This is a 24 hour non microcontroller Nixie clock using Z573M tubes. These tubes have the proper looking numeral 5, not the upside down 2. Only Hours and Minutes are displayed, seconds is just a neon lamp flashing at 1 Hz.

This project is just the clock PCB, and requires four (4) Z573M Nixie Modules for the display and that project is here.

Tens of hours does not use a decoder (SN74141) since we are not going to show leading zero for hours tens, just 1 or 2 is used and each of those are driven by a MOSFET.

The clock is powered with a 12 volt DC 2 amp wall adapter, and produces 5 volts for logic. The 5 volts is split. A battery pack (3x AAA) provides backup power to the counters only, and when there is a loss of 12 volts, the counters retain their power and are counting, and the tube drivers (decoders) stop working as well as the nixies themselves until power is restored.

Keep in mind, I made this project for my own use, I have encountered an error on the clock board where the clock does not count as it is designed, BUT I HAVE A WORK AROUND FOR THIS. On the bottom of the board, simply solder a short jumper wire from U5 pin 3 to U2 pin 2 and the clock will run as designed, however, this by passes the time set buttons. When I power the clock the time always reads 1:38 (am) and starts counting from there, so to set the clock, I had to turn the clock on at 1:38 am, a minor inconvenience but worth it for me. If anyone wants to verify/update the schematic, feel free.