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Homemade Magnetron

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Moon Bug

Sun Feb 12 2006, 08:29PM

Registered Member #109 Joined: Fri Feb 10 2006, 12:20AM
Location: On The Moon!
Posts: 4

Here it is: my narrowed thread. My thanks go to Alex and Firkragg for pointing out that it was way too broad.

I am interested in constructing a homemade magnetron of some sort. I have read up on how they are built, and I feel I have a good understanding of how they work. I realise that there are certain dangers involved with electromagnetic radiation, so I do not plan to make it very powerful at all. Of course, I have fairly limited resources, and to make a very efficient one would require a lot of money and equipment, so I do not plan on it being very effective.

To start off, I have some quetions (as always

):

* Is there any easy method for creating the vaccum required in a magnetron?
* Is it completely necessary that the resonating chambers be specially shaped?
* Would a solenoid placed around the magnetron be a suitable replacement for a natural magnet?

Marko

Sun Feb 12 2006, 08:48PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

* Is there any easy method for creating the vaccum required in a magnetron?
* Is it completely necessary that the resonating chambers be specially shaped?
* Would a solenoid placed around the magnetron be a suitable replacement for a natural magnet?

1. of course it is but you need lots of glassblowing (and metalworking) expeirence and expensive machines, nothing to be homemade. Just impossible.

2. Yes.

3. Electromagnets can be used but permanent are far easier to install in tube.

Yust kill some ovens and get for free huge magnetron, but dont toy with it as it can cook you in place when powered...

Moon Bug

Sun Feb 12 2006, 09:09PM

Registered Member #109 Joined: Fri Feb 10 2006, 12:20AM
Location: On The Moon!
Posts: 4

I agree that it would be cheaper and easier to simply take a magnetron from an old microwave oven, and I have considered doing so. However, I have decided to try making my own for several reasons:

* I would like to see if it is at all possible for one person to make one without a lot of expensive machinery.
* To experiment with various apect of magnetron design
* To build several small magnetrons and make a chamber in which I can test effects of microwaves on a small scale

I am perhaps going out on a limb on this last reason, because it does not seem too likely that I could get that far, but a person can dream, can't they (

) ? As for my other two reasons, I was wondering if there is some way to build even a semi effective magnetron without a nearly perfect vacuum (perhaps a partial vacuum or a unique concentration of gasses would do

?), or if there is any other way to produce microwaves in an effective manner.

Hazmatt_(The Underdog)

Mon Feb 13 2006, 02:06AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

The best I think you could possibly do is to make a Klystron. I think that a Magnetron is way out there. I've taken them apart for the magnets, then taken the tube apart and to tell you the truth, I can't see any way of an inexperienced person really making one of them. The core is a massive copper resonant cavity terminated to a ceramic wave guide. I don't doubt that it all has to be aligned axially too.

But you know what, a Klystron might be a good start. You don't need massive flux densities, they're semi-adjustable so that's in your favor, its low energy microwave which is in your favor, and you may be able to construct it in a vacuum chamber which is in your favor.

Moon Bug

Mon Feb 13 2006, 04:16AM

Registered Member #109 Joined: Fri Feb 10 2006, 12:20AM
Location: On The Moon!
Posts: 4

Sounds reasonable to me. I was wondering, though:

* Is it possible to construct an electron gun, or would it be necessary to buy/scavenge one?
* Is there a way to modify the design to make it more compact? Perhaps making it like a reflex klystron or some other such arrangement?
* Would this be a fairly expensive project? And if so, are there any ways I could use less expensive parts?

Just wondering.

Steve Conner

Mon Feb 13 2006, 11:43AM

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

The only really difficult bit of building a magnetron or a klystron would be pulling the vacuum. They absolutely need a high vacuum to work. Check out the Teralab site for more info on DIY vacuum techniques.

IamSmooth

Thu Feb 23 2006, 07:14PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I am curious about magnetrons and one of the replies stating that it can cook someone when powered. First, I have no current plans to use one. My question is, if I were to experiment with one, how does one go about safely powering it and directing any MW radiation away from "cookable" objects?

Marko

Thu Feb 23 2006, 07:46PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

With adequate horn antenna you can focus radiation in order to jam/disrupt/cook/blow some cookable or electronic object

Magnetron pionted into a man can cook him as well, but some ''stories'' are overbabbled and except heating (deep) magnetron does not cause cancer, long-term progressive illneses or so, everything it can is to heat and if we heat ourselves by 2kW bulb from such proximity we will also lose sight, get nasty burned and cooked (OK but here we get only surface burns).

If we do not dance in front of magnetron heating is slow enough to allow us to retreat before we are burned, maybe eyes are most critical as heating chataracts can be get quickly...

If manned wisely magnetron can be used without harm, and we can use it for interesting experiments (most of people do it in their ovens, arcing (metallic object, CDs) generating plasmoids, cooking interesting things...

sam actually made a 'magnetron gun' but horn is still not shown, intention is to use it for same effects but outside the oven.

Hazmatt_(The Underdog)

Thu Feb 23 2006, 08:10PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

To make either I would say yes its expensive. Why?

Okay, I almost have all the equipment to do this, and it's costing me quite a bit. I have almost all the resources for glassblowing, tubes, torches, cylinders, etc. But consider when you look at any electron tube there are about 100 steps to making that tube including de-gassing the metal, special plating procedures, special welding techniques, and a ton of background, I have a book on this by Fred Rosebury.
So that part is terribly involved, not to mention obtaining the high purity nickle, making the tungsten filaments, and coating them with thoriated oxides and inserting it into the cathode without causing a short or low breakdown voltages.

Now consider the vacuum system. My duo-seal cost me $150, but that't no where good enough like Steve said. That's only 1/3 there. Yes, you need a diffusion pump of some sort, which I got for free from college (because I have a friend, who I'm designing a Tesla Coil for.), and then after that you need a 'Getter' in the system. This is a mixture of Barium or Calcium and Magnesium or Aluminum to 'get' left over stuff so you can go down to 10^-8 Torr. But that still doesn't guarantee anything because as the tube 'ages' you have a boiling effect from the cathode, so you would probably want to inductivily heat the whole tube with RF and get it cherry before flashing the getters in the system and in the tube.

I'm not quite there yet because I don't have enough soft glass for the copper electrode sealing. All they sell now is Borosilicate, which means Tungsten seals, and that's very involved!

If I can do it, lord knows I want to, I will make a Crooke's tube first.

Matt

Oh, I don't know if you can find a book on electron tube technology, like I say its something like "Handbook of Vacuum tube Technology" or something by Fred Rosbury or Rosebury. I'll make sure when I get back home.
If you can't find it I may be able to have Kinkos scan the book, but its $$$$$

johnf

Mon Feb 27 2006, 09:08AM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

If you are this serious get a turbo pump and pirani vacuum gauge and do it live ie in the system being turbo pumped. I have a setup at work for my research into new devices and the turbo gives me 2 by ten to the minus seven torr while i'm doing measurements (including out gasisng from cathode / anode strutures under power

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