Overdriving Vacuum Tubes And Releasing The Magic Light Within

We’ve all seen electronic components that have been coaxed into releasing their small amount of Magic Smoke, which of course is what makes the thing work in the first place. But back in the old times, parts were made of glass and metal and were much tougher — you could do almost anything to them and they wouldn’t release the Magic Smoke. It was very boring.

Unless you knew the secret of “red plating”, of course, which [David Lovett] explores in the video below. We’ve been following [David]’s work with vacuum tubes, the aforementioned essentially smokeless components that he’s putting to use to build a simple one-bit microprocessor. His circuits tend to drive tubes rather gently, but in a fun twist, he let his destructive side out for a bit and really pushed a few tubes to see what happens. And what happens is pretty dramatic — when enough electrons stream from the cathode to the anode, their collective kinetic energy heats the plate up to a cherry-red, hence the term “red plating”.

[David] selected a number of victims for his torture chamber, not all of which cooperated despite the roughly 195 volts applied to the plate. Some of the tubes, though, cooperated in spades, quickly taking on a very unhealthy glow. One tube, a 6BZ7 dual triode, really put on a show, with something getting so hot inside the tube as to warp and short together, leading to some impressive pyrotechnics. Think of it as releasing the Magic Light instead of the Magic Smoke.

Having seen how X-ray tubes work, we can’t help but wonder if [David] was getting a little bit more than he bargained for when he made this snuff film. Probably not — the energies involved with medical X-ray tubes are much higher than this — but still, it might be interesting to see what kinds of unintended emissions red-plating generates.

53 thoughts on “Overdriving Vacuum Tubes And Releasing The Magic Light Within

  1. It is sad to see people deliberately ruin things that aren’t made anymore. It must be a youtube thing to get clicks (and revenue) above all else. Major thumbs down on this one. I’d say if red-plating a tube circuit is new to him, or a B+ of 195V seems high, he hasn’t built many tube circuits, honestly. Most will survive hell and back.

    1. There is new vacum tubes in production ( Luckily for us using them )
      In eastern Europe countries and Russia and China still make vacum tubes .
      China is still using the original old technology in production and their tubes
      is really good quality .
      I have an older vacum tube combo guitar amplifier and last I upgraded I used
      tubes from the chinese Golden Dragon company .

      Here is a little list of manufactorer I know .

      Czech Republic tube manufactorer –
      KR Audio-
      Emission Labs

      Germany tube manufactorer –

      Japan tube manufactorer –

      US tube manufactorer –
      Sophia Electric
      Western Electric

      Slovak Republic tube manufactores –

      Russian manufactores –

      Chinese tube manufactores –
      Valve Art
      Golden Dragon
      PS Vane

      Shuguang produce very high quality vacuum tubes .
      Mostly it will be easier to buy from english web pages such as –

      Chinese tube web pages typically do not have any web pages in english
      so it can be hard to navigate if not good at reading Chinese .
      But Changsha shuguang audio have a very good english page here –

      Golden dragon tubes can be found here on a french page –

      China HiFi Audio also sell tubes and tube amplifiers in very high quality –

      This Chinese internet shop have quite a few selling tubes but it is in chinese –

      We do not run out of tubes in near future at all .
      We are very lucky that they still make vacuum tubes . : )

    2. Tubes are more of a novelty these days… Low demand, and still a pretty good supply. Most CRT TVs go from storage to landfill. Few people care enough to even strip the copper out, or check to see if its tubes, or solid state. Burning a few tubes for fun, isn’t a crime, but for throwing them in the trash eventually anyway.

    3. Even excluding new production, and there are plenty of new tubes being manufactured, there’s no shortage for these things. I worked for a major tube shop and the pallets of new-old-stock 6BZ7s (or 6BQ7) could stack 20′ high. It’s a $3 component.

      Same for the 6J6/ECC91/M8081/1682/whatever other variants there are. It’s $3 on average and there are crates of them.

      I don’t like seeing good materials destroyed wantonly. I wholeheartedly agree. But there was some (limited) scientific gain here, and I don’t think anyone outside of this community, or maybe tube enthusiasts, are even going to understand half the words he used.

      I fully recognize that it is a straw man argument, but does anyone want to think about how much pla has been wasted in the name of “I wonder what this will look like in plastic”? Or how many nixie tubes (which are more or less limited) have been tossed into ANOTHER tube clock project?

      I’ve let a lot of magic engineering smoke out of a lot of hardware. Very little on purpose, but sometimes it’s cool to see the failure mode for your self.

