Cathode ray tube disassembly and explanation

I cut open a cathode ray tube (picture tube, or CRT) and explain the internal parts and their function.

[@AppliedScience]

Search for thermionic emission. The tungsten filament is often covered with a metal-oxide cathode to help electrons leave the surface, but the supply of electrons is coming from the electricity being supplied to the cathode, so nothing in the cathode itself is consumed.

[@utah133]

The aquadag is the anode. It's the positive high voltage connection, several thousand volts. It serves to accelerate the electron beam toward the phosphor screen. They actually heat the getter ring at the final stage of manufacture with an inductive coil to vaporize the metal to "get" the final oxygen and other atoms and achieve the best vacuum possible.

[@xxportalxx.]

Also worth mentioning that the getter ring is most likely a barium alloy not aluminum, although it may contain some aluminum.

[@Chris-Workshop]

in all honesty, though this is an older video i'm always reminded when watching your videos, you have a gift for explaining things very well to people. i really enjoy all of your videos, they are packed with usefull info and lack any unnessesary stuff. it's almost sad they are over at some point. for me I could always keep listening for more facts. keep'm coming, this is great!

[@AppliedScience]

Thank you! Let me know if you ever have suggestions for future video topics.

[@Chris-Workshop]

i'd love to see more of your cryo and vacuum stuff, i havent seen your coldtrap in use yet.

[@FrankLopezx]

Applied Science crt that whole interaction is worth a video

[@das250250]

Applied Science it would be nice to get it running and explore the voltages required to do so and calculations. Its also interesting to understand the gases that leach out under vacuum. That is , a metal under vacuum and does it give up impurities or atoms ? This device , a glorified original light bulb was really crucial to opening up our understanding of atoms and then cascading to help us convert cosmology to an important science.

[@RetroRecipes]

Great video! Could I have your permission to use a few clips for a video on my channel if I credit you? 🙏

[@AppliedScience]

Yes, this is an important point. The electrons are not strictly attracted to the anode. They are accelerated by the electric field created between the cathode and anode. As soon as they fly through the hole in the anode, there is no field, and the electrons will continue moving at fairly constant speed without feeling any acceleration or deceleration.

[@newldchappell1]

That was more complicated than I thought it would be. Amazing that they figured all that stuff out almost a hundred years ago.

[@unlokia]

Fascinating! I learnt all of this when I was a trainee TV/VCR engineer back in 1991 :-) Thank you! God bless you :-)

[@OrleansLane]

when i worked at RCA designing TV tubes we used Barium in the Getter .... thanks for the trip down memory lane I designed tubes in a previous life

[@thereisthespoon]

Excellent, thank you. One of the few videos where you do not end with 'Bye' :)

[@skivvy3565]

One of the most interesting video game design mechanics of the crt time was called ‘chasing the beam’ and worth reading about if you’re interested.

[@RadioChief52]

I always learn so much from your well explained videos. This video, in particular, is about the only one that I was keeping up with you on because it deals with vacuum tubes and I am of that generation. It just makes me feel my age I guess but I love this stuff.

[@dtiydr]

The black paint isn't only used as the anode but also use the glas envelope as an very high voltage capacitor to smooth out the voltage since it need to be very stable.

[@readytheeskimo]

If you're not a professor/teacher, you should definitely consider it. Your explanations are very informative and thorough! Thanks!

[@gorog]

Awesome. This was insanely well-explained. Thank you.

[@bpark10001]

The heat from a CRT filament is a few watts at most (6.3V at ~500ma). There are 2 large sources of power consumption in a CRT. The first is power imparted into the electrons. You have many KV (more than 20KV for a color CRT in a television) times the electron beam current. For a TV with 30KV & 20ma electron beam, that's 60 watts. (For color TV CRT, most of this current is lost to the shadow mask.) The second power consumption is in the deflection circuits (for magnetic deflection TV), dissipated in the yoke deflection windings. This is so large that the high voltage in most TVs is derived from the "wasted" energy in the magnetic field at the end of each sweep. This is made worse by short-neck TVs with sharp electron bend angles. This requires a stronger magnetic field to affect the sharp bending. For electrostatic (oscilloscope) tubes, deflection power is much lower as energy in electric field is low & tubes are longer, requiring less sharp bend angle. The voltage differences amongst the elements in the electron gun assembly are typically no more than 1000V (for color TV CRT) & more like 300V for oscilloscope CRT. Typically the highest voltage is on the front face. On color TV, front voltage might be 30KV, where the highest voltage in the focus assembly might be 3KV. (You will see "fat pin" on the back socket carrying this voltage with extra insulation. this could NO WAY withstand the voltage fed into the side of the CRT through the high-voltage wire (to both the funnel , shadow mask, & the front phosphor screen). In Tektronix oscilloscope CRT, there is one more element to the design. For extremely fast waves (200MHz), the electron's dwell time between the plates is longer than the period of the wave being displayed. What is needed is for the deflection signal in the plates needs to follow the electrons as they move along. This is done by segmenting the plates into parts & connecting them to a transmission line. The propagation speed in that line is made to match that of the speeding electrons.

