A re-post from Phil Taylor of Effectrode.com
As an electronics engineer and someone who’s in the business of designing tube audio equipment (effects pedals) I’ve a burning interest in anything that might help improve the sound quality and reliability of vacuum tubes. Over the many years I’ve worked with these glowing glass devices I’ve been aware that there can be variability in microphony and electrical noise between tubes, even tubes from the same factory batch, and have often wondered if there might be some kind of a fix for this as, to me at least, it always seemed a shame to bin a completely functional vintage tube just because it was subjectively slightly noisier or a little more microphonic than another. It crossed my mind that cryogenic treatment (cryo-treatment) might perhaps reduce the inherent white and fluctuation noise that tubes generate. After all, there are several tube vendors that offer this service with claims that it “causes metallurgical molecular changes in the metals within the tube which enhance tone and increase overall life”. Does enhancing tone mean lowering noise and microphony? And can cryo-treatment really improve a tube’s reliability? Here’s my nickel’s worth on the matter.
What is Cryogenic Treatment?
Cryogenic treatment is used to improve the durability of moving steel parts.
Cryogenic treatment is a process of cooling steel alloy down to low very temperatures (−190 °C) to increase its surface hardness to improve its resistance to wear, the practical application being to extend the life of cutting tools, gear teeth, moving engine parts, that kind of thing. Cryogenic treatment alters the crystal structure of steel by completing the conversion of austenite to martensite making it harder. Now, I recall making a screwdriver in metalwork class at secondary school many years ago. The tip of the screwdriver was hardened by heating it up with a blowtorch and then cooling it rapidly (‘quenching’) by plunging it into a bucket of water. It’s my understanding that quenching the steel in this way and not allowing it to cool down slowly prevents austenite from forming and makes the steel much harder and more brittle. The process isn’t 100% perfect though as steel still contains some austenite crystals. Apparently cryogenic treatment completes the conversion to further harden it.
Effect on Vacuum Tubes?
So cryogenic treatment can work to improve the hardness of ferrous metals such as steel, but what about a vacuum tube—a tube is not a lump of steel—like a wristwatch, it’s a delicate and complex mechanism composed of many different parts, which in turn are made from different types of materials. The metal electrodes are mainly high purity nickel for the plates and heater cover (cathode), tungsten alloy for the heater wire, molybdenum (sometimes with gold plating as in Sylvania ‘Gold-Brand’ tubes) for the grid wire, copper support posts and the heater is coated with a mixture of strontium/barium oxides.
Two different crystal structures that occur in steel which have absolutely no measurable effect on tone. [picture by Tom Duerig]
All these tiny metal parts are supported by thin mica discs within a glass envelope. I can only speculate on what effect chilling a tube down to extremely low temperatures will have on the materials that make up its many, intricate internal parts. There are no published noise measurement figures or life tests comparing cryogenically treated and stock tubes—it seems a serious scientific research investigation is needed here.
I did manage to find a couple of research papers describing how cryogenic treatment hardens aluminium so maybe it’s possible that the process will also harden copper, nickel and the other metals utilised in the construction of tubes too? There are no moving parts within a tube, and hence no mechanical wear, but hardening the metal electrodes could in principle make them stiffer, and stiff electrodes are good thing in tube. Any minuscule displacement or bending of the grid, plate and cathode relative to one another results sensitivity to vibration pickup—stiff, and accurately machined electrodes limit this movement keeping microphony to a minimum. But it should be kept in mind that cryogenic treatment is ordinarily employed to complete the conversion of austenite to martensite in hardened steel as described earlier; the metal electrodes, and other parts inside a tube aren’t quenched to make them super hard to begin with, which means there is no conversion to complete. So, if cryo-treatment doesn’t affect the hardness or stiffness of the electrodes then what benefits does it impart on an electron tube?
Taking a tube down to extreme low temperatures runs the risk of ruining tube permanently and irreversibly unless precautions are taken to protect it from the stresses of the procedure. [photo courtesy of ‘TheTubeStore.com’]
Well, cryo-treatment might not benefit tubes at all, in fact, it could be argued that the severe cooling process could, if anything, degrade the performance of these thermionic devices. Subjecting a tube to this kind of wide variation in temperature will result in differential rates of contraction (and expansion) of the parts that make up the electrode assembly, undoubtedly inducing unnecessary thermal stress on it and the glass envelope in which it’s housed. Tube manufacturers never designed or intended tubes to be stored at cryogenic temperatures. It’s not recommended practice to treat electronic components like this and it’s worth noting that electronics component manufacturers publish datasheets that specify temperature ranges for storing and operating their devices at—none recommend storing their components at cryogenic temperatures.
