See: http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no known
problems that could account for such nasty behavior. They were all high
mileage, so perhaps the filament at that end of the lamp opened resulting
in the discharge going to one post, near the glass, or something.

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

"Samuel M. Goldwasser" wrote in message
...
See: http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no
known
problems that could account for such nasty behavior. They were all high
mileage, so perhaps the filament at that end of the lamp opened resulting
in the discharge going to one post, near the glass, or something.

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above
is
ignored unless my full name AND either lasers or electronics is included
in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Sounds like a hot blob of tungsten or emission material was ejected from the
lamp's cathode. An arc could certainly do that. It's common in
incandescent filament lamps that arc upon failure; but I wouldn't have
thought that there's enough energy available in a low-wattage CFL to do it.
What were the wattages of the lamps?

But, there were some arcing problems with T5 and some T8 lamps a few years
ago when operated on instant-start ballasts. At end-of-life, the cathodes
failed and an arc started chewing away at the cathode mount wires. Things
got hot, lamps cracked and lamp holders were charred. This all resulted in
the development of ballasts that shut the lamp off if an arc was sensed so
as to avoid the mess of cleaning up broken lamps and the concern that
sputtering lamps, smoke and the smell of overheated plastic caused.

Terry McGowan

In article ,
(Samuel M. Goldwasser) writes:
See: http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no known
problems that could account for such nasty behavior. They were all high
mileage, so perhaps the filament at that end of the lamp opened resulting
in the discharge going to one post, near the glass, or something.

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

Caused by control gear which fails to detect when the tube has reached
end of life (emission material all sputtered off), and and provides enough
voltage headroom to continue driving the tube as a cold cathode tube,
which generates too much heat at the tube electrodes. Dead thermionic
tubes don't last long when driven as cold cathode tubes, because the
filaments and support wires are quickly burned away, until the tube cracks
and vents to the atmosphere. If the support wires are very close to the
glass tube wall, as is likely with thin tubes, it can melt the glass.
With linear tubes, it can cause the tube to break such that it drops out
of the fitting - I've had one case of this. This was in a set of T4 tubes
which come in various lengths from 6W to 24W, and all use the same control
gear. I had mostly 16W ones, and when the tube reaches end of life, the
control gear simply up's the tube voltage to maintain the current, and the
excess power is dumped into the (now) cold cathode electrodes, which start
glowing as bright red hot dots, clearly visible through the dark sputtered
coating which is now round the tube ends. The heat also did enough damage
to the plastic lampholder that it was no longer usable. I did think this
could be a fire risk too, particularly if there had been any flammable
material nearby. (I've since been phasing these lamps out of use, which
is now forced as the manufacturer has gone and no spare tubes available.)

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

"Samuel M. Goldwasser" wrote in message
...
See: http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no
known
problems that could account for such nasty behavior. They were all high
mileage, so perhaps the filament at that end of the lamp opened resulting
in the discharge going to one post, near the glass, or something.

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html


Hmmm. Another 'dangerous' aspect of these dreadful devices then. If they
don't send you blind, or provoke epileptic fits, they'll get you by venting
their mercury vapour !! :-)

Arfa

On Jul 15, 5:01*pm, "Arfa Daily" wrote:
"Samuel M. Goldwasser" wrote in ...



See:http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

I've seen this on 3 CFLs in 3 different lamps/fixtures. *There are no
known
problems that could account for such nasty behavior. *They were all high
mileage, so perhaps the filament at that end of the lamp opened resulting
in the discharge going to one post, near the glass, or something.

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

--
* *sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
* * * *| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Hmmm. Another 'dangerous' aspect of these dreadful devices then. If they
don't send you blind, or provoke epileptic fits, they'll get you by venting
their mercury vapour !! * *:-)

Arfa

Yep, soon they'll be considered as dangerous as incandescent lamps
that burn fingers, start fires, explode, send molten glass and
tungsten shooting about and electrocute those who try to change the
bulb. ;-)

Terry

"Terry" wrote in message
...
On Jul 15, 5:01 pm, "Arfa Daily" wrote:
"Samuel M. Goldwasser" wrote in
...



See:http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no
known
problems that could account for such nasty behavior. They were all high
mileage, so perhaps the filament at that end of the lamp opened
resulting
in the discharge going to one post, near the glass, or something.

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

--
sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Hmmm. Another 'dangerous' aspect of these dreadful devices then. If they
don't send you blind, or provoke epileptic fits, they'll get you by
venting
their mercury vapour !! :-)

Arfa

Yep, soon they'll be considered as dangerous as incandescent lamps
that burn fingers, start fires, explode, send molten glass and
tungsten shooting about and electrocute those who try to change the
bulb. ;-)

Terry

My my, Terry. You do live an interesting and dangerous life ... During my
many years of shuffling around on this little orb of ours, I don't think I
have ever had a domestic incandescent light bulb start a fire, explode,
reach a temperature where the glss could become molten, shoot molten
tungsten at me, or try to electrocute me (how does that one work then ??). I
would have to admit to having scorched (rather than burnt) my fingers a time
or two, but that was down to me employing stupid tactics for handling them
.... d:-)

Arfa

In article , "Arfa Daily" wrote:

"Terry" wrote in message
...
On Jul 15, 5:01 pm, "Arfa Daily" wrote:
"Samuel M. Goldwasser" wrote in
...



See:http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no
known
problems that could account for such nasty behavior. They were all high
mileage, so perhaps the filament at that end of the lamp opened
resulting
in the discharge going to one post, near the glass, or something.

