The flash may have been the cathode bond burning open. When metals are heated to incandescence in a vacuum, a plasma can form, which becomes the primary means of conduction. If the current is sufficient, it can heat the grid so that it melts, and thereafter will have little to no effect on the current passing between cathode and plate. It is the equivalent of decades of use in a few seconds.
That's actually a really interesting idea! I may have possibly turned the vacuum tube into a Thyratron, if only for a moment, haha. After seeing both the 6HA5 and 6J6 run so bright without any super dramatic stuff, I was very much so no expecting a flash out of the 6BZ7. It totally caught me off guard!
Would have been nice to have had a current meter on the plate to see what the maximum plate current was. I have seen tubes with a leaky coupling capacitor put a positive 5 volts on grid and cause a lower B+ voltage.
I thought about this, but oddly, I don't have a good current meter. All I've got is my little UNI-T 120e DMM, and I haven't been able to get it to read current properly yet (most likely, I'm too dumb to use it properly). But, looking at the datasheet, I can kind of come up with some rough ideas! My B+ voltage was right around 280V and most datasheets have a little chart with grid voltages that can almost get us there. So, at 280V with a grid voltage of 0V, the maximum plate current should have been around this: 6HA5: ~70mA 6J6: ~45mA 6H2N-EB: ~6.75mA 6BZ7: ~75mA This actually explains why the 6H2N-EB didn't glow. I didn't have nearly enough B+ to get enough current flowing through it to upset. Ideally, I would have had closer to 400V and maybe run the grid into positive voltage further. This also explains why the 6BZ7 didn't fair too well. 75mA at 280V is approximately 21W, but according to the datasheet, the 6BZ7 has a maximum plate dissipation of 2W, so we were cramming 10x the amount of power through that tube than what it's maximum rating was!
Some of the power tubes in the amps that I work on get that distinctive blue glow. When the amp is turned all the way up , if you play the instrument, you can see the blue glow change with the signal coming into the amplifier.
Not generally a fan of destroying anything deliberately, but you assured that these are not expensive components, so not that rare. The educational value was good, and to be fair I did enjoy the flares. 👍
I'm right there with you, I'm a bit of a pack rat, and if anything has any kind of usability I tend to stuff it in a draw for "one day". But, I really wanted to see some red plating, so I went through my tube collection for the ones I never use and aren't really highly sought after tubes. The 6BZ7 and 6H2N-EB can often be found for about $3 on eBay, so I figured that was cheap enough to sacrifice in the name of science! Well, maybe not science, but certainly entertainment, haha.
One tube in my collection is an Eimac 4-1000A from the power stage of a 5kW radar transmitter that was accidentally redplated when the oscillator stopped. The anode, despite having large cooling fins on it, actually melted in some spots, so that it now has holes that mirror the layout of the control grid raster. It's mostly useless as an amplifier triode anymore, but the holes make it a much better mood light bulb than before ;-)
The most impressive tube I see this in frequently is the 6BQ5/EL84, if you manage to just ride the edge of red plating so it stays intact long enough, you will see the glass soften and get sucked against the two sides of the plate.Try 350 on the plate, about 320 on the screen, and start with -15 on G1. Stick 50 ohms in the cathode and maybe a few hundred ohms as a plate load. Ride it until the glass gives way, air enters, and flash bang at the end...oh, and fuse your HT line accordingly for this test.
This video rocks dude. I did this once (by accident) to a 12L8GT when building a massive amplifier. Luckily the tube came out okay and still worked because I noticed it before any massive damage was done. You produce amazing content in general though, it was your channel that actually inspired me to build my own 4-bit vacuum tube computer
Thank you so much! The 12L8GT is a twin pentode in an octal package and that's just awesome! Tubes are surprisingly tough, the 6HA5 I red-plated here actually still works and tests fine on my (terrible) vacuum tube tester, which is just wild to think about. They can often handle five times their maximum ratings for brief periods without too many ill effects, which is insane to think about in regards to electrical components! Thank you for the awesome words on the content! Do you have any links to your work on the 4-bit tube computer? I would love to see your progress and chat with you about it!
@@UsagiElectric I haven't uploaded anything online about my computer yet, I'm still in the stage where I'm designing everything and getting everything planned. Once I get my designs finished I'll upload them and let you know. My general design goals were to build a computer completely dependant on tubes that could read programs, execute them efficiently, and give a readable output via an interface, probably going to be nixie tubes. Even the power supply has to be completely regulated via tubes.
@@straightman2 Definitely let me know when you get some stuff online, I'd love to check it out! Initially, I was thinking to build my entire 1-bit computer from tubes only, using 6AL5 dual diodes or modified multivibrator designs with dual triodes, but I ultimately went with using silicon diodes because I couldn't afford to have nearly double the tube count! (And silicon diodes in tube computers was fairly common from the mid-50s on.) Ultimately, I do intend to build my power supply from scratch, but I want to get the computer itself finished first so I have an idea of the power draw needed. For the output, I would love to use Nixie tubes, but since I'm running entirely at +24V/-12V, I just don't have enough voltage to use them. Instead, I'm thinking I'll build an output display out of little IV-3A VFDs, since they're also pretty close to period correct and can run on 24V. If you want to, come join us over on the Discord chat server and we can chat tube computers and swap ideas! ( discord.com/invite/p7UsfHD )
On the 6BZ7, the bright flash was likely the cathode bonding wire failing due to excessive current through it. Some tubes are more resilient than others, depending on the current the plate is rated to handle. It's primarily plate design that will determine how resistent a tube is to red plating.
It might be interesting to see a test rating before and after a redplate, with different timings of redplating.
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I just had a couple of 6L6s red plate in a 66 Twin Reverb tonight. Its got to be something with the socket or a resistor because it happened on multiple tubes in the same socket. Firecrackers.
If you red plate a television horizontal output tube you can melt the glass envelope, keep the plate orange color but not fully hot and leave it burn. might have to increase current until it happens. you will need enough voltage also. dosent always work.
Some of those output tubes are meant to run glowing slightly, which just blows my mind! The fact that you can get them hot enough to deform the glass without blowing the tube is just awesome though!
I think the reason they flare up red and then slowly go dim is because as the metal heats up the resistance goes up and causes the amps flowing to go down.
I think you're totally onto something here! I actually tested the 6HA5 in my tube tester the other day out of curiosity and it still tested as good. I was totally lost as to why that would be the case as I thought I was destroying it, but the heat vs. resistance aspect of the phenomenon is something I hadn't thought about!
No surprise that the 6N2P survived. Ruski tubes are generally the best available. Based on your other experiments, I got a handful of DL67 micro tubes and my first experiment red plated just like these. Lol. I need to figure out how to not do that next time. Totally dig your videos.
The Russians sure liked to engineer stuff to be tough as nails! Also, the 6N2P wasn't really designed to move a whole lot of current in the first place, so I would have needed a much, much higher voltage PSU to get it to misbehave. Sounds like you pushed a little too much current through the DL67! I've done that a few times on accident too, haha. Time to bump up some resistor values!
@@UsagiElectric the 6N2P is a low anode current type very similar to a 12AX7/ECC83 so less likely to redplate(unless you crank up the ht volts), try a 6N1P or 6N3P as theyre more like 12AU7/ECC82
I agree, the Russian tubes are more robust because they have more widely separated elements (especially ones from decades ago when they didn't have the technology for tight construction). So they have wider element spacing that makes them more robust. Thus they have less capacitance and can work at slightly higher frequencies and plate currents but have less gain. They didn't make them more robust, it's just they couldn't make them more delicate and sensitive so they ended up being more robust that as a winfall can handle more abuse but with less overall performance.
The 6H2N seems to have an anode voltage of about 250v, probably a higher maximum, your supply was 197, after the rectifier it would be 277, probably too close a margin to fail, i would increase the transformer tapping, even if it means 2 windings in series. With the 450v capacitor you 'could' go up to 300v safely
Yup! The 6H2N is not designed to move all that much current. Looking at the datasheet, at 280V anode voltage and 0V grid voltage, the 6H2N is moving about 7mA. For reference, in those same conditions, the 6BZ7 is moving 75mA! So I needed a whole lot more voltage before I could get that one to glow.
I have a couple of 120W valve amps with 4x6550's per channel. I used to use them with a pair of electrostatic speakers which was just on the edge of being stable. Every now and again one amp would go into oscillation with instant red-plating and a mad rush across the room to get to the plate "off" switch. Ended up putting them out of service and getting a more robust transistor amp. Not fun at all at £70 per tube.
Very nice, i've been wondering about this since my tube amp red plated like crazy. It had a bad coupling cap and within seconds one of the big 807 power tetrodes was glowing bright red. It had like positive 160v on the grid. The tube still works fine though. The blue emission is fluorescence and if i'm correct is either due to imperfect vacuum or imperfections in the glass envelope
Thank you! Tubes are surprisingly hardy! Another commenter asked if I could test the red-plated tubes against known good ones, so I pulled out my cheap Accurate Instruments 257 Tester. It's a pretty terrible tube tester, but it should be able to give us a bit of an idea. (Unfortunately, the 6H2N-EB didn't survive the test, but only because my clumsy self knocked it off the table and it shattered on the ground... oops.) Good 6HA5: 72 Red plated 6HA5: 66 Good 6J6: 72/70 Red plated 6J6: 16/20 Good 6BZ7: 72/68 Red plated 6BZ7: 0/0 The 6BZ7 was clearly totally dead. Something definitely shorted inside and wrecked havoc. The 6J6 registered some emission, but it was clearly hurt. The 6HA5 though soldiered on as if though nothing happened at all! I was stunned by how hardy it was!
