Cryogenically treated vacuum tubes...?

[R.G.]

If the treatment really doesn't do anything, and you can't measure any difference in the tubes, how do we know that they actually did the treatment? Maybe they just stuck the tubes in the refrigerator next to their lunch for a half hour.

I love it! We had a similar final test for manufactured computers - when the are all assembled, WEIGH them, and if that's right, they must be perfect!

[dai h.]

If the treatment really doesn't do anything, and you can't measure any difference in the tubes, how do we know that they actually did the treatment? Maybe they just stuck the tubes in the refrigerator next to their lunch for a half hour.

Yeah, I've wondered this before. How does the buyer even know they did the treatment at all, or if they did something so cursory to be pretty much meaningless. (Cynical mode again) the perfect scam? (Or maybe a bit more sophisticated,) do a non- or cursory treatment and at the same time weed out the bad tubes (or even carry out "normal" QC such as shown in youtube vid below for appearance, microphony, static, dynamic, noise tests) so there appears to be improvement (at least from the normal (usually non-quality-controlled modern) tubes (if NOS is sold, might make sense to check them as well since sometimes even they can be bad).

(No cryo treatment, but this popped into mind. This is old 1957 footage of Fujitsu TEN tube production. The narration from the beginning says the tubes were evacuated, aged, then dunked into hot water then cold(thermal shock test--around 0:30. The label next to the pot says "nettou" (boiling water), the pan/tray label says "cold water") :

???????? ??????????????2/3 ?1957?? - YouTube

[g1]

And that is a remarkably apt statement. Do you mind if I quote it other places? Very nice, indeed.

In the words of The Who, "anyway, anyhow, anywhere"
...always.

[bob p]

What I think is funny about this is that some people are acting as if this cryogenic business is a new idea that just came along, as if it is something new that had never been available before.

We all know that liquid nitrogen existed in the Golden Era. If cryogenic processing provided some tangible benefit for vacuum tubes, then why wasn't RCA doing it 70 years ago? Why is it that we had to wait until the 21st Century for the idea to come along? The obvious answer: during the Golden Era, nobody would have tolerated the BS, and a cryogenic charlatan would have been run out of town on a rail. But now that tubes are a specialty item that's marketed to audiophools, people will believe all sorts of stupid ideas and buy all sorts of worthless treatments in the quest for tone and high fidelity.

When you believers order your cryogenically treated tubes, don't forget to add something else to your shopping cart: the little Viton rubber cock rings that slip over your preamp tube envelopes to prevent microphonics. They're a great deal at only $10 each.

[flyingdutchman]

the little Viton rubber cock rings that slip over your preamp tube envelopes to prevent microphonics. They're a great deal at only $10 each.

Or get them at your local hardware store at $0.25 each

[Chuck H]

But now that tubes are a specialty item that's marketed to audiophools, people will believe all sorts of stupid ideas and buy all sorts of worthless treatments in the quest for tone and high fidelity.

We've all been trying to say the same thing in less than clever ways. The plain English speaks volumes. It's the brass tacks of the matter. In this culture it's impossible that such a demographic could exist without some underhanded sleaze targeting them. And the sheer lack of brains to ignore this reality means they get what they deserve. As mentioned, at least the cryo tube venders are culling bad tubes. It wouldn't be suitable to sell a proposed superior tube that wasn't at least in good working order. Which seems pitifully rare these days.

[Amp Kat]

The Dean Markley Blue Steel strings are cryogenically treated. I used to play them and don't recall anything significantly different about their performance against normal strings, but this was several years ago and it wasn't something I was testing for.

I can't think of anything that would differ that would make it easy for someone to tell if tubes were treated or not.

I just bought some by mistake and broke one on my second gig just like always so haven't noticed anything special yet.

Also know a guitar player that uses the Cryo tubes in his amps and he has told me several times how dissapointed he is that nobody out in the audience has noticed him using the cryo treated tubes. doh !

[Mick Bailey]

An acquantance of mine from the golden-era of tubes is suspicious of the Cryo treatment. He says there is a lower limit on tube temperature because the glass-to-metal seals are engineered to maintain integrity across a finite temperature range. Very low temperatures can result in gradual vacuum loss when the tube returns to operating temperature and will go soft quicker than a tube that hasn't been chilled. Anyone else come across this, or is it B.S.?

[Chuck H]

That's been speculated in this thread. The area of concern would be the pin or wire to envelope connections because the two materials will have different expansion/contraction characteristics at extreme temps. That is probably what your acquaintance is referring to because I can't think of any reason why cryogenic treatment should make glass more or less permeable. No significant changes to the gasses or lack thereof in the tube so it's a matter of an actual physical leak occurring. And I would think that if it doesn't occur when a tube is treated then it's probably not going to later because of the treatment.