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

--
sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Hmmm. Another 'dangerous' aspect of these dreadful devices then. If they
don't send you blind, or provoke epileptic fits, they'll get you by
venting
their mercury vapour !! :-)

Arfa

Yep, soon they'll be considered as dangerous as incandescent lamps
that burn fingers, start fires, explode, send molten glass and
tungsten shooting about and electrocute those who try to change the
bulb. ;-)

Terry

My my, Terry. You do live an interesting and dangerous life ... During my
many years of shuffling around on this little orb of ours, I don't think I
have ever had a domestic incandescent light bulb start a fire, explode,
reach a temperature where the glss could become molten, shoot molten
tungsten at me, or try to electrocute me (how does that one work then ??). I
would have to admit to having scorched (rather than burnt) my fingers a time
or two, but that was down to me employing stupid tactics for handling them
.... d:-)

Arfa

No fires here yet.

I just had one infantile failure out of a batch of 6 I bought.
9 watts at 40 watts effective halogen brightness. I don't think being outside
was a problem even thought its not for outside. These are flood
or spots. What I have found, I can get moe light out of a 1.5
watt LED spot vs a 9-12 watt CFL. The reason being, CFL's are
poor choice for spots due to the poor beam width.

A lot of CFL's say, no dimmers or relays. The same for LED's most
of the time. I can't really figure the relay bit.

greg

Hi!

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

Comments welcome.

I've seen the effect on some very narrow GE tubes in use with conventional
overhead fixtures. When the tubes die, they oftentimes crack a ring in the
glass or blow a slightly larger hole in it at either edge. This makes
changing them "fun".

I'm not sure if it is specific to the tubes or not. The GE tubes have not
proven long lived. I started dating them after some tubes from a different
maker with the wrong color temperature were purchased and installed during
late 2005. All of the misordered tubes are still going strong, nine hours a
day in most locations. The oldest GE tubes date from 2007, and there are
very few left. All fixtures are identical.

William

GregS wrote:
In article , "Arfa Daily" wrote:
"Terry" wrote in message
...
On Jul 15, 5:01 pm, "Arfa Daily" wrote:
"Samuel M. Goldwasser" wrote in
...



See:http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg
This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.
I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no
known
problems that could account for such nasty behavior. They were all high
mileage, so perhaps the filament at that end of the lamp opened
resulting
in the discharge going to one post, near the glass, or something.
The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.
Comments welcome.
--
sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html
Hmmm. Another 'dangerous' aspect of these dreadful devices then. If they
don't send you blind, or provoke epileptic fits, they'll get you by
venting
their mercury vapour !! :-)

Arfa
Yep, soon they'll be considered as dangerous as incandescent lamps
that burn fingers, start fires, explode, send molten glass and
tungsten shooting about and electrocute those who try to change the
bulb. ;-)

Terry

My my, Terry. You do live an interesting and dangerous life ... During my
many years of shuffling around on this little orb of ours, I don't think I
have ever had a domestic incandescent light bulb start a fire, explode,
reach a temperature where the glss could become molten, shoot molten
tungsten at me, or try to electrocute me (how does that one work then ??). I
would have to admit to having scorched (rather than burnt) my fingers a time
or two, but that was down to me employing stupid tactics for handling them
.... d:-)

Arfa

No fires here yet.

I just had one infantile failure out of a batch of 6 I bought.
9 watts at 40 watts effective halogen brightness. I don't think being outside
was a problem even thought its not for outside. These are flood
or spots. What I have found, I can get moe light out of a 1.5
watt LED spot vs a 9-12 watt CFL. The reason being, CFL's are
poor choice for spots due to the poor beam width.

A lot of CFL's say, no dimmers or relays. The same for LED's most
of the time. I can't really figure the relay bit.

Likely "solid state" relays. Some X-10 devices, for example, are solid
state and may not work. A mechanical relay would work fine.

--
bud--

On 15/7/09 03:00, in article , "Samuel M.
Goldwasser" wrote:

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

That would explain it. Seriously, I find GE CFLs to be about the least
reliable of any available, and their SOX and SON lamps aren't much better.
Their mercury lamps seemed to be ok, but they are rapidly becoming extinct
these days. I haven't had much experience with their metal halides.

"Arfa Daily" wrote in message
...

"Terry" wrote in message
...
On Jul 15, 5:01 pm, "Arfa Daily" wrote:
"Samuel M. Goldwasser" wrote in
...



See:http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no
known
problems that could account for such nasty behavior. They were all high
mileage, so perhaps the filament at that end of the lamp opened
resulting
in the discharge going to one post, near the glass, or something.

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

--
sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Hmmm. Another 'dangerous' aspect of these dreadful devices then. If they
don't send you blind, or provoke epileptic fits, they'll get you by
venting
their mercury vapour !! :-)

Arfa

Yep, soon they'll be considered as dangerous as incandescent lamps
that burn fingers, start fires, explode, send molten glass and
tungsten shooting about and electrocute those who try to change the
bulb. ;-)

Terry

My my, Terry. You do live an interesting and dangerous life ... During my
many years of shuffling around on this little orb of ours, I don't think I
have ever had a domestic incandescent light bulb start a fire, explode,
reach a temperature where the glss could become molten, shoot molten
tungsten at me, or try to electrocute me (how does that one work then ??).
I would have to admit to having scorched (rather than burnt) my fingers a
time or two, but that was down to me employing stupid tactics for handling
them ... d:-)

Arfa


All that stuff has happened usually because (full disclosure) I treated the
lamp rather badly. A drop or two of water on a hot 100 watt GLS lamp, for
example, is sure to cause damage and, probably, fireworks.