@@UsagiElectric how can a tester by accurate instruments be terrible? Haha I'm guessing it might depend on a lot of physical factors as well, like tube construction and materials
@@stefandumoulin1872 Haha, I actually had to rewrite my sentence a few times because I kept typing "my inaccurate Accurate Instruments 257". It's pretty good for determining if tubes are dead or not, but that's about it. I think you're totally right on the physical factors as well. The 6BZ7 seems to have really tiny tolerances between cathode, grid and plate, whereas something like the 6HA5 seems to have a bit more distance between each component. That could be why the 6BZ7 shorted out and the 6HA5 didn't, despite both getting really hot!
Redplating in the wild (unless the tube is meant to run with a hot plate like some large tubes) is not fun, red gridding is even worse. Especially when you walk away for a minute to sip your soda and turn back and nearly choke on your drink and spill it scrambling for the plug only to realize it's too late and already fried which means even more repair.
Oh man, I can totally imagine the pain when it's a proper HiFi tube that you watch die! Fortunately these were cheap, commonplace tubes so I was having a bit of a laugh, but man if it's a nice, expensive tube I would totally freak out, haha.
@@UsagiElectricFortunately, it was only the rectifier that got hit, the tube died but I saved the transformer from getting cooked too (I believe I had bypassed the fuse, but managed to unplug it in time).
Fun experiment. We used to see this in old TV’s as the horizontal output tube would run at zero bias if the horizontal oscillator failed. The 15 watt 6DQ6 would red and then orange plate in about 15 seconds. Then blow a fuse.
I have seen this happen on old style TV's when the horizontal or vertical output tubes loose grid drive. Any high power amplifier can do this as well. If the current goes high enough it can actually burn a hole in the plate. But usually the cathode either boils off it's rare earth coating or opens the cathode connection. Sometimes if enough voltage is there it can flash over and I have actually seen the envelope crack and break apart.Iin fact if it has been allowed to sit there long enough with high current and voltage it can break on the bottom seam where the tube was glass welded together.
Great video. What you made are one time use black body radiators. Next time, put shields around your cap, transformer, tube, in fact all of your electronics. No sense losing and eye to an unforseen explosion or getting burned. And do this in a well ventilated area.
The reason, as I understand it at least, for some triodes carrying more current than others is the density of the wires on the control grid. When tubes are manufactured they need specific parameters for the electrodes in the envelope to determine the characteristics. A triode that has a less densely wound control grid will allow more current to pass but have a much lower mu and amplification factor, such as the 12AU7 and the 6BZ7. A 12AX7 triode has more densely wound control grid, so it's much more sensitive to voltage changes, but can't pass as much current with the grid at 0V. The 6H2N-EB's are similar to a 12AX7, which is probably why they didn't red-plate.
I think you absolutely nailed it! I did a bit of reading through the datasheets to see what kind of plate current can be expected with a B+ of 280V and the grid at 0V and here's the results: 6H2N-EB: ~6.75mA 6BZ7: ~75mA It's wild how different the two tubes are! But, it makes sense with what you're saying. The Russian tube just doesn't move all that much current (meaning it must have a pretty tightly wound grid), so I would need to really bump up my B+ and maybe even drive the grid into positive to get some red-plating action. Thank you for the insight!
Not going to lie, the worry briefly flashed through my mind, but I do remember that x-rays needed quite a lot of voltage, so I was pretty certain my little 280V B+ wasn't enough. That blue fluorescence was awesome though!
I had a vintage eico 460 scope and two of the tubes would always glow a bright violet. The glow on the tube would even bend if you brought a magnet close to it
Ik this video is two years old but I have actually killed a sub miniature tube using a d cell, the circuit was made in the 50s new batteries are more powerful than the old copper batteries and sometimes the circuit cannot handle the constant voltage of the nee battery so it can pop it and leak the alkaline acid in doing so the pop created enough current at once to burn out the filaments of the tube
I was surprised at just how much pain I had to throw at the tubes to actually damage them. Most tubes could handle a little red plating with no problem at all. It's amazing how tough tubes really are!
Tubes are awesome because they can take so much abuse. A tube can be red-plating mildly for a while before it actually goes bad, which is just wild to think about!
I'm so bad at actual audio stuff! I find the technical side of it amazing, but my hearing is pretty shot (and I'm mostly deaf in my left hear), so I can't hear the difference unless it's pretty dramatic (like comparing our all tube Magnavox Concert Grand against pretty much anything else that makes sound in the house).
As a kid i used to play with vacuum tubes, people were throwing out their old tube tv's to replace them with modern transistor ones so every month with the garbage runs there would be several TV's ready to play with (they collected big garbage once a month in those days). I had an old transformer from a tape deck but it was only 300V 40mA or something like that So i built a powerbank that was 220V mains rectified into a huge bank of capacitors. Big enough to weld a screwdriver when discharging. And one time a metal pen that has a couple weld marks to this day :D I built 100MHz transmitters with ECC85 tubes and they were colorfull displays of destruction sometimes as all parts were scrounged from the TV's i found. I also had so many side bands that i was all over the FM band and the television in the living room would show all kinds of patterns. One of those "are you experimenting?" moments for my mom. So yeah i had a lot of fun and have red plated al lot of tubes. (And popped all kinds of electronic components as well) Fun days And yes i did survive that power supply i built ;)
Try using a 6CM5 power pentode. They were horizontal oscillator 20 W valves used in black and white televisions in the 1960s. I saw one glowing a dull orange because it drove an eht transformer which had developed shorted turns....
The 6CM5 looks like it might be a decently popular audio tube. If I destroyed one of those just to see it red-plate, the Hi-Fi audio guys would burn me at the stake, haha!
@@UsagiElectric it's not called red plating.... it's just overloading. The 6CM5 is lousy for audio, it's very non linear. But it is a nice big valve with a big plate and they're impressive when they're glowing orange....
@@UsagiElectric You might be confusing the 6CM5 with 6CZ5 which is a good substitute for the scarce and expensive 6973 audio tube (the pin out is very slightly different). I also have some 6CM6 tubes which might have audio applications but I have not tried them.
It's all about finding that balance between voltage and current. Even with only a few volts, if the load is trying to pull a huge amount of current, the plates can start to get hot!
Poor tubes! :) And what about forcing current in cold cathode mode? I think that would be interesting. You could zap the tubes that had their filament broken.
Anecdotally, I have accidentally destroyed miniature tubes by red-cathoding them on the test bench (these were cheap tubes). So this is also possible. A friend loaned me a d'Arsonval type microammeter, which turned out to have been WAY out of calibration (due to permanent magnet decay), for doing some measurements so I could characterize some late-production miniature pentodes I had. These were tubes with indirectly-heated cathodes, and presumably one of the later exotic-oxide (maybe Barium) coatings. Running the tests on the bench, warmed up a tube cathode heater, then slowly increased the output on a bench supply to act as my B+. Imagine my surprise that the needle on the microammeter barely moved, but the cathode on the tube seemed to put out a dull cherry glow. Slowly dialing up to a couple hundred "microamps" of plate current, the tube cathode began to glow a pretty bright orange. I concluded something must have been wrong, so I stopped the test. Tube then failed to test good on a separate emission tester....hm. Repeat experiment. Same result. Tube gave terrible calculated gm figure. Then I decided to test the microammerer, and it was off by a factor of about 100. 100uA apparent reading on meter tracked with about 10mA of "real" DC current. Oops. Even when your buddy tells you "sure, it's accurate", check anyway.... The upshot is that I never got any luminescence out of the tube plates, but the cathodes did, and were destroyed (presumably the exotic oxide coating was either ablated or diffused inward). Depending on internal geometry of a specific tube, I guess the plate can be physically large enough, and the cathode small enough, that cathode emission dissipates more heat than plate kinetic-collision of electrons. So, there's more than one way to "do it wrong".
Thank you! It was something I've heard about and seen some alright pictures of, but to see it in person and then on the replay through a macro lens was super rewarding!
That's actually a really interesting question! A good photomultiplier tube tuned for a specific wavelength could tell what kind of energy the tubes are giving off. There isn't enough energy for x-rays or the like, but it would be really fun to see what exactly is being emitted in these pretty nasty situations!
@@UsagiElectric Most photomultiplier tubes are tuned for blue light, with their sensitivity to red being quite low. That's because of the construction of the photocathode (bi-alkali). There are some, fairly rare, that use a different type of cathode and are tuned more towards red. Nonetheless, even so the red that you experienced would be enough to burn off even one of the regular "blue" PMTs. That's because their amplification factors can be insanely high. You would want to intentionally reduce drastically the amplification by leaving some of the dynode chain unbiased, or very poorly biased. Or else you risk blowing the PMT. Also, you'd want to do that experiment in absolute darkness or a hermetically closed enclosure. Even a dim light from a LED can burn out a PMT. (source: myself. I'm building scintillation detectors as a hobby. :) )
At most you get very low energy Xrays of several hundred eV energy. The vast majority of scintillation materials will not be sensitive enough to get a response. They only start showing a response above 1-1.5keV Detecting such low energy Xrays is a complicated matter.
what would be interesting to see in e.g. dual triodes is if you redplate one plate to death, will the second one still work? because if so you're actually destroying the plate (which feels kinda weird), if not (my suspicion) it's more of a sputtering/vapor effect ruining the vacuum? would be a neat demonstration.
