Here was his response:
yes, the clock requires AC and takes the mains frequency from the wall wart.
If you use the clock with DCF77 you can also use DC.
Wall Wart power supply – A variety of wall warts from various vendors will work, but Radio Shack catalog number 273-1631 is ideal for the Nixie clock.
It is available in their USA retail stores and at www.radioshack.com. It has the correct plug attached, with a thin 6-foot cord and an attractive white color.
Set the voltage switch to 9V.