JM2C

[bob p]

No solid data here, just armchair theory:

We know that the glass envelope and the metal / soldered pins have different coefficients of expansion. We know that when the tubes and the process to assemble them was designed, it was designed within the confines of an acceptable temperature range, specifically from cold temperatures for storage up to soldering temperature and envelope sealing temperature. During normal operation the tube would operate between these extremes. We know over a period of decades that tubes that operate within this temperature range can maintain hard vacuum. Even tubes that have been subjected to bitter cold temperatures in military applications have been known to maintain hard vacuum. All in all, tubes are fairly robust items when you think about it.

On the other hand, cryogenics deals with some pretty extreme temperatures, beyond those that a military tube might experience in the harshest winter environments in Antarctica. I am not familiar with any tube data sheets that specify minimum storage temperatures that approach the extremes that a tube might experience during cryogenic treatment. Of course, not having reliable data doesn't stop the marketing guys from knocking on wood as they abuse a batch of tubes and sell them to people who believe the cryogenic argument.

Personally, I'd worry that it is possible to weaken an envelope to pin seal by subject a tube to extreme changes in temperature, and more importantly, subjecting a tube to rapid extreme changes in temperature. My personal opinion is that cryogenic treatment involves risk to the tube, without much likelihood of being compensated with a reward, so I steer away from it.

[bob p]

cross-post, chuck!

[g1]

Oddly enough, this got me thinking about Trial by Ordeal (drowning test for witches). Earlier there was question about how to know whether the tubes had really been treated. Perhaps loss of vacuum would be the proof .

[R.G.]

My limited understanding of the glass-to-metal seal process in tubes is:

Glass and (usually) steel in the pins have different coefficients of expansion, and glass does not "wet" steel, or tin-plated steel. So there is or was a great deal of metallurgy and inorganic chemistry involved.

First, the thermal expansion issue had to be solved. If you tried to seal glass to metal without matching coefficients, no amount of sealing would work. As I understand it, the pin on a tube is not a single chunk of metal. Instead, it's a stack of different alloys along the axis of the pin. The top and bottom can be plated base metal, but the middle part is an alloy with nearly the same coefficient of expansion as glass. The next outer layers are intermediate between the middle layer and the ends of the pins, and the outer sections are the base pins.

Once you have a middle section with an expansion coefficient that matches the glass it will touch, you can use a material that will wet both glass and metal when molten. These "frits" are metal/oxide glasses that wet both. The black patterns around the edges of windshields on cars are a variety of frits that are put there to hide the internal fixing mechanisms on the edges of the glass.

Once you have the stacked pins with matched middles, you use a frit sealant and bake it to molten to seal pin to glass. For small tubes like 12AX7s, this assembly is mades as a "button" with all the pins on it, and the tube body section is fitted over the button and welded to the button around the bottom. The top of the tube is a small diameter tube which is used to evacuate the tube and then melted closed, accounting for the pointy top-knot preamp tubes have. Power tubes are fitted with body tubes having an evacuation tube on the bottom of the pin-button. In octal based tubes, the sealing-point is covered by the external pin base. The process is much more obvious in TV tubes without an octal base.

Cryo treatment almost by definition puts in internal stresses. That's its claim to fame to make metals tougher. It may or may not stress the glass-to-metal seal of the middle layer of the pins, depending on how close the coefficients of expansion of the actual glass and alloy are. They don't always match perfectly. Frits are more elastic than glass, but not much. Finally, I'm not sure what happens to the frit if it wets pin and/or glass outside the middle/matched sealing area. With well-engineered tubes from the Golden Age? With 'modern' tubes made of surplus cheese-steel and recycled window glass?

As Bob Dylan crooned "How much abuse will you be able to take? There's no way to tell by the first kiss."

[Tom Phillips]

As R.G explained, there is a lot of technology behind the lead feed through at the base of the tube. This is just one process of many that are required to manufacture a vacuum tube. When you consider all the physics, chemistry, metallurgy etc. expertise required to make a tube it becomes clear just how difficult it is to start up (or maintain) a factory that can make good tubes.

In the past I have heard rumors such as "Company X bought the tube manufacturing equipment from Sylvania when the USA factory closed." The implication was that they would be able to set it up, turn it on and start making new tubes. That's kind of equivalent to buying Jimi Hendrix' original equipment thinking that you could then reproduce his music.

[imaradiostar]

Dunno if it's true or not but I've read that some of the more recent decent tubes (EI, if I recall) were built on the hardware from one of the formerly great makers (Telefunken), but as time has marched onward and war has reclaimed parts of the country where the hardware resides (Yugoslavia) the tubes have fallen in quality and ceased to exist.

Hopefully someone, somewhere, was smart enough to write it all down so that one day the work can be duplicated. I'm OK with expensive tubes if they truly are like the ones from the good old days.

As for cryo treatment, I don't dare chill a tube that much. I find it hard to believe that the seal can be maintained when modern tubes seem to have less attention to metallurgy than the old stuff.

Jamie