After the board had been running smoke-free 😉 for a while I cranked up the HT to 200V and the nixies brightened up. One of the 5 nixies turned out to be dead (gas leaked out?) so I have no spare if any of the 4 fail. Perhaps I could plug the symbol nixie into the 10 hours position for a weird display, which is acceptable as my other clocks are weird too. 🤣
In the photo you see a drawback of nixies, i.e. the digits are not in the same plane; the 5 is noticeably further back than the 1 in front. So nixies need to be viewed face on.
Another thing I noticed was some digits were not fully-formed, part of the cathode wouldn't glow. Still readable though. I swapped the nixies around so that the deficient ones would be in less important positions. I put the nixie with a deficient 8 in the 10 minute position which will never show 6-9. I put the nixie with the deficient 0 in the 10 hours position. In this workaround I sleep in until after 10 so that I don't see the 0. 🤣
A bit of searching for information about nixie wear found a post where it was suggested that nixies that have been out of action for a long time need to be "exercised" and the cathodes will heal. I hope that is the case. I won't try those remedies that suggest overdriving the nixie for a while. In my spare time I might research deeper out of curiosity. Anyway there is nothing I can do, short of paying too much for replacements. They work as well as I can expect. I just wish the case wasn't so big.
Here you see the two extra boards added to the main board. On the left is the matchbox size 12V to 200V boost converter and the larger board is the #3 line to 32 line output expander. Hmm, I should clean it up a bit with isopropanol. The main board is now just a carrier for nixies, the rest of the circuitry on it is not connected, save through GND, and not powered. 12V from a standard SMPS adaptor powers the unit, and the MCU board is at the back of the case so that the set buttons are accessible.
So that's it then, I can have my bench space back. Closing the case now. 🤣