RE: magnetrons as diodes

["Tesla list" <tesla@xxxxxxxxxx>]

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?

Chris


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

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 <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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