The Legendary Magnetron: How It Really Works

Comments · 303

• KA

  @KasyanTV · 11 days ago (edited) · pinned

  Original <a href="https://www.youtube.com/watch?v=9PEW45H5wF8">https://youtu.be/9PEW45H5wF8</a><br>His Majesty — the LASER! <a href="https://www.youtube.com/watch?v=cFqkrDncfBw">https://youtu.be/cFqkrDncfBw</a><br>Quantum Diode <a href="https://www.youtube.com/watch?v=qtrHUSFliMA">https://www.youtube.com/watch?v=qtrHUSFliMA</a><br>Gunn Diode <a href="https://www.youtube.com/watch?v=100pUWQt4Sg">https://youtu.be/100pUWQt4Sg</a>

• IL

  @ilionreactor1079 · 2 months ago

  <a href="https://www.youtube.com/watch?v=N9cfcDlp0zM&amp;t=140">2:20</a> &quot;...noticed it could heat food.&quot; It melted the candy bar in his pocket.

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• BA

  @bain5872 · 2 months ago

  As an electronics tech, I think you did an outstanding job at presenting the Magnetron and it&apos;s properties. Job well done.

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• QU

  @quantumleap359 · 2 months ago

  BeO is very expensive to make, so you’ll not see it used on microwave oven maggies. The white or pink or purple insulator is alumina, a harmless ceramic material. The power supply, however is a killer. No joke, a killer. Thanks for a pretty good educational video.

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• HI

  @hirsitus · 2 months ago

  My Microwave oven is 41 years old and I still use it daily.

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• TO

  @tomctutor · 2 months ago

  I served my apprenticeship with EMi-Varian several decades ago, cut my teeth on Klystrons. These were massive vacuum tubes. We struggled to get the vacuum clean and comparable to that of outer space.<br>We used L,S,X band klystrons the latter were physically small devices, you could hold them in your hand.<br> The power output of the S band devices were many MegaWatts and operating in pulsed MVolt mode.<br>The magnets were made from several Electromagnets with many hundreds of amps in them.

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• ST

  @stevengill1736 · 2 months ago (edited)

  There&apos;s amateur radio enthusiasts that have converted microwave oven magnetrons into transmitters...<br>Speaking of high voltages, I was once playing with a surveying laser, trying to get it to work. It ran at several thousand volts, so of course I tried to handle it without gloves, and got a hella bad shock....<br>You&apos;re right, I&apos;ll never forget that shock! Scared the hell outta me....never again!

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• DE

  @deefective1100 · 1 month ago (edited)

  I can explain how a magnetron works in a few sentences. The magnetron is an election tube, just like the old days. It has 3 connections, ground filament and high voltage. The magnetron is essentially an electronic whistle, the frequency of the whistle is determined by the size of chambers inside. The magnets are needed because without them the electrons would simply cross to the anode. The magnets force the electrons to flow cross the chambers creating a resonance or a whistle. The energy is then piped off one of the chambers. It is a tube so it is sealed in a vacuum or inert gas. The dementions of the chambers determine if the magnetron goes into a microwave oven or a radar set.

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• PH

  @philliplopez8745 · 2 months ago

  I repaired one of those originals , it was built like an airplane ( riveted together out of aluminum sheet and channels) the replacement circuit board went from being mechanical to solid state .this must have been in the late 80s I could not believe that the replacement part was still available.

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• JO

  @johnr3435 · 2 months ago

  Nothing but admiration for the people who dreamed up these devices!!

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• DA

  @DandikAtölye · 2 months ago

  This is the best video I have ever seen about magnetrons

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• PE

  @peter7235 · 2 months ago

  Many thanks, Kasyan. This is one of the best videos on magnetrons I have found on YouTube. Well done.<br>Magnetrons are still used in radars today. These usually operate in pulsed mode, whereby the High Voltage is only briefly (a few microseconds) applied to the magnetron in the form of a rectangular pulse. After the pulse, the radar receiver &apos;listens&apos; for reflected echoes of the transmitted radiofrequency pulse. <br>Magnetron-based radar transmitters, delivering peak output power from a few kW to a few MW, can be built relatively cheap and their design is relatively simple.<br>Certainly above 3 GHz, they cannot be beaten on price when pulsed, high output power is required.<br>A disadvantage is that they are not frequency- or pulse-agile. All transmit characteristics remain fixed. They can be tuned over a range of 10% of the design frequency by mechanically decreasing or increasing the size of the cavities, but apart from tuning, there is not much you can do to change the frequency or pulse width rapidly. Therefore, they are easily jammed, unlike radars with more complex waveforms.<br><br>I would like to add my two cents for hungry readers.<br>1) Secondary emission<br>Electrons are ejected in all directions from the hot cathode and the trajectories they make under influence of the electric and magnetic field are determined by the ejection speed and direction. A considerable number of electrons do not reach the anode. Instead, their trajectory is bent towards the cathode and they bombard it with very high velocity. This heats up the cathode even more and liberates extra electrons through thermionic emission. This is called secondary emission. Most magnetron heater circuitries compensate for this effect by reducing the heater voltage when the High Voltage is applied. Otherwise, the cathode would overheat, decreasing the lifespan of the cathode significantly. Electrons that bombard the cathode are not efficient; they are not useful for generating the microwave signal.<br><br>2) Oscillation Modes and Strapping<br>The creation of the charge wheel is a random proces determined by the initial motion of the electrons when High Voltage is applied. The build-up of radiofrequency (rf) oscillations is therefore inconsistent from pulse to pulse. It is possible that the number of &apos;spokes&apos; in the charge wheel is different from pulse to pulse, and all this can create a different output frequency, pulse build-up time and power of the rf signal. For a magnetron with 8 cavities, the best scenario is a charge wheel with four spokes at 90° angles. When the spokes pass the cavities located at North, East, South and West, the potential (or voltage polarity) of the rf signal in these cavities is negative. The adjacent cavities at 45° angles have then positive polarity. There is thus half an rf period time difference, or a 180° phase shift between adjacent cavities (knowing that a full period is 360°). This is known as the π-mode, since π radians is equal to 180° or half a circle. This is the most efficient oscillation mode because the cavities are excited and oscillate at their natural resonance frequency. If there are only two spokes, &nbsp;only two cavities will have negative polarity (let&apos;s say North and South). The cavities at East and West are then positive. The rf signal in all diagonal cavities at this instant is zero. We now have a phase shift of 90° between adjacent cavities, and this is the π/2 oscillation mode. &nbsp;The output frequency is halved in this mode, and this mode is much less efficient because the cavities are no longer operating at their resonant frequency. Other modes also exist, each with a different amount of phase shift of the rf signal in adjacent cavities.<br>We can use Strapping to force the magnetron to oscillate in the &nbsp;π-mode. Two copper rings are visible Inside the magnetron of your video. If you look closely, you can see that one ring is connected to 5 cavity walls always skipping the next wall, and the other ring is connected to the other 5 walls. These straps put all the connected cavities on the same potential, so 5 cavities are positive and the other 5 are negative, alternating each other. This forces the rf oscillations to always start quickly in the most efficient &nbsp;π-mode almost immediately at the instant one cavity is exited by the developing charge wheel.

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