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Old 10th December 2010, 01:24 PM   #21
chops is offline chops  United States
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Quote:
Originally Posted by DF96 View Post
I have always been puzzled by valve heatsinks. Unless silicon grease is used, they will make only patchy contact with the glass so there will be cool spots and the rest hot - a recipe for problems? Glass is a poor conductor of heat, so even the contact points won't cool it very much. Most of the heat gained by the heatsink will be radiant heat, which was already outside the valve anyway!

The solution to valve cooling is either ceramic valves or air flow. Air does contact the whole glass fairly uniformly so it can take the heat away. Maybe Wavebourn should be looking for a very quiet fan?
I agree and don't buy into the whole "tube heatsink" thing. I think it's just more hifi snake oil at best. Just put the tubes in and let them do their thing. Old tube radios have lasted many years with the original tubes in them. In fact, my father just rebuilt a 60+ year old Zenith with all the original tubes and they all measured almost perfect. The owner says the radio has been in the family the entire time and has been used almost daily for several hours a day up until a few years ago when the caps and selenium rectifier went in it.

That's proof enough for me to not need tube heatsinks.
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Old 10th December 2010, 03:04 PM   #22
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Don't agree with the idea. I tried this on an EL34 and after a hardish session the tube packed up with cracks in the glass where the sink was fixed. Slight expansion/ contraction in the zone where the sink doesn't quite make contact all the way round is asking for trouble.
I've always thought tubes should get hot enough +100C for the Getter to function properly.
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Old 10th December 2010, 03:24 PM   #23
DF96 is offline DF96  England
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Some getters require heat, others don't.

I suspect the main effect of a "tube cooler" is to heat up the glass by preventing convection and reflecting more heat back in. Fortunately much of the reflected heat will be stopped by the glass and not contribute directly to a hotter anode.

Question: how does heat get away from the anode?
Answer: In glass valves almost all by radiation, plus a small amount via conduction through the pins. There is no convection inside the valve, as there is no gas there.

Q. As there is no convection, and glass is transparent, how come it gets hot?
A. Glass is not fully transparent at infra-red, so some radiation comes through and some gets absorbed and heats up the glass. (I'm not sure of the proportions)

Q. How does the glass lose heat?
A. Partly radiation - both inward and outward. Partly convection. (ditto)

Q. How do you cool glass?
A. Blow cool air on it.

Q. What about the radiation?
A. Don't reflect it back into the valve. Either let it spread out into empty space, or absorb it in something black which will then get hot but which is far enough away that its own radiation mainly misses the valve.
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Old 10th December 2010, 03:51 PM   #24
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Go with the chainmaille. Even world's dumbest idea, you will look cool doing it!
Claim all sorts unscientifically unprovable benefits and act like everyone else is
too ignorant or poor to play in the same league. Thermodynamics be damned.
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Old 10th December 2010, 03:59 PM   #25
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3rd the peral tube coolers. The recent redesign has made them even better, Bill has documented the actual measured results.

Click the image to open in full size.

I believe the tube cooler papers have been recently revised (the above are old):

PEARL Lit Archive

dave
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Old 10th December 2010, 04:14 PM   #26
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Aren't the Pearls made of copper. Can they be bonded to ground to act as a EMF shield? If so I would think that they would perform better thermally than a typical can shield.
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Old 10th December 2010, 04:23 PM   #27
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Quote:
Originally Posted by SGregory View Post
Aren't the Pearls made of copper
Copper yes, now powder coated.

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Old 10th December 2010, 05:35 PM   #28
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In the Valve Age, there was no need for such trinkets like "tube coolers," because tubes work just fine without. Want more power dissipation? Choose a tube with a bigger glass envelope or a ceramic tube with the anode brought out.

I wonder what has changed that they'd be needed now?

Of course a tube clothed in chain mail or silly wrinkles makes a nice conversation topic when one is entertaining guests who are no longer impressed by the sight of an unadorned vacuum tube ;-)
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Old 10th December 2010, 06:14 PM   #29
ilimzn is offline ilimzn  Croatia
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Coolers were used in some equipment I saw, but they looked more like the pearl coolers. I could immagine these would work better at NOT reflecting IR back as long as air convection on the outside of the tube was sufficient (amazing how many DIy designs completely forget about this...). The surfaces of the cooler are not parallel to the internal structures so mostly they reflect IR to each other creating a 'trap' of sorts.
Lowering the envelope temperature does indeed extend tube life. In fact, lowering the pin-glass interface temperature does so even more, the reason being the glass and pins outgas less and the differing temperature dilation coefficients are less of a problem (these ultimately result in gaseous / bad vacum tubes because of vacum loss at the glass-pin seal).
In short, a tube cooler has to be properly designed, and even them it doesn't do it's job magically on its own - it's purpose is to absorb radiated heat in order for it to be dissipated mainly by convection. if there is no airflow, or there are other heat sources nearby, or convection is not laminar (instead has vortexes and pockets) they won't be able to do their job.
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Old 10th December 2010, 06:36 PM   #30
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Click the image to open in full size.

If you put the tube with a PEARL tube cooler in a chimney it can be even more effective.

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