This machine is not finished but far enough along to show some basic operations and the massive amount of hefty components used in its construction. Lots of tubes and transformers!
It is rather long and boorish as well as not even having all the neon digits attached and operating but the solution displays are functional. The input numbers are entered on the slide switches.
The gate logic was all done with pentodes. Its a big ole wiring mess as it is point to point wired on the underside of the sockets.
The large tubes on the back are the power rectifier and VR regulator. The display segments were decoded using 6D6A-V Diodes, which are small vacuum tube diodes I got from Russia. They are jumpered across the seven segments lighting each segment required for that digit.
Here is a photo:
They are used just like a conventional diodes except you have to supply filament voltage. One of the large power transformers mounted to the side of this machine feeds these the filament voltage required.
To decode the digit 0 for example you would need 6 diodes-segments a-f all get a diode jumpered to form the digit(all except the center segment g). To decode all digits from 0-9 requires more than 30. One good thing about these tubes is they can be laid flat against the pcb to reduce space and ease layout for connections. This uses more pcb space but in this type of vintage construction space is going to get used anyway! They have nice long flexible leads. 2 are for filament and then the anode and cathode.
Here is an example I made for using solid state diodes to decode the display:
After the decoding diode are connected you end up with a ten connection devise just like a conventional nixies.