What I had been looking for was a way to easily deal with multiple nixie tube digits in various projects that I was working on. I really wanted an easy way to connect many digits together with minimum digit spacing, and have the digits controlled by a simple serial interface. You'll find all the schematics and board layouts are available through the links in this instructable, released under a creative commons license.
Voila, the nixie tube board that I came up with supports two IN-12A type nixie tubes via two printed circuit mounting phenolic sockets. The nixie tube board is designed to be supported by a nixie driver board below it, which permits a microcontroller ( Arduino, etc.) to address the two nixie tube digits, and via a shift register chain, multiple pairs of nixie tube digits. The edge connecting header pins easily allow the multiple digits to be physically connected and may be powered by an external high voltage supply. This densely packed configuration permits minimum digit spacing while threading power and serial data connections to all elements.
Step 1: Parts List
Step 2: Board Layout
The nixie tube boards can be assembled in less than half an hour. Note carefully to orient the nixie tube printed circuit board with the component side up. This is the side that will receive the two nixie tube sockets. The reverse side of the board receives the two 12-pin male headers. Also notice that there is an indent indicating pin 1 on each of the nixie tube sockets. This pin 1 corresponds to each pin 1 marked on the printed circuit board. Although the orientation of each socket has no effect on their function, this indent is present for reference, and allows you to quickly orient the nixie tubes.