Audio Research Reference 250 SE, Руководство пользователя

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14
Operation
Output Tube Bias Adjustment
As shipped from the factory, the output
‘bias’ adjustments are set for a nominal
65mA per KT150 tube. Under these idle
conditions the tubes are each dissipating
approximately 27 watts of their 75
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 250 SE at 117.5 VAC
(or 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, press BIAS switch once and
the V1 output tube LED is illuminated with
its bias level indicated on the front panel
meter. Adjust V1 tube bias level with the
plastic flat-bladed bias tool (provided),
inserted in the V1 SET hole in the front
panel so the meter reading is in the center
of the labeled bias range. Press BIAS
switch again to check V3 tube bias level
which should be within the bias range
arc. Press the BIAS switch again and check
the V5 tube bias level in the same way.
Note that the V3 and V5 tube bias levels
are controlled by the V1 bias setting.
Press the BIAS switch once more to read
and adjust V2 tube bias level with the
bias tool in the V2 SET hole in the front
panel in same way the V1 tube bias level
is adjusted. Press BIAS switch again
to check V4 tube bias level, and once
again to check the V6 tube bias level.
Note that the corresponding V number LED
is illuminated for each output tube as
you proceed through the bias adjustment
and monitoring sequence. Press BIAS
switch a final time to exit the bias status
function and return the meter to the
power level monitoring function.
The Reference 250 SE is shipped from the
factory with all tubes properly biased and
ready to use. It is not necessary to check
bias each time the amplifier is turned on.
Under typical circumstances, most owners
will find that checking the bias level once
a month or so will insure proper operation
and good service life of the output tubes.