Numitron-based tube clocks

Oh dear! NumiQueen is sick!

PowerSupplyOpenThe beloved NumiQueen started to have problems the other day. One minute it was fine, and then the next minute the display faded and then only one digit came on, and dimly. I feared the worst, especially as I have become attached to the large bright display of the IV-13s.

I have other clocks in the same room (which Nixie fan doesn't have an excess of clocks?) but that wasn't the point. It's not about knowing the time: any fool can know the time, it's about knowing the time in style...

I turned the NumiQueen off and on. Many years of using Windows taught me that turning off and on solves most problems, but it didn't solve this one. I turned it off and left it off for an hour, to let any hot components cool off. That also didn't help much. The display would run correctly for a few seconds and then dim out again. 

Clearly this was a sick clock. Jürgen from Nixiekits is in the middle of moving at the moment, and he's not online much to ask questions of, so this is a problem that will have to be solved by yours truly.

TheSweatGotOutAfter doing some investigation, the problem appears to be with the power supply. Looking at the output with a scope, the smoothing is not at all smooth. Sniffing the case of the external power supply confirms the suspicion.

I opened the power supply case and this is what is in there:

 The electrolytic capacitors for the output smoothing have indeed vented. One of them has a vaulted dome on top of it, and the other seems to have just splurged gunk over the board.

The inside of the upper part of the case is also telling. The nasty electrolyte is all over it, and it is very obvious that the capacitors are dead:

The final proof

Extracting the capacitors makes the case totally clear. The power supply is only a couple of months old, but both of the capacitors have failed in the same way. One has bulged the top and the other has vented from the base. Normally this should only happen from older, or over-stressed components.

Or... Ones that are crap.


I have never heard of the manufacturer "CTC", but it seems significant that both of these capacitors failed in the same way at the same time and after only a few weeks of service. Possibly a bad batch of components. Possibly a bad manufaturer.

But the point remains: If you have a NumiQueen and you have problems with the power supply, it could well be this the cause.

Fixing it

Fixing it was easy: Solder in two new electrolytic capacitors of the same value, but with a lower coefficient of crapness, and we are on the road again, Now it just remains to be seen if there is a further problem in the design of the supply, or if it really was just some sub-standard components.


€179 Kit without tubes, including case and power supply, €398 Kit with tubes (+ €5.50 for shipping outside of Germany) 

This is my first Numitron clock, and frankly I'm entirely taken by the elegance and clean lines of the digits presented by Numitron tubes. Probably the whole of the rest of the world already knows about Numitrons, and I'm the last person on earth to discover them, but all the same I'm happy it happened late rather then never.

Numitrons are the seven segment technology from before the time that LEDs became ubiquitous. LEDs were so cheap and robust, and made so few demands on the driving circuitry that they killed everything that came before. This stopped the production of tubes like Numitrons, and nowadays they are becoming increasingly rare and difficult to find. Even rarer are the tubes used in the "NumiQueen", the IV-13 tube, the so called queen of Numitrons. Nixies seem to be still fairly easy to come by in comparison, but Numitrons are the much exotic (and some say more beautiful) cousin. The IV-13's used in the NumiQueen are the largest and most beautiful examples of the already beautiful Numitron.

The technology itself is fairly simple: A filament s driven until it glows red hot in a vacuum, much like an under powered light bulb. Modern filament lamps with a retro look are based on the same idea: A filament glowing warm orange in a vacuum will last for a long time, provided that you run them in the correct way. If you drive them too hard, they can age quickly, and drive them too softly, and they will not glow correctly.

This is the innovation that the NumiQueen brings: The filaments are driven using a regulated constant current driver, meaning that manufacturing tolerances of each filament are rendered insignificant. The problem with driving tube filaments with an unregulated, or even regulated constant voltage driver is that the  circuit will place some filaments under stress because they have a lower resistance, leading to a higher current in that filament and shorter overall tube life. The NumiQueen manages the drive current (not the voltage), and therefore adapts the drive voltage to provide the correct current.

