Nixie-based tube clocks




Meet the B-7971 Nixie Shoutbox.  You may be wondering what exactly a "shout box" is. The term has fallen out of favor these days, but when I built the Shoutbox in 2007, it was well known. Just about every Wordpress blog on the Internet at the time had some sort of Shoutbox - sometimes called Tagbox - widget installed. The widgets allowed visitors to post short text messages - "shout outs" or "tags" - on the sidebar of the blog page, often anonymously without having to register. Shoutboxes on blogs are pretty much extinct today. I don't know exactly what brought about their demise but I suspect that their open and anonymous nature led to more abuse issues than blog owners cared to deal with.

The idea for the Nixie Shoutbox came from the convergence of several of my interests at the time. Do it yourself video streaming was becoming practical and I was involved in the development of some early home security video streaming software. I had been interested in Nixie tubes when I was a teenager and had even done a few little projects with the then-cheap B-7971 tubes. After that I'd pretty much forgotten about Nixies until years later when I happened to run across a site selling Chronotronix (now Nocrotec) Nixie clocks.

Testing B-7971sWe're talking about this B-7971, not the other one, which is a Chinese workhorse Boeing, which shuttles between Chengdu, Urumqi and Tianjin. Back in the day (in 1977), those B-7971 tubes cost 50 cents (US) each as surplus.

The Shoutbox idea really came together when I stumbled across something called The People's Cam on a site called There was a streaming webcam pointed at a CRT monitor. On the monitor was the old Flying Text screen saver à la Windows 98. Visitors could type a short message and see it appear on the screen saver. I decided to try to make my own version of the People's Cam using alphanumeric Nixies. 16 tubes sounded like a good size to shoot for, and also - since at the time I intended to control it with a PLC - 16 nicely matched the number of outputs per PLC output module. 8 tubes probably would have been adequate but I felt like why not go big "because I can".

In the mid-2000s I started gradually acquiring B-7971s as they turned up for sale online. Of course the price of the tubes had gone up drastically since the good old days. I accumulated my tubes from various sources at prices ranging from $35 to $65 per tube. Most of my tubes were bought from EBay sellers in the USA and Western Europe. The Russians never cloned this tube so they weren't available from the "usual suspects".


The Nixie Shoutbox is born

I built the Shoutbox over the course of several months, working on it part time. I had the circuit boards fabricated from my design files, and I had the glass top of the case manufactured by people who know how to work with glass, but aside from that I made everything myself. I programmed the original controller, which was an Allen-Bradly PLC-5. Running a Nixie Shoutbox is a rather unconventional application for a PLC, but it was a case of going with what I knew best at the time. Several years later I replaced the PLC with an Atmel microcontroller programmed in C. A series of construction photos can be found at


Once the Shoutbox was built and tested I registered a domain, made a web page for it, pointed a camera at it and in 2008 I opened it up to the public. The web page allowed visitors to view the webcam stream and post text on the Nixie tubes. The software handled message queueing which made it possible for multiple visitors to post at the same time and hold conversations. I had created, in effect, a Nixie chat room. I decided to allow people to post anonymously with no registration required and see what would happen.


"Everything that does not kill you makes you stronger"

Well hello, 4chan!There wasn't much site traffic at first but eventually the word got out. My site was being discussed on Something Awful, Reddit, even 4chan, and the denizens of those sites came in droves. Messages were scrolling across the tubes day and night, mostly people spouting memes or insulting one another - typical Internet stuff. At one point I added some controls on the page that let visitors turn certain lights in the room on and off, so of course I then had strobing lights in my living room as visitors battled each other over whether the lights should be off or on. Naturally numerous visitors tried to break it so I was kept busy modifying code in the usual arms race to plug loopholes faster than the users could discover them.

Inviting the Internet into my living room like that was fun for quite a while but eventually it became tiresome. The site had grown to include multiple camera streams and it seemed like every day some camera or cable or capture card would fail and need attention. The traffic would get so heavy at times that all my upstream bandwidth was being consumed by video stream and I could barely use my own Internet connection. Remember, this was 2008 and 1Mbit upstream was considered awesome on a home connection.