[@harveyhandbanana]

Your explanation of this was absolutely ace my friend. I understood every bit of what you were putting out. I look forward to watching more videos from you.

[@AppliedScience]

The cathode in CRTs is a relatively large metal can coated with metal oxides (perhaps barium oxide among others). The oxide layer has good electron emission characteristics, which allow more electrons to be emitted than plain metal would. The cathode in a SEM is sometimes a single piece of tungsten wire -- much smaller than the metal oxide cathode, which produces a much smaller beam spot size. Opening a CRT to atmosphere will ruin the oxide coating on the cathode.

[@larrybud]

it's frankly amazing this works accurately enough to create an image.

[@wafikiri_]

The first time I saw a cathode ray tube described, it was the first CRT ever built. It was described in a 19th. century physics book that my great-grandmother lent me when I was ten. It was called a Röntgen tube and it included a thin metal anode in the form of a Maltese cross shadowing the final, otherwise blank, image of the non-colimated electrons emmited by the hot cathode filament. Only those two electrodes were inside the tube. A drawing illustrated the device.

[@evil-wombat]

Thank you. This.... actually answers all the questions that brought me here

[@RonJohn63]

Your "explanation" videos are great.

[@dongshenghe3464]

I've looked at some of your video, the best ever!!!!

[@katelikesrectangles]

So nice to see somebody using a decent pair of gloves when taking something apart.

[@screwthenet]

Sadly it has taken me the longest time to find this specific video. Many thanks to you, this is a video I think many people who backwards engineer old CRT monitors or recycle and scrap parts should see. ^~^

[@w6wdh]

The conductive Aquadag coating, covering the interior of the front part of the CRT, turns that part into a Faraday cage, so the electric field in that part is zero; thus, no further deflection of the electron beam occurs. (The voltage is quite high, but the same everywhere there, so zero electric field.) I used to envision electrons getting sucked into the phosphor by the positive high voltage there, but no! The acceleration of the electrons occurs back in the electron gun assembly. As you saw in this video, two of the electrodes are at full high voltage (notice that a spring metal tab connects them to the Aquadag coating). The electrons are accelerated when they pass through the first electrode at the full high voltage.

[@AppliedScience]

Thanks, I enjoy your videos as well.

[@aerobyrdable]

Great video, I really learned a lot!

[@abandonedmuse]

You just helped me understand so much! Thank you!

[@CPUGalaxy]

Thank you for this perfect explanation!

[@kattasudhir]

I enjoyed all of your videos. fantastic and keep posting.

[@autopartsmonkey7992]

the glass bars in them are borosilicate...and when mixed up come in several unique colors...the dark brownish red ones are used to make a rare color called moss green that sells for 300$ a lb

[@Zenodilodon]

Hello, I have pulled out many CRT tubes from RGB rear projection TVs. I have a good knowledge on the CTR wiring after watching this video and cross referencing it with what I know about other similar technology. There is a small cap on the tungsten filament itself that seems that goes to a pin. I understand every other function electrically however I do not know what potential,polarity, or function this pin plays. Worry not about getting back to me any time soon. I have 6 tubes to try and I am not at all bashful about cramming voltage into things. Nice thing is they pretty much can't really be damaged through voltage break down as long as I don't burn out the tungsten. BTW the metal on the getter is usually cesium as it's a rapid oxidizing metal The getter not only burns off the atmospheric oxygen but depletes a coating, since this increases surface area when depleted on the glass it helps rapidly neutralize any leaking air as well as serves as visual indication of a bad vacuum. Any assistance will be greatly helpful, I will be trying to hack and show how to look at and understand both CRT and Vidicon tubes.

