Archive for the 'Clocks' Category

The GEN IIv7 MOD-6_7971

Carl and Michael recently released the latest version of their MOD-6_7971 Nixie clock. This is pretty much the same hardware as before, but uses a higher-powered radio transmitter in the remote GPS receiver so it can be located further from the clock. There have been a huge number of software changes, however. To give you an idea, the version that shipped with the last batch of clocks was V07-09. The version on this batch is V07-53!

A lot of that was me pestering Carl for changes, but there’s also a lot of other neat new stuff in there.

One other new thing is that the clock now has a 67 page user manual written by me. If I may be permitted to brag a little bit (Ok, a lot!) I think this sets a new standard for Nixie clock documentation. You can read it (and the accompanying updating instructions – you can update any of the older clocks to this software) here:

User Manual
Updating Instructions

For more info or to express interest in ordering a kit or assembled clock from a future batch, visit the MOD-6 page at

MOD-6 Nixie clock

Replica Elektronika 7-06 Faceplates

If you’ve been shipped as many Elektronikas as I have, from a variety of countries with very different ideas of what due care for postal parcels means, you’ll eventually encounter something disheartening like this:

No good deal goes un-smashed

You may have purchased a clock where a previous owner changed the faceplate to plastic or glass without the masking areas, or there is extensive damage to the silkscreen on either side of the glass. Or, you might be displaying the clock somewhere you don’t want random people tapping on the glass and possibly breaking it.

In any of these situations, you’re going to need a replacement faceplate. Unfortunately, it isn’t a simple matter of ordering one online from the factory – they haven’t made these clocks for many years, and any replacement glass is likely to encounter the same unkind treatment from the international postal services that got you into this mess in the first place.

Fortunately, I have created a solution for this – replacement acrylic faceplates which are nearly indistinguishable* from the original. I start with precision-cut pieces of colored acrylic (plastic). The pieces I use are cut from 1/8″ (nominal) thick sheets, the same as the original glass. There are four possible choices for color if you’re trying to match the original glass, two of which are much better than the others:

  • 3030 “Glass green” – this is a color designed to mimic real sheet glass. It has a very minimal green tint, just enough to give the edges the green color that real glass has. We don’t care about the edges as they’ll be inside the frame. This is the ideal material for replacing clear glass faceplates.
  • 2111 “Light green” – this color appears to be lighter than the original green glass faceplate, but when installed in the clock, provides a very good approximation of the original green glass color.
  • 2092 “Dark green” – this color is not recommended. While it seems to be the closest match to the original green glass when comparing materials side-by-side on a white background, it imparts much more of a green tint to the tubes and decreases the brightness substantially.
  • “Clear” – this is also not recommended. It looks quite a bit different from real glass. 3030 is a better choice when replacing clear glass faceplates.

Note that these color codes are the ones used by Altuglas International for their registered trademark Plexiglas® product. Other manufacturers also offer acrylic sheet plastic and generally use the same color codes as a common point of reference. Those colors may differ subtly from the reference Altuglas colors.

If you’re trying to change the appearance of the clock, you’re still limited to colors in the green to blue range. Since those are the colors given off by the VFD tubes in the clock, you can’t do something like using a sheet of red plastic – there’s no red light available to pass through the plastic. Unless you have one of the very rare version of this clock which uses orange MTX-90 tubes, of course.

On the original glass faceplates, lacquer paint was applied to the glass via silkscreen. That’s certainly the fastest and most accurate method for mass production, but would require a lot of prep work for making a few replicas. Instead, after carefully cleaning the acrylic, I applied masks cut from 3M 2060 green painter’s tape, in the shapes of the 4 clock digits plus the colon indicator. Remember, the paint goes on the inside of the glass, so the pattern is reversed from the normal view:

Masking tape applied

If you are making one of these replicas yourself, this would be a good time to check your mask by sliding the plastic into your clock and making sure that the mask lines up properly with all of your tubes. Even small measuring errors will be magnified as you repeat the masking process across the plastic. After removing the plastic from the test fitting, make sure that it didn’t pick up any contaminants on the masked side – if it did, they will ruin the completed paint job.