I did want to put an ammeter on there to see how much current they ended up pulling, but oddly, I don't have a good current meter. All I've got is my little UNI-T 120e DMM, and I haven't been able to get it to read current properly yet (most likely, I'm too dumb to use it properly). But, looking at the datasheet, we can kind of come up with some rough ideas! My B+ voltage was right around 280V and most datasheets have a little chart with grid voltages that can almost get us there. So, at 280V with a grid voltage of 0V, the maximum plate current should have been around this: 6HA5: ~70mA 6J6: ~45mA 6H2N-EB: ~6.75mA 6BZ7: ~75mA This actually explains why the 6H2N-EB didn't glow. I didn't have nearly enough B+ to get enough current flowing through it to upset. Ideally, I would have had closer to 400V and maybe run the grid into positive voltage further. This also explains why the 6BZ7 didn't fair too well. 75mA at 280V is approximately 21W, but according to the datasheet, the 6BZ7 has a maximum plate dissipation of 2W, so we were cramming 10x the amount of power through that tube than what it's maximum rating was!
That's actually a super fascinating part of history! In the 40s, most cars actually had 6V electrical systems, but had tube radios in them. The 6V worked perfectly for the tube heaters, but to get the HV they used something called a "vibrator". Essentially, they created an oscillator with a relay (+6V into the common and the coil was powered from the normally closed pin. The coil would trigger the relay which breaks the power to the coil, causing the relay to snap on and off as fast as it physically can.) This created a square wave that went into a transformer to create high voltage, which was then rectified and used for the tubes in the radio. The same method was used for 12V systems too, but by the time 12V systems were common, space charge tubes were starting to get used in place of the old vibrator design. These are tubes that are specifically designed to work with 12V on the plate (and 12V powering the heater). So, no high voltage anywhere in the system! But, that was pretty short lived because the transistor was starting to get cheap, so finding space charge tubes today is a bit difficult.
@@UsagiElectricI have some of those vacuum tubes designed to work at 12V plate voltage! They're rare today, but they were made exactly for this application in the 1940s, radios powered by a 12V battery. They're actually specified for a maximum plate voltage around 30V (and sometimes as low as 16V). Examples are: 12AD6, 12DV7, 12U7, 12AL8, 12DV8 and so on. You can still find such tubes on the used market if you look hard enough. :)
@@UsagiElectric , Note that prior to the development of space charge tubes for car radios there were 1 and 3 volt tubes used in "portable" radios such as the Zenith Transoceanic, 1L6 and 3V4 tubes being an example. The 1L6 is the only tube that really works correctly in Transoceanic and they are scarce and pricey nowadays. I put the word portable in parentheses because the tube type Transoceanic radios are bigger and heavier than many boomboxes.
Surprised those diodes worked at high voltage as it was for a low voltage charger. I would expect 100V diodes. I have seen guitar amps with the plates that look like swiss cheese from being driven so hard.
The 6AL5 is good up to a peak inverse plate voltage of 330V, and I was only at about 180V here, so I still had plenty of headroom! It blows my mind how hard you can drive some tubes and still have them keep on ticking!
@@UsagiElectric I think you misinterpreted the comment. Scott was talking about the silicon diodes used in the bridge rectifier of the HV supply, not some vacuum tube.
@Scott H The potentially low reverse breakdown voltage limit of the rectifier diodes was my first concern too. But here is a thought on that; if you remember your vintage lead acid car battery charger circuit, you will agree that these chargers hardly use a full-wave bridge(!) rectifier with 4 diodes. They commonly use only two diodes and a center tapped transformer (full-wave rectifier). Those who dont believe are invited to dl the manual of the Lestronic II and see for themselves... Now on the topic of reverse voltage; some thinking may make it clear, that on a full-wave bridge(!) rectifier with 4 diodes (like used by Usagi Electric) the two non-conducting diodes only need to withstand the nominal AC output voltage in reverse. On a non-bridge(!) full wave rectifier consisting of two diodes and a center tapped transformer, the non-conducting diode however faces double the AC voltage in reverse. (Simulate it on LTspice if you dont believe) Now knowing that A) classic lead acid chargers use the full wave rectifier with 2 diodes on a center tapped transformer, and B) the unloaded voltage of even an unregulated 36V system charger may exceed 45V, which puts the rectifier diode at a minimum of 2*45=90V reverse voltage, and C) there is 48V golf cart chargers, who should top up at 60V (120V reverse) It is safe to assume that the rectifier diodes are at least of the 200V reverse breakdown types.
Seeing B+ attached to the anode directly and no cathode follower resistor is kinda cursed, but this was still a great video! Now i don't have to sacrifice my own tubes xD
Pity no plate meter. Many years ago, I tried to make an audio amp, I had a 6CM5 line output tube, a speaker transformer, and a pot. I was used to single transistor amp stages, you bias it on to get some volts across the load. So I tried the same with the tube. nothing, so I must have the grid wrong (150V on the plate) I ended up sending the grid positive, whereupon there was a frizzling sound from the tube and the bias pot smoked up. I think I red plated the grid. Learned my lesson, stick to transistors.
I'm not quite sure I had enough voltage to generate any x-rays here. Usually, several thousand volts are required for x-ray emission, but I was only working with about 300V here. I think the blue fluorescence was caused by an imperfect vacuum, or perhaps even some off-gassing from the material inside the tube.
@@UsagiElectric In gas discharge tubes the color is specific to a certain gas or material. Assuming a pure gas or vapor you can get shades of blue from hydrogen, argon, krypton, xenon, oxygen, or mercury vapor. Saying a blue color is x-ray isn't necessarily correct. We're not scared of the orange glow from a neon bulb or a neon sign. I'm sure in a traditional x-ray tube that the high voltages might cause some color discharge but we're not gonna look. See the Wikipedia entry for X-ray tube. The last section gives some info on x-rays emitted from vacuum tubes, but it occurs at high voltage, >> 1 kV.
Triodes model as voltage sources, so you won't be able to red plate ones with too much plate resistance. Bet you can red plate a 12AU7 but not a 12AX7. The 6BZ7 specs close to my favorite 6BQ7. That one red plating doesn't surprise me.
Yup, that's exactly what was going on with the Russian 6N2P. I didn't have nearly enough B+ to stress it to the point of red plating. The 12AU7 is a fantastic little tube, I have much better results building with the 12AX7, and I think that's probably due to difference in plate current capabilities between the two. The 6BZ7/6BQ7 are also great little tubes and can move a decent amount of current, even at low voltages!
I have a bunch of 12AX7 that test ok but are too microphonic to actually use. So I rigged up a microwave transformer with a HV diode and connected up the plate and cathode and used a small transformer for the heater. I had a meter connected in the cathode to show the current and I calculated the plate was trying to dissipate approximately 24watts. (A 12AX7 plate is rated for only 1 watt of dissipation). Because a microwave transformer puts out 2000 volt at 2 to 300 mA this NOT something to do if you don’t know how to work with high voltages safely.
I'm not too knowledgeable about specific audio setups, but the balance of plate resistor, tube dissipation and desired drive current is a pretty common design aspect of tubes in computing situations. For example, IBM likes to use 20k plate resistors with a plate voltage of 150V. That's a relatively small resistor for that much plate voltage, but it means that one output from a logic element can drive quite a few other inputs without having to worry about fanout issues.
actually no need to destroy one tube for this purpose...if you are using a big transmitter tube like GU81M or the 813 using them in normal operation as an hf linear amplifier you can see there's plates glow without destroying them...but anyways it's a good experiment
Very, very low energy Xrays of 200-300eV at most. They can't even be detected by usual radiation detectors because they're too low energy. You need Xrays that are tens or hundreds of keV for them to be any safety concern. Medical Xray tubes are usually driven at 15-50kV for instance.
Unfortunately, the 6H2N-EB did not survive, but not because of the testing, because my clumsy self knockced it off the table and it shattered. So, I can't test that one, but the remaining three I can test! I have a cheap Accurate Instruments 257 Tube Tester, and while not all that fancy, it should give an idea! It gives emission on a scale of 0 to 100 with anything above about 45 being considered "Good". Good 6HA5: 72 Red plated 6HA5: 66 Good 6J6: 72/70 Red plated 6J6: 16/20 Good 6BZ7: 72/68 Red plated 6BZ7: 0/0 The 6BZ7, predictably, is totally dead. It wouldn't even register. The 6J6 isn't totally dead, but we definitely hurt it something fierce. It did register some emission, but that's deep in the "Bad" category on the tester. The 6HA5 though is a little trooper! It only showed slightly less emission than a known good version and honestly, could probably still work in some circuits, despite the extreme conditions it was exposed to. That one totally blew me away when I tested it!
Thank you! The Russian tube is a classic case of "should have done my homework", haha. The tube was actually totally fine, but it moves a tiny amount of plate current under normal conditions. My B+ here was right at 280V, and so looking at the datasheets for the four tubes, these are the plate currents to be expected with the grid at 0V: 6HA5: ~70mA 6J6: ~45mA 6H2N-EB: ~6.75mA 6BZ7: ~75mA The Russian tube just doesn't move that much current in the first place, so in order to move enough current to red plate it, I'd have to really crank up the voltage and probably also push the grid pretty deep into positive voltage too. Still, it was a fun test to see that it was so dramatically different than the others. For reference, on the 6BZ7, 75mA at 280V is approximately 21W, but according to the datasheet, the 6BZ7 has a maximum plate dissipation of 2W, so we were cramming 10x the amount of power through that tube than what it's maximum rating was!
