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ADJUSTING THE OUTPUT TUBE BIAS
The front panel incorporates a bias meter. Turn the volume control all the way down (full counter
clockwise) while performing bias adjustments. Use a small screwdriver and adjust the bias control
(located on the rear of the amplifier, “Tube Bias Adjustment”) for 100 mA after the unit has
warmed-up for 20 minutes. The normal range setting is from 60 mA to 150 mA, and changes here will
vary the damping factor of the amplifier slightly. More bias current increases the damping factor,
whereas less bias current provides a softer more tube-like sound. The bias current design center
should be set to 100 mA, and that should be your starting reference point if you want to experiment
from there with different settings. Personally, I preferred the sound best on my speakers when I set
the bias current to between 80 mA and 100 mA. It will vary from speaker to speaker, and more
importantly with your taste.
The meter reads the combined current for all six output tubes, and it is normal for this current to vary
slightly with changes in power line voltage.
SPEAKER CONNECTIONS
From the rear view, the black binding post is common, and (moving to the right) the next red post is
two ohms, then four ohms, and the far right post is for eight ohms. The power curve is quite flat,
hence the two ohm tap may be used for one ohm speakers, and the eight ohm tap may be used for
sixteen ohm speakers.
To connect the speaker first check the impedance of the speaker which is usually identified on
the speaker itself or in the owner's manual. Connect one lead from the common terminal of the
speaker to the common terminal on the back of the amplifier. Connect the positive lead on the red
terminal on the back of the speaker to one of the red output terminals on the back of the amplifier
based on the impedance of the speaker. When multiple speakers are to be connected to the output,
the combined load impedance must be calculated and the load connected to the appropriate
impedance tap.
If a load impedance is used that is lower than the output impedance tap, then reduced power and
possible distortion will result. If a load impedance is used that is higher than the output impedance
tap, then neither the signal nor the amplifier will be harmed but the voltage available is limited to that
stated at that tap.
