Ashdown LB-30 DROPHEAD 15H - Handbuch (Seite 5)

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USER MANUAL
VALVE
THE VU METER
The vU meter fitted to the CTm is a dual function meter detailed as
follows:
By using the push button selector switch marked “AUDIO / BIAS” the
functions are accessed in the following manner:
1/ “AUDIO” - In audio mode the meter is set to read the audio output of
each of the six power tubes and each can be measured by utilising the
rotary selector switch on the front panel. Whilst playing this is the normal
mode of operation of the meter and the reading obtained will be a direct
indication of the power being produced by each output tube, the meter
is calibrated so that when the needle reaches the start of the red section
the power tube being measured will be producing maximum clean
volume.
The switch can be rotated to select any of the power tubes and its relative output will be indicated on the meter, note that when
performing this test you will need to play at equal volume for each test.
2/ “BIAS” - In this mode the meter will glow RED.
To check the bias of the output tubes proceed as follows:
Run the amplifier for at least 10 mins to allow the output tubes to fully heat up with the amplifier set to mute. Standby on.
Select.. Tube 1 and with an insulated jewelers screwdriver gently adjust the trimmer situated on the rear panel. The reading to
aim for is the needle just at the start of the red ie 0db.
Note that although each tube can be adjusted individually it is possible to get tubes that cannot be adjusted to the correct
reading, these can still be used providing the reading is not in the red, a lower reading is acceptable and will note impact audibly
on the power output or sound quality of the amplifier.
Please also note that the trimmers are 25 turn types to make adjustment easy, This type of adjuster has no end stop so if you
reach a point where the adjuster will not give any more adjustment then the output tube will have to be replaced if the reading
is to high ie in the RED.
Repeat this for each of the six output tubes in turn.
RETURN THE mETER TO “audio” mODE AFTER BIASINg. DO NOT RUN THE AmPLIFIER IN BIAS mODE WHILST PLAyINg.
Note there is a protection fuse fitted to each of the output tubes and if no reading is obtained on the meter this fuse will have
WILL STILL WORK
AT REDUCED
POWER
IDEAL SETTING KEEP OUT!
DO NOT SET ANY
TUBE THIS HIGH
CTM-300/100