Higher voltage from the lumos.sk HV PSU

I bought a second Nixie HV PSU from the great Lumos.sk website. The stock device outputs 110 to ~190 Vdc, which may be not enough for lightly depleted Nixies. For example, my B5094 requires about 205 V to light up.

Before assembling it I checked the diagram and the MC34063 datasheet for a way to change the output swing. Why? Because I want to build a bench PSU with a higher output, just in case. And currently I don't need voltages in the lower range. Basically I need to recalculate the feedback network and after a few typings on a spreadsheet I decided to decrease R3 from 3k9 to 3k3: this should result in a 130-230 V swing.

One constraint: output cannot be more than 250V unless the output capacitor is replaced with an equivalent with a higher operating voltage. The supplied electrolytic cap is rated at 250V.

Another good mod is replacing the small resistive trimmer with a potentiometer to bring the control over to the front panel. I forgot to do it this time. Well, I will keep this variation for my next build of this useful piece of gear.