Cooling vacuum tubes, or any other electronic component, down to extreme low temperatures is a risky business, a game of chance that risks ruining tube permanently and irreversibly unless precautions are taken to protect it from the stresses of the procedure. The temperature must be cycled (decreased and increased) slowly for the reasons outlined above and the humidity has to be maintained at near zero to prevent condensation forming and oxidising exposed metal parts. Additionally, the utmost care needs be taken when handling a tube whilst it is at cryogenic temperatures as the physical properties of the materials from which the tube is constructed alter. At at around −200 °C many materials become fantastically fragile and prone to fracture or shattering, meaning cryo-treatment increases the odds of loosening something within the electrode assembly or worse still, embrittlement and fracturing of precisely engineered and delicate internal parts. There’s a dramatic scene in the “Terminator 2″ movie where a single bullet fired by Arnold Schwarzenegger shatters the frozen T-1000 terminator into a thousand pieces, however take a look at this short video of a platinum cup being submerged in liquid nitrogen for a real experimental demonstration of how embrittlement drastically alters the properties of metals.
Effect on Tone?
There’s no written evidence, no research papers, no text books, no technical support data or any documentation produced by any tube manufacturer at any time that even mentions cryo-treatment let alone advocating the procedure as a technique for reducing noise and microphony in tubes. And there’s nothing of substance online that indicates how the process might possibly improve the ‘tone’ of tubes either. Does it change the way electrons are emitted from the cathode? Does it somehow change the way electromagnetic fields form inside the tube? Does it improve the bonding of the oxide coatings to the cathode or remove residual contaminants to make the tube electrically quieter? Does cryogenic treatment affect the tube in any measurable or audible way at all?
There are no tube text books that even mention cryo-treatment, let alone advocating the procedure as a technique for improving the audio qualities of tubes.
There are a handful of tube vendors pushing cryo-treatment, their rhetoric based on a smattering of science about how they cryogenically treat tubes, but where’s the hard science of what cryogenics actually does to improve the performance of tubes? Their websites are often littered with astounding claims stating that their cryo-treated tubes possess “tighter focus from top to bottom”, “more holographic 3-D sound-stage”, “more subtle inner resolution extracted from recordings”, “tighter bass”, “increased dynamic range”, “faster transient response” and even references to NASA’s research and great scientists such as Albert Einstein. All impressive stuff, but does cryogenic treatment have any more effect on the audio qualities of a tube than the positions of the stars and planets above? I’ll put my money on the scientific method, rather than astrology, every time. If this extreme freezing process really does have a measurable effect on tone then, as an engineer, I’d expect them to support their claims with independently assessed noise and microphony tests, preferably accredited by an external body such as the National Physical Laboratory.
At this point it would be easy to write-off cryo-treatment as Tono-Bungay, flimflam, a fake or a scam or, at the very least, a placebo. But let’s just go back a step: if cryo-treatment is actually damaging tubes as speculated earlier on, then might this reasonably explain it’s apparent effectiveness? Could it be that subjecting tubes to the stresses of extreme cold provides a test methodology reveal potential early failures—a kind if negative null test? That is, the cryogenic process doesn’t improve performance, it’s simply that people are listening to hand-selected tubes because all the weak tubes would have been weeded out. Could this be the reason why some people can hear a difference?
A good engineer would want to know the truth (it’s out there somewhere). More than that, they’d need to know. Like Albert Einstein they’d want to understand the physics. And with their sights firmly set on making a genuine contribution to the art of vacuum tube manufacture, they’d perform experiments, make measurements, collect and analyse data and then subject their findings to rigorous peer review to find out if “better tone through cryogenics” is the real deal and not merely phantasmagoria—this is the way real advances in science, and tone, come about.
Didn’t Mullard Know About It?