@@UsagiElectric Ha ha. That's brilliant. The variation between different types is mind blowing. I've got a pocket book of Telefunken valves from 1966. It covers everything from IF to AF, Rectifiers and even CRT's and X-Ray tubes. I used it all the time when I was working in a radio repair shop in the 80's. The best few years of my life. :)
@@frankowalker4662 I was actually really surprised at just how different the 6BZ7 and 6H2N were, even though they're both dual triodes and even are pin compatible. It makes me curious on how wildly different the tubes would react and sound in an amplifier if hot swapped around!
hot, but kinda a waste of tubes imo, could've gotten some data in the process, testing temperature of the plate/plate dissipation and comparing them to the datasheet, and things like that.
@@UsagiElectric , six 6146B tubes were used in early versions of the 300 watt Ampeg SVT ("Super Vacuum Tube) bass guitar amplifier. The Rolling Stones used the original prototypes of this amp on tour in the early 1970's, for guitar as well as bass. The 6146 is a small transmitting tube (sometimes used for ham and mobile radio) but even the tougher B version sometimes failed in these amps, and it wasn't long before Ampeg changed the circuit to use the then-commoner, more easily available 6550's (or KT88'S) instead. The SVT is still in production in an "updated" form and can still be seen onstage at big festival concerts.
Dont go the destructive road, lets see it work then see it break Then look inside. Too easy to go lets rip it apart with out seeing it in use via a test circuit. Looking at you evilmoney
Nice! (Hope you had glasses on.. :O) Any idea what temp you hit? (and what temp do they normally run at, once warmed up? Heck, why do they need warming..?) ... why do the tubes have silver top end? This calls for a post-mortem teardown of killed tubes and a microscope?
Thank you! I didn't have glasses on, but to be fair, I've never actually heard of a tube shattering due to electrical misuse! As for the temps, I didn't measure, but I can say that the 6HA5, 6J6 and 6BZ7 are all pretty warm to the touch in normal operation, but after my shenanigans, they were hot enough that I couldn't hold them! Tubes often run at wildly different tempteratures. The 6AU6s that I use for everything get warm, but never hot enough to hurt in your hand or on your fingers. But, my Magnavox concert grand radio has a bunch of 6V6 output tubes on the amplifiers, and they run at 300* F (150* C) or more depending on how loud you got it cranked up! Those will definitely hurt if you try to hold your hand on one when it's running at full tilt. The little silver bit at the top is actually called a "Getter". This is a bit of metallic material that chemically reacts with any impurities in the vacuum (due to an incomplete vacuum or off-gassing of the elements inside the tube). You can actually tell if a tube has gone to air at a glance by looking for the getter. If it's all milky white or brown, then air got into the tube and the getter reacted completely. And speaking of cutting tubes open, well, I just so happen to have a video where I did just that! th-cam.com/video/6DM1qBgtxrs/w-d-xo.html
The temperature of the internal material can be estimated from the color. Red to orange color means 600 to 1000 C. The one which went white probably hit over 1300 C. At least that's my estimate from reading about the phenomenon.
That's the quality content I subscribed for. Also a fun way to get some beautiful glow out of tubes is to get some gassy tubes and putting a whole lot of voltage through them. As soon as that getter is gone far enough you will start to see some blue and violet glow from the gas inside getting ionized. Would love to see you do that too if you got some gassy tubes ✌️
Thank you! As I get a little more comfortable with working with this massive transformer, I definitely want to start playing with getting into some of the more interesting side of tubes that require a bit more high voltage. There's enough windings on the transformer that I can gang them together and get like 100VDC rectified out of it, which should make some tubes glow real nicely!
With my projects usually using just 24V, I've been lucky enough to never have red-plated a tube, but I can definitely see how easy it would be to get the plates glowing in an amplifier when trying to get as much power as possible out of it!
Hahaha, I had to look it up and that's one hell of a tube! The first problem would be figuring out how to even power the filament. 7.5V isn't tough, but getting 75A of current is beyond anything I have in the shop! If I do get it powered up, if I want to thrash it hard to blow, I need to build a power supply that can get to about five times the maximum ratings. The datasheet says the max is about 6,000W, so let's aim for a power supply that can provide up to 50,000W just to make sure we got enough in the tank to finish the job. That means I need a power supply that can give 4,000V at 12A, which is a frighteningly large amount of power. With that much power on tap, I should probably build a Faraday cage to house it all in and then operate from a safety bunker in another room, haha.
Yup, I'm chalking this one up to "old habits die hard". When I first got the tube, it was in a lot and I had no idea what it was, so I googled "6H2N" and got enough results that I thought I had it right. Much later I learned it's actually 6N2P, but my brain is having a hard time making the change!
It's definitely an over-engineered tube! But, also, after digging through the datasheets a bit more, it moves much less current for a given grid voltage as compared to the other tubes. My B+ voltage was right at 280V and according to the datasheets, this is the level of plate current with a grid voltage of 0V: 6HA5: ~70mA 6J6: ~45mA 6H2N-EB: ~6.75mA 6BZ7: ~75mA The Russian tube just moves so much less current than the other tubes that I'd really have to crank up the voltage and probably also push the grid pretty deep into positive voltage to get the plate to start glowing red. For reference, on the 6BZ7, 75mA at 280V is approximately 21W, but according to the datasheet, the 6BZ7 has a maximum plate dissipation of 2W, so we were cramming 10x the amount of power through that tube than what it's maximum rating was!
The Cyrillic butchering in TH-cam videos is starting to annoy a little. It would be nice to take that 5 minutes and check the letter pronounciations on Google and Wikipedia in the age of internet because in my opinion it's not up to us to how we want to interpret the alphabet, especially in the engineering field. Accents aside, I haven't seen or heard Russians butchering Latin alphabet though, maybe they are, too. Edit: I'm okay with BORAT and KoRn doing it though.
I'm sorry that you got annoyed at my poor transliteration of the Russian language. I'm actually a Japanese to English technical translator by trade, and so I'm very familiar with people butchering romanization of a foreign language. Granted, the Japanese language does have some quirks to it that makes romanization sometimes difficult with a bit of contention over how best to do it. Regardless, as I mention in the video, I know it's 6N2P, but when I first got the tubes over a year ago, I knew nothing about them, so I googled the closest thing to what was silkscreened on the tube itself (6H2N) and got enough results that I thought that was correct. I discovered much later that 6N2P is the proper transliteration of the Cyrillic on the tube, but my brain had already internalized the incorrect method. So, I still get it wrong. Again, I apologize that this is starting to annoy you a little, I'll try to get it more correct in the future.
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The flash may have been the cathode bond burning open. When metals are heated to incandescence in a vacuum, a plasma can form, which becomes the primary means of conduction. If the current is sufficient, it can heat the grid so that it melts, and thereafter will have little to no effect on the current passing between cathode and plate. It is the equivalent of decades of use in a few seconds.
That's actually a really interesting idea! I may have possibly turned the vacuum tube into a Thyratron, if only for a moment, haha.
After seeing both the 6HA5 and 6J6 run so bright without any super dramatic stuff, I was very much so no expecting a flash out of the 6BZ7. It totally caught me off guard!
Would have been nice to have had a current meter on the plate to see what the maximum plate current was. I have seen tubes with a leaky coupling capacitor put a positive 5 volts on grid and cause a lower B+ voltage.
I thought about this, but oddly, I don't have a good current meter. All I've got is my little UNI-T 120e DMM, and I haven't been able to get it to read current properly yet (most likely, I'm too dumb to use it properly).
But, looking at the datasheet, I can kind of come up with some rough ideas!
My B+ voltage was right around 280V and most datasheets have a little chart with grid voltages that can almost get us there. So, at 280V with a grid voltage of 0V, the maximum plate current should have been around this:
6HA5: ~70mA
6J6: ~45mA
6H2N-EB: ~6.75mA
6BZ7: ~75mA
This actually explains why the 6H2N-EB didn't glow. I didn't have nearly enough B+ to get enough current flowing through it to upset. Ideally, I would have had closer to 400V and maybe run the grid into positive voltage further. This also explains why the 6BZ7 didn't fair too well. 75mA at 280V is approximately 21W, but according to the datasheet, the 6BZ7 has a maximum plate dissipation of 2W, so we were cramming 10x the amount of power through that tube than what it's maximum rating was!
Pulling down the B+ rail, lol....
Love valves!
Some of the power tubes in the amps that I work on get that distinctive blue glow. When the amp is turned all the way up , if you play the instrument, you can see the blue glow change with the signal coming into the amplifier.
I died a little inside when you said "6H2N-EB". It's in cyrillic my man..
Not generally a fan of destroying anything deliberately, but you assured that these are not expensive components, so not that rare. The educational value was good, and to be fair I did enjoy the flares. 👍
I'm right there with you, I'm a bit of a pack rat, and if anything has any kind of usability I tend to stuff it in a draw for "one day". But, I really wanted to see some red plating, so I went through my tube collection for the ones I never use and aren't really highly sought after tubes. The 6BZ7 and 6H2N-EB can often be found for about $3 on eBay, so I figured that was cheap enough to sacrifice in the name of science!
Well, maybe not science, but certainly entertainment, haha.
Student says to teacher,
"Mr Beaker, I've never tried converting mains electricity into direct current!"
Teacher: "Let's rectify that."
I legitimately had some electronics teacher's class visitor try to tell me, "that's what the power transformer does!"...