I was electrically shocked when I tried to put a 60-watt lamp into a
portable lamp socket with the socket turned on and didn't realize it was an
old portable which didn't have a polarized plug. It's easy to touch the
threaded part of the base when you reach under the shade with the lamp and
try to position it in the socket.

Terry McGowan

"TKM" wrote in message
...

"Arfa Daily" wrote in message
...

"Terry" wrote in message
...
On Jul 15, 5:01 pm, "Arfa Daily" wrote:
"Samuel M. Goldwasser" wrote in
...



See:http://repairfaq.cis.upenn.edu/Misc/cflhole1.jpg

This is a ~1 mm hole in the glass near one of the filaments.
Something got hot enough for the glass to melt, and after
that, as they say, the rest was history.

I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no
known
problems that could account for such nasty behavior. They were all
high
mileage, so perhaps the filament at that end of the lamp opened
resulting
in the discharge going to one post, near the glass, or something.

The CFLs were all from GE but I don't know if they are of the same
ballast/lamp design.

Comments welcome.

--
sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Hmmm. Another 'dangerous' aspect of these dreadful devices then. If they
don't send you blind, or provoke epileptic fits, they'll get you by
venting
their mercury vapour !! :-)

Arfa

Yep, soon they'll be considered as dangerous as incandescent lamps
that burn fingers, start fires, explode, send molten glass and
tungsten shooting about and electrocute those who try to change the
bulb. ;-)

Terry

My my, Terry. You do live an interesting and dangerous life ... During
my many years of shuffling around on this little orb of ours, I don't
think I have ever had a domestic incandescent light bulb start a fire,
explode, reach a temperature where the glss could become molten, shoot
molten tungsten at me, or try to electrocute me (how does that one work
then ??). I would have to admit to having scorched (rather than burnt) my
fingers a time or two, but that was down to me employing stupid tactics
for handling them ... d:-)

Arfa


All that stuff has happened usually because (full disclosure) I treated
the lamp rather badly. A drop or two of water on a hot 100 watt GLS lamp,
for example, is sure to cause damage and, probably, fireworks.

I was electrically shocked when I tried to put a 60-watt lamp into a
portable lamp socket with the socket turned on and didn't realize it was
an old portable which didn't have a polarized plug. It's easy to touch
the threaded part of the base when you reach under the shade with the lamp
and try to position it in the socket.

Terry McGowan


Ah ! That all makes more sense now. That last 'problem' can't occur in the
UK as the outer part of the bayonet type bulb holders we normally use here,
is not part of the electrical connection to the bulb, and is either sheilded
with a bakelite type material anyway, or grounded if not. That said, we are
starting to see more lamps with standard ES holders - allbeit shielded - and
a lot more with MES holders that would be quite hard to stick your finger
into to make contact with the centre pin. The wall plugs are not reversible
like some U.S. ones are, but that of course doesn't stop people putting
re-wirable ones on, backwards ... :-\

Arfa

On Thu, 16 Jul 2009 17:38:16 +0100, Arfa Daily wrote:

I don't think I have ever had a domestic incandescent light bulb [...]

This commentary reminded me of a quite-unpleasant experience in late
boyhood. Apparently, an incandescent bulb in the cellar had a film of
moisture on it (it had just been turned on). When I touched the glass, I
got a nasty shock; damp concrete floor, etc. The socket must have been
wired with its threaded shell to the hot side of the line.

Not the bulb's fault, of course.

Btw, hot glass is conductive, just about certain.

Regards,
--
Nicabod =+= Waltham, Mass.

"Nicholas Bodley" wrote in message
news
On Thu, 16 Jul 2009 17:38:16 +0100, Arfa Daily wrote:

I don't think I have ever had a domestic incandescent light bulb [...]

This commentary reminded me of a quite-unpleasant experience in late
boyhood. Apparently, an incandescent bulb in the cellar had a film of
moisture on it (it had just been turned on). When I touched the glass, I
got a nasty shock; damp concrete floor, etc. The socket must have been
wired with its threaded shell to the hot side of the line.

Not the bulb's fault, of course.

Btw, hot glass is conductive, just about certain.

Regards,
--
Nicabod =+= Waltham, Mass.

Well, if it is, and I rather suspect it's not, the amount of conductivity is
very small. I work a lot with power valves (tubes) which run hot enough to
take your fingerprints off in decimals of a second, and these often have as
much as 800 volts on the anode pins. Some years back, I used to work with
high power audio distribution amplifiers on a community radio network. The
(foot high internally assembled with nuts and bolts) tubes on these 7 foot
tall amplifier cabinets, often used to run so hot that the glass was
actually glowing dull red. I have seen dents in the glass where the vacuum
has started sucking on areas that have got *so* hot that they have softened.
The HT supply on these beasts was about 2.5Kv as I recall, derived from
mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would
pretty soon be into having leakage paths between the pins, and to the
grounded retainer metalwork, that holds the devices into their sockets,
wouldn't you ?

Arfa

On Tue, 21 Jul 2009 19:40:49 +0100, "Arfa Daily"
wrote:


"Nicholas Bodley" wrote in message
news
On Thu, 16 Jul 2009 17:38:16 +0100, Arfa Daily wrote:

I don't think I have ever had a domestic incandescent light bulb [...]

This commentary reminded me of a quite-unpleasant experience in late
boyhood. Apparently, an incandescent bulb in the cellar had a film of
moisture on it (it had just been turned on). When I touched the glass, I
got a nasty shock; damp concrete floor, etc. The socket must have been
wired with its threaded shell to the hot side of the line.

