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.

[utah]

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.

[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]

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.

[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

[unlokia]

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

Thank you! God bless you :-)

[RadioChief]

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.

[newldchappell]

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

[readytheeskimo]

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

Thanks!

[skivvy]

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.

[thereisthespoon]

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

[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.

[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.

[bpark]

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.

[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.

[wwdh]

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.

[garyraab]

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!

[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.

[autopartsmonkey]

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

[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?