the magnetron except the heat sink fins, in case it needs cooling, but noticed that there were two small inductors, each one in series with the filament leads. Will these be necessary? Also, my actions are somewhat controlled by people who don't know much about this stuff, but in my opinion, are somewhat overly cautious. They don't want me to try this unless there's some way I can prove that there would be no microwave production. Theoretically there shouldn't be, even with some small stray magnetic fields, but is there a simple setup that can be used to test this?


-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Wed 1/3/2007 2:50 AM
To: tesla@xxxxxxxxxx
Subject: RE: magnetrons as diodes


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 <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.


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