    4. Good thing you have no moral or legal right to tell another man what to do with his own money or property then lest you are fine with others doing the same to you!

    5. He buys large lots of tubes, many probably used, for his tube logic/computer project, tube op amp project, and tube-based 555 project. Destroying one each of a few types from all of those lots is no big deal. And there’s no shortage of tubes. Search for “tube lot” on eBay.

      1. He even built a Lm 741 out of tubes .
        Yes hes channel is awesome , especially hes new restoration project of a
        1980’ties mini computer .
        Well mini is underestimating , because it’s a big server in two very big racks
        with several terminals .
        Really interesting to follow –
        Part one start here –

        Oh yes there is plenty of tubes and older ones still gets produced : )

    6. I’m sorry that you didn’t enjoy my video!
      As others have said, there are plenty of vacuum tubes still being produced today, and the tubes I used here have massive quantities of new old stock still available. Of the four tubes I tested, the average price per tube was just $3 and they can all be readily found in large quantities on eBay or other tube sites. So, please rest easy knowing that I didn’t do any untoward harm towards valuable or rare components.

      As for the voltage, I was actually running about 280V B+, but even that was still very high for me. My other projects are building a vacuum tube computer that runs at just +24V B+, so extremely low voltage (and very, very safe). So, this was a fun experiment for me to learn a lot more about how tubes react in situations different to the one I currently put all my effort and thought into.

      My channel is minuscule, less than 3k subscribers. I make practically on average about $0.50 off each video, so I promise you this wasn’t made for the “clicks (and revenue)”. I spend hundreds of dollars a month buying and building fun things and make videos of them for fun and because some people might find some entertainment or educational value out of them. This was just me having some fun. I absolutely would have done this same experiment if the cameras weren’t rolling, but since they were, I feel I managed to snag some really great footage of this phenomenon.

      And, it inspired me to do a bunch of research afterwards as to what was happening. I learned a ton about how to properly read vacuum tube datasheets and what kind of characteristics to expect out different tubes in different situations. It was hugely educational for me while also being massively fun, so for $12 worth of vacuum tubes, I consider that a total win!

      1. I have two ham radio RF amplifiers that use 3-500z tubes. These red plate under normal operation when under heavy load. It’s cool to see and unnerving when not expecting it. In fact, red plating is necessary as this is how it maintains gettering.

  2. No chance of x-rays at the voltages he is playing with. You might get a few x-rays at 5kv but you would need a real sensisitve detector. 10kv you get some more and by around 30kv you are pumping them out pretty good like. That’s why the old color tvs had the tube rectifier in a steel box, they ran at about 30kv and that was enough to do it. In fact there are projects where they use those rectifier tubes as little x-ray tubes.

    1. An old TV technician I used to know told me that the maximum anode voltage on a CRT was 28.5kV exactly because above that it emitted harmful X-rays. Maybe a rule-of-thumb, but it sounds about right, so just passing it on…

      1. There’s no exact figure – wouldn’t go with the 28.5kV though. While there might have been something in it for a particular system, it doesn’t sound overly well referenced (sorry). Generally use NIST data when calculating x-ray shielding and designing sources. It’s trickier than first imagined to be sure of how safe you’ll be behind a given bit of stuff. Silicon for example (handy stuff in glass):

        As the energy decreases, shielding gets better till the K ionization where it becomes somewhat more transparent before building back up again. In short it’s not linear.

        At UKAEA, there’s a rule of thumb that keeping it under 5kV keeps it safe, but there’s also the knowledge that it’s being done on a nuclear site, with safety review anyhow.

        From eBay, purchased a Maltese cross electron gun physics demo to show off early x-ray production. It took 30kV to make it bright enough to see and screamed off a boat load of dose while doing so as it’s glass is so thin. While low energy photons, certainly worse for the skin and the layer below than any UV! 30kV is reasonably penetrating too. It’s been on for a total of about 10s behind a shielding screen and won’t be on again. Too dodgy!

        So there’s no rule of thumb other than don’t let current flow in a vacuum. And if you do, get a detector. They’re fun and it’s way better than having “well some bloke told me it’s OK” written on the tomb stone :)

        Spent a good few years designing x-ray sources and nuclear containment systems. Most recent numpty project – leaded glass filter between thoriated lens and mirrorless camera to reduce speckling at high ISO.

    2. Not only the high voltage rectifier, but also some sets had high voltage regulator triodes, like the 6BK4. On those, the plate voltage could go as high as 50kv and at that point you can definitely produce some X-rays. Also a common trick in using those to generate X-rays, is to reverse bias them, basically using the cathode as the anode and vise versa, and as a cold cathode with no power to the heater. This way the voltage can go much higher and therefore produce harder X-rays.

