|. . .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
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" Eequiv.in. 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
. . .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.