Notes on the PEARL, INC. CRYOVALVE Treatment Process

. . .We originated the cryogenic treatment of vacuum tubes over twenty five years ago, during which time we steadily refined and enhanced the PEARL CRYOVALVE treatment processes whilst treating tens of thousands of tubes subsequently purchased by end-users the world over. To download an extensive PDF documenting users' unsolicited comments on their experiences with our CryoValves,click here.

. . .With respect to our unique process, the question we are most frequently asked is, "How can just freezing a tube, a cable, whatever, cause its sound to change ?"

. . .A proper answer to this reasonable inquiry takes one into the fields of metallurgy, crystallography, materials science, mechanics, and electrostatics.

. . .Simply put, the cryogenic treatment of metals has for decades been known to cause significant changes in the nature of their "molecular matrix." While such terminology might seem somewhat "loose" the facts are that in many metals, including those used in electron tubes, such transformations involve the "transition" or "self-conversion" of larger, softer molecules of austenite to smaller, harder molecules of martensite.
. . .In the case of steels used for cutting tools this transformation is accompanied by an evenly distributed release of smaller carbide particles throughout the molecular matrix. By these and other changes, a dense and very uniform microstructure is generated which, along with a reduction in residual internal stresses, produces, essentially, a "new" material whose physical properties show substantial, almost remarkable, improvement over the original. See the series of before and after photomicrographs at the bottom of this page.
. . .Amoung these changes is an increase in what can be thought of as the "internal friction" amoung matrix / martensite and martensite / martensite interfaces. Thereby, the effects of microscopic processes through which impinging vibratory energy is converted to, primarily, heat are significantly enhanced. This substantially improves the "internal damping" of the material, with the upshot that the "peaking" behaviour of resonant systems in which the cryo-treated material is involved is reduced to a great degree.

. . .In electron tubes used for audio purposes this increase in internal damping is greatly beneficial . . .

. . .Because the grid structures in the sorts of tubes used in audio are typically fine, delicate, wound-wire constructs, they are extremely responsive to both mechanical and electrostatic forces. Typically having very low internal and structural damping, they will oscillate for significant periods of time when stimulated at, or near, their resonant frequencies.
. . .Note that such stimulation can be a) external - from impinging mechanical or acoustical energies or b) internal - from varying electrostatic forces between the plate and the grid(s) always present under dynamic-signal conditions.

. . .The outputs from these two sources can be called then "exomicrophonic" or, commonly, "microphonic" and "endomicrophonic" or, uniquely, "electrophonic" respectively; with endomicrophonic/ electrophonic output being always present under dynamic-signal conditions, irrespective of the presence of external stimuli.

. . .
Due to the very construction of electron tubes, any resonant behaviour stimulated by such forces will modulate current flow through the tube to a greater or lesser extent. Such modulation is a form of distortion that can manifest as dynamic compression, a reduction of dynamic contrasts and the loss of microdynamics and microdetail, all of which result in a less accurate rendering of the sonic landscape.

. . .For more more on these phenomena see our PEARL AUDIO NOTE, "The Measurement of Microphonic Effects in Vacuum Tubes."

. . .Excellent information on microphony is found in "Mullard Technical Communications, Nov, 1962", while "Trustworthy Valves, STC, UK, Sept, 1954" provides further details on microphonic issues.

. . .Due to the significant improvements in internal damping wrought by our 100 hr, deep soak, immersion cryo process the sonically harmful effects of microphony and electrophony are markedly reduced. This results in improvements in sonic performance that are, first: remarkable in their nature and extent and second: uniformly experienced by end-users worldwide, using all manner of equipment to enjoy tremendously diverse musical tastes and across a time span of over two decades. To download a several page collection of technical information and the unsolicited comments of many very happy end users click here.

. . .Moving on from the cryogenic treatment aspect of our CRYOVALVE process we come to an overview of the entire process which involves:

  • incoming inspection,
  • 8 hr. chill down to -320º F with ultimate, complete submersion in liquid nitrogen for 100 hrs. followed a 24 hr. warm-up back to typical, warm room ambient,
  • a proprietary, 100 hr. "vacuum enhancement" process,
  • a lengthy "triple-anneal' process that furthers the cryogenic stress relieving,
  • a degaussing step to neutralize any remaining magnetic polarizations,
  • a 100 hr. burn-in during which stochastic electrostatic forces are employed to further stress relieve the tubes' inevitably vibration sensitive and often highly resonant grid structure(s),
  • cleaning and polishing of the pins of all 7- and 9-pin parts when they have not previously been cleaned and/or gold plated, see the picture at the bottom- right,
  • placement of serial numbered stickers around the base of the tube that show both the manufacturer and the tube's type, see below,
  • careful, accurate measurements of plate current, transconductance and mu; along with an assessment of the section-to-section AC and DC balance in dual triodes, see the spreadsheet at the bottom of the following page,
  • measurement of the unweighted, broadband equivalent input noise within -3dB points of 10Hz. and 30KHz. The "Noise Grade" measurement seen in the diagram below is referenced to the average or "bogie" noted as the "0 dB" value shown in microvolts,
  • oscilloscope, 1/3 octave analysis and listening evaluation of the noise and microphonic output runs concurrently with the previous step,
  • color coding of the tested tubes by noise grade noting that dual triodes are always graded by the noisier section. meaning that a tube graded "Low Noise" could have a "Gold Grade Plus" section. All GG+ tubes must have two GG+ sections.

. . .Note that while we apply an individual, serial numbered sticker to each tube we make every effort to maintain the branding on tubes passing through our process.

. . .Only in the case where we know for a fact that tubes have been re-branded away from their original maker do we then revert the brand on the sticker to the original manufacturer's brand and remove the re-brand from the glass. We need to do this in only a very small percentage of cases.

. . .Because many users are surprised to learn that tubes will even survive the ride to -320º F and back, much less sound the better for it, we are often asked what the failure rate through the cryo process might be. To date we have seen it to be <.1%

. . .In all, ours is a truly exceptional process that over its twenty five year lifetime has proved itself time and again to provide altogether remarkable improvements in the sonic performance of every tube we treat.

. . .Detailed data on the Tung-Sol JTL5687WA shown below which provides in addition to the original, factory data, graphical indication of the operating points at which the part is tested in the custom-built PEARL DYNATRAN tube test rig can be downloaded here.



Specifics of This Tube:



= Black Plates =
= Round Getter =
= Double Micas =



Recommended Service




Moving Coil Phono: Input  


Moving Magnet Phono: input



Line Stage: Input & Output



Power Amp: Input & Driver



Balanced or Differential Stages



Voltage Regulator







Tube pins before and after cleaning and polishing.
This procedure results in dramatic improvements in sound quality.
The PEARL AUDIO NOTE, "Making Contact with Your Tubes" provides more information on cleaning tube pins.

  . . . .Photomicrographs of Materials Before and After Cryogenic Treatment