Next, I masked off the back side (which will become the front / outside of the completed faceplate). You may be wondering why I didn’t simply leave the protective paper in place that comes on the sheets – that’s because I needed to see through the plastic in order to properly position the mask pattern. I applied 5 thin coats of Valspar 68100 gloss black spray paint, which is a special paint designed to adhere to plastic. One spray can will be sufficient to paint 3 replica faceplates. I alternated painting lengthwise and across the faceplate, waiting 10 minutes between coats. After the last coat was applied, I let the paint dry for 2 hours:

Painted - back

I removed the tape that covered the unpainted side of the panel and carefully inspected the paint for any flaws:

Painted - front

This particular faceplate is for a newer 11-tube clock, as shown by the wider border below the digits and colon. The 12-tube clock has approximately equal border widths, top and bottom.

I then proceeded to carefully peel off the painted masking tape to expose the clear areas of the faceplate:

Mask removed

Here’s a closeup of the painted side showing the finished paint job:

Mask removed - close-up

After leaving the paint to fully dry for two days, I prepared to install the vinyl decals that I had custom-cut for the project:

New vinyl artwork

After carefully applying the decals, I had completed replicas, ready to use. From bottom to top:

  • Original clear glass 12-tube faceplate
  • Replica 12-tube faceplate in 3030 plastic
  • Replica 11-tube faceplate in 2111 plastic

Completed replicas

These are certainly good enough to look original until examined very closely. See the footnote below for ways to detect replicas.

Here is a picture of the 11-tube 2111 replica installed on the clock with the broken glass shown at the top of this article:

Installed on clock

* I have intentionally made it easy to detect a replica versus an original, to prevent people from passing off the replica as an original piece. There are a number of clues, some of which I’m keeping confidential. However, I am documenting three of them here:

  • The “Э” in Электроника is very circular and doesn’t appear to be italic in the original, while my replicas use a more oval shape with an obvious italic tilt to the letter.
  • The digit “7” in the original has constant line width and only uses straight lines, while my replicas use a slightly curved shape of varying width.
  • If you tap gently on the faceplate with your fingernail, a replica will make sort of a dull “plonk” sound as the plastic is more flexible than glass. A genuine faceplate will make a sharp “tink” sound.

The Big Elektronika

In a previous post, I covered the small (relatively speaking) Elektronika 7-06M clock. At the other end of the scale is today’s topic, the Elektronika 7-06 and 7-06K. For background info, consult my prior article as I won’t be repeating duplicate info here.

The operation manual says that the 7-06K version includes a radio correction board not included on the 7-06, and that this is the only difference between the 2 versions. All of the big Elektronika clocks I have in my collection include the radio correction board, regardless of whether the label on the back of the clock shows the model as 7-06 or 7-06K. For convenience, I’ll refer to both of these models as “7-06″ here, except when I need to distinguish between them.

The 7-06 is nearly twice as large as the 7-06M. It is 27″ wide x 9.5″ high x 3.75″ deep. The individual digits are 3″ wide x 6” high. It completely dominates any room it is in, both by its size and by the brightness of the display. Even clock collectors who feel that “bigger is always better” might be intimidated by this clock’s imposing presence. The Elektronika 7-06 digits are both taller and wider than the largest CD-47 Nixie tube.

To give you an idea just how large the display is, the clock’s operation manual says that the time is legible from a distance of 75 meters (about 250 feet). That’s before any fading of the display (and may be somewhat optimistic) but I would have no difficulty believing this clock could be read from 100 feet away.

Here is the smaller Elektronika 7-06M sitting on top of the 7-06. Both have new tubes and are running at high brightness (dim mode turned off on the 7-06M, not adjustable on the 7-06). The difference in brightness and dot color is due to the green glass on the 7-06M vs. the clear glass on the 7-06.

Small and large Elektronika

Here’s a video of the clock during the transition from 23:59 to 00:00. Being a Soviet clock, it only displays in 24 hour mode.

(Click the Icon icon on the top right to go fullscreen.)

This particular clock bears a label showing the model as “ЭЛЕКТРОНИКА-7” with a date code of “06.1984”. The 06 definitely indicates June, as another clock in my collection has the same abbreviated model number and a date code of “01.1984”. The following picture was taken after I completed my restoration of the clock, replacing the power cord and hardware (screws, bumpers).

