Fading out IN-16

[padler...@gmail.com]

Hi all,
I just built a 6-digit nixie clock using NOS IN-16 tubes. The clock was working fine for about a day but then suddenly one of tubes went dark, except for the right hand decimal which is used as a status indicator. When the clock is power cycled, the errant tube comes back to life for maybe 30-40 seconds and then fades out again. It’s in the seconds position so I can see it sequence through each digit before it fades out. When I swap it into another position on the clock, the problem follows the tube. I’ve replaced it with another NOS tube and the clock is working fine again.

Does anyone have any thoughts on why tube would come to life for a short period of time when power cycled and then fade out?

Thanks,
Randy

[Nicholas Stock]

IN-16 tubes are the worst... I gave up making clocks with them as the failure rate was so high (maybe I had a bad batch?).

Tis odd that it keeps coming back to life on a power cycle though.... sounds like it could be thermally related?

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[padler...@gmail.com]

Huh… I’m surprised to hear that Nick! I have another clock I made using used IN-16s and it’s been going strong for about 8 months now. Granted that’s not a long time in the big scheme of things, but I figured since they appear to have that same mercury amulet as the IN-14s they would last.  I did have one of the used IN-16s go dead suddenly a while back, so to your point, maybe I just haven’t had as much experience with them as you have to better see their failure rate. 

That one went dead shortly after I built the clock and it had relatively short leads — maybe 4mm or so — so I thought perhaps I may have stressed one of them when installing it in the clock and caused the gas leak out (although I could see no signs of distress where any of the leads entered the tube). 

But this current tube was NOS.  It’s just strange how it lights up on power cycle and then fades out. But I don’t see how it could be a thermal issue.  

On Jun 6, 2025, at 2:20 PM, Nicholas Stock <nick...@gmail.com> wrote:



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[Nicholas Stock]

My experience was a high rate of failure through leaks... the digits would start to glow with a brighter pink intensity and then die....

Even though they're 'cold cathode' tubes, they do generate some heat.... maybe after 40 seconds or so, thermal expansion of one of the anodes shorts something out? Grasping at straws here...

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[Jeff Walton]

I’ve also experienced a higher failure rate on the IN16 tubes.  Definitely a leakage issue on all of the failures.  I haven’t seen the bright pink phenomena but partial digits from the bottom up is what I have experienced. 

 

I have a PV clock that uses them and after multiple replacements of tubes, the PCB is in tough shape to the point, I may not be able to make any more successful replacements if another goes out.  Unfortunately, PV does not offer the kit anymore.  My notes are that it has had 7 new tubes since it was put into operation in May 2016.

 

In the future, if I ever built another IN-16 clock, I would not use the spacer/lead separator that comes with the tube.  They make tube replacement very difficult.  I prefer to chop the leads from the tube and then de-solder one at a time, which can’t really be done with the spacers in place.  On my particular clock, there is also a baselight LED to remove and the PCB did not play well with the heat gun for doing a removal all at once. 

 

Jeff

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[gregebert]

IN-1 gets my vote for the worst nixie tube. If you want a truly outstanding Soviet-era tube, the IN-18 is the crown jewel.

[padler...@gmail.com]

Fortunately I build my IN-16 and IN-14 clocks using milled socket pins for the tubes.  The little buggers ain’t cheap and they add a few $$ to the cost of the clock, but they make replacing the tubes a breeze. It’s a little fiddly inserting the leads into the pins, but once you do a couple and get the hang of it, it’s pretty simple. I cut the leads to 5mm and preform the tips so they point straight down which makes it easier to insert them into the sockets.  Also, for the IN-16s, I use the footprint diameter of the IN-14s which is wider and gives the tubes a bit more stability and also allows enough room for a neopixle LED under it. Obviously you need to remove the spacer from the tubes for the under lighting to be effective. 

Randy

On Jun 6, 2025, at 4:10 PM, Jeff Walton <jwalt...@gmail.com> wrote:



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[dudu sa]

I'm guessing it's because you soldered it for a longer period of time when you soldered it. When heat is transferred to the sealing joint between the glass and the wire, the wire expands with the heat, causing the glass to rise apart generating tiny cracks. 

To reduce the probability of failure, you can take the following measures:

 1. Don't leave the IN16 pin too short, which can reduce the heat transfer to the sealing 

2. don't solder at too high a temperature, 

3. don't solder for too long.
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