One tube in my collection is an Eimac 4-1000A from the power stage of a 5kW radar transmitter that was accidentally redplated when the oscillator stopped. The anode, despite having large cooling fins on it, actually melted in some spots, so that it now has holes that mirror the layout of the control grid raster. It's mostly useless as an amplifier triode anymore, but the holes make it a much better mood light bulb than before ;-)
The most impressive tube I see this in frequently is the 6BQ5/EL84, if you manage to just ride the edge of red plating so it stays intact long enough, you will see the glass soften and get sucked against the two sides of the plate.Try 350 on the plate, about 320 on the screen, and start with -15 on G1. Stick 50 ohms in the cathode and maybe a few hundred ohms as a plate load. Ride it until the glass gives way, air enters, and flash bang at the end...oh, and fuse your HT line accordingly for this test.
This video rocks dude. I did this once (by accident) to a 12L8GT when building a massive amplifier. Luckily the tube came out okay and still worked because I noticed it before any massive damage was done. You produce amazing content in general though, it was your channel that actually inspired me to build my own 4-bit vacuum tube computer
Thank you so much!
The 12L8GT is a twin pentode in an octal package and that's just awesome! Tubes are surprisingly tough, the 6HA5 I red-plated here actually still works and tests fine on my (terrible) vacuum tube tester, which is just wild to think about. They can often handle five times their maximum ratings for brief periods without too many ill effects, which is insane to think about in regards to electrical components!
Thank you for the awesome words on the content! Do you have any links to your work on the 4-bit tube computer? I would love to see your progress and chat with you about it!
@@UsagiElectric I haven't uploaded anything online about my computer yet, I'm still in the stage where I'm designing everything and getting everything planned. Once I get my designs finished I'll upload them and let you know. My general design goals were to build a computer completely dependant on tubes that could read programs, execute them efficiently, and give a readable output via an interface, probably going to be nixie tubes. Even the power supply has to be completely regulated via tubes.
@@straightman2 Definitely let me know when you get some stuff online, I'd love to check it out!
Initially, I was thinking to build my entire 1-bit computer from tubes only, using 6AL5 dual diodes or modified multivibrator designs with dual triodes, but I ultimately went with using silicon diodes because I couldn't afford to have nearly double the tube count! (And silicon diodes in tube computers was fairly common from the mid-50s on.) Ultimately, I do intend to build my power supply from scratch, but I want to get the computer itself finished first so I have an idea of the power draw needed.
For the output, I would love to use Nixie tubes, but since I'm running entirely at +24V/-12V, I just don't have enough voltage to use them. Instead, I'm thinking I'll build an output display out of little IV-3A VFDs, since they're also pretty close to period correct and can run on 24V.
If you want to, come join us over on the Discord chat server and we can chat tube computers and swap ideas! ( discord.com/invite/p7UsfHD )
"Full wave Bridge rectifier" ---- Electroboom takes notice.
I really should have been wearing his shirt for this one!
On the 6BZ7, the bright flash was likely the cathode bonding wire failing due to excessive current through it.
Some tubes are more resilient than others, depending on the current the plate is rated to handle. It's primarily plate design that will determine how resistent a tube is to red plating.
You may have re-created a mini " Big Bang" when that last valve turned " White-hot"!
It might be interesting to see a test rating before and after a redplate, with different timings of redplating.
I just had a couple of 6L6s red plate in a 66 Twin Reverb tonight. Its got to be something with the socket or a resistor because it happened on multiple tubes in the same socket. Firecrackers.
If you red plate a television horizontal output tube you can melt the glass envelope, keep the plate orange color but not fully hot and leave it burn. might have to increase current until it happens. you will need enough voltage also. dosent always work.
Some of those output tubes are meant to run glowing slightly, which just blows my mind!
The fact that you can get them hot enough to deform the glass without blowing the tube is just awesome though!
I think the reason they flare up red and then slowly go dim is because as the metal heats up the resistance goes up and causes the amps flowing to go down.
I think you're totally onto something here! I actually tested the 6HA5 in my tube tester the other day out of curiosity and it still tested as good. I was totally lost as to why that would be the case as I thought I was destroying it, but the heat vs. resistance aspect of the phenomenon is something I hadn't thought about!
Negative temperature coefficient? Interesting!
No surprise that the 6N2P survived. Ruski tubes are generally the best available. Based on your other experiments, I got a handful of DL67 micro tubes and my first experiment red plated just like these. Lol. I need to figure out how to not do that next time.
Totally dig your videos.
The Russians sure liked to engineer stuff to be tough as nails! Also, the 6N2P wasn't really designed to move a whole lot of current in the first place, so I would have needed a much, much higher voltage PSU to get it to misbehave.
Sounds like you pushed a little too much current through the DL67! I've done that a few times on accident too, haha. Time to bump up some resistor values!
@@UsagiElectric the 6N2P is a low anode current type very similar to a 12AX7/ECC83 so less likely to redplate(unless you crank up the ht volts), try a 6N1P or 6N3P as theyre more like 12AU7/ECC82
I agree, the Russian tubes are more robust because they have more widely separated elements (especially ones from decades ago when they didn't have the technology for tight construction). So they have wider element spacing that makes them more robust. Thus they have less capacitance and can work at slightly higher frequencies and plate currents but have less gain. They didn't make them more robust, it's just they couldn't make them more delicate and sensitive so they ended up being more robust that as a winfall can handle more abuse but with less overall performance.
The 6H2N seems to have an anode voltage of about 250v, probably a higher maximum, your supply was 197, after the rectifier it would be 277, probably too close a margin to fail, i would increase the transformer tapping, even if it means 2 windings in series.
With the 450v capacitor you 'could' go up to 300v safely
Yup! The 6H2N is not designed to move all that much current. Looking at the datasheet, at 280V anode voltage and 0V grid voltage, the 6H2N is moving about 7mA. For reference, in those same conditions, the 6BZ7 is moving 75mA! So I needed a whole lot more voltage before I could get that one to glow.
I have a couple of 120W valve amps with 4x6550's per channel. I used to use them with a pair of electrostatic speakers which was just on the edge of being stable. Every now and again one amp would go into oscillation with instant red-plating and a mad rush across the room to get to the plate "off" switch. Ended up putting them out of service and getting a more robust transistor amp.
Not fun at all at £70 per tube.
With 6N2P sitting at Vg=0 Ua=200V, you'll get 5mA of plate current and Pa=1W, not enough to get it red hot, tho
the -EV specimen is military grade as well, if I'm not mistaken.
You're totally right! I should have done a bit more homework on the tube before trying to give it a shot, it's just not moving enough current!
Very nice, i've been wondering about this since my tube amp red plated like crazy. It had a bad coupling cap and within seconds one of the big 807 power tetrodes was glowing bright red. It had like positive 160v on the grid. The tube still works fine though.
The blue emission is fluorescence and if i'm correct is either due to imperfect vacuum or imperfections in the glass envelope
Thank you!
Tubes are surprisingly hardy! Another commenter asked if I could test the red-plated tubes against known good ones, so I pulled out my cheap Accurate Instruments 257 Tester. It's a pretty terrible tube tester, but it should be able to give us a bit of an idea. (Unfortunately, the 6H2N-EB didn't survive the test, but only because my clumsy self knocked it off the table and it shattered on the ground... oops.)
Good 6HA5: 72
Red plated 6HA5: 66
Good 6J6: 72/70
Red plated 6J6: 16/20
Good 6BZ7: 72/68
Red plated 6BZ7: 0/0
The 6BZ7 was clearly totally dead. Something definitely shorted inside and wrecked havoc. The 6J6 registered some emission, but it was clearly hurt. The 6HA5 though soldiered on as if though nothing happened at all! I was stunned by how hardy it was!
@@UsagiElectric how can a tester by accurate instruments be terrible? Haha
I'm guessing it might depend on a lot of physical factors as well, like tube construction and materials
@@stefandumoulin1872 Haha, I actually had to rewrite my sentence a few times because I kept typing "my inaccurate Accurate Instruments 257". It's pretty good for determining if tubes are dead or not, but that's about it.
I think you're totally right on the physical factors as well. The 6BZ7 seems to have really tiny tolerances between cathode, grid and plate, whereas something like the 6HA5 seems to have a bit more distance between each component. That could be why the 6BZ7 shorted out and the 6HA5 didn't, despite both getting really hot!
Ionized oxygen atoms.....
Redplating in the wild (unless the tube is meant to run with a hot plate like some large tubes) is not fun, red gridding is even worse. Especially when you walk away for a minute to sip your soda and turn back and nearly choke on your drink and spill it scrambling for the plug only to realize it's too late and already fried which means even more repair.
Oh man, I can totally imagine the pain when it's a proper HiFi tube that you watch die! Fortunately these were cheap, commonplace tubes so I was having a bit of a laugh, but man if it's a nice, expensive tube I would totally freak out, haha.
@@UsagiElectricFortunately, it was only the rectifier that got hit, the tube died but I saved the transformer from getting cooked too (I believe I had bypassed the fuse, but managed to unplug it in time).
Fun experiment. We used to see this in old TV’s as the horizontal output tube would run at zero bias if the horizontal oscillator failed. The 15 watt 6DQ6 would red and then orange plate in about 15 seconds. Then blow a fuse.
I have seen this happen on old style TV's when the horizontal or vertical output tubes loose grid drive. Any high power amplifier can do this as well. If the current goes high enough it can actually burn a hole in the plate. But usually the cathode either boils off it's rare earth coating or opens the cathode connection. Sometimes if enough voltage is there it can flash over and I have actually seen the envelope crack and break apart.Iin fact if it has been allowed to sit there long enough with high current and voltage it can break on the bottom seam where the tube was glass welded together.
