With this post I will continue to unveil myths about nixie tubes, and answer your questions. Feel free to add new questions in comments. Thank you for taking time. David.

Hey everyone! I’m working with this Nixie tube clock and there’s one question I have. Many people on the internet say nixie tubes don’t live longer than a year. Does anyone know how to extend their life?

Maybe I could use a mosfet to change the voltage via PWM, will it result in a lower average voltage? I’m using the IN-14 tubes and I’m thinking of 170VDC and 3mA.

Dmitry answered:

Well, once I repaired IN-1 nixie tubes with a low-voltage power supply. The problem with the first tube was that two numerals were shorted together. For example, when 6 was powered, 1 illuminated as well. I used my ohmmeter and there were 5-10 ohms between the numerals. I thought that there was a tiny metal whisker between these numerals so I applied a low-voltage and slowly increased the current until I saw a glow. That whisker vaporized somewhere between 100 and 300 mA. So far, so good — all tubes work properly.

The other two tubes had problems with the “1” numeral. The thing was that the cathode from the “1” numeral was shorted to the anode. In this case, I had to take more current (400-1200 mA). Everything works great now.

How long will they work? Will they fail again? That’s the question. I’ve read that the ionization voltage may increase with time, so using a larger dropping resistor with a higher supply voltage seems to be a solution (the resistor will keep the current the same).

If you keep the current at the nominal rating, it will certainly result in less age degradation than when running above the maximum current. However, some tubes are more reliable than others. I have two 6-digit clocks with Burroughs 5092 tubes, and none of these tubes failed after a year of operation. There are 50 years old tubes that still work perfectly. On the other hand, I’ve got a clock with IN-1 tubes, and six tubes out of fifteen failed after a month of testing.

David answered:

IN-14 are good. These tubes are mercury doped so they are positioned as “long-life” tubes. If you see the violet tinge, that’s a tell-tale signal. I’ve never had any problems with IN-14.

Even those IN-1 which are not doped can work great, but you’ll have to be more careful with them. If you want to increase their life I suggest that you turn the digits off, when not in use, and use PWM for proper dimming. I have three IN-1 clocks that work non-stop, and only one tube out of 18 failed in the last two years. Multiplexing tubes also might help.