|. . .We
originated the cryogenic treatment of vacuum tubes over two decades ago and during
that time we have steadily refined and enhanced the PEARL
CRYOVALVE treatment processes. During this period
we have treated tens of thousands of tubes that have been purchased by end-users
the world over. To download an extensive PDF that documents their 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
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 "endomicrophonic" respectively; with endomicrophonic output being always
present under dynamic-signal conditions, irrespective of the presence of external
. . .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
to download our Audio Note, "The Measurement of Microphonic Effects in Vacuum
. .Excellent excerpts on microphony from "Mullard Technical
Communications," Nov., 1962 can be downloaded here,
while an article on "Trustworthy Valves," that details 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
- 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 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,
- 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
- 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
- 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
. . .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, one that over
the last two decades 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