Great video. What you made are one time use black body radiators. Next time, put shields around your cap, transformer, tube, in fact all of your electronics. No sense losing and eye to an unforseen explosion or getting burned. And do this in a well ventilated area.
I had a PL508 in a television whose glass melted on a short circuit. It was the worst red plating I have ever seen.
The reason, as I understand it at least, for some triodes carrying more current than others is the density of the wires on the control grid. When tubes are manufactured they need specific parameters for the electrodes in the envelope to determine the characteristics. A triode that has a less densely wound control grid will allow more current to pass but have a much lower mu and amplification factor, such as the 12AU7 and the 6BZ7. A 12AX7 triode has more densely wound control grid, so it's much more sensitive to voltage changes, but can't pass as much current with the grid at 0V. The 6H2N-EB's are similar to a 12AX7, which is probably why they didn't red-plate.
I think you absolutely nailed it! I did a bit of reading through the datasheets to see what kind of plate current can be expected with a B+ of 280V and the grid at 0V and here's the results:
6H2N-EB: ~6.75mA
6BZ7: ~75mA
It's wild how different the two tubes are! But, it makes sense with what you're saying. The Russian tube just doesn't move all that much current (meaning it must have a pretty tightly wound grid), so I would need to really bump up my B+ and maybe even drive the grid into positive to get some red-plating action.
Thank you for the insight!
You might make some x-rays if the voltage is high enough.
not enough with 137*sqrt(2) volts, but probably these tubes would create xrays even if they're broken (as long as they're not vented)
Not going to lie, the worry briefly flashed through my mind, but I do remember that x-rays needed quite a lot of voltage, so I was pretty certain my little 280V B+ wasn't enough. That blue fluorescence was awesome though!
@@tpa6120a2dwp I would love to see how bright the plates would glow with 7kV crammed through them, haha!
No chance at all for x-rays - None.
There is a threshold voltage before X-rays are possible, it’s around 13,000 volts.
Thankyou so much for doing that, it was the first time that i see the blue path of plasma inside of a vacuum tube!
I had a vintage eico 460 scope and two of the tubes would always glow a bright violet. The glow on the tube would even bend if you brought a magnet close to it
Those were regulator tubes, they have gas in them
@@krz8888888 no they were not
@@krz8888888 the glow was only on the surface of the glass due to bombardment from electrons
Ik this video is two years old but I have actually killed a sub miniature tube using a d cell, the circuit was made in the 50s new batteries are more powerful than the old copper batteries and sometimes the circuit cannot handle the constant voltage of the nee battery so it can pop it and leak the alkaline acid in doing so the pop created enough current at once to burn out the filaments of the tube
Do you think that there are any xrays being emmitted? Really enjoy all your videos. cheers
does red plating come with hum?
It happened to my tuning a vttc tube was pl504 but the tube survived!
I was surprised at just how much pain I had to throw at the tubes to actually damage them. Most tubes could handle a little red plating with no problem at all. It's amazing how tough tubes really are!
@@UsagiElectricso tube pops out when big voltage is present
What about 0.7 volts
Can vacuum tube red plate at 0.7 volts
Used to be common to see a TV horizontal output red plate when horizontal drive stopped working.
Tubes are awesome because they can take so much abuse. A tube can be red-plating mildly for a while before it actually goes bad, which is just wild to think about!
Glowing plates are much more fun in audio amps. It's part of the "swan song" tone that players like SRV relied on.
Also a good way to kill transformers in the process. Not very recommendable
I'm so bad at actual audio stuff! I find the technical side of it amazing, but my hearing is pretty shot (and I'm mostly deaf in my left hear), so I can't hear the difference unless it's pretty dramatic (like comparing our all tube Magnavox Concert Grand against pretty much anything else that makes sound in the house).
As a kid i used to play with vacuum tubes, people were throwing out their old tube tv's to replace them with modern transistor ones so every month with the garbage runs there would be several TV's ready to play with (they collected big garbage once a month in those days).
I had an old transformer from a tape deck but it was only 300V 40mA or something like that
So i built a powerbank that was 220V mains rectified into a huge bank of capacitors. Big enough to weld a screwdriver when discharging. And one time a metal pen that has a couple weld marks to this day :D
I built 100MHz transmitters with ECC85 tubes and they were colorfull displays of destruction sometimes as all parts were scrounged from the TV's i found. I also had so many side bands that i was all over the FM band and the television in the living room would show all kinds of patterns. One of those "are you experimenting?" moments for my mom.
So yeah i had a lot of fun and have red plated al lot of tubes. (And popped all kinds of electronic components as well) Fun days
And yes i did survive that power supply i built ;)
Where would one find a multitap transformer like that in the Test Rig chapter?
Try using a 6CM5 power pentode.
They were horizontal oscillator 20 W valves used in black and white televisions in the 1960s.
I saw one glowing a dull orange because it drove an eht transformer which had developed shorted turns....
The 6CM5 looks like it might be a decently popular audio tube.
If I destroyed one of those just to see it red-plate, the Hi-Fi audio guys would burn me at the stake, haha!
@@UsagiElectric it's not called red plating.... it's just overloading.
The 6CM5 is lousy for audio, it's very non linear. But it is a nice big valve with a big plate and they're impressive when they're glowing orange....
@@UsagiElectric EL84 or 6551 with 500 V B+.....
Could be SAVAGE!
@@UsagiElectric You might be confusing the 6CM5 with 6CZ5 which is a good substitute for the scarce and expensive 6973 audio tube (the pin out is very slightly different). I also have some 6CM6 tubes which might have audio applications but I have not tried them.
I've seen TV signal diode red plate with only a few volts.
It's all about finding that balance between voltage and current. Even with only a few volts, if the load is trying to pull a huge amount of current, the plates can start to get hot!
Poor tubes! :) And what about forcing current in cold cathode mode? I think that would be interesting. You could zap the tubes that had their filament broken.
Anecdotally, I have accidentally destroyed miniature tubes by red-cathoding them on the test bench (these were cheap tubes). So this is also possible.
A friend loaned me a d'Arsonval type microammeter, which turned out to have been WAY out of calibration (due to permanent magnet decay), for doing some measurements so I could characterize some late-production miniature pentodes I had. These were tubes with indirectly-heated cathodes, and presumably one of the later exotic-oxide (maybe Barium) coatings.
Running the tests on the bench, warmed up a tube cathode heater, then slowly increased the output on a bench supply to act as my B+. Imagine my surprise that the needle on the microammeter barely moved, but the cathode on the tube seemed to put out a dull cherry glow. Slowly dialing up to a couple hundred "microamps" of plate current, the tube cathode began to glow a pretty bright orange. I concluded something must have been wrong, so I stopped the test. Tube then failed to test good on a separate emission tester....hm.
Repeat experiment. Same result. Tube gave terrible calculated gm figure. Then I decided to test the microammerer, and it was off by a factor of about 100. 100uA apparent reading on meter tracked with about 10mA of "real" DC current. Oops. Even when your buddy tells you "sure, it's accurate", check anyway....
The upshot is that I never got any luminescence out of the tube plates, but the cathodes did, and were destroyed (presumably the exotic oxide coating was either ablated or diffused inward). Depending on internal geometry of a specific tube, I guess the plate can be physically large enough, and the cathode small enough, that cathode emission dissipates more heat than plate kinetic-collision of electrons. So, there's more than one way to "do it wrong".
This was fun. Thank you for the video! I also haven't seen red plating in person.
Thank you!
It was something I've heard about and seen some alright pictures of, but to see it in person and then on the replay through a macro lens was super rewarding!
I wonder how a scintillation counter would react to these experiments...
That's actually a really interesting question!
A good photomultiplier tube tuned for a specific wavelength could tell what kind of energy the tubes are giving off. There isn't enough energy for x-rays or the like, but it would be really fun to see what exactly is being emitted in these pretty nasty situations!
@@UsagiElectric Most photomultiplier tubes are tuned for blue light, with their sensitivity to red being quite low. That's because of the construction of the photocathode (bi-alkali). There are some, fairly rare, that use a different type of cathode and are tuned more towards red. Nonetheless, even so the red that you experienced would be enough to burn off even one of the regular "blue" PMTs. That's because their amplification factors can be insanely high. You would want to intentionally reduce drastically the amplification by leaving some of the dynode chain unbiased, or very poorly biased. Or else you risk blowing the PMT. Also, you'd want to do that experiment in absolute darkness or a hermetically closed enclosure. Even a dim light from a LED can burn out a PMT. (source: myself. I'm building scintillation detectors as a hobby. :) )
At most you get very low energy Xrays of several hundred eV energy. The vast majority of scintillation materials will not be sensitive enough to get a response. They only start showing a response above 1-1.5keV Detecting such low energy Xrays is a complicated matter.
what would be interesting to see in e.g. dual triodes is if you redplate one plate to death, will the second one still work? because if so you're actually destroying the plate (which feels kinda weird), if not (my suspicion) it's more of a sputtering/vapor effect ruining the vacuum? would be a neat demonstration.
Unlike with dead transistors, the magic smoke is still sealed inside the tube!
Haha, but we let out all the magic light instead!
I saw a tv damper tube red plate and actually softened the glass and it imploded a hole in the envelope.
@1:27 You have the capacity to do this! 😊 - ❤️ your channel, keep up the good work and take care, be safe. 💪
05:58 : I recognized the transformer as I saw it , I had long ago a tektronix oscilloscope.
