Octave V 80 SE, Руководство пользователя

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8. TUBES
8.3. Bias measurement system
The bias measurement facility makes it easy for you to check and adjust the idle current of the
output tubes. Getting the bias setting right for all four tubes is critical for both the sound of the
power amplifier section and for the service life of the tubes. This feature guarantees consistent
sound quality over the entire lifetime of the output tubes.
That is why we have built this bias measurement facility into the V 80 SE – to allow you, the user,
to carry out the adjustment yourself without the need for test equipment. The use of precision op
amps makes it possible for you to set the bias to an
accuracy
of 0.3%, making it superior to any
other method.
Using selected output tubes only makes sense if the idle current is adjusted accurately, as is
clearly shown in Fig. 1 Technical Data.
How to set the bias
Turn the mode selector knob [8] anticlockwise to the BIAS position to activate the measurement
circuit. Signal/input selection is disabled. The 3 LEDs above each screw in the display panel show
whether the bias setting is too low, correct, or too high. Use the small screwdriver supplied to
adjust the bias. While you are setting the bias, the adjusters are illuminated to make them easier to
see in unfavourable lighting conditions.
To increase the bias current to each output tube, turn the screwdriver clockwise.
The adjusting screws are fully insulated. There is no risk of electric shock and the adjustment
procedure is completely safe.
The LED display:
Red LED only
Setting is too high
Green + red LED Setting is OK for KT 150, KT 120, KT 88, 6550, etc. = high bias
Green LED only Setting is OK but inaccurate
green LED Setting is OK for EL 34, 6L6, KT 66, etc. = low bias
Yellow LED Setting is too low