Neutralizing a CRT

S

silvershadow7

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Feb 29, 2008
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First off, I read through the other thread on this topic, but couldn't find the information I was looking for. I apologize if this isn't the place for this or if this is a redundant thread, but my question wasn't answered by the other one.

Basically, what I am trying to do is safely neutralize the vacuum in an old CRT. I've thought about drilling a hole in the thickest part (so it doesn't implode) but would that be a good idea? From what I know about CRTs, isn't there a conductive coating on the inside that's connected to the anode? If this is the case, I would be drilling into it, which from what I understand would give me a pretty major shock.

So would it be best to poke a hole somehow in the weakest part, towards the back? I've heard of people doing this before but I'm not quite sure how to go about it, any help would be appreciated. Maybe I'm just in way over my head and it's not something that could feasibly be done. I realize there's the fact that there's literally tons of pressure on the outside so the risk of implosion is very high...so given this, would a small hole be ideal or a larger one?

By the way, I'm just curious to see what would happen when the electrons collide with the air molecules once you turn it on and there's no vacuum...guess I'm more curious than I am smart, but I have opened a CRT before, and I'm familiar with the dangers involved. In fact, if anyone can tell me definitively what would happen, please do; I've searched google but haven't been able to come up with anything at all.
 
Hmm.. good question. I've put a sizable 10lb hammer through one and not much happened. But it was very old and had been sitting for a long time, probably nothing left in the capacitors.
 
You will not get shocked if the monitor is unplugged and has fully discharged, but your experiment is a wast of time and dangerious. When you allow air into the vacume the electron gun will no longer work, because air and the particals in it will increase the resistance between the anoid and the cathoid dramatically. That is why there is a vacume in the first place. This experiment would become dangerious when you plug the modified device back in and and the voltage arcs to something you did not expect. You may get the shock of your life or start a fire and learn nothing in the process.

Here is a better idea. Either search the internet to learn more about how a CRT works, or go to your local library and read up on it. Or take some electronics courses at your local community college.

I have a degree in electrical engineering and all that i can tell you is that education was an amazing experience.

Best of luck

Dave
 
I would be more worried about a high voltage shock from the flyback more than anything else.
 
shot it with a .50 Cal ,250 Feet away ?

hehe it will work, also say good bye to ur crt.
 
WhDemon said:
shot it with a .50 Cal ,250 Feet away ?

hehe it will work, also say good bye to ur crt.
Click to expand...
Shooting electronics is generally prohibitted on public firing ranges. Unlike the hundreds of pounds of lead sent downrange on a busy day the ounce or so of mercury and cadmium represent unacceptable heavy metal contamination. *rolls eyes*
 
Thanks for the quick replies everyone. The reason I don't want to do the obvious solution of brute force is because I wanted to preserve the phosphor screen, so I could tell if any electrons actually made it to the screen. Well I looked into how CRTs work a little more and from what I can tell, the suction cup thing absorbs extra electrons, while the anode that attracts the electrons is right in front of (as in <1 centimeter) the cathode. Also it seems the cathode produces electrons by being heated, and the anode only serves to accelerate them towards itself. Thing is, I'm still a little confused as to how it would be more dangerous with air, considering how close the anode and cathode are to each other...my gut says that wouldn't be a lot of resistance, especially given this image.

I'll take daveswantek's word over my gut though, so I probably won't end up doing this. I think what I need to do is research general electronics some more, that will probably answer my questions anyway. Well thanks for the input!
 
Most CRTs also have a heavy strap encircling the tube that puts a few tons of compression pressure on it to help resist impacts to the face which would result in imploding due to the vacuum. All in all, screwing around with a CRT isn't a bright idea.
 
Even if the cathode would survive the air (it's almost heated like a light bulb to emit electrons..) the electron beam would fade to nothing after a few centimeters.
If you want to see the lightsaber in working condition (http://www.physics.ucla.edu/plasma-exp/beam/) you'll need some specialized equipment.
 
You know...electron beams do have some interesting applications as weapons. I've heard of experiments being done for particle beam weapons, but I think they're mainly for in space, where you don't have to worry about the atmosphere. For a lightsaber probably all you'd have to do is limit the length with a magnet...except to my knowledge it could only work in space. :(

Anyways, I ended up taking apart a tiny (~5") monochrome TV. There's a relatively thin, hollow piece made of glass that houses the electron gun, so I broke it so as to neutralize the vacuum. As you can probably guess, when I turned it on again, nothing happened...the audio worked, but I got no display, so I'm guessing either it was unable to produce electrons or they collided with the air molecules and lost their energy really quickly. I guess you could call it a success, as I was just seeing what would happen.
 
My .02 is that the filament heater that heats the cathode, would burn out in a fraction of a second when powered up in air due to the oxygen content. The vacum is there as much to keep the filament from burning up, as it is to keep the electrons from scattering. Old CRTs eventually get enough air infiltration that the filament and cathode gets scummed up with oxides and this impedes electron flow enough that the picture gets dim. There used to be an old trick where you could boost the filament voltage to get it to run that much hotter and get back some brightness. Of course, this only made the deterioration that much faster, but generally you could prolong the life of a CRT by 6-12 months by doing that.

O.O.
 
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