Not the bulb's fault, of course.

Btw, hot glass is conductive, just about certain.

Regards,
--
Nicabod =+= Waltham, Mass.

Well, if it is, and I rather suspect it's not, the amount of conductivity is
very small. I work a lot with power valves (tubes) which run hot enough to
take your fingerprints off in decimals of a second, and these often have as
much as 800 volts on the anode pins. Some years back, I used to work with
high power audio distribution amplifiers on a community radio network. The
(foot high internally assembled with nuts and bolts) tubes on these 7 foot
tall amplifier cabinets, often used to run so hot that the glass was
actually glowing dull red. I have seen dents in the glass where the vacuum
has started sucking on areas that have got *so* hot that they have softened.
The HT supply on these beasts was about 2.5Kv as I recall, derived from
mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would
pretty soon be into having leakage paths between the pins, and to the
grounded retainer metalwork, that holds the devices into their sockets,
wouldn't you ?

Arfa


Ordinary incandescent lamps are made from soda lime glass,
which has enough conductivity at 100C to maintain a low
frequency (DC or 60Hz) discharge in T12 fluorescent lamps
using electrodes on the outside of the bulb. The place
where the wires are sealed in an incandescent lamp (the
pinch seal) is made from lead glass, that has much lower
conductivity than soda lime glass. Vacuum tubes are usually
made from borosilicate glass (Pyrex(R)) that has even lower
conductivity than lead glass, and much lower than soda lime
glass.


--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

"Victor Roberts" wrote in message
...
On Tue, 21 Jul 2009 19:40:49 +0100, "Arfa Daily"
wrote:


"Nicholas Bodley" wrote in message
news
On Thu, 16 Jul 2009 17:38:16 +0100, Arfa Daily wrote:

I don't think I have ever had a domestic incandescent light bulb [...]

This commentary reminded me of a quite-unpleasant experience in late
boyhood. Apparently, an incandescent bulb in the cellar had a film of
moisture on it (it had just been turned on). When I touched the glass, I
got a nasty shock; damp concrete floor, etc. The socket must have been
wired with its threaded shell to the hot side of the line.

Not the bulb's fault, of course.

Btw, hot glass is conductive, just about certain.

Regards,
--
Nicabod =+= Waltham, Mass.

Well, if it is, and I rather suspect it's not, the amount of conductivity
is
very small. I work a lot with power valves (tubes) which run hot enough to
take your fingerprints off in decimals of a second, and these often have
as
much as 800 volts on the anode pins. Some years back, I used to work with
high power audio distribution amplifiers on a community radio network. The
(foot high internally assembled with nuts and bolts) tubes on these 7 foot
tall amplifier cabinets, often used to run so hot that the glass was
actually glowing dull red. I have seen dents in the glass where the vacuum
has started sucking on areas that have got *so* hot that they have
softened.
The HT supply on these beasts was about 2.5Kv as I recall, derived from
mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would
pretty soon be into having leakage paths between the pins, and to the
grounded retainer metalwork, that holds the devices into their sockets,
wouldn't you ?

Arfa


Ordinary incandescent lamps are made from soda lime glass,
which has enough conductivity at 100C to maintain a low
frequency (DC or 60Hz) discharge in T12 fluorescent lamps
using electrodes on the outside of the bulb. The place
where the wires are sealed in an incandescent lamp (the
pinch seal) is made from lead glass, that has much lower
conductivity than soda lime glass. Vacuum tubes are usually
made from borosilicate glass (Pyrex(R)) that has even lower
conductivity than lead glass, and much lower than soda lime
glass.


--
Vic Roberts
http://www.RobertsResearchInc.com


Thanks for that Vic. Always good to learn from someone 'in the know' on the
more specialist aspects of electronics.

Arfa

In , Arfa Daily wrote in part:

The (foot high internally assembled with nuts and bolts) tubes on these
7 foot tall amplifier cabinets, often used to run so hot that the glass was
actually glowing dull red. I have seen dents in the glass where the vacuum
has started sucking on areas that have got *so* hot that they have softened.
The HT supply on these beasts was about 2.5Kv as I recall, derived from
mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would
pretty soon be into having leakage paths between the pins, and to the
grounded retainer metalwork, that holds the devices into their sockets,
wouldn't you ?

The glass around the pins is not as hot as the glass on the sides and
the top.

Meanwhile, even soda lime glass is not that much of a conductor at
200-300 degrees C.

I have heard of HID lamps requiring any metal supports to be isolated,
to avoid problems with electrolysis of the glass bulb. I imagine this
problem involves amounts of current low enough to not be a shock hazard.

On the other hand, I have seen glass heated to the point of being soft
conduct impressive amounts of current (several milliamps, possibly more)
at a few kilovolts. I do not know what kind of glass was involved -
either soda lime or a cheaper flint glass, probably soda lime.

- Don Klipstein )

On Thu, 23 Jul 2009 22:14:05 +0000 (UTC),
(Don Klipstein) wrote:

In , Arfa Daily wrote in part:

The (foot high internally assembled with nuts and bolts) tubes on these
7 foot tall amplifier cabinets, often used to run so hot that the glass was
actually glowing dull red. I have seen dents in the glass where the vacuum
has started sucking on areas that have got *so* hot that they have softened.
The HT supply on these beasts was about 2.5Kv as I recall, derived from
mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would
pretty soon be into having leakage paths between the pins, and to the
grounded retainer metalwork, that holds the devices into their sockets,
wouldn't you ?

The glass around the pins is not as hot as the glass on the sides and
the top.

Meanwhile, even soda lime glass is not that much of a conductor at
200-300 degrees C.

