Everybody loves Nixie tubes.

I came across those lovely tubes last month...

IN-12A Nixie tubes... You can still see a "CCCP" logo. Gotta love old Soviet surplus.

Those things are pretty cool: they're the ancestors of the modern 7-digit display, and they give a nice and warm light! People now build blocks out of those, I just wanted to see what they're like, and maybe use them for something else one day (who nows, maybe another watch?).
So I bought four IN-12A off eBay, and built a small power supply for them.
I just wanted to light them up, nothing using a complex microcontroller control...

The power supply. I uses 5V AC, and turns it into 180V.

Inside view. Nothing really complicated, just a backwards wired transformer, capacitor, along with a few other things.

I used a case from an old 220 to 110V transformer that burnt out. The plug you see there is wired with a 4K7 resistor to discharge the capacitor when not in use... You don't want to get a 180V shock from this...

The schematic... As I said, I wanted something quick and easy to build :)

I just love that sweet glow!

Along with that, I built a small "tester box" that plugs directly into the power supply, and has a socket to correctly test the tubes... It has a rotating switch to toggle between each digit and a potentiometer to regulate the current going through the Nixie. 

Nixie tube tester... The switch you can see on the left side of the box selects the different digits... Because it's a 5-pos, I had to use another switch to toggle between digit 1-5 and 6-0.