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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Tubes! To Cryo Or Not To Cryo? That's The Question! posted by thetubeguy1954 on January 17, 2010 at 11:21:04:
First, I will tell you that I own cryogenic processing companies. I am the co-chair of the ASM Cryogenic Processing Sub-Committee, and work closely with the Cryogenic Society of America. So I have biased point of view.
Metals are crystalline and as such are subject to change due to temperature changes down to absolute zero. Statements that cryo cannot affect metals such as copper (and high CU alloys), wolfram (and high W alloys), aluminum (and hight Al alloys), titanium (and high Ti alloys), etc others." are not born out by the research, nor are they born out by common basic metallurgical theory. NASA has published a paper on the results of cryo treating aluminum. Linde (a liquid nitrogen supplier) has published on the use of cryo on copper. I treat titanium, magnesium and virtually all common metals except mercury and customers have reported success. I treat diamond and CBN grinding wheels that show up to ten times the life.
The crystal structure of metals depends on a lot of things. As you go down in temperature, point defects in the crystal structure start to migrate. Impurities, alloying elements, vacancies and other point defects start to move. The solubility of the alloying elements in the matrix decreases. This is why carbides are formed in steels. Another thing thought to be happening is involved with the distance between the atoms in the atomic structure. There is a specific distance between atoms that represents the lowest energy for the structure. By removing energy from the crystal lattice structure, it is thought (but not yet proven) that the crystal lattice structure becomes more “regular”. Also relevant is the release of residual stresses that has been proven time and again.
Regarding vacuum tubes apparently the relief of residual stress in the metal structures within the vacuum envelope results in reduced microphonics. That is, the cathode, grids, and plate vibrate less in response to an impinging sound field after they are cryogenically processed. Odd order harmonic distortion is significantly reduced. This is desirable because small variations in the separation of the elements in the vacuum result in corresponding changes in electric field strengths; the sound field modulates the plate current in a way that distorts the original signal. That is why frozen tubes sound better than the standard variety.
More recently we have been processing high value materials at temperatures significantly lower than those attained in the standard cryogenic processing. Using liquid Helium we are able to cool sample to near absolute zero; we routinely get down to –450 oF. A “golden eared” customer has provided vacuum tubes for standard processing and for the extremely low temperature treatment and has done comparative listening tests. His conclusion is that the standard treatment yields sound that is superior to untreated tubes and that the tubes that get close to absolute zero sound even better.
Admittedly these are subjective judgments; but, our investigator has gone one step further. He has measured the grid-plate transconductance of the three classes of tubes. He reports that standard cryotreated tubes show some small increase in transconductance. The tubes treated at –450 oF. show a transconductance increase of 15% above that of the standard treatment tubes. Here is hard data confirming a change in performance resulting from cryogenic treatment with lower ultimate temperature producing a bigger effect.
It is fact that cryo processing works on non-ferrous metals. It is fact and elementary metallurgy that metals change as you go down in temperature. Tests such as the ones above show that something has changed.
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Follow Ups
- RE: Tubes! To Cryo Or Not To Cryo? That's The Question! - warbird 01/31/1007:36:54 01/31/10 (0)
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