Audio Research Reference 750 SE, Manual

Page: 13 / 18

13
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 750 SE at 117.5 VAC (or 230 VAC).
Adjustment must be made under zero-
signal conditions after at least 30 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 repeatedly
and check the V5, V7, V9, V11, V13 and V15
tube bias levels in the same way. Note that
each of the odd V number the 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. Again,
press the BIAS switch repeatedly to check V4,
V6, V8, V10, V12, V14 and V16 tube bias levels,
which should all be within the bias range arc.
Note that each of the even V number tube bias
levels are controlled by the V2 bias setting.
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 750 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.
Hour Meter
An LCD hour meter of elapsed tube operating
time can be viewed on the back panel of the
unit (see illustration on page 8). This displays
accumulated hours of vacuum tube service
life. If the amplifier is unplugged from A.C.
supply, the total accumulated hours are
retained. Below the hour meter is the hour
meter reset button; after replacing vacuum
tubes, press this button to reset the hour
meter back to zero. Note that once the hour
meter has been reset, it is no longer possible
to recall the previous hour count.
Operation