Very keen eye! This one did indeed come out of a 545, and it's an absolute beast of a transformer. Tons of taps, lots of power, and just super useful!
Great visual aid for valve basics, and fun !....cheers.
Thank you for checking the video out!
14:50 wahahaha ! Great video !
I'd like to have seen an analog ammeter hooked up to the anode to see how much these pulled
I did want to put an ammeter on there to see how much current they ended up pulling, but oddly, I don't have a good current meter. All I've got is my little UNI-T 120e DMM, and I haven't been able to get it to read current properly yet (most likely, I'm too dumb to use it properly).
But, looking at the datasheet, we can kind of come up with some rough ideas!
My B+ voltage was right around 280V and most datasheets have a little chart with grid voltages that can almost get us there. So, at 280V with a grid voltage of 0V, the maximum plate current should have been around this:
6HA5: ~70mA
6J6: ~45mA
6H2N-EB: ~6.75mA
6BZ7: ~75mA
This actually explains why the 6H2N-EB didn't glow. I didn't have nearly enough B+ to get enough current flowing through it to upset. Ideally, I would have had closer to 400V and maybe run the grid into positive voltage further. This also explains why the 6BZ7 didn't fair too well. 75mA at 280V is approximately 21W, but according to the datasheet, the 6BZ7 has a maximum plate dissipation of 2W, so we were cramming 10x the amount of power through that tube than what it's maximum rating was!
I was wondering how did old cars work with 12v battery and a tube radio ?
That's actually a super fascinating part of history!
In the 40s, most cars actually had 6V electrical systems, but had tube radios in them. The 6V worked perfectly for the tube heaters, but to get the HV they used something called a "vibrator". Essentially, they created an oscillator with a relay (+6V into the common and the coil was powered from the normally closed pin. The coil would trigger the relay which breaks the power to the coil, causing the relay to snap on and off as fast as it physically can.) This created a square wave that went into a transformer to create high voltage, which was then rectified and used for the tubes in the radio.
The same method was used for 12V systems too, but by the time 12V systems were common, space charge tubes were starting to get used in place of the old vibrator design. These are tubes that are specifically designed to work with 12V on the plate (and 12V powering the heater). So, no high voltage anywhere in the system! But, that was pretty short lived because the transistor was starting to get cheap, so finding space charge tubes today is a bit difficult.
@@UsagiElectricI have some of those vacuum tubes designed to work at 12V plate voltage! They're rare today, but they were made exactly for this application in the 1940s, radios powered by a 12V battery. They're actually specified for a maximum plate voltage around 30V (and sometimes as low as 16V). Examples are: 12AD6, 12DV7, 12U7, 12AL8, 12DV8 and so on. You can still find such tubes on the used market if you look hard enough. :)
@@UsagiElectric , Note that prior to the development of space charge tubes for car radios there were 1 and 3 volt tubes used in "portable" radios such as the Zenith Transoceanic, 1L6 and 3V4 tubes being an example. The 1L6 is the only tube that really works correctly in Transoceanic and they are scarce and pricey nowadays. I put the word portable in parentheses because the tube type Transoceanic radios are bigger and heavier than many boomboxes.
Surprised those diodes worked at high voltage as it was for a low voltage charger. I would expect 100V diodes.
I have seen guitar amps with the plates that look like swiss cheese from being driven so hard.
The 6AL5 is good up to a peak inverse plate voltage of 330V, and I was only at about 180V here, so I still had plenty of headroom!
It blows my mind how hard you can drive some tubes and still have them keep on ticking!
@@UsagiElectric I think you misinterpreted the comment.
Scott was talking about the silicon diodes used in the bridge rectifier of the HV supply, not some vacuum tube.
@Scott H The potentially low reverse breakdown voltage limit of the rectifier diodes was my first concern too. But here is a thought on that; if you remember your vintage lead acid car battery charger circuit, you will agree that these chargers hardly use a full-wave bridge(!) rectifier with 4 diodes. They commonly use only two diodes and a center tapped transformer (full-wave rectifier). Those who dont believe are invited to dl the manual of the Lestronic II and see for themselves...
Now on the topic of reverse voltage; some thinking may make it clear, that on a full-wave bridge(!) rectifier with 4 diodes (like used by Usagi Electric) the two non-conducting diodes only need to withstand the nominal AC output voltage in reverse.
On a non-bridge(!) full wave rectifier consisting of two diodes and a center tapped transformer, the non-conducting diode however faces double the AC voltage in reverse. (Simulate it on LTspice if you dont believe)
Now knowing that
A) classic lead acid chargers use the full wave rectifier with 2 diodes on a center tapped transformer, and
B) the unloaded voltage of even an unregulated 36V system charger may exceed 45V, which puts the rectifier diode at a minimum of 2*45=90V reverse voltage, and
C) there is 48V golf cart chargers, who should top up at 60V (120V reverse)
It is safe to assume that the rectifier diodes are at least of the 200V reverse breakdown types.
Alternate title: Electronics hobbyist becomes convicted murderer
Seeing B+ attached to the anode directly and no cathode follower resistor is kinda cursed, but this was still a great video! Now i don't have to sacrifice my own tubes xD
Pity no plate meter.
Many years ago, I tried to make an audio amp, I had a 6CM5 line output tube, a speaker transformer, and a pot.
I was used to single transistor amp stages, you bias it on to get some volts across the load. So I tried the same with the tube. nothing, so I must have the grid wrong (150V on the plate) I ended up sending the grid positive, whereupon there was a frizzling sound from the tube and the bias pot smoked up. I think I red plated the grid.
Learned my lesson, stick to transistors.
The blue light is x-rays btw
I'm not quite sure I had enough voltage to generate any x-rays here. Usually, several thousand volts are required for x-ray emission, but I was only working with about 300V here. I think the blue fluorescence was caused by an imperfect vacuum, or perhaps even some off-gassing from the material inside the tube.
@@UsagiElectric In gas discharge tubes the color is specific to a certain gas or material. Assuming a pure gas or vapor you can get shades of blue from hydrogen, argon, krypton, xenon, oxygen, or mercury vapor. Saying a blue color is x-ray isn't necessarily correct. We're not scared of the orange glow from a neon bulb or a neon sign. I'm sure in a traditional x-ray tube that the high voltages might cause some color discharge but we're not gonna look. See the Wikipedia entry for X-ray tube. The last section gives some info on x-rays emitted from vacuum tubes, but it occurs at high voltage, >> 1 kV.
Wow that Xray when tube is burn out i like it
Triodes model as voltage sources, so you won't be able to red plate ones with too much plate resistance. Bet you can red plate a 12AU7 but not a 12AX7. The 6BZ7 specs close to my favorite 6BQ7. That one red plating doesn't surprise me.
Yup, that's exactly what was going on with the Russian 6N2P. I didn't have nearly enough B+ to stress it to the point of red plating. The 12AU7 is a fantastic little tube, I have much better results building with the 12AX7, and I think that's probably due to difference in plate current capabilities between the two. The 6BZ7/6BQ7 are also great little tubes and can move a decent amount of current, even at low voltages!
I have a bunch of 12AX7 that test ok but are too microphonic to actually use. So I rigged up a microwave transformer with a HV diode and connected up the plate and cathode and used a small transformer for the heater. I had a meter connected in the cathode to show the current and I calculated the plate was trying to dissipate approximately 24watts. (A 12AX7 plate is rated for only 1 watt of dissipation). Because a microwave transformer puts out 2000 volt at 2 to 300 mA this NOT something to do if you don’t know how to work with high voltages safely.
Electrons doesn't move
are power resistors put in a circuit to prevent red-plating?
I'm not too knowledgeable about specific audio setups, but the balance of plate resistor, tube dissipation and desired drive current is a pretty common design aspect of tubes in computing situations. For example, IBM likes to use 20k plate resistors with a plate voltage of 150V. That's a relatively small resistor for that much plate voltage, but it means that one output from a logic element can drive quite a few other inputs without having to worry about fanout issues.
actually no need to destroy one tube for this purpose...if you are using a big transmitter tube like GU81M or the 813 using them in normal operation as an hf linear amplifier you can see there's plates glow without destroying them...but anyways it's a good experiment
12:26 6Н2П-ЕВ in Cyrillic is 6N2P-EV in Latin.
You essentially have no bias, how I blew up some EL34 valves in my amp
Yup, I built this as the worst case scenario!
Those tubes can generate x-rays when overdriven like that.
Very, very low energy Xrays of 200-300eV at most. They can't even be detected by usual radiation detectors because they're too low energy. You need Xrays that are tens or hundreds of keV for them to be any safety concern. Medical Xray tubes are usually driven at 15-50kV for instance.
Any chance you can test the tube characteristics before and after red plating?
Unfortunately, the 6H2N-EB did not survive, but not because of the testing, because my clumsy self knockced it off the table and it shattered. So, I can't test that one, but the remaining three I can test!
I have a cheap Accurate Instruments 257 Tube Tester, and while not all that fancy, it should give an idea! It gives emission on a scale of 0 to 100 with anything above about 45 being considered "Good".
Good 6HA5: 72
Red plated 6HA5: 66
Good 6J6: 72/70
Red plated 6J6: 16/20
Good 6BZ7: 72/68
Red plated 6BZ7: 0/0
The 6BZ7, predictably, is totally dead. It wouldn't even register. The 6J6 isn't totally dead, but we definitely hurt it something fierce. It did register some emission, but that's deep in the "Bad" category on the tester. The 6HA5 though is a little trooper! It only showed slightly less emission than a known good version and honestly, could probably still work in some circuits, despite the extreme conditions it was exposed to. That one totally blew me away when I tested it!
