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Let’s talk about cryogenics and tubes

Awhile back I wrote and article titled “Cryogenics Treatment of Tubes: An Engineer’s Perspective“. Like politics and religion it’s, ironically, one of those topics that people can get pretty hot under the collar about and I have to admit to being skeptical, even cynical of the value of the process when applied to vacuum tubes to improve their audio performance. But I try to keep and open mind, hence this post; if you’ve worked in the tube manufacture business, perhaps you’re an ex-employee of Mullard, a materials scientist, physicist or worked on the assembly line then do feel free to chip and have your say. Any guitarists and recording engineers with an opinion are also welcome to contribute their views on cryo-treated tubes—this is the place to do it!

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2 COMMENTS

Frederick J Diekman June 4, 2018 at 04:30:15 Log in to Reply

I've read your article. I agree people need to be careful when making claims about what Deep Cryogenic Treatment (DCT) can do. But they also need to be careful about making claims about what it cannot do. You claim that DCT is used to increase surface hardness. This is incorrect as the process affects every atom of the treated part. Your article seems to be stuck on the austenite to martensite transformation as the only effect of cold temperatures. A simple perusal of basic metallurgy courses and books puts that assumption to rest. Temperature affects the atoms in the crystal structure by reducing vacancies, making the distribution of alloying materials more even, reducing stresses. The distance between atoms in the crystal structure becomes more uniform as excess energy is removed from the structure.DCT affects most metals and some plastics. It does increase abrasion resistance, but does not make a huge increase in hardness unless in the case of steels that the heat treat is not done very well. Besides making metal more wear resistant (as proven in many research papers) it increases the fatigue resistance of metals. For instance, automotive valve springs have a reliable six times increase in life under racing applications.So what does DCT do to a tube? Well, it relieves stresses in the welds, it gives a better path for electrical currents due to its more even distribution of alloying materials and its increased uniformity in atom to atom distance.As to requiring careful handling at cold temperatures, since the tubes are not handled at cold temperatures, this is not a problem. The only problems we have had with tubes not surviving DCT is where workers drop them or customers modify them before treatment. Yes, things get brittle at -300F. So we do not handle them at that temperature,, the same as heat treat companies do not handle delicate components at high temperatures. Your Terminator 2 reference is not relevant, because Hollywood is involved, the same as with Roadrunner and Wile E Coyote.As far as weeding out weak tubes, it just doesn't happen. Our customers don't report any outlier dropout. And Mullard didn't know about it because the first attempts to treat vacuum tubes were done probably in the 1970's when it became easier to precisely regulate time vs. temperature cycles. (You can't just dip things in liquid nitrogen, that would destroy vacuum tubes, crankshafts, etc.)The reason little scientific studies have been done on DCT and vacuum tubes is the market is not big enough to support the cost, and tube manufacturers do not want to add to the expense of making tubes and they don't want make them last longer which would decrease their sales.That's about all I have time for. To thoroughly explain what goes on in DCT could take days of lectures. If you want to see the results of scientific studies on DCT, go to www.cryogenictreatmentdatabase.org/. I would be happy to discuss this with you.

Phil June 4, 2018 at 11:57:00 Log in to Reply

Hi Frederick,Thank you for taking the time to respond to my article and your link to the "Cryogenic Treatment Database". I've had a good look on there and many of the papers are on the topic of hardening steel by cooling (to transform austenite to martensite) to improve its resistance to wear. Eg, "Influence of Cryogenic Treatment on Microstructure and Properties Improvement of Die Steel", so I think I'm making a fair point about surface hardening. However I can see there are other interesting articles on their website too, which brings me on to your statement, "The distance between atoms in the crystal structure becomes more uniform as excess energy is removed from the structure." I'd be interested to know more about this - are there any papers on the subject, and how it affects the performance of tubes, and other electronic components too for that matter? As far as welds go, they aren't a significant source of self-noise in a tube. So, even if cryo-treatment does measurably lower the ohmic resistance of the welds, my educated guess (as I've seen no experimental data giving figures for percentage decrease in resistance for welded joints in vacuum tubes, it could be 5%, 50%, perhaps you know?) is that it will have no practical effect on the noise in a vacuum tube. By the way, I can highly recommend "Noise in Electron Devices" by Louis D. Smullin and Hermann A. Hass - it covers just about everything there is to know about noise in tubes.Yes, the tube industry isn't what it used to be, however I don't think performing a few electrical noise measurements is beyond the ability of anyone selling cryo-treated tubes. It would be relatively easy to do, in fact, I'm motivated to undertake this experiment myself and use it for the basis of a second blog article.Anyway, thanks again for your input on this cryogenics discussion. Let me just finish by saying that cryogenics has it's uses for sure, but I still remain to be convinced that imrproving the noise performance of tubes is one of them.Yours sincerely, Phil

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