The Shoutbox made a comeback - just for you guys

Finally after several years of running the Shoutbox site and basically having 4chan hanging out in my living room I got tired of it all and shut the site down. For this article I have brought the core feature of the site - the Shoutbox - back online for a limited time. Unforunately, that time is now past. I got sick of stumbling over wires draped through my living room, and while it is certainly nice to see old friends, the enjoyment is somewhat limited if that friend never sleeps, drops around at 3 in the morning to flick the lights on and off a few times, says a few profanities or non-sequiturs and then leaves without saying "thank you" or "excuse me".


To give you a little idea of how the Shoutbox was when it was still public, here is a short video of a screen capture of a couple of people playing around on it. For some reason I had the spotlights turned off that day. Probably they were just getting on my nerves a bit too much that day.



Some details for the technically curious


Transformers in their cageThe electronics can be roughly divided into four sections: power, interface, control and tube drivers. The power section is split between the right and left metal-mesh "cages". In the right side cage are power transformers, a fuse and the connector for the mains cord. The smaller transformer steps the 120VAC mains down to 9VAC which is fed over to the left side cage where it is rectified, filtered and regulated to provide 5VDC for all the logic. The large transformer is a 1:1 isolation transformer: both its primary and secondary are 120VAC. While not strictly necessary this transformer isolates the 120VAC from earth ground, which greatly reduces the risk of spectacular smoke and sparks when probing around the circuitry with a grounded oscilloscope probe. It also decreases the odds of finger-poking onlookers getting a nasty shock, no matter how much they may deserve one.


Interface board in cageThe isolated 120VAC is fed over to the left side cage where it is rectified and then filtered by a couple of rather massive capacitors. This is how I obtain the high voltage needed to light the Nixie tubes. When 120V RMS is rectified and filtered the resulting voltage is 120 * √2 = 169VDC, which is perfect for Nixies. As long as the mains voltage is at least somewhat stable - and it is - this rather crudely derived high voltage is quite adequate for the application. Since someone is sure to wonder why I didn't use a boost converter instead, I will explain. With all 16 tubes lit the high voltage demand is 350mA. That's 60 watts of power. In 2007 I could not just go out and buy a 170V 60W boost converter and I'm not so sure I could even do that now in 2019. I did look into making my own boost circuit but quickly decided that SMPS design was well outside my skill set.


A PLC-5The rectifiers, 5V regulator and all filter capacitors are located in the left side cage on what I'll call the interface board. Also on the interface board are several connectors and some pull-up resistors. The Phoenix Euro-connectors along the rear edge of the board were originally for plugging in cables that ran to the original controller - a PLC with 2 16-bit output modules and an Ethernet "sidecar" module that sat on a shelf below the Shoutbox. The PLC output modules provided TTL open collector outputs, hence the need for the pull-up resistors.


The present controller, made in 2011, is based around a "naked" (non-Arduino) ATMega 328P microcontroller. Four 74HC595s function as an I/O expanders to give me the needed 32 outputs from 3 GPIO pins. More about that in a minute. A gadget called a Wiz110SR interfaces the ATMega's UART to Ethernet. It isn't a "real" network adapter but it's good enough for this application. It appears as a virtual serial port to PCs on the network. Aside from that there isn't much else on the controller board except a piezo beeper, a backup battery, a header to connect some buttons for setting the time, and Phoenix Euro-connectors along the rear edge of the board that mirror the connectors on the interface board. The controller board is designed to sit on top of the interface board. The boards are connected together with a sort of wiring harness as shown in the photo. It's not terribly elegant but it works!Microcontroller board


The tube driver boards handle high voltage switching to all the tubes' cathodes with a whole lot of MPSA42 high voltage transistors. Additionally each tube board has 4 74373 8-bit latches configured as 2 16-bit latches. If I was doing it over today I'd probably use the more modern Supertex SIPO/latch/HV-driver combination chips instead of TTL latches and transistors, but in 2007 I did not know they existed. Encoding of characters into segment patterns is handled by the ATMega, not the tube driver boards. The tube boards are perhaps better called "buffer/driver boards", because they primarily latch and buffer data.



A tube boardThe ribbon cable that connects all 16 tube boards together and to the controller carries 15 Data lines that correspond to the 15 segments of the tubes, 16 Select lines that correspond to the 16 tubes, and one Go line that connects to the strobe pin of certain latches on each tube board. This sounds a bit like multiplexing but the display is NOT actually multiplexed - only the data is. This is why there are 2 sets of 16-bit latches on each board. One set of latches on every board, which I will call the "back" latches, listens to the 15 Data lines with its parallel data input pins. Each board's back latch's strobe pin is connected to one of the Select lines. A jumper on the board determines which Select line the board connects to: tube board 1 to Select line 1, tube board 2 to Select line 2, and so on. To update the display the controller will output the segment pattern for tube 1 and then fire Select line 1, which strobes the 15 bits of segment data for tube 1 into the board 1's back latch. Then it sets up the data for tube 2 and fires Select line 2, and continues the process all the way to tube 16.


