9
BIAS CONTROLS
This is a powerful feature and tool for exploring more tonal possibilities with the BONES
amplifier. You can mix and match different tube types together for an almost unlimited
range of tones. More on this later. Since there is individual bias adjustment for each tube,
there is no need to obtain matched tubes! BONES will accept EL34, 6CA7, KT77, 6L6,
5881, KT66, 6550, KT88, KT90, KT100 type tubes and any other derivations of the
above. The output power will range from 100 to 180 watts RMS depending on the output
tube selection. The added benefit of having output tubes fused in pairs is in case of tube
failure, you will be able to finish your gig. Only a small volume reduction and slight tonal
change will occur.
Biasing the BONES amp is simple and does not require removal of the chassis. You will
need a simple voltmeter or digital multimeter set to the lowest DC voltage range,
typically 200mV (millivolts). Please note that some meters display may indicate 25.0 for
25 mV and others may display .025 for 25 mV.
Make sure you know your meter and refer
back to the meter’s owners manual to be certain
. Then follow the these directions:
1. Unplug any cords from the INPUT, make sure the MASTER volume control is
turned all the way down, counterclockwise. Unscrew the lock nuts on all the bias
pots located on the rear panel, then turn all the bias controls all the way down,
counterclockwise. Connect a load to the appropriate speaker jack, plug in the AC
cord and turn on the amplifier. Wait a few minutes then put the STANDBY
switch in the up position.
2. Put the black negative probe lead of your meter into the black tip jack. Place the