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Low powering magnetron

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LAN_403

Sat May 15 2010, 09:33PM

Registered Member #2372 Joined:
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Posts: 62

You cant limit the current going into the magnetron without limiting the voltage. The device will draw some specific current at a given voltage. The magnetron will not operate without being at a specific voltage given by something called the Buneman-Hartree condition which relates the voltage and magnetic field necessary for a crossed field device to have an electron beam interaction with the slow wave structure. If you want 10 watts buy a 10 watt source as was mentioned above. Trying to run such a high power device will likely lead to personal injury and destruction of electronic equipment that is close to the experiment. People who do this for a living do it under controlled conditions and are standing in another room when the experiment is turned on.

radiotech

Sun May 16 2010, 05:03AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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I've got a watercooled magnetron that i want to make a lamp out of. No, the bulb wont be powered by microwaves. There is bag of old tricks that can make common radio tubes produce microwaves.Even some lightbulbs made 40 years before TV came out can produce radiation that can wipe out TV reception for miles. It took TV and the FCC to discover this charming fact.

Sun May 16 2010, 08:21AM

Registered Member #2372 Joined:
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The mention of the positive grid oscillator sounds very similar to the vircator or virtual cathode oscillator. What book is that from?

IntraWinding

Sun May 16 2010, 09:12AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

What form of discharge takes place in a magnetron? Is it like an arc where, once struck, the voltage drops and the current rises, or does it require a constant high voltage?

Steve Conner

Sun May 16 2010, 09:47AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

You can lower the output power of a microwave oven by using a smaller capacitor in the voltage doubler circuit. Say 0.01uF instead of 1uF. The peak power is still fairly high, but the pulses are shorter, and the average power is reduced to a safe (?) level.

There is no discharge in a magnetron, it's a vacuum tube. Electrically it looks like a Zener diode, the current rises sharply above a threshold voltage which depends on the magnet strength. If you take the magnet off, it becomes an ordinary diode.

A magnetron is a fair electrical analog of a wind instrument, you only get the right "pitch" (frequency and spectral purity) if you "blow" it at the intensity it was designed for. Under- or over-powering one can give you the wrong frequency, an unstable frequency, multiple frequencies, or just noise. So, you can't get radar- or HERF-like pulses out of an oven magnetron, and you can't get modest CW power out of a radar magnetron.

Proud Mary

Sun May 16 2010, 10:24AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

There's a super essay on the use of 2.45 GHz oven magnetrons for other applications here:

The Magnetron - A Low Noise, Long Life Amplifier

But that doesn't mean I endorse potentially very dangerous experiments by inexperienced people.

As others have said above, there are plenty of other ways of getting experience with microwaves
and waveguides without acting in an illegal or dangerous way, including small reflex klystrons which
can be bought very cheaply from Russia, miniature UHF lighthouse triodes (also very cheap from Russia)
GaAsFETs and Gunn Diodes.

When you have found a way of making the microwaves behave in the way you want them to behave,
coming and going at your bidding, then you might consider moving up to high power devices.

radiotech

Sun May 16 2010, 04:43PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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the book is : WL Emery, Ultra High Frequency Radio Engineering, ,Macmillan, New York, 1944. (was written before the U.S. entered WW2) the MIT crowd

Sun May 16 2010, 06:27PM

Registered Member #2372 Joined:
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Posts: 62

Here is a video on youtube that attempts to explain how a magnetron works

LutzH

Fri May 28 2010, 07:14PM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
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Posts: 136

Hello:

Yes you can run a garden variety oven magnetron at reduced power, even in CW mode to boot. 10 watts may be asking a little much, but a little more up to about 100 watts can be done easy.

There is a brilliant gentleman named Doug Coulter who contibutes regularly to the fusor.net forum. He designed an RF discharge ion source powered by a garden variety microwave oven magnetron which he runs in CW mode at reduced power with a modified home brew power supply.

Just go to the fusor.net forum and follow the ion source thread and read Doug's work. He is an amazing fellow, one of those people who are in it for the science, and not for the ego, or the money. I plan to use his ion source design in my acellerator, so I am very familiar with it and I have emailed with him about it a lot. Read the thread for the Q & A. Here also is the direct link to Doug's CW microwave ion source project I just found it, enjoy :)

Before you do anything like this: Do yourself a favor and read, read, and read some more, on the subject of microwave safety. This is simply the first step, the technical part comes after if you value things like your vision, testicles etc.

Take care and good luck.

cedric

Tue Jul 27 2010, 09:43AM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
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Posts: 143

I try to low power a magnetron ,simply plunging it to a obit (6 kv 100 w)with a diode and a filtering capacitor ,the heater was just 5volt 4 amp transformer ,it work well ,all the wireless in the apartment was down...,but we could not found other way to detect microwave...

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