. . . .PEARL TUBE
COOLERShave 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
. . . .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 O-rings.
. . . .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 Nov. 1959 data manual Brimar
Valves, UK stated:
. . . .“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
. . . .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
. . . .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.
. . . .Over the years an entire industry has sprung up following our lead; with
two of our previous audio-industry customers having purchased cryogenic treatment equipment of their own.
. . . .Noteworthy however is the fact that our cryogenic treatment is an immersion
process run for fully 100hrs. at a -325ºF soak temperature. This, as opposed to the 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 "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.