Output Tube Bias Adjustment; Servicing - Audio Research Reference 75 Owner's Manual

Output Tube Bias Adjustment

As shipped from the factory, the output
'bias' adjustments are set for a nominal
65mA per KT120 tube. Under these idle
conditions the tubes are each dissipating
approximately 27 watts of their 60 watt
rating. This point of operation provides
'enriched' Class AB1, and will satisfy the
most critical listener.
For best results, operate and adjust the
Reference 75 at 117.5 VAC (230 VAC).
Adjustment must be made under zero-
signal conditions after at least 15-20
minutes of uninterrupted stabilization time.
With the amplifier warmed up and signal
set to zero, switch the rotary knob to one
of the 'V' settings. Insert only the supplied
non-conductive bias adjustment tool into
the appropriate bias adjustment holes.
Slowly turn the
potentiometer in each
marked with the output tube 'V' number
position only when the bias switch is set to
that associated 'V' number position. The
meter should be set to read in the center
of the tube bias arc (@65mA) for each of
the four output tubes V1 – V4 for optimum
sonic performance.
8
bias adjustment
of the holes

Servicing

Because of its careful design and exacting
standards of manufacture, your Reference
75 amplifier should normally require only
minimal service to maintain its high level of
performance.
Caution: The Reference 75 amplifier
contains sufficient levels of voltage and
current to be lethal. Do not tamper with a
component or part inside the unit. Even
with the power turned off, a charge
remains in the energy storage capacitors
for some time. Refer any needed service
to your authorized Audio Research dealer
or other qualified technician. Additional
questions regarding
maintenance or servicing of your amplifier
may be referred to the Customer Service
Department of Audio
Corporation at 763.577.9700 (CST). When
ordering a service manual from Audio
Research or an authorized dealer, be sure
to identify the serial number on your
amplifier.
the operation,
Research