Tube boards pluralAt this point the back latches are filled with the new data but it isn't being displayed on the tubes yet. The tubes display the data that is stored in the second set of latches, which I'll call the "front" latches. This is where the Go line comes into play. Once the back latches are filled the controller will fire the Go line, which causes the data in all 16 tubes' back latches to be copied synchronously to the front latches and displayed. This way all tubes update simultaneously. Thus I get the signal count benefit of multiplexing (32 lines instead of an impossible 256 lines) without the flickering of multiplexing. For a device that was designed specifically to be on camera, multiplex flicker would have been totally unacceptable.


 And that's basically it. To answer a few common questions: Yes, I do have a stash of spare B-78971s. No, I don't want to sell any, at least not at 2019 prices. No, I've never needed to tap into my stash. The Shoutbox has been running 24/7/365 for about 11-1/2 years now with no tube failures.



It's time to review one of the most popular Nixie kits around. The Spectrum from PV Electronics is one of the standards of Nixie Kit builders since it was launched. It supports large tubes, and in this review we're using IN-18 tubes, which are still quite easily available, but which are starting to reach quite high prices. Expect to pay around $50 per tube for them, so that means a clock with IN-18 tubes will set you back around $400 before you have a case. I paid around £85 for the kit, so that's a bit over $100 dollars at the current exchange rate. Cases are available, but I didn't get one. I probably still will, but that's a thing for another day.

I have never looked at the Spectrum 18 before getting the kit to review it. I was aware that it is large format tube clock, the PCB measures 280mm x 80mm, but had not looked at the circuitry in detail. The package arrived quickly, but slightly damaged. Fortunately, the contents of the package was not affected by the damage to the packaging.

The PCB appears to be of high quality, with gold-plated pads and matt back solder mask. Before starting, I did a quick check I found several problems. Contacted Pete and told him about this, and he immediately replaced the PCB free of charge, and no questions asked. That's service!

The build manual is excellent, with plenty of clear illustrations and explanations. It is clearly laid out and takes you step by step through the build. I intend to more or less blindly follow the manual for this build. Scanning what there is to be done, it does not seem a challenging kit at all. All the tricky parts seem to have been dealt with (for example, the high voltage power supply comes already assembled). Things like pull up resistors for the back light LEDs are supplied as 9-pin SIL resistor network arrays, so also they are easy to install.

With this review, I'll also take you through a couple of "gotchas" that you should avoid doing. I'm building it so that you can learn from my mistakes.


Talking to Pete about the design decisions he made assures me that this is a clock intended for a long life. First of all, the tubes are already long-life doped tubes, secondly, the IN-18 tube seems to appreciate being used in a "direct-drive" clock. This means that the tubes are not rapidly multiplexed (switched on and off), and instead each digit element is supplied with a constant voltage, but at a lower current. Multiplexed clocks, although simpler, drive one tube at a time, and to achieve the brightness, each tube must be supplied with more instantaneous current. The average current remains the same, but the dreaded blue dot can appear in cases where the drive current is not exactly right.

Also the fact that tubes are socketed shows that this is a maintainable, high quality clock. One word of warning here though: Even if the tubes are socketed, refrain as much as possible from plugging and unplugging the tubes: the tubes are fragile, and the strain put on the pins during insertion and removal can cause out-gassing, which means the end of the tube. You should unplug and replug tubes only for valid reasons, such as replacing a damaged tube for good.

The High Voltage generator board is a separate board for the simple reason that if any part of the electronics needs replacing, it will be this part. The high voltage generator circuit gets hot and each time there is heat, the life of an electronic component is reduced. The rest of the circuitry is not under strain at all, and can be expected to last indefinitely. Having said this, even the HV board almost never fails, but if it does, it is a 2 minute job to change it.

Tube Holders & Resistor Networks (section 4.1 - 4.3)

The tube holders are acrylic mounting boards which diffuse the light of the RGB LED underneath the tube and also serve to hold the pins in place. Taking the covering off the acrylic can be a bit tricky, but rubbing the foil hard with a thumb can cause it to release easily. There is only one thing you have to be careful about with the tube holders, and that is to make sure you insert the pins from the right side and with the pin jaws pushed into the acrylic first.

