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
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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:
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