I have heard of HID lamps requiring any metal supports to be isolated,
to avoid problems with electrolysis of the glass bulb. I imagine this
problem involves amounts of current low enough to not be a shock hazard.

On the other hand, I have seen glass heated to the point of being soft
conduct impressive amounts of current (several milliamps, possibly more)
at a few kilovolts. I do not know what kind of glass was involved -
either soda lime or a cheaper flint glass, probably soda lime.

- Don Klipstein )

There's an interesting demonstration that can be done with a
rod of soda lime glass. If it is connected to a source with
the appropriate voltage output and current capability, and
then heated, it will conduct enough current to sustain the
temperature required for conduction when the external
heating supply is removed. I'm sorry to say I don't know
how much voltage is required to do this on any particular
size rod of soda lime glass.


--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

On Tue, 21 Jul 2009 19:40:49 +0100, "Arfa Daily"
wrote:


"Nicholas Bodley" wrote in message
news
On Thu, 16 Jul 2009 17:38:16 +0100, Arfa Daily wrote:

I don't think I have ever had a domestic incandescent light bulb [...]

This commentary reminded me of a quite-unpleasant experience in late
boyhood. Apparently, an incandescent bulb in the cellar had a film of
moisture on it (it had just been turned on). When I touched the glass, I
got a nasty shock; damp concrete floor, etc. The socket must have been
wired with its threaded shell to the hot side of the line.

Not the bulb's fault, of course.

Btw, hot glass is conductive, just about certain.

Regards,
--
Nicabod =+= Waltham, Mass.

Well, if it is, and I rather suspect it's not, the amount of conductivity is
very small. I work a lot with power valves (tubes) which run hot enough to
take your fingerprints off in decimals of a second, and these often have as
much as 800 volts on the anode pins. Some years back, I used to work with
high power audio distribution amplifiers on a community radio network. The
(foot high internally assembled with nuts and bolts) tubes on these 7 foot
tall amplifier cabinets, often used to run so hot that the glass was
actually glowing dull red. I have seen dents in the glass where the vacuum
has started sucking on areas that have got *so* hot that they have softened.
The HT supply on these beasts was about 2.5Kv as I recall, derived from
mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would
pretty soon be into having leakage paths between the pins, and to the
grounded retainer metalwork, that holds the devices into their sockets,
wouldn't you ?

Arfa

Any links to these giants?



--
Boris

"Boris Mohar" wrote in message
...
On Tue, 21 Jul 2009 19:40:49 +0100, "Arfa Daily"
wrote:


"Nicholas Bodley" wrote in message
news
On Thu, 16 Jul 2009 17:38:16 +0100, Arfa Daily wrote:

I don't think I have ever had a domestic incandescent light bulb [...]

This commentary reminded me of a quite-unpleasant experience in late
boyhood. Apparently, an incandescent bulb in the cellar had a film of
moisture on it (it had just been turned on). When I touched the glass, I
got a nasty shock; damp concrete floor, etc. The socket must have been
wired with its threaded shell to the hot side of the line.

Not the bulb's fault, of course.

Btw, hot glass is conductive, just about certain.

Regards,
--
Nicabod =+= Waltham, Mass.

Well, if it is, and I rather suspect it's not, the amount of conductivity
is
very small. I work a lot with power valves (tubes) which run hot enough to
take your fingerprints off in decimals of a second, and these often have
as
much as 800 volts on the anode pins. Some years back, I used to work with
high power audio distribution amplifiers on a community radio network. The
(foot high internally assembled with nuts and bolts) tubes on these 7 foot
tall amplifier cabinets, often used to run so hot that the glass was
actually glowing dull red. I have seen dents in the glass where the vacuum
has started sucking on areas that have got *so* hot that they have
softened.
The HT supply on these beasts was about 2.5Kv as I recall, derived from
mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would
pretty soon be into having leakage paths between the pins, and to the
grounded retainer metalwork, that holds the devices into their sockets,
wouldn't you ?

Arfa

Any links to these giants?
--
Boris

Friend of mine still has a couple I believe. I'll get him to check the
numbers on them (it's been a long while ago, and I can't remember any more).
I'll also see if I can get a coupla piccies of them. The amps in question
fed a radio relay network around large areas of the town. They were located
in the cellar of a house in the centre of town. Above them on the ground
floor, was our workshop, which was always lovely and warm in the winter :-)

On the first floor, above that, was the control room. The radio receivers
were located there, and a large patchboard, where the distribution lines
were routed, using the big old three pin Bulgin plugs and sockets. There was
also a desk console, with an array of meters, which measured 'load'. They
were actually measuring audio current going out on the lines.

We used to have fun on a slow Saturday afternoon, when there was no no
bosses about, by waiting for an important set of sports results, and then
either pulling the plug on a whole area, or switching in the spare receiver,
which we had pre-tuned to an offshore pirate radio station. Then wait for
the phone to start ringing off the hook down in the office, where some poor
part time lady would be located to take any service calls ... :-))

Arfa

In article ,
Victor Roberts writes:

Ordinary incandescent lamps are made from soda lime glass,
which has enough conductivity at 100C to maintain a low
frequency (DC or 60Hz) discharge in T12 fluorescent lamps
using electrodes on the outside of the bulb. The place
where the wires are sealed in an incandescent lamp (the
pinch seal) is made from lead glass, that has much lower
conductivity than soda lime glass. Vacuum tubes are usually
made from borosilicate glass (Pyrex(R)) that has even lower
conductivity than lead glass, and much lower than soda lime
glass.

Thanks, interesting.