Back in the days of tungsten filament light bulbs, you may remember that they usually broke when the light was first turned on, and this is due to the inrush current at the moment of turning the light on while the filament is cold: tungsten filaments have a positive temperature coefficient, and the initial current drawn when the light turns on is higher than during normal usage, because the filament has not reached operating temperate and its resistance is low. After a few milliseconds, the filament heats up and the current falls. However, the inrush current at the moment of turning on is stressful for the filament. Constant current sources don't have this problem: The current reaches the limit level and the filament has time to heat up without being stressed.

Additionally to the current limiting circuitry, the NumiQueen has another trick up it's sleeve: The filaments are pre-heated with a low current before turning them on fully. This further reduces the stress on the tubes.

 The NumiQueen does everything possible to preserve the life of these valuable and rare Numitrons. Just because so much emphasis has been given to this doesn't mean that you should worry too much about the life of the tubes: They have a rated life of 50,000 hours, which is about 6 years in constant use. The NumiQueen is clearly trying to extend this already long life by treating them as gently as possible.

I bought the tubes for about $30 dollars each, as the kit came without tubes (there is a kit option including tubes, but I preferred to source them myself), but had to look around to find someone able to sell me the tubes. If this is too much trouble for you, Jürgen at NixieKits can supply the kit with tubes, which means that you'll have an easier time of it.

Brian used to do a size comparison with a standard "Diet Coke" can, but for two reasons that standard device is going to have to be changed. First of all, I don't drink that crap, and secondly the cans where I live are a different size and shape to the ones that used to be used. Perhaps Brian can ship me the standard can that he's been using. I promise I'll only use it for the size comparison and I promise won't drink it. (That was not hard to promise). In the mean time, we'll just have to find another size comparison object.


The Clock itself

Here we see the clock built from the parts I received in the kit. As I said, I sourced my own IV-13 tubes. You can see the tiny filigree filaments that there are inside, arranged as a standard seven segment display. There is also a decimal point which you can see on the last digit. Each clock also has a serial number, which you can see on the bottom

The acrylic case is a nice touch as well. It allows you to finish the clock to be something that you can proudly show to others, without having to wait for a case or build one yourself. You can easily build this clock in an evening, right up to and including the case.

There is also a power supply in the kit package, with a plug suited to your country available by selecting the appropriate option on the NixieKits site. I chose the back lights that randomly change colour, so you can see that it looks a bit like a circus, but there are other, more sober options also available when you order.

Another feature that you can just make out in this light is the filament pre-heating. You can see the faint glow of the filaments which are not lit up. This is the controller making sure that they are ready to go without the risk of giving them a thermal shock. This is a great feature and really shows the attention to detail.


Kit Construction

There is a separate article about the process of constructing the kit. However it suffices to say that the construction is not particularly difficult, and no special tools are required. Construction time is about 3 hours if you are moderately experienced.

The kit comes complete with a power adapter and a neat and tidy acrylic case, which is a nice touch, meaning that you will have a presentable clock right away at the at the end of the build, which is highly satisfying.



The NumiQueen offers a fairly standard set of features for a tube clock, and if you have previous experience of either a PV Electronics or a NixieKits clock, you will find no surprises here. The NumiQueen is a totally faithful translation of Nixie clock features into a Numitron clock. Normally the features of this firmware doesn't really excite me very much, but along with the Numitrons, it works very well. The Numitrons themselves become the talking point of this clock, not the stunts that the firmware can do.

There are all the normal features you would expect:

  • 12/24 hour time mode
  • A variety of date formats
  • Battery (supercap) backed up real time clock
  • Configurable "night mode" (auto dimming or blanking of the tubes during the hours you have configured as being at night)
  • Configurable day blanking (auto blanking of the tubes on certain days)
  • Very flexible DST configuration
  • Quick change between DST on and off with a specialized button
  • Many different options for using an external time provider module (DCF/MSF/WWVB, GPS or NWTS)
  • Alarm with configurable snooze
  • Temperature display and detector.

The clock has 4 buttons on it, meaning that setting is quite straight forward and logical. One of the buttons is used for turning DST on and off, another is used for managing the alarm, and the last two are used for setting the clock up.

I set up the clock to use an NWTS, and this was really quite easy.  Set option 12 to "4" (GPS module) and option 13 to "1" (9600 baud) and that was it. The unit acquired the time right away. I did have to play with the DST settings for a few minutes to make them right, with option 14 set to "0" no hours difference and option 16 set to "1" (add the hours). 