[@jayc2469]

Great vid thx! It is Aqua-dag - plus Barium is commonly used in the 'Getter' (former Philips/Mullard employee)

[@MicroscopicAllan]

Incredible explanation!!! Amazing to thin about all the calculations and thought that went into these when they where first invented.

[@hmvnetopa]

Amazing explanation!!

[@dougspair]

At the right hand side of the filament/leads area, there's a small glass tube where the air is sucked out by vacuum pump, hen the glass is heated and sealed off. This is pretty much the procedure for all types of vacuum tubes.

[@thomasgamsjager7045]

Excellent, even after 10 years.

[@miller4980]

Incredible! Thank you!!

[@moncef0147]

wow, that was pretty well explained man, thanks

[@RODALCO2007]

Very good video, Thanks for making the effort putting it on KZbin

[@glasstronic]

You got it right. Well done! Thanks for posting.

[@garyraab9887]

Cathode Ray Tube…electron gun! I have been watching Sean Carroll's The Big Picture 'videos"...reviewing: the double slit experiment, the electron wave particle duality, the measurement/observer implications, the electron as vibration in the electron field, entanglement, etc.. The mathematical physics word problems in high school entailed electrons as particles ...with an electrical force, magnetic force and force due to gravity acting on the straight line path and momentum of an emitted electron. My interest in watching cathode ray tube videos comes from wondering whether the electrons leaving the cathode are emitted as waves or as particles? First, I watched a video explaining the ray tube of a black and white TV, with two coils of electromagnets deflecting the "electron" in the X and Y plane via magnetic fields. In this video, the electron deflection is by electric fields between a perpendicular pair of parallel charged plates. If a 'particle' is emitted from the cathode, the magnetic fields generated by the two coil, or in this case the set of parallel charged plates, directing a particle or stream of particles, horizontally or vertically, seems reasonably intuitive. However, if the electron leaves the cathode as a wave/wave function, do the x and y electric or magnetic fields 'condense' a wave to a particle...or do the x and y electric or magnetic field focus a wave, with a particle 'appearing', 'being observed', with the "observation"... the emission of visible light at the 'detector' - the florescent screen surface. At time 11:42 of this video the image on the screen appears to be very close to an interference pattern around a central bright zone. Hmm!

[@badshabz1]

Wow iv just researched it and it is similar to the photo-electric effect with supports the partical theory of light as light is a partical and a wave. Thanks again.

[@zafranullah8328]

Awesome! and Very well explained

[@singhpk99]

Great explanation! Thanks!

[@badshabz1]

Oh that makes more sence, great video. Thanks from a future physicist

[@robertgift]

CRT Very clever invention. Well done video! Wish we could have seen the getter oxidize and turn white.

[@SuperBrainAK]

very nice video. i learned alot about CRT's thank you.

[@sbreheny]

Because the flyback transformer in a TV (unlike the more general term flyback as applied to switchmode power supplies) was originally designed as a way to produce the necessary magnetic deflection currents in addition to the high voltage, all in one circuit. Electrostaticly-deflected CRT's do not need magnetic deflection currents.

[@ashutoshramarathnam1445]

Bro......God level..thanks a lot !

[@pcbheaven]

That is so brilliant! my congratulations! i will feature it in my site. thanks.

[@seriousCADninja]

Your videos are awesome!

[@priyanksisodia5889]

Its very helpful,,, thanku sir very much

[@rajibkudas123]

nice explanation...really good..

[@TripleMoonPanda]

Very informative video, thank you.

[@spagamoto]

Ah that makes sense. Thanks! Love the videos!

[@jimburnsjr.]

way awesome stuff, thanks much

[@MiladP]

Great video. Thanks

[@samykamkar]

Great explanation and investigation as always, thanks for sharing! I'm curious about the trace rotation equalizer/coil, I don't understand how that would rotate the beam since its magnetic field is parallel (center nearly collinear) to the electron beam so I would imagine it could only dampen or speed up the beam in its existing direction, or is there something inside that alters the direction based on the magnetic field?

[@ameturephysicist]

How've you been Samy? Working on anything cool?