However note that Pyrex(R) no longer implies any particular
glass type, and in particular, it's no longer borosilicate
glass in the US.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 24 Jul 2009 08:43:43 GMT,
(Andrew Gabriel) wrote:

In article ,
Victor Roberts writes:

Ordinary incandescent lamps are made from soda lime glass,
which has enough conductivity at 100C to maintain a low
frequency (DC or 60Hz) discharge in T12 fluorescent lamps
using electrodes on the outside of the bulb. The place
where the wires are sealed in an incandescent lamp (the
pinch seal) is made from lead glass, that has much lower
conductivity than soda lime glass. Vacuum tubes are usually
made from borosilicate glass (Pyrex(R)) that has even lower
conductivity than lead glass, and much lower than soda lime
glass.

Thanks, interesting.

However note that Pyrex(R) no longer implies any particular
glass type, and in particular, it's no longer borosilicate
glass in the US.

Pyrex seems to still be a registered trademark of Corning,
at least in the US, though I do see that the use of the
Pyrex name has expanded well beyond borosilicate glass, for
example, to metal cookware.


--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

"Victor Roberts" wrote in message
...
On Thu, 23 Jul 2009 22:14:05 +0000 (UTC),
(Don Klipstein) wrote:

In , Arfa Daily wrote in part:

The (foot high internally assembled with nuts and bolts) tubes on these
7 foot tall amplifier cabinets, often used to run so hot that the glass
was
actually glowing dull red. I have seen dents in the glass where the
vacuum
has started sucking on areas that have got *so* hot that they have
softened.
The HT supply on these beasts was about 2.5Kv as I recall, derived from
mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would
pretty soon be into having leakage paths between the pins, and to the
grounded retainer metalwork, that holds the devices into their sockets,
wouldn't you ?

The glass around the pins is not as hot as the glass on the sides and
the top.

Meanwhile, even soda lime glass is not that much of a conductor at
200-300 degrees C.

I have heard of HID lamps requiring any metal supports to be isolated,
to avoid problems with electrolysis of the glass bulb. I imagine this
problem involves amounts of current low enough to not be a shock hazard.

On the other hand, I have seen glass heated to the point of being soft
conduct impressive amounts of current (several milliamps, possibly more)
at a few kilovolts. I do not know what kind of glass was involved -
either soda lime or a cheaper flint glass, probably soda lime.

- Don Klipstein )

There's an interesting demonstration that can be done with a
rod of soda lime glass. If it is connected to a source with
the appropriate voltage output and current capability, and
then heated, it will conduct enough current to sustain the
temperature required for conduction when the external
heating supply is removed. I'm sorry to say I don't know
how much voltage is required to do this on any particular
size rod of soda lime glass.


--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

Fascinating. I wonder if there are glass furnaces that switch from gas to
electrical glass-conductive heating once the glass is molten.

Terry McGowan

Terry McGowan

On Fri, 24 Jul 2009 12:14:06 -0400, "TKM"
wrote:


"Victor Roberts" wrote in message
.. .
On Thu, 23 Jul 2009 22:14:05 +0000 (UTC),
(Don Klipstein) wrote:

In , Arfa Daily wrote in part:

The (foot high internally assembled with nuts and bolts) tubes on these
7 foot tall amplifier cabinets, often used to run so hot that the glass
was
actually glowing dull red. I have seen dents in the glass where the
vacuum
has started sucking on areas that have got *so* hot that they have
softened.
The HT supply on these beasts was about 2.5Kv as I recall, derived from
mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would
pretty soon be into having leakage paths between the pins, and to the
grounded retainer metalwork, that holds the devices into their sockets,
wouldn't you ?

The glass around the pins is not as hot as the glass on the sides and
the top.

Meanwhile, even soda lime glass is not that much of a conductor at
200-300 degrees C.

I have heard of HID lamps requiring any metal supports to be isolated,
to avoid problems with electrolysis of the glass bulb. I imagine this
problem involves amounts of current low enough to not be a shock hazard.

On the other hand, I have seen glass heated to the point of being soft
conduct impressive amounts of current (several milliamps, possibly more)
at a few kilovolts. I do not know what kind of glass was involved -
either soda lime or a cheaper flint glass, probably soda lime.

- Don Klipstein )

There's an interesting demonstration that can be done with a
rod of soda lime glass. If it is connected to a source with
the appropriate voltage output and current capability, and
then heated, it will conduct enough current to sustain the
temperature required for conduction when the external
heating supply is removed. I'm sorry to say I don't know
how much voltage is required to do this on any particular
size rod of soda lime glass.


--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

Fascinating. I wonder if there are glass furnaces that switch from gas to
electrical glass-conductive heating once the glass is molten.

Terry McGowan

Terry McGowan


I had forgotten about that, but the answer is yes.
See US 2,280,101, issued April 21, 1942. I've put a copy on
my web site:

http://www.robertsresearchinc.com/Papers/US2280101.pdf


--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

In , Victor Roberts wrote:
On Thu, 23 Jul 2009 22:14:05 +0000 (UTC),
(Don Klipstein) wrote:

SNIP to edit for space

Meanwhile, even soda lime glass is not that much of a conductor at
200-300 degrees C.

I have heard of HID lamps requiring any metal supports to be isolated,
to avoid problems with electrolysis of the glass bulb. I imagine this
problem involves amounts of current low enough to not be a shock hazard.

On the other hand, I have seen glass heated to the point of being soft
conduct impressive amounts of current (several milliamps, possibly more)
at a few kilovolts. I do not know what kind of glass was involved -
either soda lime or a cheaper flint glass, probably soda lime.

