|. . .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.
. . .To
read more about these phenomena, click here to download our PEARL
AUDIO NOTE, "The Measurement of Microphonic
Effects in Vacuum Tubes."
. . .Excellent
excerpts on microphony from "Mullard Technical Communications," Nov., 1962 can be downloaded here, while an article on "Trustworthy
Valves," detailing microphonic issues is available here.
. . .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
- 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
- cleaning and polishing of the pins of all 7- and 9-pin parts
which 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" Einequiv 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. this means 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 brand do we then
revert the brand on the sticker to the original maker's brand and remove the re-brand from the glass. This we need
to do 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 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