. . . PEARL
been doubling the service life of hot-running audio vacuum tubes for nearly 30 years, during which time over 300,000
pieces have been fitted into audio systems the world over.
. . . Perhaps the longest running, best documented, best
warranted and most successful tube audio accessory of all time PEARL TUBE COOLERS have inspired several much more costly imitators; none of which combines the functions of cooling and microphonic
reduction, nor anything like the cost/benefit ratio achieved by the long-established PEARL design.
. . . Continuously refined, our heatsink design has evolved
from an oxide blackened, louvered fin device with black EDPM
O-rings – later found to have inadequate long-term thermal withstand – to the present day solid copper device with
3D-contoured, contiguous fins coated with 2 mils
of high metal content, high temperature powder coat and held in place by high thermal withstand, red-orange, silicone
. . . With heat from the within tube’s envelope and pressure
from the external O-rings the powder coat slightly softens to then flow in a conformal manner with an intimate
thermal interface and unmatched microphonic control resulting.
. . . Based on research begun in the early 1950s by the
US military and the aeronautics industry, PEARL
coolers achieve the sorts of glass temperature reductions shown over 60 years ago to greatly increase the operating
life of soft-glass enclosed electron tubes.
. . . Determined during the 1950s research is the fact
that the “soft glass” typically used in receiving tube manufacture is susceptible to high temperature operation
in that it becomes effectively “porous” at elevated temperatures, thereby allowing atmospheric contamination of the high vacuum within the glass. By several extensively
researched and solidly confirmed mechanisms such contamination has been shown to have destructive effects on the
electron emitting surfaces upon which tube functioning is completely dependent and extended service life relies.
. . . All major vacuum tube manufacturers of the day clearly
illuminated the benefits of envelope temperature reduction.
. . . In a November 1959 data manual Brimar Valves, UK
. . . “The use of close-fitting screening cans of high
thermal conductivity in intimate thermal contact with a large area of the [soft glass] bulb, in conjunction with
an adequate heatsink can materially reduce the operating bulb temperature and very considerably improve the life
of the valve.”
which is an exact description of the PEARL electron
tube cooler's form, function and effect.
. . . The 198 pg. PEARL Audio Note, “PEARL Tube Coolers and
Equipment Reliability” provides both a present-day overview and several magazine reviews as well as an extensive
overview of the period literature and patents. It can be downloaded here.
. . . As of Jan. 1, 2017, PEARL TUBE COOLERS are underwritten by a lifetime, transferable end-users' warranty that is also retroactive, meaning
that every PEARL cooler in the hands of an end-user
is now warranted against defects in materials and/or workmanship.
. . . If your coolers have black O-rings, please contact
us for no-charge, replacement high temperature, silicone O-rings.
. . . While consulting in 1987
to Museatex, the Calgary-based company that has since grown into EMM Labs we were presented with
an opportunity to chill down a quantity of tubes to -300ºF in Museatex' liquid nitrogen chilled "cold
box" freezer. To say that we were taken by the changes wrought is to make rather an understatement and, after
much research and development, we have been treating tubes ever since.
. . . A noteworthy outcome of
our research is that our cryogenic treatment is an immersion process run for fully 100hrs. at a -325ºF
soak temperature. This, as opposed to the only 8hr. "soak" in what amount to "cold boxes" that
typically chill to only -300ºF by liquid nitrogen vapor alone employed by those following our footsteps. Because
the extent of metallurgical change that occurs during cryo-temperature processing is a well established "time
at temperature" product, longer treatment at lower temperatures will produce more of the changes so beneficial
to audio performance.
. . . Subsequent to cryo treatment
we do a 100hr. vacuum enhancement procedure followed by a lengthy triple-anneal process. Following these processes
we do a 100hr. 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). This done we clean and polish
away the hard, and very bad sounding oxide coating from the thru-glass pins not cleaned by the manufacturer, as
most are not. Finally, we do a comprehensive series of parametric gain (and gain match in dual triodes), noise
and microphony measurements and provide all the data on the box in which the tube is shipped.
. . . While others claim to provide
the industry's best services, we remain the process innovators and continue to provide a level of service that
is simply unmatched, much less bettered.