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BIASING SWITCH
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Although the unit will be factory fitted with EL34 valves, the power stage can also use
either 6L6, 5881 or 6550 valve types.
The bias switch allows quick and easy selection of two power valve types. All the user
has to do while the unit is off, is to replace current valves with new type, flick the bias
switch and then power up.
The amplifier will be set at the factory so the BIAS switch allows selection between
EL34 and 6L6 valve types, the most popular types for guitar amplifiers.
Selection between any two of the valve types mentioned can be achieved by
re-biasing using the preset trimmer pots, under the rubber grommets. This should be
carried out by a competent engineer with the correct epuipment. A bias voltage
test point is provided: this is in line with the bias switch on the top of the head or
underneath on the combo. To measure the bias voltage connect voltmeter (set to DC
100V range) as follows:- Black lead clip on to bias switch, Red lead touch test point
underneath grommet, the voltage can be set by using a trimmer tool to adjust the
appropriate preset trimmer pot on the rear panel.
When changing power valves, matched pairs should be used. On the head version,
looking at the unit from the rear, left to right valves 1 and 2 are a pair, and valves 3
and 4 are a pair.
MUTE SWITCH
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When this is selected the power stage is muted, therefore the preamp can be used,
by taking an output from the EFFECTS SEND socket, without any need to load the
power amp.
MAINS FUSE
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In the event of having to replace the mains fuse always use the same rating and type
as marked on the unit's rear panel. Using one of a higher rating will invalidate the
guarantee.
If after replacement the mains fuse should blow a second time, immediately refer the
unit to a TRACE ELLIOT approved service engineer for checking.
POWER ON/OFF SWITCH
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When switched on this supplies power to the valve cathode heaters and the relay
switching circuit. Check that the correct mains voltage is applied to the mains inlet
socket and that the front panel STANDBY switch is in the standby mode before
switching ON or OFF.
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