Homebrew PCBs

On Thursday 05 May 2005 09:07 pm, Brian Clancy wrote:
>  Grant.
> Light bulbs contain inert gas at atmospheric pressure.

I was of the impression that it was at somewhat lower than atmospheric 
pressure,  otherwise you wouldn't get that "pop" when they break.

> Vacuum tubes (thermionic valves) contain? a vacuum.

As close as they could get to it,  yeah.

> This is why the glass is so much thicker than a light bulb.

Not that much thicker,  overall.  I sure broke enough of them when I first 
started messing around with this stuff.around with it,  about 40 years or so 
ago.  Maybe more so if you're talking large transmitting tubes,  but those 
aren't exactly common.

> The most dangerous example of the devices is the large TV picture tube.

Those are rather dangerous,  yeah.

> If you have a look the faceplate glass is quite thick, especially on the
> super flat screens.

The reason for that is two things --  that the outer layer of it isn't glass, 
but instead is a rather thick plastic that won't shatter.  Early sets had a 
separate safety glass and the face of the tube was much thinner.  The other 
reason it's that thick is because of lead in the glass to absorb x-rays,  at 
least for color tubes,  which is what makes TV sets and monitors a bit 
"hazmat" rather than just being able to put 'em in the trash.  Monochrome 
monitors and old B&W tv sets don't have that issue.