26 Oct
2011
26 Oct
'11
11:04 a.m.
On Tue, 25 Oct 2011 20:47:13 +0100 (BST), ard at p850ug1.demon.co.uk (Tony
Duell) wrote:
Heat is seriously ungood for CRT glass. It
reduces the dielectric
strength of the glass which can lead to arcing through the glass.
Prolonged arcing will hole the glass, thus venting the vacuum and
destroying the tube. Magnetic deflection yokes need to be designed not
to run too hot, the glass needs to stay well below 100 degrees C. Above
120 deg C the glass has not much dielectric strength left.
/Jonas
Given that
there are devices for easily breaking glass that are
> essentially sharp points, would a jab from a soldering iron be able to
> implode a CRT? I've done this by accident several times. Before anyone
Possibly. The soldering iron is hot which could set up thermal stresses i
nthe glass too. I do know that soldering to a socket contact while the
socket is plugged onto a CRT or valve can damage the glass-to-metal seal
around the pin, for esample, and is thus a bad idea. Thist doesn't
normally cause an implosion, but... 
27 Oct
27 Oct
12:59 p.m.
Heat is seriously ungood for CRT glass. It reduces the
dielectric
strength of the glass which can lead to arcing through the glass.
Does the diellectric strength increase back to its original value on
cooling again? If so, then this is not really a problem if you happen to
heat a CRT part (pin, bit of the envelope) with a soldering iron while
working on the device.
I'd be much more worried about thermal stresses causing the glass to crack.
Prolonged arcing will hole the glass, thus venting the
vacuum and
destroying the tube. Magnetic deflection yokes need to be designed not
to run too hot, the glass needs to stay well below 100 degrees C. Above
120 deg C the glass has not much dielectric strength left.
As an aside., if oyu conenct a glass rod (just about any type of glass
will work( in series with a suitable load (an electric fire element, for
excample) across the mains, not a lot happens. The glass is a good
insulator at room temperature. But if you then heat the glass rod with a
bunshn burner or gas blowlamp, it'll start to conduct, and will in fact
glow. Often it 'runs away' and gets hot enough to melt.
-tony
4:52 p.m.
As an aside [...hot glass conducts electricity...]
How peculiar! What on earth is acting as the charge carriers?
How do things like valve envelopes work? Many of them run quite hot;
are they made of glass carefully formulated to not conduct when hot, or
what?
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7:41 p.m.
As an aside [...hot glass conducts electricity...]
How peculiar! What on earth is acting as the charge carriers?
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alexeyt＠freeshell.org -
ard＠p850ug1.demon.co.uk -
jonas＠otter.se -
mouse＠Rodents-Montreal.ORG