On Jan 17, 12:48*pm, Chuck Harris
No, but don't let that stop you from trying it anyway.

-Chuck

:-) What keeps me is the fact that I have no idea how I could measure
the core temperature in a tube!

Is heater current temperature-dependent enough as to provide a proxy?

Hints anyone??

On Jan 17, 12:49 pm, spamhog wrote:
On Jan 17, 12:48 pm, Chuck Harris

No, but don't let that stop you from trying it anyway.

-Chuck

:-) What keeps me is the fact that I have no idea how I could measure
the core temperature in a tube!

Is heater current temperature-dependent enough as to provide a proxy?

Hints anyone??

This test was done using a Raytek laser digital thermometer.
Temperatures
were taken from a 6BZ6 1st RF amp tube on a John R. Leary SP-600JX no
suffix
number, serial number 1262. Ambient room temperature was 75°F. I'm not
a
scientist nor should this be misconstrued as a scientific test. I
have
always been curious as to whether the IERC tube shields "actually"
prolong
tube life. As noted there were several different tube shields used in
this
"test." Also note there are several different types of inserts inside
these
tube shields.

The bare tube bulb temperature was "shot" immediately after removing
the tube shield.

The "Real McCoy" IERC Tube Shields have a finger grip type of insert
that
acts as a heat sink and the test results show that the temperature
difference between the shield and the tube itself is little. That
should
tell us that that type of shield is the "Standard." For your
information, I
don't use tube shields and my tubes seem to last a long time.


Take this information as it's meant to be, strictly informational.


1.. Shiny metal Eby tube shield no insert. 94°, bare tube 124°F.


2.. Shiny metal Eby tube shield with seven-sided black aluminum
insert.
96°F, bare tube 127°F.


3.. Dull metal Elco tube shield no insert.108°F, bare tube 135°F.


4.. Black heat resistant painted Eby tube shield no insert. 104°F,
126°F
bare tube.


5.. Black anodized Eby tube shield with "waveform, nine ridges"
aluminum
black heat shield insert. 107°F, bare tube 127°F.


6.. Collins black anodized tube shield with "waveform, nine ridges"
aluminum black heat shield. 100°F, bare tube 122°F.


7.. W.P.M. tube shield with five-sided aluminum insert. 106°F, bare
tube
118°F.


8.. IERC tube shield with "finger grip" type beryllium insert. "The
Standard." 102°F, bare tube 104°F. ( has to be the insert)


9.. Bare tube, no shield. 6BZ6 114°F.
YMMV

wrote in message
...
On Jan 17, 12:49 pm, spamhog wrote:
On Jan 17, 12:48 pm, Chuck Harris


No, but don't let that stop you from trying it anyway.

-Chuck

:-) What keeps me is the fact that I have no idea how I
could measure
the core temperature in a tube!

Is heater current temperature-dependent enough as to
provide a proxy?

Hints anyone??

This test was done using a Raytek laser digital thermometer.
Temperatures
were taken from a 6BZ6 1st RF amp tube on a John R. Leary
SP-600JX no
suffix
number, serial number 1262. Ambient room temperature was
75°F. I'm not
a
scientist nor should this be misconstrued as a scientific
test. I
have
always been curious as to whether the IERC tube shields
"actually"
prolong
tube life. As noted there were several different tube
shields used in
this
"test." Also note there are several different types of
inserts inside
these
tube shields.

The bare tube bulb temperature was "shot" immediately after
removing
the tube shield.

The "Real McCoy" IERC Tube Shields have a finger grip type
of insert
that
acts as a heat sink and the test results show that the
temperature
difference between the shield and the tube itself is little.
That
should
tell us that that type of shield is the "Standard." For your
information, I
don't use tube shields and my tubes seem to last a long
time.


Take this information as it's meant to be, strictly
informational.


1.. Shiny metal Eby tube shield no insert. 94°, bare tube
124°F.


2.. Shiny metal Eby tube shield with seven-sided black
aluminum
insert.
96°F, bare tube 127°F.


3.. Dull metal Elco tube shield no insert.108°F, bare tube
135°F.


4.. Black heat resistant painted Eby tube shield no
insert. 104°F,
126°F
bare tube.


5.. Black anodized Eby tube shield with "waveform, nine
ridges"
aluminum
black heat shield insert. 107°F, bare tube 127°F.


