A couple of years ago, I built a Nixie clock, mostly as a project to use some B-5092A Nixie tubes I scored off of eBay for $2.50 each. The clock itself is a PIC microcontroler, fed from a 60 Hz line reference, and multiplexes the display as a 3x2 set of digits. The digits themselves are actually scanned at 600 Hz, which lets you do PWM (pulse width modulation) fades between digits. Two NE-2 neon lamps function as "flashing" colons, in the European style of "period" instead of the tacky American "colon" style.
I built an external crystal controlled clock board, as well, but ended up just using the zero crossing of the power lines' AC as the clock reference instead. The clock board I built divided a 3.93 Mhz crystal down to 60 Hz. I had provisions to put a simple oven on the board, but found the power line was more than adequate for what I needed as far as stability, so I abandoned that board.
The case is quarter inch acrylic, which I designed and cut out on a 50W carbon dioxide laser that I have access to. The whole thing is simply glued together, and access and components are mounted with black hex cap screws. It compliments the rest of my tube gear nicely.
I still have a batch of four GC-10B dekatron tubes that I have to do something else with...maybe a clock or some kind of peverse analog indicator... if you have an idea, let me know.