Some of the holes are too big to take the pins, and this is intended. Not all of the pins on the IN-18 need to be used, and the larger holes are to remind you that the pin does not need to go in that hole.

Next you have to put the resistor networks onto the board. Make sure you do this from the bottom side of the board! If you do it from the top side of the board, the resistor network packages foul the tube holders and it gives an ugly result. In general, look for the silk screen marking that should guide you which side to mount components from. In this case, the silk screen rectangle is on the bottom side of the board.

The long SIL (Single In Line) packages for the resistor networks are not polarised, so you can put them in either way round.

Next you can put the tube holders onto the board. These should be mounted from the other side to the resistor networks, so, from the top of the board. The "notch" in the acrylic holder has to go near where the RGB LEDs pins go,

Low Voltage Supply (Section 4.4 . 4.5)

The low voltage power supply is a run of the mill buck regulator circuit using an LM2576. This has the advantage that it does not dissipate a lot of energy, and therefore increases the efficiency of the clock. The circuit is extremely straightforward and is taken almost directly from the data sheet:

 Spectrum LV Circui tFrom Data Sheet

 The only modification is that the input and output smoothing capacitors have slightly different values, and the Schottky diode is a generic 1N5819 instead of the 1N5822.

The capacitors and the regulator are laid down to reduce the profile of the board. You have to be careful to mount the capacitors with the correct polarity: make sure that the white stripe on the capacitor matches the markings on the board.

 The inductance and the socket are mounted on the bottom of the board.

Testing the low voltage circuit is easy. Power on the board, by connecting the power and check that nothing gets hot. After a few seconds if nothing gets hot, you can test the voltage at the test points on the top of the board. The test points are conveniently located on the top of the board, and are clearly marked.


High Voltage Supply (section 4.6 - 4.7)

The high voltage supply is usually the hardest part of a clock to build, but PV Electronics has taken a good route for the Spectrum: Instead of having individual components on the board to make the high voltage generator, the high voltage is generated by a pre-built and tested module. From one point of view, I think this is a clever move. If any part of the clock is going to wear out, it is going to be the high voltage generator: it gets hot and does a tough task, and for sure doing it this way means that there are less support calls. On the other hand I feel that part of the fun has been taken away. I'm sure it is not the general feeling that people will have.

The high voltage generation is therefore much easier to build than on a traditional clock. It only takes a few minutes, and if I understand the circuit correctly, the controller only needs to be installed to turn the generator on via he module's "enable" line. 

Tube Drive Circuit (section 4.8)

The tube drive circuit is made up of two HV5622 specialised controller ICs, which are purpose designed for driving high voltage circuits. The are 32 bit shift registers, with 32 output drivers capable of easily driving Nixies. They are quite easy to control, and in total there are 64 outputs. These are arranged as 6 x 10 outputs (for the tube cathodes) plus 2 x 2 further high voltage drivers for the separator neons.

The HV5622 appears to be running out of specification: The data sheet says that the supply voltage should be 10.8V - 13.2V, of course meaning that 12V is the ideal voltage, but in the Spectrum, it is being run at 5V. This rather neatly gets around a interfacing problem with the logic levels that the PIC controller can supply. If you had the HV5622 running from 12V, normally the defined logic levels should be that LOW is less than 2V, and HIGH is greater than 10V (which is vcc - 2V). Running the 5622 out of spec, makes the login interfacing easy, but it is outppf spec. I suppose here that he PIC can't drive the 5622 at anything near the 8MHz data rate, and this makes the combination reliable at 5V.

The only other point to note is that the sockets for the PLCC packages have to be put in the right way round, with the notch on the socket matching the notch marked on the silk screen. Get this wrong and you will suffer a lot.

Crystal (section 4.9)

The PIC controller has a great feature that Atmel controllers don't: they have an on-board Real Time Clock circuit (RTC) which only needs an external 32.768kHz crystal to make it work. The controller processor clock is then derived from this using a PLL. This part of the circuit is really easy.