    3. As a kid I tore down my fair share of old, non functioning televisions, and it’s funny how the steel cages around those flyback rectifiers, the ones with the rad-hazard symbols, usually had dozens of holes in them, talking about 5mm sized holes about 15mm apart. More or less. If memory serves. Presumably this was to let the excess heat out, but probably let significant amounts of 30keV X-rays out along with.

    1. “Don’t sit so close, you’ll go blind!”

      But the CRT face was actually lead crystal, on the order of an inch thick. Thickness mostly to withstand atmospheric pressure vs the vacuum behind it, but fringe benefit was extra rad shielding.

    1. I do happen to have about 20 more 6HA5s in my collection!
      They’re not a particularly rare or expensive tube, but if you have some projects that need them, let me know and I’ll be happy to send some 6HA5s to you!

    1. I’m sorry that you didn’t enjoy my video!

      There are plenty of vacuum tubes still being produced today, and the tubes I used here have massive quantities of new old stock still available. Of the four tubes I tested, the average price per tube was just $3 and they can all be readily found in large quantities on eBay or other tube sites. So, please rest easy knowing that I didn’t do any untoward harm towards valuable or rare components.

      In making this video, it inspired me to do a bunch of research afterwards as to what was happening. I learned a ton about how to properly read vacuum tube datasheets and what kind of characteristics to expect out different tubes in different situations. It was hugely educational for me while also being massively fun, so for $12 worth of vacuum tubes, I consider that a total win!

  3. BTW How can one comply with “Please be kind and respectful to help make the comments section excellent. ” to stuff like this? How about being kind and respectful of the tubes?

    1. I’m sorry that you didn’t enjoy my video!

      There are plenty of vacuum tubes still being produced today, and I know it may still seem a bit wasteful, but these tubes were dirt cheap and are very readily available. There are still massive quantities of the tubes I used available through tube stores or even eBay. On average, the tubes I used cost less than $3 per tube. So rest easy knowing that nothing rare, valuable, or even sought after was destroyed in the making of this video.

      I currently have over 2,000 vacuum tubes in my collection, most of which are unwanted or undesirable tubes like the 6AU6, 6CB6, 6GH8, etc. These are tubes that were most likely destined for the bin because they have very little value in the HiFi audio community. But, I love them nonetheless and am constantly looking for interesting projects to use them in. I’m doing as much as I can to save as many tubes as I can and put them to use in new and fun projects.

      But, sometimes the best way to learn about interesting aspects of tubes, including failure modes, is to experiment. So, I chose just four tubes to keep the carnage to a minimum and pushed them hard enough to red plate. I learned a massive amount about not only power supply design and loads, but also how to properly read datasheets and what kind of characteristics to expect out of different tubes. For $12 of unloved/unwanted tubes, the educational value was absolutely worth it in my book!

  4. My parents had a Packard Bell color TV, and every so often I needed to replace the horizontal output tube. It got so hot the glass would soften and form a dimple in the side.

  5. Shame to see vacuum tubes deliberately destroyed. When I worked it television repairs, occasionally you would see a tube (valve UK) in the line output stage of color TV sets (sweep stage US) which had got so hot, due to a fault overrunning it, that the glass melted inwards.

    1. That maybe comes with a lack of recognizing tubes as something unique and useful. I can see how sacrificing a few tubes for data and high quality footage can generate educational content and keep others from repeating the “experiment”, but the video fails to provide any of that.
      Just a guy repeating how cool his content is and that you should like and subscribe.

      1. I’m sorry you feel that way about my video!

        Although, I feel obliged to ask: did you watch the video? I don’t think I ever asked anyone to like or subscribe. I don’t think I’ve ever asked for likes or subscribes in any of my 60+ videos on my channel.

        I learned so much about failure modes and reading datasheets and what kind of characteristics to expect from tubes by making this video, so the educational aspect of it for me was massive for me! I was going to do the experiment anyways to sate my curiosity and to learn more about tube failure modes, but I figured why not let the cameras catch the phenomenon and let others see.

        I’m sorry that you felt the video was a waste and failed to provide any entertainment or educational value. That’s a failure on my part as a content creator. Thank you for your feedback though, I will continue to try to make better and better videos, and I do always try to put some educational aspect into my videos, so any feedback is good feedback as it allows me to steer this hobby of mine into a better direction.

