Comment by nucleardog
1 year ago
> The glass is obviously fragile.
Ever broke one?
Like 2/3 of the weight is that front glass. It's _thick_.
When I was younger and dumber (well, at least younger) I tried breaking one. Took a running swing at the screen with a wrecking bar. It bounced off and all I got for my trouble was a sore shoulder.
In the YouTube video they explain that CRTs have a layer of safety glass in front of the actual screen to protect viewers in the event that the screen implodes. You were actually trying to break through multiple pieces of glass! I've taken a crowbar to a broken CRT before for fun and can confirm that it takes a lot more effort than one might think.
It depends on the CRT. Some use steel bands wrapped around the edge of the faceplate and tightened to keep the glass in compression where it's strongest.
The fun way to do it is to pull the deflection yoke off and shear the neck of the tube. I was pretty far away the only time I experienced somebody do that, but it sounded like a rifle round.
I believe the thick front (leaded) glass is to try to block the produced x-rays.
People were starting to get scared of the cancer those xrays might produce, and I suspect CRT manufacturers predicted a huge court settlement for cancers caused by TV's with insufficient shielding.
So far, it seems that hasn't materialized - not, I suspect because those xrays didn't cause cancer, but because it is simply impossible to produce any kind of evidence of cause/effect.
Only the oldest CRTs used leaded glass for the front, because leaded glass gradually turns brown on exposure to X-rays. More modern CRTs used glass with barium and strontium for X-ray shielding in the front. They still used leaded glass for the back and sides, presumably as a cost saving. I don't see any reason why you couldn't use the barium-strontium glass for the whole thing. Alternatively, CRTs could be made with ceramic bodies like Tektronix used to do.
The energy of the X-rays produced is limited by the CRT's acceleration voltage. The electrons get almost all of their energy from the field produced by the acceleration voltage. Electrons can produce photons when they hit matter, and one electron produces at most one photon, so by conservation of energy the X-ray cannot have greater energy. Smaller CRTs typically use low acceleration voltages, which means the X-rays are low energy and thus easy to block.
AFAIK, the shielding was also just very effective. "Soft" x-rays (below 50-100 kV or so) are rather easy to shield and what screens had was pretty overkill.
> Ever broke one?
Yes, drop one from a few feet, and the immense weight will do the work for you.