Dull, black, heat resistant paints
have been used to help cool engines for ages.

It would be cool (literally) if one could
spray and heat-cure unshielded tubes
and improve their heat-shedding

Is there any indication that such paints,
or some vacuum-tube specific types,
would help keeping tubes cool
by improving heat radiation?

I'd love some factual info, if it exists, or educated guesses,
rather than uninformed blind guesses,
as I am awfully good at doing uninformed blind guesses already! :-)

spamhog wrote:
Dull, black, heat resistant paints
have been used to help cool engines for ages.

It would be cool (literally) if one could
spray and heat-cure unshielded tubes
and improve their heat-shedding

Is there any indication that such paints,
or some vacuum-tube specific types,
would help keeping tubes cool
by improving heat radiation?

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

-Chuck

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

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

Chuck Harris ) writes:
spamhog wrote:
Dull, black, heat resistant paints
have been used to help cool engines for ages.

It would be cool (literally) if one could
spray and heat-cure unshielded tubes
and improve their heat-shedding

Is there any indication that such paints,
or some vacuum-tube specific types,
would help keeping tubes cool
by improving heat radiation?

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

-Chuck
Of course, there were tube shields that seemed intended to act
as heat sinks. I can't remember if I merely thought that, or
if I knew that somehow. But they real contact with the tube
glass and certainly seemed as if they could draw heat from them,
the same way heatsinks dissipate heat from semiconductors.

Michael VE2BVW

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:
Dull, black, heat resistant paints
have been used to help cool engines for ages.

It would be cool (literally) if one could
spray and heat-cure unshielded tubes
and improve their heat-shedding

Is there any indication that such paints,
or some vacuum-tube specific types,
would help keeping tubes cool
by improving heat radiation?

I'd love some factual info, if it exists, or educated guesses,
rather than uninformed blind guesses,
as I am awfully good at doing uninformed blind guesses already! :-)

One might think that the metal shields would "catch" the radiated heat
after it has left the tube. I feel that the black paint would act as a
heat insulator, preventing efficient transfer of the filament heat to
the outside. Unless you can put a thermocouple in the tube, it will be
hard to know how hot it gets Inside. (Yes, it can be done, despite the
"how to build a triode" nonsense. Tubes were fabricated and evacuated
with mercury pumps by amateurs in the 19 'teens and 20's).

And will it make any difference? Most equipment was designed to operate
over a rather wide range of ambient temperature. Heat dispersion might
be important with power tubes (rectifiers, audio/rf amplifiers), but
most of that is due to the power inefficiencies of operating the
tube,(see the red or white-hot plates!), not from mere filament heat. In
that case fans or liquid cooling would be a better alternative. Try
painting a 3-500 tube black and fire it up!

--afcsman

On Thu, 17 Jan 2008, spamhog wrote:

Dull, black, heat resistant paints
have been used to help cool engines for ages.

It would be cool (literally) if one could
spray and heat-cure unshielded tubes
and improve their heat-shedding

Is there any indication that such paints,
or some vacuum-tube specific types,
would help keeping tubes cool
by improving heat radiation?

I'd love some factual info, if it exists, or educated guesses,
rather than uninformed blind guesses,
as I am awfully good at doing uninformed blind guesses already! :-)


I'm not sure that a layer of black paint (as in exploiting what physicists
call "black body radiation" [or rate of heat transfer is proportional to
wavelenght raised to a power greater than one, and I don't remember the
power]) of is going to help you very much. Yes, mirrors, white surface,
black surface reflect, respectively, high, medium, or low amounts of
impinging radiation but at some point down the time scale, it will all
come to equilibrium anyway.

Several additional thoughts:

1. The layer of paint probably won't act as much of an insulator (silicon
grease, an insulator at high thicknesses, is used in thin layers between
computer CPUs and heatsinks and nobody gets worries about this).

