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How are electrons recycled in a Cathode Ray Tube (C.R.T.), after being absorbed by the phosphor material?

6 Answers
How are electrons reclaimed to complete a full 'circuit' in a C.R.T. without accumulation at the screen wide-end? The full route from start to restart...
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Some more "notes" about CRTs:

The red lead you describe which attaches to the rubber pad is the EHT (Extra High Tension) lead. This connects to the final anode inside the tube which accelerates electrons towards the screen. EHT supply voltages can be anything up to 30kV. When a CRT is switched off, the coating inside the tube can hold a charge for up to a week and although not dangerous, can startle you causing you to drop the CRT or hurt your hand if you withdraw it suddenly.

The bare wire making contact with the graphite coating is a ground . Charge build up on the tube can leak to this coating and also if the air is humid or there is condensation on the back of the tube, current also discharges from the EHT to the coating with an audible hiss.

The front of a CRT is made from leaded glass for strength. Scratches on a tube can cause it to fracture suddenly and result in an implosion. The neck of the tube is the most fragile part. I always wondered why an implosion would be hazardous because fragments should fly inwards. However it is the rebound of air after the implosion which throws everything outwards again.

A pre-stressed steel reinforcing band is sometimes wrapped around the front of the screen. This allows the glass to be made thinner. Removing this band can cause the tube to implode.

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No, no, I encourage people to ask back and forth since I may get one part better any you other portions, providing a final "full answer"!

I have the luxury of a computer business that I am in the process of probably shutting down, and still have a LOT of CRTs laying around that I'd love to find use for as they are worth less than $5 each in general! The large Capacitor(s)/Transformer and a few other items are worth more than this so I'm looking for ideas to mess around with, currently a electron and a proton accelerator, which is why I've asked another question about the pressure inside of a CRT and if it's possible to open one without implosions! (I don?t have the URL of the question at the moment)

but they do all seem to have graphite or carbon black coating - your right. And there are severl connectors/probes, including one that is a bare wire on the external of the front of the screen wrapping it's circumference tightly! Then that inner red wire one that I don't know much baout as of yet! It seems to perforate the outer glass shell (although not entirely) and has a rubber ground sealing the hole - it couldn't be holding any pressure though!

I have many vacuum tubes to CD's and audios and oscilloscopes as well ( on old Navy scope that has around 1000 tubes included inside it, it's quite a sight! But maybe I'll start there - trying to manupulate the electron beams/heaters and pressures.

The forums you supplied I will probably find useful when I get a chance to check into it closer, thnak you! If I don't hear anything else I'll try to come up with some answers to the questions you asked! I'm interested to know too!

Thanks, anyone else?

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But once an electron is absorbed by a phosphor, it is subsequently lost as the atom emits a photon (visible light portion of a pixel) and leaves the 'vacuum' of the CRT. So the photons produced by the electron 'accelerator' collisions is lost through he glass, and can't be recycled. So the energy required (to produce the electron beams anyway - not necessarily aim it) must be equal to the energy lost (plus frictional losses) is this correct?

I'm working on a proton accelerator (a very small design) but If I can re-purpose an electron gun it may be easier than starting from scratch. But of course I would need a source of protons (hydrogen gas injection I assume) any thoughts?


ADDITION: And if there is no 'circuit' so to speak, where do the electrons accumulate?

Maybe you answered it, but I failed to understand...

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According to a member on Physicsforums.com, the electrons charge up the glass and eventually the charge leaks away to ground (the back of a tube is sometimes coated with graphite which is then grounded). The final anode which is connected to the EHT supply is close to the front of the screen but unless it covers the entire internal surface of the screen, I don't see how it can "collect" electrons. Can electrons which have hit the phosphor coating travel along the surface or through the bulk of the glass and end up at the anode? Sorry, I am asking more questions than providing answers!

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They don't actually flow in a circuit in the as such. High positive voltages on the various anodes accelerate the beam. They flow through holes in the control grids and hit the screen without flowing back through the anode. However the phosphors are chemically reduced by the addition of electrons and this leads to loss of ability to glow and even a phosphor "burn" if the beam hits the same point for a prolonged period or a static image is continuously displayed e.g. information screens in airports.

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There is an electric connection from the screen to ground. The electrons get to flow through that wire and eventually back to the filament.

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