[@jacobcleveland1594]

Hey Samy, I had the same exact question. The closest thing I found was w140.com/tekwiki/wiki/Trace_rotation which mentions that for "Electromagnetic trace rotation: Current is passed through a coil near CRT, creating a magnetic field that counterbalances the magnetic field in the environment" but this still doesn't explain the mechanism. Just a guess, but I think what's going on can be explained by the right hand rule for the Lorentz force and the fact that a horizontal line on the screen means the electron beam is actually moving side to side, not just straight down the barrel. Looking down the CRT from back to front, with the magnetic field from the coil moving in the same direction as the center of the beam, then when the beam is angled to the right, there is a little bit of a difference in angle between the electron beam and the B field, so according to the right hand rule, the force should point up. Moving further to the right the force is greater, so the deflection is greater. The effect is that the right hand side of the beam overall is deflected up. For the left hand side of the beam, the difference in angle between the beam and the field is negative, so the Lorentz force will point down, and the beam on this side is deflected down. In total, this means the horizontal line should be rotated counterclockwise in proportion to the magnitude of the B field induced by the coil. The same logic should apply for the magnetic field going the opposite direction (i.e. towards you instead of away) but the rotation would be clockwise instead. Hopefully this makes sense. TLDR: The electron beam for a horizontal line does not always point parallel with the magnetic field. Where the beam isn't parallel, the beam gets deflected up or down, causing a rotation.

[@reesewebster9149]

Yes you are correct that when the electron is traveling in the z direction it is parallel to the magnetic field, however when it is deflected it gains a velocity in the x or y direction and the electron will experience a force perpendicular to its x and y velocity and the magnetic field

[@hmpaiNitte]

Thanx 4 the dissection.

[@psyborg303]

that dwarf white gun mount is some of the best white boro ever made

[@garyr7027]

That's was some good information.

[@cortexedge]

excellent explaining video!

[@antonygr7564]

very helpful thanks

[@mhywld]

thanks for the good video. what is the highest vacuum pressure allowed for the electrostatic deflection to work?

[@Gex121]

no bye?? This video answered nearly all my questions regarding electron tubes. The hard part for me is to try to understand how fast all this is happening. And its hard to think of how accurate the gun must be in color tubes. if im right there is 1.44 mil different spots a electron can hit in a color crt with a resolution of 800x600. Mind Blown

[@laurdy]

@bkraz333 the cathode is coated with a mixture of barium, strontium and calcium oxide. when the tube is assembled the cathode is coated with barium, strontium and calcium carbonate, during evacuation the cathode is heated to decompose the carbonates into oxides and CO2. the CO2 is then also pumped out

[@hernancoronel]

Hi Ben, love this explanation and tear down. Thank you! I was looking all over KZbin for a similar thing done with a Trinitron tube with no success. How about doing a commemorative reedition of this video with a Trinitron gun? It would be really interesting to find differences between the two! Thank you and keep up the great content!

[@augurelite]

How fascinating!!!!!!!!

[@guilloutube]

Thanks this helped a lot

[@svenpetersen1965]

Very comprehensive explanation and fun to watch. It is really long ago, that I have messed around with crts. I never did anything with a scope, because it was the most expensive thing in my lab. The tvs, that I pulled out of the trash (end of the 1970s, when people dumped their spare b&w tvs) all had an inductive deflection system (coils in a can, that were placed at the behind the acceleration electrodes). For a scope, the inductivity might limit the bandwidth. How did you prevent implosion, when opening the crt? That is, what I have always been concerned about.

[@Wildcatbeer]

Great vid, thanks

[@michalhaubner2104]

The e-beam does not diverge due to space charge effects nearly as much as due to the divergence of the emitter and acceptance angle of the extractor optics. Otherwise beautifully explained! ❤

[@robertgift]

Excellent video, bkrz. Thank you. Wish that you could cut the e-gun cans right down to middle to see their design. Is there a hole for the electon beam through them?

[@hpekristiansen]

I have been using a CRT in a physics experiment, but I have never measured the spot size. The oxide coating is not ruined, but it needs reconditioning once in vacuum. You basically just turn up the filament current, and raise the suppression grid until you see a lot of beam current... and wait 10 minutes.

[@spagamoto]

Thanks for the explanation. Could someone perhaps clarify one thing for me? OK, so let's follow an electron as it's leaving the negatively charged heated cathode. It's being attracted by the positively charged anode, and is thus accelerated towards the screen. Now at some point, as the electron passes through the middle (ish) of the anode, does the electron start slowing down as it starts getting attracted back by the same positive charge of the anode?