6.. Collins black anodized tube shield with "waveform,
nine ridges"
aluminum black heat shield. 100°F, bare tube 122°F.


7.. W.P.M. tube shield with five-sided aluminum insert.
106°F, bare
tube
118°F.


8.. IERC tube shield with "finger grip" type beryllium
insert. "The
Standard." 102°F, bare tube 104°F. ( has to be the insert)


9.. Bare tube, no shield. 6BZ6 114°F.
YMMV

This is extremely interesting data. I imagine that
envelope temperatures have been researched in the past but
can't remember ever seeing anything published.
I think it might be possible to measure the envelope
temperature using some sort of sensor, such as a small
thermocouple, fastened to the envelope. Direct comparisons
of envelope temperature could then be made with bare bulb
and various sorts of shields or paint. Paint might help
radiate heat more efficiently but it might also act as an
insulator but measuring that should be simple because a
plain thermometer could be used to make comparison
measurements.
Because tube heaters are pretty far removed from the
envelope and are at a much higher temperature and because
there are other sources of heat even in receiving tubes
(plate dissipation for instance) I doubt if the effect of a
heat sink on the envelope would affect heater current enough
to make a reliable measure of envelope temperature.


--
---
Richard Knoppow
Los Angeles, CA, USA

spamhog wrote:
On Jan 17, 12:48 pm, Chuck Harris
No, but don't let that stop you from trying it anyway.

-Chuck

:-) What keeps me is the fact that I have no idea how I could measure
the core temperature in a tube!


Is heater current temperature-dependent enough as to provide a proxy?

Yes, it is rather temperature dependent.

What I might do, is put two identical tubes with their filaments in series
into a bridge configuration with two identical resistors, and measure the
voltage between the junction of the two filaments, and at the junction of
the two resistors. Then paint the one tube, and leave the other unpainted.
If the paint causes any change in the tube's internal heat, it should cause
the bridge to move one way or the other. Tungsten's resistance rises as
its temperature rises, and lowers as its temperature lowers.


~ +12.6V(REG)
~ |
~ +---------+-----------+
~ | |
~ FIL-A R
~ | |
~ +--------DVM----------+
~ | |
~ FIL-B R
~ | |
~ +---------+-----------+
~ |
~ -+-
~ ///

The inside of the tube is a hard vacuum, so the only way heat will pass the
void is by conduction (through mica, and leads...), and direct radiation.
Direct radiation is where the lion's share of the heat goes. Since the filament
is surrounded by the plate, it should see as much radiant energy as the tube
radiates out through the glass.

-Chuck

spamhog wrote:
On Jan 17, 12:48=A0pm, Chuck Harris
No, but don't let that stop you from trying it anyway.

-Chuck

:-) What keeps me is the fact that I have no idea how I could measure
the core temperature in a tube!

With an infrared thermometer or optical pyrometer. Auto parts stores
should have a model in the $20 range.

Is heater current temperature-dependent enough as to provide a proxy?

No, because the plate temperature is very different than the cathode
temperature, and the plate temperature is what you worry about.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:
spamhog wrote:
On Jan 17, 12:48=A0pm, Chuck Harris
No, but don't let that stop you from trying it anyway.

-Chuck
:-) What keeps me is the fact that I have no idea how I could measure
the core temperature in a tube!

With an infrared thermometer or optical pyrometer. Auto parts stores
should have a model in the $20 range.

The hand held infrared thermometers will end up measuring the
temperature of the glass, not the elements inside.

An optical pyrometer would be the way to measure the filament's
temperature (quite crudely), but they are expensive.

Is heater current temperature-dependent enough as to provide a proxy?

No, because the plate temperature is very different than the cathode
temperature, and the plate temperature is what you worry about.

The heater temperature should be somewhat dependent on the plate temperature,
half of the plate's radiation goes into the center of the tube, which is
where the heater is. The heater temperature should vary slightly with
plate temperature. A sensitive bridge might be able to measure it, but
it would be down in the noise.

The plate of a tube doesn't wear out, so it's temperature isn't
by itself important. When the tube is evacuated, the plate is
induction heated to a nice red/yellow temperature. This is done
to remove any absorbed gases and other contaminants. As long as
the plate is never heated above this temperature, it won't release
more gas.

The big reason to worry about the plate getting too hot is the
heat it radiates will heat the glass envelope, and may cause
it to crack, or melt.

-Chuck