- Don Klipstein )

There's an interesting demonstration that can be done with a
rod of soda lime glass. If it is connected to a source with
the appropriate voltage output and current capability, and
then heated, it will conduct enough current to sustain the
temperature required for conduction when the external
heating supply is removed. I'm sorry to say I don't know
how much voltage is required to do this on any particular
size rod of soda lime glass.

I do remember seeing somewhere on the Web how to melt a soda bottle (or
was it a beer bottle?) in a microwave oven. The glass bottle to be melted
required a hot spot pre-heated with a "blowtorch" / "propane torch" or the
like, to temperature that I visually estimate to be in the 800's degrees C.
It appears to me that soda lime glass that hot achieves conductivity and
resistivity suitable for being sufficiently receptive for heating by a
microwave oven.

=========================

Disclaimer: I sense that this is adventurous usage of a microwave oven,
attempt to do such only at your own risk of damaging your microwave oven or
burning down the real estate that such microwave oven is in/on and
injuring/killing life forms in/on such real estate including loved-ones,
friends and pets by starting a fire.

- Don Klipstein )

In , Victor Roberts wrote:
On 24 Jul 2009 08:43:43 GMT,
(Andrew Gabriel) wrote:

In article ,
Victor Roberts writes:

Ordinary incandescent lamps are made from soda lime glass,
which has enough conductivity at 100C to maintain a low
frequency (DC or 60Hz) discharge in T12 fluorescent lamps
using electrodes on the outside of the bulb. The place
where the wires are sealed in an incandescent lamp (the
pinch seal) is made from lead glass, that has much lower
conductivity than soda lime glass. Vacuum tubes are usually
made from borosilicate glass (Pyrex(R)) that has even lower
conductivity than lead glass, and much lower than soda lime
glass.

Thanks, interesting.

However note that Pyrex(R) no longer implies any particular
glass type, and in particular, it's no longer borosilicate
glass in the US.

Pyrex seems to still be a registered trademark of Corning,
at least in the US, though I do see that the use of the
Pyrex name has expanded well beyond borosilicate glass, for
example, to metal cookware.

This makes me wonder if the name "Pyrex" "expanded" to glass types other
than borosilicate, as opposed to merely being "expanded" to non-glass
items.

- Don Klipstein )

In article ,
(Don Klipstein) writes:
In , Victor Roberts wrote:
On 24 Jul 2009 08:43:43 GMT,
(Andrew Gabriel) wrote:

However note that Pyrex(R) no longer implies any particular
glass type, and in particular, it's no longer borosilicate
glass in the US.

Pyrex seems to still be a registered trademark of Corning,
at least in the US, though I do see that the use of the
Pyrex name has expanded well beyond borosilicate glass, for
example, to metal cookware.

This makes me wonder if the name "Pyrex" "expanded" to glass types other
than borosilicate, as opposed to merely being "expanded" to non-glass
items.

In the US, Pyrex is currently tempered sola lime glass:
http://www.pyrexware.com/thetruthaboutpyrex/manu.htm
A factory in Europe also licenses the name, and apparently
produces borosilicate glass.

Pyrex is now simply used as a respected brand name, still
owned by Corning, but licensed out to whoever wants to use the
name. It doesn't imply glass, or any particular type of glass.
Corning no longer make anything under the Pyrex name themselves.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Thu, 16 Jul 2009 17:38:16 +0100, "Arfa Daily"
put finger to keyboard and composed:

During my
many years of shuffling around on this little orb of ours, I don't think I
have ever had a domestic incandescent light bulb start a fire, explode,

I had a bad batch of incandescent light bulbs where the glass
separated from the base and fell, or was ejected, onto the floor.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Yep, soon they'll be considered as dangerous as incandescent lamps
that burn fingers, start fires, explode, send molten glass and
tungsten shooting about and electrocute those who try to change the bulb.

Please don't say that too loud, lest the electrician's union
place a seal and/or lock on every fixture
to assure only a licensed union electrician ever changes a lamp.
Don't laugh. With all the microcontrollers embedded into everything,
it's possible to add lockout codes so only authorized people may restart it,
just like you car's "service required" light and reset code.

It's bad enough my TV, monitor, radio and such all say
"No user servicable parts inside".
Pray, don't let that happen to my home too.

My my, Terry. You do live an interesting and dangerous life ... During my
many years of shuffling around on this little orb of ours, I don't think I
have ever had a domestic incandescent light bulb start a fire, explode ...

I had a night light bulb shatter, fresh from the package.
I'd say that counts as an explosion.
I swore off dollar store bulbs ever since.

As to fires, I refuse to use lamps over 100 watts at home,
thus avoiding the 300-500 watt halogen torchiere fires
that were terribly common for a while.
The closest I came to a lamp induced fire was a plastic figurine
melting and smoking from being too close to a reflector halogen lamp.

Please don't say that too loud, lest the electrician's union
place a seal and/or lock on every fixture
to assure only a licensed union electrician ever changes a lamp.
Don't laugh. With all the microcontrollers embedded into everything,
it's possible to add lockout codes so only authorized people may restart
it,
just like you car's "service required" light and reset code.

It's bad enough my TV, monitor, radio and such all say
"No user servicable parts inside".
Pray, don't let that happen to my home too.

Nobody else seems to have brought up that scenario with BPL. How about your
refrigerator needing automatic updates and sending usage tracking back to
the server, then crapping out because the most recent update no longer
supports your model.

