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7. TUBES
LED graphs, advanced adjustments of the BIAS setting
There is an upper adjustment limit to the "high" BIAS setting, which is indicated by the green and
red LEDs lighting up at the same time, and a lower limit to the "low setting, where the yellow and
green LEDs light up. The lower limit should be used with "smaller" output tubes such as the KT 88,
KT100, 6550, KT 90, EL 34 and similar. The upper value, which provides a higher BIAS current for
the output tubes, can be used with the KT 120 in both positions of the power selector.
Exception: The BIAS high setting can also be used with the KT 88 in the power LOW position.
Certain loudspeakers may benefit from the higher BIAS current, as it will increase the damping
factor and provide slightly better control of the speakers.
LED graphs
The BIAS LOW setting corresponds to the plate current of 33mA
The BIAS HIGH setting corresponds to the plate current of 40mA
The crossover setting yellow / green or green / red is an adjustment with a very high precision.
Small changes in the brightness of the LEDs are normal due to the long time drift of the tubes or
the mains voltage.
