My retro digital clock has developed a fault after running continuously for over seven or more years. The problem started with the minutes Nixie tube that displayed a faint 1 when 5 was on. As a quick fix I swapped it with the hours decade so the 5 was not used and it’s been fine for several months.
But now it just glows at the base when trying to display 1. As you can see from the pictures it looks rather sad.
Nixie clock with faulty decade hour indicator
Close up showing glow at base of Nixie tube
A quick Google search reveals this is not an uncommon failure for these OTK IN-8 tubes. With a date code of December ’92, they are nearly 25 years old and probably used stock when I bought the clock.
I tried measuring the resistance between all pins and found a low reading of 1.4kΩ between pins 1 and 5 (cathodes for 1 and 5 digits). Expectation was an infinite resistance at the low voltage from my multimeter. Several taps of the tube on a craft mat removed the reading but the fault remained. Strangely no low resistance was found between any other pins (pin 11 is the common anode). So the fault must lie within the tube – possibly a faulty cathode connection to the wire 1 digit. All the remaining digits work with the addition of a small dot at the base of the 5 which could be a fine piece of wire filament.
Now to find a replacement. The Nixie tubes fitted to my clock have pins making it easy to replace a tube just like a valve. There are several eBay suppliers based in the Russian federation or Ukraine but most sell the wired versions and sets of six for a whole clock at around £50 with shipping. A bit steep for one tube that may arrive broken…
Maybe I’ll wait and hope to find a local source – if you know of supplier or have one to sell please let me know 🙂
Update: Spare tube ordered and arrived from Ukraine in just over a week and it’s working again. As expected new old stock with date code ’83 and seems fine.
21/01/2025 at 10:17 am
Hi. Just Googled and found this post. A similar think happened to me with a different tube. It developed a short between digits 1 and 6. There was a dead short between the pins. I blew this away using a power supply set to only 250mA (10V). Tube is back working again!
21/01/2025 at 2:52 pm
Hi Graeme, thanks for sharing this tip and glad to hear your tube’s fixed. Hope it helps others with similar Nixie tube faults. It didn’t occur to me at the time to try applying current to fuse the debris away. Mine was a bit higher resistance, not a dead short, so I tapped the tube hoping to dislodge it and it must have moved to another area. Unfortunately it still refused to work. I’ve had some success using your approach on AF117 series transistors that suffer from the lead filament ‘cat’s whisker’ problem. see Bush Transistor Radio TR132 Repair and Revival
26/01/2025 at 3:25 pm
Where can i find these clocks
03/02/2025 at 4:25 pm
Nixie clocks with real neon Nixie tubes are very rare. You can find imitations that use IPS LCD displays to simulate the Nixie tube on Amazon and other online sites – don’t be fooled though. If you want the real thing, it’s best to search for specialist suppliers such as https://www.pvelectronics.co.uk or keep a look out on auction sites such as eBay for preloved clocks. Again don’t be fooled by kits that you have to build yourself and don’t come with the tubes unless that’s what you’re looking for!