On Tue, 21 Jul 2009 19:40:49 +0100, Arfa Daily wrote:

"Nicholas Bodley" wrote in message
news
On Thu, 16 Jul 2009 17:38:16 +0100, Arfa Daily wrote:

I don't think I have ever had a domestic incandescent light bulb
[...]

This commentary reminded me of a quite-unpleasant experience in late
boyhood. Apparently, an incandescent bulb in the cellar had a film of
moisture on it (it had just been turned on). When I touched the glass,
I got a nasty shock; damp concrete floor, etc. The socket must have
been wired with its threaded shell to the hot side of the line.

Not the bulb's fault, of course.

Btw, hot glass is conductive, just about certain.

Regards,
--
Nicabod =+= Waltham, Mass.

Well, if it is, and I rather suspect it's not, the amount of
conductivity is very small. I work a lot with power valves (tubes) which
run hot enough to take your fingerprints off in decimals of a second,
and these often have as much as 800 volts on the anode pins. Some years
back, I used to work with high power audio distribution amplifiers on a
community radio network. The (foot high internally assembled with nuts
and bolts) tubes on these 7 foot tall amplifier cabinets, often used to
run so hot that the glass was actually glowing dull red. I have seen
dents in the glass where the vacuum has started sucking on areas that
have got *so* hot that they have softened. The HT supply on these beasts
was about 2.5Kv as I recall, derived from mercury vapour rectifier
tubes.

Given these facts, if the glass had much conductivity when hot, you
would pretty soon be into having leakage paths between the pins, and to
the grounded retainer metalwork, that holds the devices into their
sockets, wouldn't you ?

Arfa

Sorry for the delayed reply. If the glass is hot enough to soften, it's
probably conductive to some extent. However, if surrounded by cooler
glass, its resistivity would be too high to matter.

Try this, but be aware that you're dealing with lethal voltages, high
enough to jump a short gap (1 cm or so). You, specifically, most likely
know how to protect yourself! If in doubt, others should not try this.

Take a [neon] sign or oil burner ignition transformer (the latter is
probably better) and arrange temporary electrodes (or use those in a
discarded oil burner) to create a steady arc. That arc is like a flame --
it will melt and ignite materials. place a piece of well-insulated glass
in the arc (safety glasses!), and let the arc heat the glass. When it
starts to glow, or possible a bit sooner, it will become conductive;
you'll see the arc divert so current passes through the glass.

As to your power tubes/valves, you might have been lucky.

Regards,

--
Nicabod =+= Waltham, Mass.

On Wed, 22 Jul 2009 09:47:11 -0400, Victor Roberts wrote:

On Tue, 21 Jul 2009 19:40:49 +0100, "Arfa Daily"
wrote:


"Nicholas Bodley" wrote in message
news
On Thu, 16 Jul 2009 17:38:16 +0100, Arfa Daily wrote:

I don't think I have ever had a domestic incandescent light bulb
[...]

This commentary reminded me of a quite-unpleasant experience in late
boyhood. Apparently, an incandescent bulb in the cellar had a film of
moisture on it (it had just been turned on). When I touched the glass,
I got a nasty shock; damp concrete floor, etc. The socket must have
been wired with its threaded shell to the hot side of the line.

Not the bulb's fault, of course.

Btw, hot glass is conductive, just about certain.

Regards,
--
Nicabod =+= Waltham, Mass.

Well, if it is, and I rather suspect it's not, the amount of
conductivity is very small. I work a lot with power valves (tubes) which
run hot enough to take your fingerprints off in decimals of a second,
and these often have as much as 800 volts on the anode pins. Some years
back, I used to work with high power audio distribution amplifiers on a
community radio network. The (foot high internally assembled with nuts
and bolts) tubes on these 7 foot tall amplifier cabinets, often used to
run so hot that the glass was actually glowing dull red. I have seen
dents in the glass where the vacuum has started sucking on areas that
have got *so* hot that they have softened. The HT supply on these beasts
was about 2.5Kv as I recall, derived from mercury vapour rectifier
tubes.

Given these facts, if the glass had much conductivity when hot, you
would pretty soon be into having leakage paths between the pins, and to
the grounded retainer metalwork, that holds the devices into their
sockets, wouldn't you ?

Arfa


Ordinary incandescent lamps are made from soda lime glass, which has
enough conductivity at 100C to maintain a low frequency (DC or 60Hz)
discharge in T12 fluorescent lamps using electrodes on the outside of
the bulb. The place where the wires are sealed in an incandescent lamp
(the pinch seal) is made from lead glass, that has much lower
conductivity than soda lime glass. Vacuum tubes are usually made from
borosilicate glass (Pyrex(R)) that has even lower conductivity than lead
glass, and much lower than soda lime glass.

Aha! In the experiment I just posted a message about, I was using a glass
rod, perhaps for stirring mixed drinks. It might well have been soda-lime
glass. While typing, I was wondering about the conductivity of various
kinds of glasses. Thank you, kindly, for the enlightenment.

I s.t.r. reading, a long time ago, that Corning Glass used the
resistivity of molten glass to keep it hot by passing a lot of current
through it. I don't know how it mas heated to begin with, though.

Best regards,

--
Nicabod =+= Waltham, Mass.

On Thu, 23 Jul 2009 22:14:05 +0000, Don Klipstein wrote:

On the other hand, I have seen glass heated to the point of being soft
conduct impressive amounts of current (several milliamps, possibly more)
at a few kilovolts. I do not know what kind of glass was involved -
either soda lime or a cheaper flint glass, probably soda lime.

That surely describes the case in the experiment I described in a post a
few minutes ago.

Best regards,

--
Nicabod =+= Waltham, Mass.