Rear covers

There is also a variant of this clock which uses 11 tubes per digit instead of the 12 tubes used in this clock. This introduces an asymmetry in the displayed digits, as there are 2 dark rows of dots on the upper part of the “8”, but 3 dark rows on the bottom part. This seems to have been done on newer production – I have two 12-tube clocks from 1983 and 1984 and an 11-tube one from 1989. The 1983 manual (available below) only describes the 12-tube version, while a newer manual from 1990 only shows the 11-tube version. The 11-tube version seems to have other cost-saving measures as well, such as a lighter internal frame. The case dimensions are exactly the same as the 12-tube version. The paint mask on the inside of the glass is slightly different, as it only exposes the area used by the 11 tubes.

The battery compartment holds 6 Type 373 (D equivalent) batteries for timekeeping during power outages. While the clock will keep time without external power, the display will not illuminate.

The mounting of the electronics / display frame in the case is done in an unusual manner. Unlike the smaller 7-06M where the frame simply comes out the back of the case after removing 4 screws, the 7-06 was initially quite puzzling. After removing the screws that attached the 2 metal back plates and the phenolic battery compartment cover to the case, I could see the circuitry of the clock on the back of the frame, but it wasn’t obvious how to get the frame out of the case. The battery compartment is made of wood and is part of the clock case, so it was obvious the frame couldn’t come out through the back.

Rear covers removed

However, the front glass was fitted into a recessed groove that ran completely around the case, so there was no apparent method to remove the glass. Operating on the “when in doubt, remove more screws” theory, I unscrewed the 4 screws that held the control panel onto the the left side of the case. These screws were much longer than expected, and when they had all been removed, the control panel could be pulled away from the case. The side panel of the case came along with it, revealing another side panel beneath it. This second panel was fully slotted, so the glass could then be removed by sliding it out to the left.

Unlike the smaller 7-06M clock, the glass on this clock is clear. The black lacquer mask around the display areas has the same construction as the smaller clock, and the ЭЛЕКТРОНИКА lettering on the front is applied in the same manner, though enlarged from the size used on the 7-06M. The clear glass provides a much brighter display than the green glass of the 7-06M, although it does make it easier to see the un-lit dots of the tubes. This was probably done to make the display readable from longer distances. A newer 11-tube 7-06K in my collection has green glass, while both 12-tube clocks have clear glass.

After removing the glass and setting it aside in a safe location, I carefully worked the control panel through the gap on the loose side piece and set that piece of wood aside. With the glass removed, I saw 6 pieces of blue plastic tubing screwed to the inside of the case, presumably to help prevent shocks from cracking the glass. When I removed the 6 screws holding those in, only 4 screws remained, one near each corner of the frame.

Glass removed

Those 4 screws held the frame to the case via flexible metal tabs. After removing them, I was able to carefully pull the frame a few inches out of the case. There were still 2 wires attaching it to the battery compartment, which I disconnected at the battery terminals. Lastly, I had to work the control panel through the gap on the side of the case. Finally, the frame was free of the case and I could get to work studying it.

The first thing I noticed was that the IV-26 tubes each had 9 wire leads, as if they were Type 1 tubes. All 9 leads on each tube were soldered to the display boards, which is a total of 432 connections! I had expected the tubes to be Type 2, which only have 5 leads and would have reduced the number of connections to 240. Examining a tube more closely, it was obvious that the construction was type 2, as there were internal connections between dots 1-2, 3-4-5, and 6-7. It is a mystery why the tubes were built with additional, non-functional pins. Later, while I was replacing the tubes with new ones, I discovered that the tubes were labeled ИВ-26, with no type designation. The date code was IV-84, the format used on earlier tubes where the month was written with Roman numerals. Like the 7-06M in the previous article, the tubes carried the Orzep manufacturer logo. The newer 11-tube version uses Type 2 tubes with only 5 pins, and its display boards only have holes for the 5-pin tubes.


The clock’s operation is almost identical to the smaller clock, with hours, minutes, and run/stop switches. Unlike the smaller clock, the hours and minutes buttons are of the latching type rather than momentary switches. The bright / dim switch found on the smaller version is not present on this clock, which always operates at full brightness. There is a 5-pin DIN connector which provides 9V, ground, a 1 PPS output and a radio data input. The 11-tube Elektronika in my collection has a similar control panel, but of a newer style, similar to the small 7-06M, with rectangular white buttons in a black plastic frame. The 11-tube clock’s buttons are all momentary, even the run/stop buttom. Apparently these clocks were built with whatever switches were on hand at the time of manufacture.

