A Magnetron Tear Down

Microwave ovens are everywhere, and at the heart of them is a magnetron — a device that creates microwaves. [DiodeGoneWild] tore one apart to show us what was inside and how it works. If you decide to do this yourself, be careful. The magnetron may have insulators made of beryllium oxide and inhaling dust from the insulator even one time can cause an incurable lung condition.

Luckily, you can’t get a lung problem from watching a video. In addition to just seeing the guts of the magnetron, there are also explanations about how everything works with some quick sketches to illustrate the points.

While we now think of a magnetron as a microwave oven component, they are important in many microwave devices including radar. They are interesting because all they can do is oscillate. You can’t use a magnetron as an amplifier (although it can pump a parametric amplifier). While they were instrumental in building compact and high-resolution radar during World War II, they have fallen out of favor today in that application because there are better alternatives. But there are over 1 billion magnetrons out in the wild, largely thanks to microwave ovens where the signal quality isn’t as important and the inexpensive construction is a big plus.

The beast has been around a long time, too, as an early form showed up in 1910. In 1925 there was a similar device but it topped out at 30 kHz. There was a time when the magnetron was top secret, but now you can make your own.

26 thoughts on “A Magnetron Tear Down

  1. You might fine BeO in some commercial mags but you won’t find it in microwave ovens. It’s way too expensive. When you do find one there will be stickers all over it warning that it is BeO.

    1. You most certainly will find BeO in most microwave ovens from before 2005. After that, results may vary. If the insulator is pink, like in the video above, you can be sure it is BeO. (Though it being another color does not mean it can’t be BeO!)

      1. BeO is white. The pink insulator in earlier magnetrons is most likely chromium-doped alumina. Googling for pictures of pink beryllium oxide just gives pictures of oven magnetrons, which only proves how common this myth is. It doesn’t make sense that they would use an expensive engineering ceramic with in a consumer application, where safer and much cheaper alumina would do the same job.

        1. I have some Soviet RADAR tubes with pink or red ceramic, which is reportedly BeO.
          So that stuff might exist. Reportedly the GI-7bt tubes ware used in the IFF transponder of some Soviet jet fighters, along with other radar/pulsed use.

    2. There is absolutely NO BeO in oven magnetrons. Most ceramic transmitting tubes likewise. There is a persistent rumor that BeO is in all sorts of things but it really isnt, except for some very high performance microwave tubes like some TWTs, and also some high power RF transistors. There are some BeO thermal links used in some other exotic equipment also, but your chances of finding it by chance are very slim, and anything using it since the 1960s will have a warning. You can tell if some ceramic is BeO quite simply. It is a phenomenal thermal conductor – put your finger on one side, and touch a hot soldering iron to the other side – you will feel the heat come through almost immediately. That is why it is used when it is – to conduct heat out of things where a lot of heat is being generated and needs to be removed while maintaining electrical insulation. Oven magnetrons arent such a beast – the heat is mostly generated in the anode and pumped directly out to the fins. Also they are super cheap, and BeO would add to the expense, so if anyone did consider using it (they didnt), they would find a way to modify the design to not use it very quickly.

  2. Very clear and interesting explanation. It did take a minute for my ears to acclimate to the accent, but I have the same reaction to Dave Jones. Imagine a podcast cohosted by DiodeGoneWild and Dave Jones, and your head might explode.

    1. I was trying to place the accent, and my ears have failed me. The slight lyrical nature to the speech pattern would make me ASSume that they either learned English from someone who lived in some part of Wales or possibly Kerry. But I could be, and probably am, totally wrong.

        1. Hand-writing is just old school, as well as the accent. He’s probably learned English during the communism era, where there was a distinct lack of teachers who actually heard spoken English in real life, so the pronunciation and accent people learned were usually totally off (and most people didn’t study English at all).

    2. I’m usually pretty good understanding thick accents, but I’m finding this one really difficult due to the extreme variations in pronunciation speed. Needs a speed equalizer to slow the hell down the fast parts and speed up the slow parts.

  3. Pretty sure the DIY magnetron sputterer mentioned is a much different beast than a microwave oven magnetron. In the sputterer, the magnet just concentrates/manipulates electrons, to separate the electric field and the magnetic field, so the plasma’s electrons don’t recombine with the ions (as well as to draw the electrons away from wafer/substrate you’re etching/coating). In the microwave oven magnetron, the spiral (manipulation) of electrons and interaction with the tabs/cavities causes a resonance effect, and RF radiation to be emitted. The sputterer isn’t built for radiation generation at all. I think the right way to say this is that they function in completely different modes, the microwave oven in a resonant mode.

  4. He is of my nationality, Czech. This guy is very smart, and his intonation is quite uncommon even if applied to Czech language. I even cannot assign his intonation to any Czech region. It is real fun to listen to his voice indeed and very informative as well. Go, DGW, go!

  5. My signals teacher had very similar intonation as this guy… pretty sure he was was originally a czech. He wasn’t so hard to understand but his intonation was very unusual for english. He had been in the USA at least 30 years though.

    Also he was one of my worst teachers when we would go to his office to turn in HW because the TA was unavailable he wuold just repeat like a broken record “I cannot handle pepers” which was obvious enough as the two chairs in his office were stacked 4 feet high in magazines as was his entire desk….

  6. Am sure it’s explained somewhere, but from his explanation, am thinkink the magnets really have nothing to do with resonance, their purpose is to direct the electrons in a spiral outward so they hit the receiver-fins near the ends, rather than flowing straight out and many missing the receivers altogether, hitting the outter shell, or hitting the fins at different points in the waveform.
    Ala, a flute’s resonating with wind [a steady stream of impulses/response] across the mouthpiece, at a node [antinode?], it wouldn’t work if the wind blew across all the holes.
    But unlike wind, it’s easier to direct electrons with magnets… thus the circular arrangement.
    Then, the resonance occurs from the LC tank, repelling spiralling electrons from one fin and attracting them to the other, then alternating polarities [and repulsion/attraction] due to the resonance.
    This shizzle’s Wild! Whoda thunk it?
    Gotta go do some research…

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