2. A question about heat dissipation would have to involve knowing that
most heat is dissipated (from the plate) as infra red (unless the tube
plate is warm enough to start glowing red). Black paint would have to be
examined in terms of its spectral absorbtion as a function of visible-IR
wavelengths and compared with how well glass (which, IIRC, passes IR but
not UV) passes a given quantity of heat at the same operating
temperature. The passband and transmission spectrum may also be dependent
on any doping (dyes with bandpass absorptions, etc) but I certainly
recall no writings about this in terms of tube cooling.

3. Some tube sheilds were shiny, some were blackened. Good question as to
whether the difference helped or hurt temperature, but some tube sheilds
were advertised as helping with heat transfer (had some kind of slots).
However, all of the metal enveloped tubes had a dull black surface and
there may have been a minor component of contribution to surface cooling
through black body radiation, or it was simply the cheapest surface to
make.

4. Personally, an opaque tube envelope means I can't tell by looking at
the tube if the filaments are lighting up when I turn on the power.

Its not clear to me that you need to worry much about running tubes at a
lower bulb temperature since glass (and even the metal covered glass
tubes) won't melt until you get a way much quite a bit hotter than they
usually run. If you are worried about heat causing a variety of
accellerations of temperature-based aging processes in other components
(transformers, capacitors, etc), then put a small fan somewhere to draw
out the heat or blow in cooler air. If you are thinking about pushing
tubes beyond spec limits, then I'd suggest just not doing that (or, to
get more power, or whatever, put more tubes in parallel or
use bigger tubes, but that did not seem to be part of yor goal).

afcsman wrote:
spamhog wrote:
Dull, black, heat resistant paints
have been used to help cool engines for ages.

It is not done to cool the engine, it is done to make the
engine look cool.

It would be cool (literally) if one could
spray and heat-cure unshielded tubes
and improve their heat-shedding

Is there any indication that such paints,
or some vacuum-tube specific types,
would help keeping tubes cool
by improving heat radiation?

I'd love some factual info, if it exists, or educated guesses,
rather than uninformed blind guesses,
as I am awfully good at doing uninformed blind guesses already! :-)

One might think that the metal shields would "catch" the radiated heat
after it has left the tube. I feel that the black paint would act as a
heat insulator, preventing efficient transfer of the filament heat to
the outside.

Empirical evidence that most everyone has witnessed, shows
that black objects absorb light from the sun, and get hot.

So, that is exactly what you should expect to happen with
painting a tube's envelope black. The paint will absorb
the radiant heat from the plate, and conduct it to the
glass envelope. The glass envelope will then get much
hotter than it would have if the radiant heat had been
allowed to escape through the glass and radiate out into
space.

The black EMC tube shields cool the tube envelope by conducting
the glass's heat to the metal shield. This is done not to
make an unshielded tube cooler, but rather to make a tube that
must be shielded less hot than it would be in a conventional
shield that lacks the heat conducting structure.

Unless you can put a thermocouple in the tube, it will be
hard to know how hot it gets Inside.

It is a hard vacuum, vacuum doesn't get hot or cold. You could
measure the temperature of some of the tube's elements, but why
would you care if they get hot? As long as they don't get hotter
then the yellow heat they were heated to when they were evacuated,
there is nothing to be concerned about.

(Yes, it can be done, despite the
"how to build a triode" nonsense. Tubes were fabricated and evacuated
with mercury pumps by amateurs in the 19 'teens and 20's).

True, but I would bet that you can't do it! Building a triode
requires a wide variety of knowledge and capabilities. The French
guy that did it in one of the videos built every piece of equipment
that he used in making the triodes, and successfully built a nice
little hard sealed glass triode too. It was impressive, whether or
not it impressed you.


And will it make any difference? Most equipment was designed to operate
over a rather wide range of ambient temperature. Heat dispersion might
be important with power tubes (rectifiers, audio/rf amplifiers), but
most of that is due to the power inefficiencies of operating the
tube,(see the red or white-hot plates!), not from mere filament heat. In
that case fans or liquid cooling would be a better alternative. Try
painting a 3-500 tube black and fire it up!

It would melt the pyrex glass envelope, particularly around the already
highly stressed filament pins.

-Chuck