Control panel

You can download a copy of the manual here (8MB PDF).

Internal construction

As on the smaller Elektronika 7-06M, all components are mounted to a metal frame which is then attached to the case with 4 screws. As this is a much larger and heavier clock than the 7-06M, the frame has slotted brackets to hang the clock on a wall, whereas the smaller clock just uses slots in the back metal cover, not connected to the frame. To make it easier to identify the internal components, I’ve split the photo into left and right sides to accomodate the column width of this blog.

Internal view - left

Internal view - right

Clockwise from the left side, the components are:

  1. Two input fuses, one for each leg of the power cord
  2. Filter capacitor
  3. Power supply diode
  4. 1’s of minutes decode / display circuit board
  5. Input power transformer
  6. 10’s of minutes board
  7. IV-17 colon display tube
  8. Power supply bridge rectifier
  9. 1’s of hours board
  10. 10’s of hours board
  11. Control panel
  12. Main logic board

The 2 dangling wires in the above photographs connect the clock’s circuitry to the battery compartment. I slipped some heat-shrink tubing over the wires to indicate which wire went to the positive battery terminal and which one went to the negative. As mentioned earlier, the battery compartment is part of the wood case.

The blue and white connectors on the left edge of the main logic board are used for installing the radio synchronization daughterboard, not shown in these pictures. There is a retaining bracket mounted to the frame bracket that runs vertically across the main logic board. This is used to hold the daughterboard in place.

There is an inspection tag (which you can see above the main logic board) but it is nowhere near as complex as the one on the smaller 7-06M clock. This one just has some faded rubber stamps and the date written on it.


Each digit of the clock has its own circuit board. As with the smaller clock, all circuit boards are single-sided brown phenolic. All 4 of the digit boards are identical – it seems that the economy of mass production outweighed the cost savings that could be realized from using fewer components on the 10’s of hours and 10’s of minutes boards as was done with the smaller clock.

The wiring coming into the display boards provides the filament and anode voltages, along with the signals for the emulated 7-segment display. Diodes are used on the boards to “or” certain display elements together to complete the 7-segment decoding into the 84 individual dots that make up the digit. Of those 84 dots, 18 are never illuminated (the voids in the digit “8”). I have seen pictures of a different version of this clock which show 4 integrated circuits (instead of 7 transistors) on each display board, and using real Type 1 tubes (not Type 2 tubes which have extra, unused pins).

Display board - top

Display board - bottom

The left sides of the tubes are held rigidly in place by the display circuit board. The right sides of the tubes are held in position by a retaining bracket which is lined with foam, as is the portion of the frame underneath the bracket.

Displayed digit

The IV-17 tube used for the colon is just soldered to a 6-pin terminal strip rather than using a circuit board, since all elements are switched on and off together.

IV-17 colon


The main logic board on this clock is nearly identical to the one used on the smaller version. Refer to my earlier article for details of the design. The only apparent difference between the two versions is that this clock has a single 2-row connector for the wiring harness, while the smaller clock has a pair of 1-row connectors. The newer 11-tube clock I have in my collection, dated 11-1989, has the pair of 1-row connectors. Thus, this seems to more related to the date of manufacture than the model of clock.

A copy of the schematic is available here (3.5MB PDF).

Radio synchronization

This clock has a DIN connector on the control panel which is used to input a signal to the clock for radio synchronization, which is routed to a plug-in daughterboard. This board is not an actual radio – in fact, it consists solely of digital logic integrated circuits. The connections between the boards provides 9V, ground, 1KHz and 32KHz outputs, as well as the radio signal from the external DIN connector, to the daughterboard and an input from the daughterboard labeled “input correction”. This daughterboard receives audio via the clock’s external DIN connector, and looks for a burst of 6 1KHz tone signals broadcast at the top of each hour. If the logic validates the tones as a proper signal, it will send a “top of hour” correction pulse to the main logic board. The clock will operate on its internal timebase with no external radio signal, and even when the daughterboard is removed.

Radio synchronization board

A newer version of this board with 9 integrated circuits instead of 11 (2 of the decade counter ICs were removed) is used on the 11-tube clock.