And it’s worth considering this: if there is any merit in the cryogenic treatment of tubes then surely manufacturing giants Mullard-Philips or Sylvania would have utilised the process. They were in the business of making tubes, not just for guitar and hi-fi amplifiers, but for mission critical military, aerospace and scientific instrumentation applications. They were highly motivated to improve their production processes. They had vast pool of scientific and engineering resources at their disposal. Mullard’s 43 acre site at Blackburn, Lancashire, Great Britain had it’s own liquid oxygen and liquid hydrogen manufacturing plant.
Oxygen and hydrogen production plant on the Blackburn site – Mullard had the motivation and resources to explore cryogenics.
The site employed almost 7000 people amongst which were all kinds of specialists including physicists, chemists and metallurgists, resources far beyond the small handful of eastern tube factories that serve the guitar industry today. If there had been anything in cryo-treatment then surely Mullard must have known about it. Perhaps they did; perhaps somewhere, buried in some university basement, library or an old radio ham’s attic, is a technical paper written by a Mullard engineer in the early 1960s titled ‘An Investigation into the Effect of Cryogenic Temperatures on Thermionic Emission’. I’ll leave it to the reader to decide how long the odds are of that paper ever seeing the light of day and if it would put the big freeze on the cryo-treatment industry for vacuum tubes.
How to Avoid Tube Marketing Hype 101!
The vacuum tube industry today certainly does seem to suffer from more than its fair share of marketing hype. Like the washing-up powder market, the tube market is awash (sorry!) with all sorts of flimflam, not just cryo-treatment, but tube dampers, tube coolers and even rebranding modern manufacture tubesunder the names of once great manufacturers—cheap (sometimes not so cheap) gimmicks that are no substitute for real engineering. All this marketeering noise and nonsense achieves is to make the task of purchasing a good quality tube more challenging than it really should be. So, my advice when buying tubes would simply be this: invest in tubes from a reputable vendor that checks and matches them on a tube tester and guarantees them or, better still, seek out vintage N.O.S. vacuum tubes made by the likes of Mullard, Sylvania or the other giants from the golden age of tube manufacturing—we’re fortunate that they are still supplies of N.O.S. tubes available and there are deals to be had.
On a final note, the best means of avoiding being duped by marketing hype is to educate yourself. I can highly recommend taking a look at Materials and Techniques for Electron Tubes (1960) by Walter H. Kohl the Senior Engineering Specialist of Special Tube Operations at Sylvania and Electron Tube Design by RCA (1962). You’ll find nothing about cryo-treatment in these texts only information relating to the construction methods and quality of materials, that is, the stuff that’s genuinely relevant in the design of a good quality tube, and, these texts also provide a fascinating, nostalgic glimpse into the world of the 1960s, a time when manufacturers went to unprecedented lengths to design and construct tubes that were as near perfect as possible. After an hour or so’s reading from either book you’ll be in the know, a bona fide tube guru knowing what’s important in tube design and, what’s not so important.
In Conclusion
There is variation in the noise and microphony of vacuum tubes because of engineering limitations or to put it another way, tube manufacturers’ ability to accurately and consistently fabricate these complex devices. Mullard (or perhaps it was Sylvania) in their heyday, with vast resources and a wealth of expertise at their disposal got as close as anyone to manufacturing the perfect vacuum tube, however even their tubes were subject to variance in component tolerances which allow electrode movement and sensitivity to microphonic pickup; DC leakage paths in the mica insulation spacers that allow small currents to flow where they shouldn’t and fluctuations in thermionic emission from the cathode oxide coatings, both of which result in self-noise. It would be magical if cryogenic treatment were some kind of ‘silver bullet’ that improves the insulation properties of mica spacers, reduces inter-electrode movement and improves the emission of the cathode coatings to reduce noise and microphony. But I cannot begin to imagine how this works—’magical’ really is the right word to use here because cryogenic treatment of tubes certainly isn’t science—there are no well-considered explanations describing how the cryogenic process works to improve the electrical characteristics of a tube or even the most sparse comparative test results to validate claims for improved performance. The bottom line is that cryogenic treatment is no remedy for inferior materials or defects in tube construction and it won’t transform a rebranded modern manufacture tube into a genuine N.O.S. Mullard a or Sylvania tube—it just doesn’t work that way.