Testing the Tubes (section 4.10)

While I like the idea of having the IN-18 tubes socketed (there is really no alternative), I'm not a huge fan of the sockets on the Spectrum 18. I had to fiddle about with them for a long time, and to my (rather conservative) tastes, they grip the pins on the tubes a bit too well. I know that a good connection is important, but these fragile old tubes don't like to be forced to do anything. They might not fail right away, but I always get the feeling that it is so easy to damage the tubes in the process of forcing them into the sockets.

I do see the need to have the acrylic holders, so that the pins don't get out of alignment, but I get the feeling that they constrict the pins a bit, meaning that excessive force might be necessary. I have no proof for this assertion, it's just a feeling I get.

Various Resistors (Section 4.11) and drivers (section 4.12)

These two sections of the manual deal with filling in some of the discrete components that are used in the clock. R8 - R11 are ballast resistors used on the neon indicators. R12 - R14 are current limiting resistors for the LED indicators, R17 - R19 are used for the speaker. R16 is a pull up resistor for the temperature sensor and R20 appears to be a total waste of time.

The drivers are the Q1, which is an MPSA42, which drives the speaker. This is a high voltage transistor, but I suppose it was chosen because it can withstand the voltages used in Nixie tubes, and the MPSA42 is being used here as a jelly-bean NPN transistor. Q2 - Q4 are used to drive the three channels of the RGB backlights.

Super Cap (Section 4.13)

C5 and C6 are a super capacitor and a decoupling capacitor, as well as a header to allow the board to be quickly reset. This circuit allows the clock to keep running which the power is turned off for a limited period of time. This means that the clock does not immediately forget the time. 

LEDs, Buttons and connectors (Section 4.14)

This section of the manual deals with installing the LEDs (D4 to indicate if the alarm is active, D5 to indicate if GPS module is active, D6 to indicate that Daylight Savings Time is on), the switches and the connectors the for external PIR and GPS/DCF module). I decided to install the LEDs standing upright, because I didn't want them protruding over the edge of the board, btu then found out that the switches protrude anyway. Depending on the sort of case you install, you might need to install some of these components on the botton of the board, so read the manual carefully!  

Buzzer (Section 4.15)

Well, that didn't take long! The buzzer is installed on the bottom of the board. I can't really find anything else to say about it.

RGB LEDs (Section 4.16)

Up until now, the clock has seemed to be a really well-designed and thought out kit, but this step feels a bit "how you doing" in comparison. The installation of the RGB LEDs is fiddly, hard to get right, and unnecessarily troublesome. The bending of the leads is a bit approximate, and you need to pay good attention to the orientation of the LED when you start bending the leads. In my kit, I had a spare RGB LED, and I suppose that this is because lots of people get at least one wrong. If you don't pay good attention to the way up you hold the LED when you start bending, it comes out with the common lead in the wrong position. Take good care!

Soldering the LEDs is also a bit awkward. The leads to be trimmed are difficult to trim, even wth tiny side cutters.

In the end, soldering the LEDs happened without any great mishaps, but I would have hoped for a better solution than what was offered. 

Temperature sensor (Section 4.17)

 Well, that didn't take long.

The neon separators (Section 4.18)

This is a fiddly task, and while going through it, I found that the manual is wrong. It says to cut the heat shrink sleeving for the neons with the long legs to 45mm, but that is too long for the glass tubes that are supplied. Instead I cut them to 40mm and that turned out just perfect. I also shrank the heat shrink sleeving before the final soldering, so that the heat of the soldering would not cause the extensions to drop off.


Final test

After installing the separators, I gave the clock a quick test. My tubes have cathode poisoning, and I'll show you in a later article how to deal with that, and also give the clock a full user review. 


I'm totally satisfied with the resulting clock. The Spectrum 18 kit is easy to build, and works well. The instructions are clear where they need to be, and short enough when there is no need for additional explanation. There are no complicated components to deal with, and as an overall impression, the kit is well worth the money. It has a good set of features, and is well thought through.

There are a few parts of the construction that don't match the overall quality of the rest of the kit. The tube holders don't fill me with confidence, and I feel that they are a bit brutal with the delicate and expensive IN-18 tubes. The mounting of the RGB LEDs feels a bit improvised, and a jig or on board LEDs might be a great addition to the kit. The leg extensions on the neons is a bit fiddly, and seems also a bit improvised.