The “input correction” signal is very clever, and shows the elegance of the design of the main logic board, which uses only 6 integrated circuits of low complexity. When the “input correction” signal is pulled up to 9V, the minutes (and internal seconds counter, not displayed) are reset to 00. Normally, the hour is unchanged, but if the clock is showing a time between xx:50 and xx:59, the pulse will also increment the hours. This allows the clock to be slow by up to 9 minutes and still be reset to the correct time. Since it is more common that a user would have held the setting button down for too long when setting the time manually, the clock can be up to 49 minutes fast and still correct to the radio time signal at the top of the hour. This worked throughout the Soviet Union as all time zones were in offsets of 1 hour (this was not entirely the case in the rest of the world).


Like the smaller version, this clock is designed to operate on 220V 50Hz. However, the power transformer used in this model can be rewired for 120V operation. One of the 3 green jumpers shown in this picture connects the two primary windings in series for 220V operation.


It is possible to remove the jumper and configure the transformer for 120V. I decided not to do this as I have 220V available and the jumpers were installed by the factory before the transformer was dipped in varnish, so I would have had to cut through the varnish to remove the jumper. I decided to leave the clock as original as possible.

It is interesting to note that this clock has fuses on both sides of the power cord, while the smaller 7-06M only has one fuse on one side of the power cord. I’m not sure why this was done. The newer 11-tube clock in my collection only has a single fuse.


Compared to the previous Elektronika, this one shows far more evidence of living a hard life on the wall of some Soviet building. The finish on the case is chipped and the ЭЛЕКТРОНИКА artwork on the glass has some pieces missing as well. A previous owner had added a pair of metal tabs to the back of the case, extending up above the top of the clock, for some reason. It is unclear why this was done, as the spacing between the added tabs is the same as the mounting slots in the back of the case. I set the tabs aside with the other pieces I’d removed / replaced on the clock. I cleaned the case and polished it with furniture polish, but decided to not refinish the wood.

There was evidence that this clock has been in and out of its case multiple times. Quite a few of the screws holding the back plates on were missing and the remaining screws were loose due to being overtightened at some point, stripping out the holes in the wood. While I had the clock out of its case I used toothpicks secured with wood glue to fill all of the holes, then drilled new pilot holes for the screws and installed a full set of replacement screws. Originally, there were 4 plastic spacers that held the back of the clock about 1/2″ away from the wall to prevent the ventilation holes from being obstructed. Two of those had disappeared along the way, so I replaced the two remaining ones and added the missing ones, so now the clock has a full complement of hardware again.

As I mentioned above, the glass slides out of the case once the wood side panel is removed. There were a number of places where the painted black mask had chipped off the inside of the glass. Some of these were around the edges where they wouldn’t be noticed, but there were a number of spots where the missing paint would allow light from the tubes to shine through. After considering a number of possible methods for repairing the paint (including glass paint, black electrical tape, and so forth) I settled on using black UV-cure nail polish. I was concerned about the adhesive in electrical tape reacting with or lifting the original paint, and I was having difficulty locating a glass paint that was guaranteed to stick without invasive surface prep on the glass.

Turning my attention to the display, I replaced all 48 IV-26 tubes. Since the original tubes (and the circuit boards) had 9 pins, I used IV-26 Type 1 (7 individual dots) tubes instead of the 5-pin Type 2 version. This preserved the appearance of the wiring between the tubes and the circuit board. I replaced the tubes in groups of 12 (1 digit) at a time. I inserted the new tubes onto the board, but did not solder them yet as I needed to perform the final alignment with the board back on the frame. As on the Elektronika 7-06M, I reused the original insulating sleeves on the tube leads:

Tubes waiting for solder

As with the earlier clock, I replaced the degraded orange-brown foam padding with new open-cell foam. With the board back on the frame and the retaining bracket loosely installed, I adjusted the tubes by angling them so they were parallel to the frame of the clock. This is a much easier adjustment than on the smaller Elektronika 7-06M, where there are no real clues as to the needed angle. With the tubes all level, I then adjusted them from left to right so that the columns of dots would show as a straight line. If this isn’t done, the completed display will have a wavy appearance with some dots out of position. Lastly, I made sure that all the tubes were rotated properly so that the dots faced forward. A rotated tube would have dots pointing either slightly upward or downward, which would cause variations in apparent brightness depending on the angle you were looking at the clock from.