If you’re interested in what the Mullard Blackburn factory was like in its glory days then do take a look at the following article ‘Speed, Efficiency & Perfection – Aims That Have Built a Mammoth Factory in 16 Years’ originally published in 1954 in the ‘Blackburn Times’ not long after the factory opened.
We, the audiofans want to listen music better and better so the audio vendors invent what is necessary to sell as much as possible.
Excellent article
I would like to think if it would help that someone would figure it out and say for sure because my Long plate Mullard 12AX7 sure are noisy sometimes. Lol. But they sound so good in my Marshall Jcm 900 SL-X
Thank you for this excellent article and for taking at least a basic scientific approach to the issue. The audio industry (sadly, IMHO) is rife with misinformation, unsupportable claims, conjecture and delusion. Your approach at least helps to clear the air and I applaud you for it.
A tube aficionado and satisfied customer,
Dan Lilley
Raleigh, NC
Great article. Some tubes had a dirty weldings inside – so noisy then!
Interesting…..but as many stuff in this audio-field, completely subjective. What always impress me is how malleable some people can be.
I would not attributed great importance to this text, because the author of the engineer.
He has no audiophile’s ear, and hear with engineering head !
When engineers wondering about the role of power cords, he will give you ” expert” to respond to whatever the cable you use. For them there is no difference between the stock cable and Shunyata Research KC cx .
This is just another opinion, which has no meaning for true audiophiles .
Engineers should know (but often do not know) that there is a lot of natural phenomena that science has not yet explained. It would be good to follow the observations of some audiophiles, this may be a good hypothesis for a new research.
Aleksandar – Whoooosssshhhhh !
What i do now for sure is that the “audiophile” industry will be forever grateful, and thankful,
that ‘Aleksandar’ and those “true audiophile’s” will always keep the cash register’s ringing !
Oh, and that an unbiased article published by a respected audio engineer that details vacuum tube construction, performance and history among other thing’s, is just an “opinion” that has no meaning among the very special and elite group that is the “true audiophile’s”.
And i’m not sure what all the natural phenomena out there is that he speaks of ( Aleksandar that is ) but my guess is he is part of the group that ignore’s any proven science, when that proof doesn’t fit within his argument / stance. ( and then the conspiracy theory’s start ! )
Aleksandar that is bullshit: anything and everything the human ear can physically hear can be measured in some way, shape or form. To say an engineer doesn’t know what he’s talking about when it comes to this sort of thing is pure horseshit. And if that doesn’t satisfy you, a recent double-blind test with half engineers and half “audiophiles” yielded the same results. Not a single one of them could even tell when tubes were swapped out, let alone which ones were cryogenically treated and which ones were not. You are full of it.
Just go on believing horseshit mate. I could put you in double-blind tests and you would make a fool of yourself. You’re in fantasy land.
Look up the Youtube channel Blueglow Electronics. It is run by a dyed in the wool tube audiophile. He did a video on this, and his conclusion was the same: cryo treatment doesn’t provide any audible improvement. You can belive anything you want. You beliefs do not constitute fact. The people here at the tube store here, have said that there is no difference. The guy from Blueglow Electronics says there isno difference. The gentlemen who wrote this article has explained why there won’t be a difference. That is good enough for me.
typo – ‘What i do know’ not now
Too Bad Alex cannot assimilate well explained background including fundamental design considerations. Emperors clothes always on sale
I go back to the days of vidicons and plumicons and very much appreciate the history disclosed here. He is correct at the efforts and resources brought to bear to build a better tube at no expense be spared. If they could squeeze out another watt, another electron, another dB of performance, they would be all over it. When you see that circuits are now built in sub mm acreage, it is amazing what they accomplished with point to point wiring and large racks and rooms of equipment
Mr. Taylor,
Your article on YOUR perspective on Cryo Treatment of tubes is well written but filled with suppositions that are not correct. Yes, there is a lot unknown about what Deep Cryogenic Treatment (DCT) really does, but there is more than the austenite to martensite transformation that you assume is the only result. Your statement that cryo “…is just a finishing process used to complete the conversion of austenite to martensite…” is flat out wrong. DCT reduces point defects in the crystal lattice structure. It reduces residual stresses. It helps refine the atom to atom distance in the crystal lattice structure. It refines the distribution of alloying elements. In steels, it creates tiny carbides evenly distributed within the crystal structures. It also modifies how the metal vibrates. DCT has a definite effect on welded structures. It stabilizes metals to prevent changes of shape. It increases the fatigue life in metals up to six times. As you can see, most of these changes occur in the crystal structure of the metal, not the microstructure.
