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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: cryogenically treated tubes? posted by slapshot on July 31, 2008 at 19:46:47:
Cryogenics is an interesting process and judging from responses very misunderstood.
First in terms of differences in thermal expansion, the process properly done involves the slow descent of the temperatures. I believe most facilities have a controlled rate of temperature change and at least two holding periods where the the product being treated has time to stabilize.
While any sudden thermal shift can cause the metal to glass seals to break, one should remember that the in the assembly of the tube, the glass envelopes are melted to fuse the outer envelope to the glass button holding the metal structure. The temperature differential there is greater than the cryogenic treatment. In regular operation, there is quite a bit of thermal differential also.
The key to successful treatment is careful temperature control.
In metallurgy the cryogenic process is quite well documented and in steel products, there is a definite change in the crystalline properties and structure. Steel is the product with the most documentation, but there are elements within a vacuum tube which employ a lot of nickle and other metals with analogies to steel, in fact, IIRC, the pins are usually a form of steel. Thus, even if on a small scale there are definite components which may be affected.
There may be other factors too, many of which are speculative, as I do not believe anyone has dissembled a treated tube and analyzed the change in the constituent parts.
Cryogenic tubes came to my attention from the work of Bill Perkins (PEARL) and I received some treated tubes he had been experimenting with. This must have been in the very early 90's and I received some Yugo and Russian tubes which were treated. They were claimed to be quieter than stock and indeed they were. Very quiet tubes, with very little microphony. I felt , at the time, that they achieved some of this quietness at the expense of limiting the high frequency extension.
At the time I had also been experimenting with heat treatment of tubes, baking them out in order to improve the vacuum and that was quite a bit more effective in my experience. I communicated my experiences with Bill and we sort of left things as is. Many months later I received a call from him concerning his cryogenically treated tubes. I am not sure if he had changed the process, but somehow the treated tubes would break the heater filaments after a few weeks of use, and he was interested if I had experienced the same issue. Not being 100% satisfied with the cryogenically treated tubes I received from him, I had also heat treated some of the tubes he had sent. and that had increased both frequency response and dynamics which I had told him. I also never had any of his thus treated tubes fail on me.
I am not certain if he has modified his processing of the tubes, but I believe he has solved the issue. The fact that that the filaments were breaking, again, to me, indicates that something is going on within the tube envelope. We may not fully understand the process, but in some way changes are being created.
I have further experimented with home cryogenics, using dry ice and liquid nitrogen (not recommended unless you do some research into the dangers). I had purchased a 100 of the same tubes, GE 12AU7's and treated them in batches of 20, heating them, and alternately cryoing them in different procedures. No tubes failed, but the sound was quite different with various procedures.
Cold treatment seems to smooth out the sound, limiting dynamics to a certain degree and the heat seems to do the opposite. Once cryo'ed though, I never seemed to regain the initial "raw" edge that the untreated tubes seemed to possess, even with repeated heat treatments.
Incidentally sonic change can be heard using just the dry ice cold soak, which does not reach true cryogenic temperatures.
As I did not have any real scientific means of controlling temperature, my results are open to doubt, and should be repeated with a more stringent process in place. However, Cryogenic tubes can make a sonic difference. Whether that difference is one that you want is only determined by trying.
Stu
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Follow Ups
- RE: cryogenically treated tubes (long) - unclestu52 08/1/0811:18:56 08/1/08 (2)
- RE: cryogenically treated tubes (long) - danlaudionut 14:16:14 08/1/08 (0)
- RE: cryogenically treated tubes (long) - lelandaudio 12:59:22 08/1/08 (0)
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