Once I had all 3 parameters (tilt angle, extension, and rotation) adjusted on the tubes, I tightened the retaining clamp down to keep the tubes from shifting, and carefully soldered as many tube pins as I could reach – generally the first few rows on each tube – to hopefully lock each tube into position. Next, both the retaining clamp and the circuit board itself were dismounted from the frame so that I could swing the board (with tubes attached) into a position where I could solder the remaining pins on each tube. Remember, there are 108 tube pins on each digit display board. After clipping the excess length of the wire leads and checking to make sure no solder bridges were causing short circuits, I powered up the clock with the display board still dismounted from the frame to check for proper operation. Problems would normally show up as some sections not lighting at all, being permanently stuck on, or by turning on and off when an unrelated section changed. After cleaning up some solder splash left over from desoldering the old tubes with a vacuum pump tool, there were a few whiskers of solder which proved to be troublesome in the tight spaces between the traces on the display board. A quick wash with some board cleaner and a wipe with a bristle brush cleared those problems up, and the digit displays were soon re-attached to the mounting frame and the retaining clamp.

One display board had evidence of a rushed field repair at some point in the past. One of the KT209K transistors that converts the 7-segment drive signals into switching voltage to a group of tube anodes had apparently failed, and a new one was soldered on top of the original leads after the old transistor body was clipped off and discarded. This led to an intermittent problem where different numbers of dots would not display in one of the emulated 7-segment areas of the tubes. There’s a technical reason why the number of missing dots varies – you can post a reply comment if it isn’t obvious from the schematic. I removed the whole replacement transistor and the leads it was soldered to, so that I could install a new KT209K directly through the PC board holes, just like the other 6 on the board. After I’d de-soldered the 3 leads from the display board and gave a gentle tug on the part I was replacing, the transistor and 2 of its extension leads came away cleanly, but one of the extension leads just flopped around the hole in the PC board. Apparently it had never been properly soldered to the transistor when the original repair was done, which is what led to the ongoing problems. Perhaps whoever was trying to repair it decided there was a more complex problem that was not cost- or time-effective to diagnose, and that’s how the clock ended up on eBay. Just a theory, though…

While the existing tubes didn’t seem that dim by themselves, there was a very visible difference in a side-by-side comparison with new tubes:

New vs. used brightness

If you are considering purchasing an Elektronika, you can get a rough idea of the condition of the tubes if you have a photograph of the display. When new, each of the dots will be slightly brighter where the filament crosses the dot. After some hundreds of hours, this will become less apparent, so that the dots are evenly illuminated. As the tubes age, the area under the filament will not illuminate as brightly as the rest of the dot. Eventually this will develop into an obvious dark stripe across the dot. In extreme cases, the dark area will expand to obscure some or nearly all of the dot. This will be accompanied by some darkening of the dot phosphor material when not lit, although there isn’t an exact correlation between this darkening and the brightness level when the dot is lit. Here is a picture (from a different clock) showing a relatively extreme case of tube wear:

Tube wear

It is a simple (but labor-intensive) task to replace the tubes with new ones. The tubes are relatively inexpensive (under $2 each) on eBay at the present time. However, that does mean that re-tubing the big Elektronika will cost over $100 (including the IV-17 tube). When purchasing replacement tubes, make sure you select the appropriate variant (Type 1, 2, or 3) for your clock. Type 2 and 3 are not interchangable. Type 1 will work in all displays, but if the clock was not originally equipped with 9-pin tubes you will need to jumper some tube pins together to form the dot groups. It will be much easier to use the appropriate tube type.

When purchasing replacement tubes, I’d suggest getting a few extra. In the 150 or so tubes I’ve installed so far, I’ve found a few duds. Two of them each had one dot that wouldn’t illuminate. One had an obvious blemish on one of the dots (some sort of contaminant inside the tube) so I didn’t install it. And one other replacement tube didn’t achieve sufficient brightness.

Regarding brightness, there’s a relatively large variation in brightness between different tubes when first used, even from the same manufacturing lot (in addition to the date code stamped on the outside of the tube, there is an additional handwritten code inside the tube itself). This affects all dots within the tube, regardless of how frequently the dots are illuminated. This seems to even out within the first 24 to 72 hours of operation. Even the tubes with the highest initial brightness will become somewhat brighter after a day or so of operation.

