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Old 03-07-2018, 12:12 AM
cluelessgame cluelessgame is offline
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CRT Ideas

I've had a couple of ideas (questions) regarding CRTs floating around in my head for a while now and would like to bounce them off you guys here to see if they'd work and/or are practical:

Idea #1:
Would it be possible to manufacture new replacement picture tubes via 3D printing? As RCA has shown, the bell of a picture tube doesn't have to necessarily be entirely glass. Would it be possible to print the body in the dimensions of the desired tube with readily available plastics, coat the inside with a conductive layer, and then attach a glass face and neck? I'm sure that by now (or at least, in the near future) there would be materials available that are strong enough to hold a hard vacuum as well as solid glass. If its possible then theoretically we could make replacement picture tubes of any kind (so long as we can mimic the original specs) at relatively low cost and make nearly any set in existence feasible to restore!

Idea #2:
When rebuilding black and white CRTs, would it be possible to replace the original gun with a color (3-gun) assembly and then hook it up (possibly with a selector switch) to where one gun is used at a time? That way, when the gun you're currently on goes weak/fails, you can just switch to the next one, effectively tripling the life of the tube. Not quite sure if it would work on tubes that aren't aluminized as the gun needs to be at an angle with a trap magnet to bend the beam back, but I would think this would work for the newer stuff.

Your thoughts?
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Old 03-07-2018, 09:51 AM
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MIPS MIPS is offline
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1: No, the plastics currently used for 3D printing would not handle the immense vacuum for prolonged periods. Also there was good reason why RCA abandoned metal bodied CRT's.

2: No, switching from one gun to another would also cause the beam alignment to change slightly. If I'm doing this in my head correctly at 7AM, this would require tuned electronic compensation via the deflection yoke.
Also a triple gun arrangement is FAR bigger than the neck of most black and white tubes.
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Old 03-07-2018, 08:37 PM
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Electronic M Electronic M is online now
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Quote:
Originally Posted by MIPS View Post
1: No, the plastics currently used for 3D printing would not handle the immense vacuum for prolonged periods. Also there was good reason why RCA abandoned metal bodied CRT's.

2: No, switching from one gun to another would also cause the beam alignment to change slightly. If I'm doing this in my head correctly at 7AM, this would require tuned electronic compensation via the deflection yoke.
Also a triple gun arrangement is FAR bigger than the neck of most black and white tubes.
I agree with you on #1. 3D printing tends to also not make consistent structure the way casting would. Even if one were to make a CRT entirely out of clear plastic I think a cast piece would be stronger and less prone to leaking. Also, CRTs during evacuation need to be heated to hundreds of degrees to force all internal materials to outgas rapidly to form a good vacuum this and the process of using an induction heater to flash the getters and electron guns would both likely melt most plastics...

If one wanted to make new CRTs based on old ones I could see using 3D printing to make a mold to cast new glass with (like how wax positive molds of cast metal statues are made).

Even if you could 3D print a CRT, a color CRT would be a wild engineering challenge due to the logistics of a shadow mask and the phosphor silkscreening process.

On #2 I think it is possible*, but I would recommend against it to preserve the stock of color guns for color CRTs. Rectangular era delta and inline guns were about the same size as most monochrome CRT necks from WWII up to ~1960...The centering rings on most yokes may have enough pull (especially with inline guns) to properly compensate for the offset.
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