22A3 Monaural Amplifier Rev 1.0
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All tubes from Bandwidth Audio are matched in this fashion.
3.3
Biasing
Your amplifier has been biased from the factory. However, the bias setting should be checked on
first startup and periodically thereafter to maintain performance as well as longevity of the power
tubes.
Note:
preamp tubes are automatically biased. No adjustment is needed
A. Checking the Bias:
To check the bias, power the amp on and let it warm up for at least 10 minutes. The bias reading
for the power tubes can made off of the two analog ammeters located on the back face of the
amplifier.
Bias Set Point: 50 to 60mA
With the volume turned all the way down, the bias should be set between 50 - 60mA
by the screwdriver adjustment potentiometer labeled
“Bias”
on the back of the amplifier. This
range is based on sound preference as well as desired output tube life. The lower the bias, the
longer the tube life with the expense of higher distortion.
If using 2 matched pairs that are split between each amplifier as discussed in
3.2
,
each meter
should read +/- 5mA or Less for best performance.
A well-matched quad of tubes will measure
much better than this.