However, these are minor niggles, and on the whole, the kit is excellent! I would recommend it to anyone wanting a large tube clock. 


zip-3HV5622 HOT
(3 votes)

This is the data sheet for the Microchip HV5622 high voltage (Nixie) driver chip

Date-3Tuesday, 19 June 2018 19:14
File Size-3 886.36 KB
Download-3 1,492



 This clock was kindly supplied by Millclock for review, so many thanks to them for sending the clock to me. Previously we reviewed one of the simpler clocks produced by Millclock (the IN-12 Walnut clock) and this time we're looking at the other end of the range.

The Nixie Six is a six digit IN-14 clock with compact digits and a whole load of features. The version I have comes in a formed black acrylic case, with a sturdy transparent base plate, neon separators, and an external 12V power supply. The appearance is pleasing:


Nixie Six Front


The power supply has a slightly smaller than usual jack, but is a standard DC jack, and has quite a short lead, but I'm sure that you can find a supply with a longer lead if you need it. For most purposes, the lead supplied will be adequate.

The unit has GPS time synchronisation, meaning that it keeps good time. The GPS antenna unit has a very long lead on it, meaning that you can easily and unobtrusively mount the antenna in the vicinity of a window, which is a pre-requisite for good time synchronisation.

Whereas the IN-12 clock gave the impression of being a pre-production unit, the Nixie Six is very definitely a mature production design. There are no rough corners or loose ends, and everything fits properly and clearly a lot of time has gone into making it a polished unit. Indeed, the clock version number, printed on the bottom of the PCB is v2.0.1, again with the slightly strangely motto "properly assembled in UKRAINE". I do understand why Millclock is trying to say with this motto, and I do know that I am being somewhat facetious, but in English it just sounds a bit strange. I wonder what the difference in assembly would be if it was "improperly assembled". Would that mean that it is assembled by children? Or by slaves? Or perhaps by adults, but with their trousers down? Or all three? I know that Millclock are trying to say "assembled in the UKRAINE with care and attention, using state of the art technology and tools, great quality control and an eye for detail", but somehow "PROPERLY ASSEMBLED IN UKRAINE" has a better right to it,


The pitch of the tubes is quite tight, with only about 1mm between adjacent tubes in the digit pairs. This gives the clock a very "upright" appearance, especially because of the relatively large base height. The mixture of the black acrylic and transparent acrylic base work well. One slight improvement that I would suggest to Millclock: It would be good to have some rubber feet on the bottom of the acrylic base: acrylic scratches easily and the beautiful finish will deteriorate quickly if it is left as a raw acrylic on any hard, rough surface.


Packing and delivery

The clock arrived very quickly and was well packed,with no damage to the unit at all, and with very little risk of being damaged, even given the fragile nature of the IN-14 tubes and the fairly large size of the assembled clock. The box it came in was a sturdy "Ukraine Post" official box, and priority postage was used. Note that the cost of the postage is in the price.


Using the Nixie Six

The first thing to say about the Nixie Six is that it works well, keeps time reliably, and is in no way "needy". I have been using it for a couple of months, and it has never put a foot wrong. It's totally silent in operation, and has been a "fit and forget" experience. The GPS unit means that it tells the right time and you won't need to fiddle or adjust the clock at all. Even changes to Daylight Savings Time (DST) are automatic if you are in Europe or the US, or in a country that follows either of these DST change standards.

The GPS time is backed up by a battery powered Real Time Clock (RTC), and so the clock can run even there is currently not any GPS signal available. As with all GPS devices, it can take a couple of minutes to sync the time the first time, because the inbuilt GPS receiver has to understand where it is, and which of the GPS satellites are in the sky above it.

If you don't have the GPS version, there is the possibility to fine adjust the RTC unit, in units of about 5 seconds per day. RTCs are usually very accurate, but even these can drift over time or under certain circumstances, and the adjust feature allows you to correct this.

The manual is much longer and more detailed than with the very simple IN-12 4 digit clock, covering five A4 pages, and the specifications and the usage of the clock are covered. The main "settings" are laid out in an easy to use table, and the clock has three buttons ("menu", "+" and "-"):


 A feature that I do like, is that the neon colons flash can be set to one of seven different modes:

1 - slow flash: One second on, one second off

2 - fast flash: 0.5 second on, 0.5 second off

3 - fast burst flash: two rapid flashes at the beginning of each second

4 - medium burst flash: two medium flashes at the beginning of each second

5 - "ping pong right": both separators on, but the brightness switches between the left and right separator (right colon mostly bright)

6 - "ping pong left": both separators on, but the brightness switches between the left and right separator (left colon mostly bright)

7 - "ping pong alternate": As "ping pong" but the bias changes each second (alternating between left and right bias).


