Your thoughts on vaccum tube coolers & glass expanding (heat) ?

[Silvas]

Hello guys,

I've seen a couple tube cooling devices out there, most notoriously the Pearl tube coolers. Which got me curious about the mechanical stresses involved.

What about tube glass expansion due to heat? Will physically getting the tube somewhat constrained by the cooling solution might cause long-term issues or possible cracking of the glass due to the expansion on every power cycle? Will this be negligible? What about clamping tubes, for instance, on a mic build, clamping a subminiature or pencil tube to a PCB by the means of a metal clip thingy like a fuseholder instead of the usual wire clamp i've seen? May i assume the cooling solution or metal clamp will also expand thus causing no mechanical issues to the tube? I guess this has been taken into account into a product like the Pearl coolers but still curious about the possible drawbacks. But i know nothing about this specific topic.

Thank you!

 

[trobbins]

Sometimes you do have to have some faith in products that are based on technical design. I mean you are using valves and they have glass that gets quite hot, and have a mechanical life well in excess of nominal life, and were used in aviation and high stress environments (where they often used covers for mechanical attachment that also had to be the cooling path).

I'd suggest you get one of the vintage coolers and do some self-assessment on how they manage valves of different diameter (either base dimensions or tolerances), and then get some books out of the library and start exploring.

 

[Tubetec]

Ive used one of these type tube shieilds over an EL84 , theres a corrugated liner inside that allows space for expansion due to heating but remains in close contact with the tube itself , air flow is better than the usual types .

 

[Gus]

Heat transfer
conduction) mostly by the pins
radiation) from the elements to the glass
convection) none because of the vacuum

Heat sinks on the socket pins might help however that will cause other issues

The pearl coolers look like the O ring allows expansion

I am GUESSING the Pearl coolers are used to reduce vacuum permeation thru the glass

https://www.pearl-hifi.com/03_Prod_Serv/Coolers/Coolers.html
some light reading

https://www.normandale.edu/departme...llection/articles/vacuum-envelope-penetration
https://www.pfeiffer-vacuum.com/en/...ms/desorption-diffusion-permeation-and-leaks/

 

[Tubetec]

I have also used aluminium tube of approximately the same diameter as the tube bulb , thats heat sunk to the metal casework of the mic The issue is that it only suits Mullard EF86's which have a slightly narrower bulb diamteter than the Russian/eastern made tubes . The case runs warm but not hot to the touch , that definately helps prevent any chance of condensation appearing on the capsule or other parts which could lead to leakages and noises . Typical solid state mics create very little heat and can be prone to condensation under certain environmental conditions , AKG 414's Ive seen misbehave on a few ocassions ,especially straight out of a cold mic cupboard . Usually the unit heats upto ambient and the moisture evaporates but of course dampness can attract dust and other particals that leave you with worse problems .
Allowing your tube mic to warm up and acclimatise before letting the talent near it is always a good plan .

 

[Silvas]

Thank you, guys! This is great insight. I'll keep reading! Maybe I should measure the actual expansion of any given tube when hot.