I've heard of this but never seen it. It was awesome. Maybe the Russian valve was already damaged ? Thank you for this.
Thank you!
The Russian tube is a classic case of "should have done my homework", haha.
The tube was actually totally fine, but it moves a tiny amount of plate current under normal conditions. My B+ here was right at 280V, and so looking at the datasheets for the four tubes, these are the plate currents to be expected with the grid at 0V:
6HA5: ~70mA
6J6: ~45mA
6H2N-EB: ~6.75mA
6BZ7: ~75mA
The Russian tube just doesn't move that much current in the first place, so in order to move enough current to red plate it, I'd have to really crank up the voltage and probably also push the grid pretty deep into positive voltage too. Still, it was a fun test to see that it was so dramatically different than the others.
For reference, on the 6BZ7, 75mA at 280V is approximately 21W, but according to the datasheet, the 6BZ7 has a maximum plate dissipation of 2W, so we were cramming 10x the amount of power through that tube than what it's maximum rating was!
@@UsagiElectric Ha ha. That's brilliant. The variation between different types is mind blowing. I've got a pocket book of Telefunken valves from 1966. It covers everything from IF to AF, Rectifiers and even CRT's and X-Ray tubes. I used it all the time when I was working in a radio repair shop in the 80's. The best few years of my life. :)
@@frankowalker4662 I was actually really surprised at just how different the 6BZ7 and 6H2N were, even though they're both dual triodes and even are pin compatible. It makes me curious on how wildly different the tubes would react and sound in an amplifier if hot swapped around!
NEED MORE AMPS😡
wow I didnt know tubes would Red Plate interesting
Great fun! But educational too!
Electrons doesn't move and you are measuring the fake current with a microvoltmeter that is called Amperemeter so electrons doesn't move
The Russian tube held out very well.
hot, but kinda a waste of tubes imo, could've gotten some data in the process, testing temperature of the plate/plate dissipation and comparing them to the datasheet, and things like that.
Electrons are not moving they are just mirroring each other
Try a 6146 tube
I actually have a few of those, but they can move so much current, I'd really have to upgrade my "test" rig here!
@@UsagiElectric , six 6146B tubes were used in early versions of the 300 watt Ampeg SVT ("Super Vacuum Tube) bass guitar amplifier. The Rolling Stones used the original prototypes of this amp on tour in the early 1970's, for guitar as well as bass. The 6146 is a small transmitting tube (sometimes used for ham and mobile radio) but even the tougher B version sometimes failed in these amps, and it wasn't long before Ampeg changed the circuit to use the then-commoner, more easily available 6550's (or KT88'S) instead. The SVT is still in production in an "updated" form and can still be seen onstage at big festival concerts.
Tube torturer!
Dont go the destructive road, lets see it work then see it break Then look inside. Too easy to go lets rip it apart with out seeing it in use via a test circuit. Looking at you evilmoney
try to do that with transistors
I much prefer a light show than a smoke show, haha!
hahahaha - "I want to rectify that"
I was wondering if anyone would catch my pun!
Nice! (Hope you had glasses on.. :O)
Any idea what temp you hit? (and what temp do they normally run at, once warmed up? Heck, why do they need warming..?)
... why do the tubes have silver top end?
This calls for a post-mortem teardown of killed tubes and a microscope?
Thank you!
I didn't have glasses on, but to be fair, I've never actually heard of a tube shattering due to electrical misuse!
As for the temps, I didn't measure, but I can say that the 6HA5, 6J6 and 6BZ7 are all pretty warm to the touch in normal operation, but after my shenanigans, they were hot enough that I couldn't hold them! Tubes often run at wildly different tempteratures. The 6AU6s that I use for everything get warm, but never hot enough to hurt in your hand or on your fingers. But, my Magnavox concert grand radio has a bunch of 6V6 output tubes on the amplifiers, and they run at 300* F (150* C) or more depending on how loud you got it cranked up! Those will definitely hurt if you try to hold your hand on one when it's running at full tilt.
The little silver bit at the top is actually called a "Getter". This is a bit of metallic material that chemically reacts with any impurities in the vacuum (due to an incomplete vacuum or off-gassing of the elements inside the tube). You can actually tell if a tube has gone to air at a glance by looking for the getter. If it's all milky white or brown, then air got into the tube and the getter reacted completely.
And speaking of cutting tubes open, well, I just so happen to have a video where I did just that!
th-cam.com/video/6DM1qBgtxrs/w-d-xo.html
@@UsagiElectric *fans self* its gettin' hot in here :O
The temperature of the internal material can be estimated from the color. Red to orange color means 600 to 1000 C. The one which went white probably hit over 1300 C. At least that's my estimate from reading about the phenomenon.
Does it not produce X-RAYS?
No, a much higher plate voltage would be needed to generate x-rays.
What did these poor tubes ever do to you? Tube killer.😁
@15:24 Oppenheimer moment 💥
That's the quality content I subscribed for.
Also a fun way to get some beautiful glow out of tubes is to get some gassy tubes and putting a whole lot of voltage through them. As soon as that getter is gone far enough you will start to see some blue and violet glow from the gas inside getting ionized. Would love to see you do that too if you got some gassy tubes ✌️
Thank you!
As I get a little more comfortable with working with this massive transformer, I definitely want to start playing with getting into some of the more interesting side of tubes that require a bit more high voltage. There's enough windings on the transformer that I can gang them together and get like 100VDC rectified out of it, which should make some tubes glow real nicely!
I've red plated a vacuum tube before by accident
With my projects usually using just 24V, I've been lucky enough to never have red-plated a tube, but I can definitely see how easy it would be to get the plates glowing in an amplifier when trying to get as much power as possible out of it!
what about trashing a 4CX5000A
Hahaha, I had to look it up and that's one hell of a tube!
The first problem would be figuring out how to even power the filament. 7.5V isn't tough, but getting 75A of current is beyond anything I have in the shop! If I do get it powered up, if I want to thrash it hard to blow, I need to build a power supply that can get to about five times the maximum ratings. The datasheet says the max is about 6,000W, so let's aim for a power supply that can provide up to 50,000W just to make sure we got enough in the tank to finish the job. That means I need a power supply that can give 4,000V at 12A, which is a frighteningly large amount of power. With that much power on tap, I should probably build a Faraday cage to house it all in and then operate from a safety bunker in another room, haha.
Was just a suggestion but now seems indestructible
6Н2П-ЕВ actually transliterates to 6N2P-EV, just sayin
Yup, I'm chalking this one up to "old habits die hard". When I first got the tube, it was in a lot and I had no idea what it was, so I googled "6H2N" and got enough results that I thought I had it right. Much later I learned it's actually 6N2P, but my brain is having a hard time making the change!
Negative voltage doesn't exist you are just measuring wrong the voltage
these experiments are good to learn from
so I say good job
(also could you please awnser your discord pm's)
Thank you!
(Sorry, I've been busy and spent some time out of town recently, I'll catch up on PMs one of these days!)
Try some 1T4's! LOL!!!
เสียงของหลอดให้เสียงที่เสมือนจริงครับ
Those Russian tubes are built like Russian concrete
It's definitely an over-engineered tube!
But, also, after digging through the datasheets a bit more, it moves much less current for a given grid voltage as compared to the other tubes. My B+ voltage was right at 280V and according to the datasheets, this is the level of plate current with a grid voltage of 0V:
6HA5: ~70mA
6J6: ~45mA
6H2N-EB: ~6.75mA
6BZ7: ~75mA
The Russian tube just moves so much less current than the other tubes that I'd really have to crank up the voltage and probably also push the grid pretty deep into positive voltage to get the plate to start glowing red. For reference, on the 6BZ7, 75mA at 280V is approximately 21W, but according to the datasheet, the 6BZ7 has a maximum plate dissipation of 2W, so we were cramming 10x the amount of power through that tube than what it's maximum rating was!
Photonicinduction it's you?
Hoo boy, I wish!
Photonicinduction gets about 4x as many views per video as I get in an entire year, haha!
Very nice, but stop being so conservative! Crank up those voltages!
Rusia tubes are beter .:)
I know
The Cyrillic butchering in TH-cam videos is starting to annoy a little. It would be nice to take that 5 minutes and check the letter pronounciations on Google and Wikipedia in the age of internet because in my opinion it's not up to us to how we want to interpret the alphabet, especially in the engineering field. Accents aside, I haven't seen or heard Russians butchering Latin alphabet though, maybe they are, too.
Edit: I'm okay with BORAT and KoRn doing it though.
I'm sorry that you got annoyed at my poor transliteration of the Russian language.
I'm actually a Japanese to English technical translator by trade, and so I'm very familiar with people butchering romanization of a foreign language. Granted, the Japanese language does have some quirks to it that makes romanization sometimes difficult with a bit of contention over how best to do it. Regardless, as I mention in the video, I know it's 6N2P, but when I first got the tubes over a year ago, I knew nothing about them, so I googled the closest thing to what was silkscreened on the tube itself (6H2N) and got enough results that I thought that was correct. I discovered much later that 6N2P is the proper transliteration of the Cyrillic on the tube, but my brain had already internalized the incorrect method. So, I still get it wrong.
Again, I apologize that this is starting to annoy you a little, I'll try to get it more correct in the future.