Your defining of DCT leaves a lot out that is essential. The cooling of the component being treated must be slow. It must be held at the lowest temperature for a period of hours and then slowly brought back to ambient temperature. You also say that DCT is done to “increase the surface hardness.” Please be aware that DCT affects every atom of the component being treated
Your statement treating a tube will be harmful to the tube is also conjecture. We have treated thousands of tubes without damage due to the process. Our customers report increased life, not decreased life. There is evidence of improved microphony. Our experiments indicate that there is reduced vibration in treated parts, and the vibration that is left has resonant frequencies greatly reduced. We have found this in many metals. Yamaha and Powell Flute have both tested DCT in blind tests and use DCT because of their tests.
It appears that you have stated reasons why DCT would not improve vacuum tubes based on false perceptions and failure to actually test treated vs. untreated tubes. One reason manufacturers don’t like it is that a major cause of tube failure is thermal cyclic fatigue and DCT reduces that and creates a huge increase in tube life. Another is that they ask the opinion of engineers and metallurgists who only know about the conversion of austenite to martensite. This leads them to the wrong answers. Most of what DCT does is done at the crystal lattice structure level, not the microstructural level. If you want to see tests, I would be very happy to work with you or tube manufacturers on valid testing to prove the concepts. I’ve studied DCT for over 20 years. I wrote the definition of DCT used in Volume 4A of the ASM Handbook. I work with the Cryogenic Society of America to help dispel the myths written on DCT.
You believe that it is conjecture to state that cryogenic treatment could be harmful to a tube, even though it is well established that different substances react (i.e. expand differently in response to extreme temperature changes), but I fail to see how any of your claimed benefits are anything other than conjecture as well. “It creates tiny carbides evenly distributed”, “it increases fatigue life up to six times” “it helps refine the atom to atom distance”…you use pseudo scientific words, but can you point to one reliable scientific study that backs up these claims, or points to the audible differences attributable to these changes?
The big tell is your use of individual reports. Please tell me how a person can tell that any particular tube has “increased life”. I’ve had multiple tubes from the same manufacturer and vendor, and they all fail at different times. some within days, others last for years. The difference was not cryo treatment – in fact, without expert analysis it’s impossible to tell what led to the difference.
Your assertions are not made more valid by don’t of length of reply or your membership is an organization specifically dedicated to advocating for the benefits of cryogenics. The blog author may have holes in his argument and rely on conjecture, but he’s not an expert. What’s your excuse?
At least you announced your allegiance at the end.
We’ve treated thousands of tube without harming them. Therefore any theory that DCT is harmful to vacuum tubes is disproved. As for the formation of carbides being conjecture, read these papers:
Role of Eta-Carbide Precipitations in the Wear Resistance Improvements of Fe-12Cr-Mo-V-1.4C Tool Steel by Cryogenic Treatment
Meng, Fanju
ISIJ International
Volume 34, Number 2, February 1994, pp. 205-210
Influence of the holding time of the deep cryogenic treatment on the strain hardening behavior of HY-TUF steel
Ahmad Zare, H. Mansouri and S.R. Hosseini
International Journal of Mechanical and Materials Engineering
December 2015 1:24
Deep Cryogenic Treatment of H11 Hot-working Tool Steel
Pavel Suchmann, Dagmar Jandova, Jana Niznanska1
Materials and technology
49 (2015) 1, 37–42
There are more at https://cryogenictreatmentdatabase.org/. There are several hundred scientific papers there.
As for increases in fatigue life, that has been proven. Read Improving the Durability of the Wheel Hub Bearings by Utilizing the Sub-zero Treatment Technique
Qiucheng Wang, Lixing Tou, Hongyan Xing and Ruihui Wei
DEStech Transactions, Asia-Pacific Engineering and Technology Conference (APETC 2017)
May 25-26, 2017
Besides this study and others we have worked with multiple racing teams that have found their valve springs lasting six times as long after DCT. Valve springs fail in fatigue. Failure can cause total loss of the car via crash, so it is not take lightly.