This clock won't give you "feature overload", the ones the clock offers will cover the vast majority of user wishes, and you won't have to get exasperated by wading through the manual to fine what you want. It is mostly very intuitive. 


Inside the clock

Millclock didn't know that I was going to tear the clock down, but I think it is worth having a look inside it to see what you are getting. In general, if you are scared to have your clock torn down, then don't send it in!

The case comes apart quite easily and non-destructively, meaning that it will be a fairly simple task to change the RTC battery if you need to in the future. The clock itself is a two board design, one board housing the driver, and the other board holding the tubes, the separators and the RGB back lights.


 Two Board Design


The internals are really clean and professional. The board is well laid out, logically divided and neat and tidy. The tubes are all perfectly aligned, and have been clearly inserted using a jig, or by someone with a good level of skill.

The clock uses an STM32F103C8 controller, which is a powerful ARM Cortex-M3 device with 64kB of flash and a maximum clock speed of 72MHz, but in the case of this clock, it is using it with a 32.768kHz external crystal for the inbuilt RTC and probably uses the internal RC oscillator running at 8MHz for the control circuitry. The RTC consumes just 1.5uA when the clock is off, so a standard CR1220 battery with a capacity of 36mAh will last about 24000 hours, or about 1000 days. However, the 32.768kHz crystal is not temperate compensated, and therefore the need for the RTC calibration. I would complain about this if the clock did not have the GPS antenna, but it does have GPS, and is unlikely to give you any problems in practical use.

The display is multiplexed using a K155ID1, and uses classic NPN-PNP discrete drivers for the anodes, using SOT-23 transistors marked 1D (NPN) and 2D (PNP), presumably the MMBTA92 which has a voltage rating of 300V, or the KST93. 

The tubes are mounted close to the display board, with just enough clearance under them to allow the SMD 5050 RGB LEDs to be mounted. The RGB LEDs, which are divided into three sets of two RGB LEDs, one for each pair of digits, using NPN transistors marked 1GW, which is a general purpose SOT-23 NPN transistor.



Millclock are following a strategy which I think is the right for them to build a brand over the long term: Offer high quality items at the price which allows you to guarantee the quality. Millclock clocks are not cheap, but if you want to have a no-nonsense, "get-it-done" clock, you will not be disappointed if you buy Millclock.

Buyers of luxury items (and let's face it, Nixie clocks are luxury items: a $3 LED or LCD clock will tell the time just as well) forgive the price if the quality is there, but will not forgive failure and unreliability. From this point of view, I think Millclock are on the right path, and the Nixie Six is good choice.

Millclock offer a one year warranty, and will give you a 10% discount if you mention this article!











Price $164.99, including shipping

Manufacturer: Millclock

Millclock are based in Ukraine and offer a range of assembled clocks and thermometers, as well as some kits. We're going to focus on an assembled clock in this review, which is one of the more simple clocks available from Millclock.

One point before we start about the kits: There's been some negative press about the kits, but you should take that with a pinch of salt; The complaints were that the assembly was difficult because the components used are SMD (Surface Mount Devices), but that's entirely clear from looking at the pictures on the site. The complaints are a little unfair, and the Millclock site states that there is some assembly skill needed.

However, we're talking about a fully assembled and tested item in this review: The IN-12 Nixie Tube Clock With Walnut Wood Enclosure.

Walnut IN-12 


Ordering, delivery, unboxing

The package arrived quickly from the Ukraine; the shipping costs part of the price, and the priority postage that Millclock uses means that you won't have to wait very long for the clock to arrive. The clock itself was well packed and in perfect condition, well padded with polystyrene against the worst that a postal service can do. Inside the box, there was a power supply, the clock unit, and a very short instruction sheet, which covered half a side of paper. Clearly there isn't a lot to configure in this clock.

A 12V 1A power supply with a EU plug on it was in the box, and all you need to do to get the clock going is to plug it in and set the time! Very easy indeed.


Overall impressions

The clock is very small, and is quite a triumph of miniaturization. The front panel is barely larger than the 4 IN-12 tubes, and the depth of the unit front to back is slightly larger than the height. There are two buttons on the top of the case, and a small hole in the top. This is for cooling on the pre-production unit, but will be removed for the mass production, because the clock does not produce very much heat. 

