As the picture shows, is this a potentiometer, or is it supposed to be two resistors?
Figure 1. Equivalent circuits.
- R1 allows selection of a bias voltage between 0 and -12 V.
- R2 limits the current from the bias to the next stage of the circuit.
- Note that your coarse pot wiper resistor is 100 kΩ and the fine is 1 MΩ. If they both feed into the same circuit the fine pot adjustment will be ten times more sensitive than the coarse pot because the 1 MΩ resistor reduces its effect to one tenth that of the coarse pot.