Regarding longer life our customers have noted that their customers report longer life. No reports of shorter life have been recieved. So over a sample of thousands of tubes the only comment on life is that it is longer.
I need no excuse. I work with this process and have seen the results. They are not conjecture. I work with the Cryogenic Society of America because besides the cryogenics used in medicine and in outer space and to freeze food and to do research they looked into this tiny corner of their subject and found value.
Please show your “evidence” then. Make it available to the public for rigorous peer review without hiding behind the old “intellectual property” and “trade secrets” excuse for nondisclosure.
Working at, and thinking on the ‘Quantum Level’ requires a completely different mindset of knowledge whose origins begin in observations of how particals behave in the Atomic world.
Without a background in Physics or advanced Metalurgy, understanding how metals react to being exposed to extreme temperatures is almost impossible. For example, when metals are exposed to extreme temperatures,
and a process called ‘Recrystalization’ can occur. The occurrence of this process can change the appearance and formation of the entire ‘playing field’. Applications of extreme temperatures to metals, can alter the placement of, the size of, and the amount of Atoms in the crystal lattice.
Understanding how electrons behave after they have been exposed to a variation of extreme temperatures, is highly speculative. Especially if the speed or the direction of the spin is altered, no one can precisely predict how Atoms will react to each other and what new characteristics of the altered metals will be. To observe any conclusive results, would require an Electron Microscope or similar equipment. Even if a new metal evolved because of unique treatments,
there is no guaranty that a new behavior will be observed. It may have to be doped with additional substances to reveal its secrets. Even after the latest scientific treatments from multiple sources has been applied to varying metals, there is no guarantee that we will be able prove anything conclusively( even if the altered metal is performing 100 times better than it did prior to it being altered. In no way am I saying that Cryogenically treated metals are superior to untreated metals used for the same purpose. What I am trying to make a point of is that it is ridiculous to take sides- are cryogenically treated products superior to non-treated products- or is this Cryo- treatment worthless. My point is that there is no simple answer. I believe the truth is that there are always two right answers to every question. In my opinion, siding to be on the ‘right side’ and proclaiming that the other side is wrong is where Human Beings get into
severe trouble!
I have a 12axy preamp that I just converted to DC power, what an amazing improvement. That being said it still doesn’t make my badly recorded CD’s sound much better. Why so many will spend 10,000 on a speaker cable and not a better recording is beyond me. Buy some Jesse Cook, Chesapeake, Al Dimeola, Weather Report, Pink Floyd and enjoy the music. Find the best musicians and their best recordings, couple that to a decent audio system to get amazing sound. I use a Conrad Johnson sa 400 200 watts per channel into Thiel 3.6 with a basic 12ax7 tube preamp and an Onkyo CD player and better than generic cables; for under $3000 you cannot find a much better system. For Ten Thousand in speaker cables I can buy 500 audiophile recordings. Why buy a Lamborghini if you live in Paris with no highways. Get a Shelby Mustang and go to Montana where you will get to drive a Hundred different roads really fast. Get a decent system but get better music and lots of it…my two cents
Very sensible comment vonfiat.
All the positive benefits of submitting a tube to cryo…
My, my!
The magic bullet. “Spooky science” (A. Einstein).
I’m amazed at how much we chase the one percent of difference and pay exhorbitant amounts for just one component in a whole signal chain. Sure, a bad ingredient can ruin a recipe but it’s like the difference between baking a cake with gmo grown wheat flour and the branded organic wheat flour. Most of the time I can’t really tell the difference. It still makes a cake.
I would have much more respect for the original author had he simply ponied up a few bucks and actually TRIED a set of cryogenic tubes to see if there was any appreciable difference.
That said, from what I recall from my college metallurgy course, Mr. Diekman has provided more credible information than did the original author. Have you ever heard an annealed copper IC cable compared to one that was not? Try some audio note or Kondo wire in your system one day and you’ll see that annealing much like cryo relaxes and realignes the crystal structure of “worked” materials and will provide a more relaxed and natural sound.
annealed, yeah nah.
cryo, yeah nah.
Electrons don’t give a schiit what pathway they take — cryo or non-cryo. Cryogenesis is another big scam to keep fleecing naive audiophiles like Aleksandr. Apply science and all houses of cards fall down.