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I'd like to be able to dial the amperage down. I think a potentiometer would need to go somewhere, but where? Right before one of the electrode leads?
I would strongly recommend against using it until it behaves in the expected way.I don't totally understand the circuit and don't have experience doing this sort of thing, so take my advice with a grain of salt.But I made it exactly as the instructions said to and got 2.01mA at 36 volts.Double check everything, including: Make sure the pins on the transistor are correct. Make sure the diodes are going in the right direction. Measure the resistor values and make sure they're correct.