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You might wonder why your DMM is set to millivolts and not milliamps – simply, we have a 1 Ohm resistor placed between your
probe jacks and ground to convert a current reading to a voltage reading. That way, a bias current of 24mA measures as 24mV
on your DMM.
NOTE – Only set your DMM to mV for measuring bias on the OTS amplifiers. Not doing so may damage your DMM.
Now that you know how to calculate bias, all you need to do is:
1) Follow steps 1-5 on page 11
2) Calculate what bias voltage reading you will set your tubes to (in this case, we will use 24mV)
3) Place your red probe on the previously mentioned power tube pin connected to the 1 Ohm resistor, and the black probe
on the other end of the 1 Ohm resistor.
4) Turn the bias potentiometer shaft SLOWLY until your DMM reads 24mV
5) Wait 1 minute
6) Recheck all power tube bias measurements
7) Readjust bias potentiometer shaft if necessary
A FEW COMMENTS ON BIASING
Due to the nature of vacuum tube amplification, there are inherent risks when biasing your amplifier. Extremely high-voltages
are present, and vacuum tubes reach high temperatures during use.
The risk of electrical shock and/or skin burns should ALWAYS be kept in mind. Therefore, bias at your own risk, and only while
paying attention and taking all precautionary measures.
Biasing should only be done on a clean workbench with no distractions. Do not wear loose clothing or any jewelry. Take your
time, and think carefully before each step.
Again, bias at your own risk. Ceriatone Amplification is not responsible for any damages or injuries resulting from user biasing.
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