[@4n2earth22]

"See ya next time"; the start of a trend.

[@GClephMusique]

Cmon now people, it's so easy to see. Electrons everywhere just wanna be free.

[@pryletoncyo]

A lot of the invention was by experiment. Only way to discover a functional technology is to apply theory to reality, and often the materials weren't pure enough, or wrong alltogether. That of course led to more findings about physics, and theorists had a field day, while the people trying to apply the theory in practice were a bit miffed. The CRT was a developement of the vacuum tube (electric valve), used as an amplifier, but before that as a radio tuner.

[@jozefnovak7750]

Thank you.

[@mattpelzek3809]

Looks like it would look fitting on the end of a raygun.

[@ovalwingnut]

Fantastically Stupendous! EXACTLY what I was looking for... 10 years late apparently. Is it to late to tell you that in the year 2021 those tubes are worth ~$10,000 and for Darwin's sake don't dissemble it? Well, it could happen :) I'm in ShOcK & AWE that the beam can be controlled to such perfection. Mind blowing. Thank you for the video.

[@cj691]

I had to check the video date when you said PLASMA displays! xD

[@engineprof]

thaks for your explanation

[@hpekristiansen]

Great videos. -keep posting. How small can the spot size be made? What is the limiting factor? Why can this e-gun not be used in your microscope project? -and what spot size do you have there?

[@quicknuclearscience]

How long do the heater(filament's) last in open air?

[@JorgeRodriguez-kw7pc]

Thanks for the video is great. it clarified many thing for me!!! Again Thank you very Much I'm checking a oscilloscope than I buy on ebay and say it was fully functional but it come with the image showing in half of the screen, I check the voltage, like you did and they are ok . I think some one hit the tube or something worn with one the defection plate... what you think ?

[@JackOfAllTradesThe]

heres a question to get the beam to work is the glass enclosure needed? or could a beam actually shoot still? and what is the potential output

[@realvanman1]

I really enjoy you and your videos, and I gave a thumbs up, as I always do, but I do take exception to destroying that old tube. Vintage equipment and parts are irreplaceable. A nice diagram could have served equally well.

[@conoba]

@bkraz333 Interesting. Did they have to assemle it in an inert athmosphere? Or did they use a trick to boil off the contaminated cathode surface?

[@FrankLopezx]

well i was actually interested in how the magnet or coils energizes the rays as it shoots out the gun and the rgb gets controlled in a actual image, and even better how the tv rx picks up the tx transmission and gets reorganized by the crt? that whole interaction is worth a video "specially w/ you been the host lol"

[@xxportalxx.]

But there are no magnets or coils energizing the ray lol, it's thermionic emissions being accelerated across a difference in potential, like marbles rolling down a hill

[@mtdeezy]

If you take the electron gun out of a CRT can you use the electron gun for other experiments, or is it broken?

[@theonlyreallaz5302]

you're doing great marvels! I've been been lurking for a long time,now I cannot resist from asking : have you ever mede an "hairpin circuit" ? What's your take on the "cold electricity" ???

[@nxxxxzn]

Nice!

[@hpekristiansen]

If you look down into a CRT, you can see that the hole in the suppression grid is very small, and it is the field that controls the emission(as you yourself explains). You also have the build in focus. Are you sure that is matters wether the cathode is a wire or it is indirectly heated?

[@badshabz1]

What is ionised to release electrons is it the tugsten? I would think after a while the ray tube would have to replace as the metal would no longer release electrons as the energy required would be too high.

[@260830107]

@bkraz333 also, did you forget to mention the grid electrode or there isnt a control grid in a scope CRT at all?

[@stardeep6344]

very helpfull

[@engineprof]

i learn from you

[@Tehcarp]

I'm assuming that the 'dot' is circular, because the emitter is also circular? I've thought about the assembly of the CRT, but I can't help but think that the dot should be more squared than it is on ever oscilloscope I've ever used (a one handed number).

[@nihonam]

So pity that CRT are not produced anymore. Scopes with CRT made so sharp and smooth graphs, and aperture grills gave us that deep velvet black.

[@soulmasterdw]

they are still made just a specilized equipment

[@ImperatorIng]

OLED is Here now for the CRT lovers :) Perfekt black, better than crt, perfect motion sharpness, nice colors