Re: High voltage standing waves with a magnetron?

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Original poster: "S & J Young" <youngs-at-konnections-dot-net> 

OK, I am the "someone" referenced below.  Correct me if I am wrong, but I
believe the voltage on a magnetron needs to be high enough to cause the
electrons to have enough velocity to end up in circular (actually a many
turn spiral) orbit.  It is the electrons whizzing by the cavity gaps that
generates the microwave RF.  So, I believe if you reduce the voltage so the
tube only draws a few ma, the electron trajectory will only slightly bend on
its way from filament to the cavity assembly, and no RF will result (i.e. it
will act like a vacuum tube diode).  I would think by the time the voltage
is high enough to allow the electrons to sweep past at least a few cavity
gaps the current is going to be fairly high and the output power probably
will be in the dangerous range.

Maggie experts - comments??

--Steve Y.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, February 03, 2004 1:08 PM
Subject: Re: High voltage standing waves with a magnetron?


 > Original poster: Ed Phillips <evp-at-pacbell-dot-net>
 >
 > "Hi,
 >
 > Someone earlier suggested that the only way to stop the magnetron
 > drawing 'normal' current is to reduce the voltage a lot, which of course
 > kills the oscillation.
 >
 > Frankly, I don't know enough about magnetrons to be authoritative, but I
 > would expect one to oscillate when fed from a current-limited supply of
 > the appropriate voltage.
 >
 > I'm not suggesting it's simple, but it's certainly possible to build
 > such a supply."
 >
 > Simple enough - just a series resistor!  Note that the magnetron
 > volt/ampere curve is not like a Zener diode (battery in series with a
 > low-resistance diode, but that it also has a series resistance. I
 > couldn't find an oven magnetron characteristic data sheet in a Google
 > search but came up with a lot of hits on non-oven uses, primarily ham
 > radio.
 >
 > If I were going to play around I'd start with a 10k 10 watt resistor
 > in  series with the regular oven supply, measure the voltage across it
 > (and hence the current).  If the resistor blows because of too high
 > current increase it, etc.  I suspect it wouldn't take too much fiddling
 > with a box of resistors to find a combination which would let the thing
 > put out a watt or so, which should be good for a lot of experiments.
 >
 > Remember that tissue damage is due to thermal effects (heating), which
 > are a function of the exposure time and the amount of energy absorbed
 > during that time.  Runs of a few seconds at lower power should be safe
 > enough if you keep your wits about you.
 >
 > Ed.
 >
 >
 >