You can adjust the cascode without hooking up the high voltage power supplies, by using a 15-20 volt supply (2 nine volt batteries in series will do). Connect the positive terminal of the battery to the positive PS terminal on the board and the negative battery terminal to the end of the 100 ohm resistor closest to the 100 ohm trim pot. Then put a meter across the 250 ohm resistor and adjust the trim pot until you get 2.5 volts, which corresponds to 10 mA for the current source. If you can't get to 2.5 volts, decrease the fixed resistor to 200 ohms, and adjust the trim pot until you get 2.0 volts across the 200 ohm resistor. If the voltage is always higher than 2.5 volts for the 250 ohm resistor, replace it with a resistor around 300 ohms and adjust the trim pot to correspond to 10 mA.