        1. I wouldn’t worry about it. The manufacturer probably sacrificed more as part of their destructive testing. If people were really concerned, they’d pull a PETA, break in, grab a bunch, and set them free into the wild.

        2. The type of people who complain about destruction of property they don’t own, or youtubers making money that isn’t theirs don’t bother watching or reading something before criticizing. All they care about is subjecting the world to their opinion and executing some sort of vendetta of a strawman they’ve built in their minds and conflated with their target. Logic or truth doesn’t matter, only the mentality of an angry villager with a torch. Don’t let it bother you, I’ve seen your content and in general I’ve found it interesting/creative so just do what makes you happy and ignore the naysayers (it’ll only get worse the bigger your channel gets so it’s good to practice blocking out the dregs of the internet now).

  6. I used to run too much power in my old ham radio transmitter – it’s really interesting when the tubes get so hot, the glass melts and gets sucked in! Radio Shack had a lifetime warranty on them, so I’d take them back for some new ones, this went on for multiple times until they stopped replacing them for me. Something about “mistreatment”.

    1. I recall my dad’s DX-100, with a pair of 6146s for the final, ran .. idk I think about 650V on the plates. You could turn the drive current up and make those finals glow. You know, theoretically.

  7. As someone who’s just gotten into building vacuum tube amplifiers I found this video to be both fun and instructional. In addition to seeing an example of red-plating at no cost to myself, I now also know that I need to research tube data sheets and Tube characteristics. I now have a bunch of ideas for further research. The comment section alone was a perfect exercise in critical vs. reactionary thinking …

  8. @Nakazoto – just tell these folks that the tubes you used were past their useful lifetime and going to be trashed anyhow. Then they can go find something else to whine about.

  9. Hey, no, this is instructional! There’s a “teaching moment” here — this is What Not To Do with a vacuum tube, if you’re building an amplifier. I.e. if your tube looks like this tube, you’re driving it too hard and probably will get some unwanted harmonics!

    You know, unless you’re mad at your tube, and want to teach your tube a lesson, by showing it Who’s –ing well the Boss around This Workbench, then yeah, this is probably *Is* the way you want your tube to look.

    But you know, this is why tube stuff could survive an EMP, little bits of silicon explode into smoke long before you get to this point on the operating curve.

  10. When I saw the headline of the article, I immediately had throughs about X-rays being generated. I would definitely have a Geiger Counter sensitive to X-rays monitoring when doing a vacuum tube over drive experiment. The high voltage rectifier diode tube on the flyback transformer output (often 27 KV or more) was typically inside a steel box to block X-rays. Old TVs from the 1950s and 1960s often had a single vacuum tube rectifier rather than the solid state tripler module common in more modern TVs and monitors.

    I accidentally “red plated” the output tube in my old Heathkit HW-16 transceiver when I was an inexperienced teenager. I bought the HW-16 used and I was trying to find a short. I mistakenly disconnected the suppressor grid. When I powered up the radio, I had the bottom side of the chassis facing me and after a few seconds I heard a strange crinkling sound. I powered off quickly and peered around to the other side and saw the innards od the output tube still glowing bright red. The tube was dead; shorted internally.

  11. Saw ‘Red-plate’ a few times when trying to correct (unwanted) distortion in stage amps. EL84 or EL34 output valves/tubes where the grid resistor went open or the coupling capacitor was leaky would glow nicely. Usually worked OK afer fixing at least for long enough to get replacements.
    (Happy days when touching the wrong bit would throw you across the room.)
    I suppose vacuum technology is out of many peoples experience these days.

  12. Interesting experiment. I remember conducting my own vacuum tube experiment back in the 1960s with my grandmother’s old round-picture-tube B&W TV. It had already been replaced with a newer model so I decided to see what kind of noise the old tubes would make if I threw them as high as I could and let them pop on the street outside. (I left the picture tube in the cabinet probably because I didn’t have the tools to remove it.) The experiment was a success, they popped quite nicely, and that was the end of my experiment. Also the end of that old TV, as well as my TV watching privileges for the next week after my parents found out. Of course I was only 8 at the time and didn’t know any better.

    Now, half a century and a full career later, I’m back playing with vacuum tubes but in a more constructive manner trying to learn more about what I missed about the technology in the 1960s.

    I’m all for experimentation “in the name of science” but only if done safety. I’m not keen on wanton destruction “in the name of entertainment”. It’s okay to learn from our experiments. I just don’t think it’s necessary to tell the whole world about how to destroy things for fun over the internet where “less scrupulous people” might be encouraged to do something similar that could get themselves or other people hurt.

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