Octave JUBILEE Mono, Руководство пользователя

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17
5. ADVANCED FUNCTIONS
5.1 Bias measurement facility
5.1.1. How the bias works
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
eight tubes is relevant to both for the sound of the
power amplifier and for the service life of the
tubes. This is why we have incorporated a bias
measurement facility into the JUBILEE MONO
SE blocs that allows you to set the bias yourself
without the need for test equipment.
The protective screen does not have to be
removed to do this.
The driver tubes inside the unit require no
adjustment.
Changes caused by aging of the tubes
can be compensated for. The sound of
the
amplifier remains constant
throughout the service life of the tubes.
5.1.2. How to set the bias
Make sure that no signal is playing through the
amplifier when you are adjusting the bias.
The
preamplifier should be switched off, although
you do not need to disconnect the
loudspeakers.
Procedure
1. The amplifier must be operated for at least
15 minutes to allow the tubes to reach their
operating temperature. The adjustment is
made in the bias high setting (blue LED in
the display).
2. Turn the bias measurement selector switch
to position V 1. The meter in the display
should read 950 - 1050. In case of
misadjustment you have to adjust the value.
The corresponding bias-regulators for the
output tubes are located on the rear panel.
Turn regulator 1 clockwise in case the
reading of tube 1 is less than 1000 and
counterclockwise in case the reading is
higher than 1000. Check the bias of the
other tubes, V2 …V8, and adjust their bias
via the corresponding regulators.
3. After adjusting all tubes you should check V
1 up to V 8 again. A small re-adjustment
may be necessary to reach the final
matching reading of all eight tubes. The
reading of all tubes should be equal within
the tolerance range from
950 to 1050
.
Special cases: Faulty tubes
4. You should remove any tube that fails to
provide a stable reading after an initial
warm up period.
5. Any tube that reads 0 is defective and
non-functional and must be replaced.
Tubes showing a reading of 0 cannot be
corrected by turning up the bias control.
6. If you notice a constantly rising reading on
a tube, accompanied by the red protection
LED E turning on at some point, this
means that the power amplifier has
switched itself off electronically. The
readings for tubes V 1 - V 8 fall to 0. No
adjustment is possible if the electronic
protection is triggered.
(See chap. 5.2 “Electronic protection”)