The case is entirely in wood, and nicely finished, with an etched logo on the back panel, which  is a nice touch. The rounded corners and the grain of the wood give the clock a nice feel. The unit is comfortingly heavy in the hand. In the front between the hours and the minutes, there is a single small neon indicator.

The unit measures 113mm wide, 44mm high and 44mm deep, and weighs about 160g. The new international Nixie measurement standard of a 100g Toblerone, which is 210mm, so that means that it's just over 0.5T wide in the new units.

There were a couple of slight problems in the final assembly of the case, but I think there are because the unit I have is an early pre-production model. They are not very serious problems: The back panel is glued on, and it does not look to be easy to change the battery. Some screws would have been a better solution, because eventually the battery will need to be replaced.

Also, on the review unit, the power lead is very short, it is only xx cm, and this means it's sometimes difficult to find a good location for the clock close enough to a power outlet. The power adaptor is glued directly into the case, and it's not possible to change it. The application of the glue was not very pretty.

Operation of the clock is quite straightforward, justifying the single page of instructions. It covers all the normal functions of a small clock. You can set the time and date, you can set the time format to 12 hour or 24 hour mode, you can turn on or off the back light, and you can set whether you want to have the date displayed. It's that simple!

Clearly, inside this clock there is a small SMD PCB which holds the electronics and the tubes. Measuring an IN-12 against the unit we can see that it looks like the tubes are mounted directly on the board, and that is not going to leave much room for electronics. My statement about the miniaturization seems to be true. 



The operation is super simple, and it's perfect for a small, easy "fit and forget" clock that you might keep in an office or a bedroom. The left hand button is the "menu" button, to move between menus when you are setting the clock, and the right hand button, adjusts the setting, or shows the date when you are in normal time mode. Each time the date is shown, the display does a little scroll through animation, which also serves as a rudimentary anti cathode poisoning.

The menu is easy to understand. First press the "menu" button (the left one), and the neon stops flashing. This is an indication that you are in setting mode. Then you can press the "adjust" button (the right one) to change the settings. After you have set the hour, press the "menu" button again to move onto the minutes, and again you can press the "adjust" button to set the minutes. When you move onto the minutes, the neon stays on. This is the clock's way of telling you that you are in setting mode, and you are working on the right hand pair of digits, in this case, the minutes.

Pressing the "menu" button again takes you into the date settings. The neon is off, so we are working on the first two digits, which is the day of the month. Set this, and then press the "menu" button again, and the neon shows us that we are looking at the right hand digits, which is the month.

Press the "menu" button again, and now we move onto the year. The next option is the 12 hour or 24 hour mode. "00" means we are in 24 hour mode, which is the default, and "01" is 12 hour mode.

The next pair of options is the back light which can be "01", meaning back light on, which is the default, or "00" meaning back light off. It would be nice if the back light was turned on or off when you change the setting, but it only sets the back light LEDs once you exit the settings mode. The next setting is whether to show the date by default. This means that every so often the date will be shown automatically. "01" means show the date (the default) and "00" means do not show the date.

You will notice that there is no option to set the seconds, because this is done automatically when you exit settings mode. When you finish the setting up, the seconds are set to "00" automatically. 

IN-12 tubes are super robust, so the anti cathode poisoning isn't really that necessary.

The time is battery backed, meaning that if you turn it off, it still keeps time perfectly. It's not using something like a super-capacitor, which will keep the time for a few minutes, it has a battery so that it will keep counting time as long as the battery runs, and the life of these batteries is usually measured in years. Millclock tell me that the life of the battery is rated as 10 years.



Millclock LogoThis is an excellent tiny little clock, pretty much the smallest enclosed clock that you can make with the hardy IN-12 tubes. It doesn't have a lot of functions, but the ones it has are dead easy to use, and cover what you want for a clock in an office or a bedroom. It has all the beauty of Nixies, in a small, modern package, with a high quality case. I think it's a little pricey for what it is, but bear in mind that the cost includes priority shipping and some high quality materials.

There are one or two little finishing touches which it would be nice to take care of (the glued back to the case and the missing strain relief around the short cable), but apart from that, it's a high quality, uncomplicated, accurate clock.

There is also a "dark chocolate" version available.

The guarantee is 1 year.

All in all, a nice little clock. 



There is also a tear down of the clock. Bear in mind that this is a pre-production version of the clock, and the electronics looks pretty complete, but there are a few little rough edges in the case and construction. The teardown video is here:


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