The Numitrons

I was impressed by the brightness and elegance of the Numitron tubes. It's the first time I have seen them in real life, and it is a learning experience with them. They fit tightly into the sockets on the board, and putting them in for the first time was quite stressful: The new sockets are tight, and the tubes look so fragile. By a process of "wiggling" them in, they fit snugly against the case and all work perfectly. The sockets are really nice, high quality items, but you need to spend some time getting them aligned on the board so that the tubes stand up straight.

In use, they emit some heat: This was worrying at first to someone more used to Nixie tubes, which tend to stay more or less cold, even after hours of use. However, this is normal, and they didn't get so warm that it really worried me. It wasn't clar how much of the heat came from the tubes themselves, and how much came from the driver circuitry.


Time Keeping

The time keeping of the clock is of course excellent, especially with the addition of the nwts which is already in my collection, and which seems to work with pretty much everything. The time seems to be consistently up to 1 second out, but the time drift does not get worse over time when using the nwts unit. 

Changing from and to DST is easy to do because there is a button and an indicator for it, but there must be a better way to achieve this in 2017. It seems somehow a bit perverse that a high tech time keeping device needs a human to intervene to tell it the time. Admittedly, it's definitely a first world sort of problem, but really? DST rules are being largely simplified, and we're not dealing with a space shot, so a second here or there is not going to kill anyone, but there must be a better way than this.



The NumiQueen is a great product. It is well presented, not that hard to build, gives a really professional looking result, right down to the case. The Numitrons are a bit hard to find, and moderately expensive (but not as expensive as large tubes), but any troubles finding them, and Jürgen can supply the tubes with the kit.

Do I like the NumiQueen? Well I guess that this is already clear: It is my favourite clock of the moment.

Would I recommend to buy it? Yes, if you are looking for something a bit different from the more of less run of the mill Nixie experience, then the NumiQueen is a great answer to that. It's a bit expensive, but it gives a result that is out of the ordinary.


We're waiting for the NumiQueen to arrive from, and will be doing a full build and video review on it in the new year!


Here's a video of the NumiQueen from Jürgen at




You get what you pay for!

That's the lasting impression when working with this clock. It's not very cheap, but there seems to be no corner cut, or compromise made. It's worth every penny you paid, and you'll end up thinking it's probably worth more than you paid.

NumiQueen BoxFrom the moment of receiving the box (you have to sign for it, it is sent via tracked post), the impression is good. "That's a big box" for a clock kit, but when you open it up, all the surprise of receiving such a big box dissolves. The box is big because it contains lots, and it's beautifully packed, well padded and full of electronic and retro goodies. One thing to note is that the IV-13 Numitron tubes are not included in the kit I received, and you'll have to shop around for them.

A power supply is provided, with the appropriate plug for the county the package is sent to. That's a nice touch, and shows that care and attention has gone into every aspect of the clock presentation. The power supply is not some cheap no name brand. It's heavy, chunky and clearly a quality unit, with certifications on the rear side. The difference between this supply and some other supplies is that the certifications are real.

Inside the box 

NumiQueen Kit ContentsThe impression of quality remains when you open up the box. There is a case included in the kit, and it looks nicely made, and includes all of the hardware needed, right down to the rubber feet. All the ICs are provided with sockets, as well as ceramic sockets for the tubes.

The number of components is not particularly high, and while the instructions say that this is a kit build for the experienced electronics enthusiast, the level of skill needed does not seem all that high. Nearly all of the components are "through hole" (which means they are easier to handle and mount for the average hobbyist, because they don't need special tools. There are two large format surface mount devices, but neither these are a problem to mount without special tools. Tweezers help, but are by no means an absolute necessity.

The Assembly Manual

The instruction manual is available online and this is an area that could do with a little more explanation for clock constructors without much experience. To be fair, Jürgen does aim this kit at people with a fair level of experience, but addition of a few more words in the manual would lower the experience bar a good deal. The assembly instructions are correct, but a little short in places. If you have plenty of experience, you will sail through the assembly, but if you are quite new to constructing clocks, you might find it a little confusing or vague in places. If you can read the schematic, you'll be just fine.

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