Congratulations!
The Margules U280-SC 25th Anniversary Stereo Tube
Amplifier combines the superior sound of vacuum tubes
with new and innovative technology. The results are
clearly apparent in its quick detailed dynamics and ultra-
smooth transient response. Unusual versatility and
unprecedented
reliability
provide
an
exceptional
performance upgrade to an already remarkable amplifier.
Class-A Output Stage & Active-Servo Bias
Vacuum tube power amps with class-A outputs are rare.
Class-A operation causes the tubes to run quite hot, and
increases
the
chance
of
saturating
the
output
transformer.
Margules has resolved this problem by incorporating an
Active Servo Bias (patent pending). The bias actively
tracks the input signal, permitting full class-A output,
without overdriving the tubes.
Active Servo Bias also sets DC bias and AC drive levels,
assuring optimum electrical and sonic performance.
Throughout the useful life of the output tubes, no drive or
bias adjustments are ever needed. New tubes can be
installed without test equipment or time-consuming setup.
Active Servo Bias also makes it possible to use a variety
of output tubes. The 6550, KT88, KT99, KT100, KT 120,
KT150 can be interchanged without modification.
Active Servo Bias is implemented with semiconductors,
which are designed for the aerospace industry, assuring
long, trouble-free operation.
The New U280-SC 25th Anniversary Stereo Tube
Amplifier includes a new and improved differential output,
as well, further reducing the THD and transient distortion.
Ultralinear / Triode & Strapped Operation
Audiophiles have argued the merits of Ultralinear vs
Triode operation for 50 years. Triode operation provides
lower distortion, at the price of reduced power output.
The U280-SC resolves this predicament by providing
switchable Triode / Ultralinear operation. For those
listening sessions where you prefer a more soft sound,
you simply switch to Triode Mode. And when more
power, dynamics, detail and punch is needed, you simply
switch to Ultralinear Mode.
Unlike most vacuum tube amplifiers, the U280-SC's
outputs can be strapped, for twice the output. Start with a
single amp and then add a second U280-SC for
increased power
—or to convert to triode operation at the
same power level.
Separate gain controls for each channel make precise
balancing easy. This simplifies the setup of bi-amped
systems, as well.
Regulated Shunt Power Supply
The input stages of the new U280-SC 25th anniversary
include a special SHUNT power supply for these critical
circuits.
Shunt
technology
provides
a
dramatic
improvement in Q damping, the key factor in regulating
voltage for those stages.
Good regulation reduces the loss of signal integrity that
occurs when the signal itself shifts the amplifier’s
operating point. Each channel uses separate regulators
