Bottom Panel
Fuse
–
In the unlikely event that a tube fails, the Impala is protected by a 2 Amp slow blow
fuse for 120v and 100v (North America and Japan) models or a 1 Amp slow blow fuse for
220v and 240v (Europe and Asia) models. Please consult us or a qualified tech for assistance
in the event of a fuse blowing. The fuse is located on the bottom of the chassis by the power
cord.
Speaker output jack
– The speaker output jack is located between the power tubes on the
back of the chassis (see
Chassis Diagram
). The Impala is designed to drive an 8 ohm load.
Maximum power and tone will be realized when connected to an 8 ohm speaker or cabinet.
The speakers in Impala combos and extension cabinets are configured to provide the
amplifier with an 8 ohm load.
The Impala will work with a 16 ohm or 4 ohm cabinet with the following caveat - you will
lose a little power from the impedance mismatch and the power tubes will have to work a bit
harder and thus age faster. This effect though is minimal.
To run an external cabinet, turn the Impala OFF, unplug the internal speaker (combo amps)
and plug in the external cabinet’s speaker cord. Alternatively, a “Y” speaker cord can be
used to run an 8 ohm external cabinet along with the internal speaker(s) of a combo amp
without damage to the amp (the total impedance or speaker load in this case will be 4 ohms
– see the previous paragraph).
Damage will result from operating the Impala without a speaker load.
Biasing Your Impala
The Impala is a Fixed Bias amplifier and requires a Bias adjustment any time the power
tubes are replaced. The Impala is designed around the 6L6GC family of tubes.
6L6GC, 5881, and 7581A are all compatible.
To adjust bias you will need a Volt Ohm Meter. These are readily available for as little as
$10 from any electronics supply store.
Look at the amp from the back. You will find two test points on the bottom of the chassis to
the right of the power tubes. Insert the red meter probe into the red test point and the black
probe into the black test point. Set the meter to Volts DC. Turn the amp on, let it warm up
in the standby position then turn the amp to play.
You will see the meter read the voltage over a 1-ohm resistor in the powers tube cathode
circuit. On the back of the chassis between pre amp tubes 3 and 4 you will note the shaft of
a potentiometer sticking out – this is the bias pot and what you will turn to vary the bias. As
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