To drive a decimal separator (colon-) tube, you must first connect its anode pin to 170 VDC. Compared to a normal nixie-tube, the decimal separator needs a cathode resistor on every cathode (68,000 Ω or 68 kΩ recommended value). To light up the two dots, it is necessary to short the cathode resistors to ground (0 VDC, please also refer to Driving-Circuit for the R Nixie tube).
This is a simple driving circuit using a discrete high-voltage transistor MPSA42. To light up the separator, connect the base of the transistor to 3V to 12V. To turn it off, connect the Base to 0V or leave it floating. In this circuit, the two dots are lit up together, but it is also possible to drive them separately.