As I mentioned in my previous article, use a low wattage soldering iron at the lowest possible temperature as the traces tend to lift off the circuit board when de-soldering. Also, there is no solder mask on these boards – instead, the whole solder side was varnished after soldering. This means that there is varnish covering the solder connections to the tube pins, which will inhibit heat transfer from your soldering iron to the solder joint as well as contaminating the tip of the soldering iron. You’ll need to re-tin the tip before using the iron for other tasks (including soldering the replacement tubes).

Like the earlier clock, this version uses a smaller display tube as a colon between the hours and the minutes. The tube is either an IV-4 or IV-17 sixteen-segment (plus decimal points) display. It was completely unlabeled, with no type or date code markings. Both the 1983 and 1990 versions of the manual state that it is an IV-4. I replaced it with an IV-17, which is identical to the IV-4 except that it is claimed to have a longer life.

You may recall from my previous article on the 7-06M that it arrived with a power cord spliced onto the original short cord, but with bare wire ends instead of a plug. This clock came with a plug, but the wire zipcord it was attached to was very thin – what we’d refer to as “speaker wire”. As with the previous clock, I replaced all of this with a new Europlug cord.

With all 49 tubes replaced, the clock really lights up the room. Unlike the earlier clock, this one does not have a bright / dim switch, so you get full brightness all the time:

All new tubes

The user’s manual for the clock suggests unplugging the clock when there are no people around (for example, at night) and using the batteries for timekeeping while the clock is unplugged. This is because the radio time signal doesn’t tell the clock which hour it is, only that it is the top of the hour. And, of course, if the radio isn’t connected the clock doesn’t even have that information. I’m rather surprised that the clock doesn’t include a display on/off or dimming switch (as was done in the smaller Elektronika 7-06M). Unplugging it seems like a bit of a hack, particularly if it is mounted high up on a wall, adjacent to a dedicated outlet. On the other hand, this probably explains why so many of these clocks have very weak tubes.

The Elektronika 7-06M Clock

In addition to making Nixie and VFD display tubes, the Reflektor factory in Saratov, Russia built clocks for use in office buildings and other large spaces such as Moscow Metro stations. These were produced under the Elektronika1 7 (Электроника2 7) name. These clocks have a bit of a cult following in the West and were described by Brian Stuckey of TubeClockDB as being “so unique it has its own Wikipedia entry”. While the English Wikipedia article is a rather small orphan article, the Russian Wikipedia has far more information here and here.

The Elektronika 7 isn’t a single model of clock, but instead is a whole series of clocks of different sizes and functions. The one discussed in this article is the “baby” Elektronika 7-06M. It uses 16 IV-26 Type 3 (ИВ-26 тип 3) VFD tubes, each with 7 dots, arranged as 4 groups of 4 tubes, one for each digit. An IV-6 (ИВ-6) seven segment tube3 serves as the separator between the hours and minutes. The clock is 15″ wide x 7″ high x 2.75″ deep. Each digit is approximately 2″ wide x 3.25″ high.

Elektronika 7-06M

It is actually quite difficult to get a good picture of an assembled and operating Elektronika 7 due to the highly reflective nature of the glass and the high contrast between the lit dots and the rest of the clock. Digital cameras also have a different color response than the human eye, and the combination of the green-tinged blue of the bare VFDs combined with the green glass makes for a particularly challenging subject. The above picture is a best approximation of the actual appearance and is the result of an actual photograph manipulated in Photoshop. The thin vertical lines adjacent to illuminated dots are caused by the light from the dot reflecting off the glass envelope of the adjacent tube(s).

Here’s a video of the clock during the transition from 23:59 to 00:00. Being a Soviet clock, it only displays in 24 hour mode.

(Click the Icon icon on the top right to go fullscreen.)

Both this video and the photograph above it were shot in “dim” display mode after the tubes had been replaced (see the restoration section later in this article). The still photo has a much more accurate rendition of the display color when viewed through the green front panel glass.

Here’s a view of the back of the clock after I completed my restoration project. The sticker on the right is the original manufacturer / date / serial number sticker, which was defaced at some time in the past (more information later in this article). Above that is the battery compartment door for the backup timekeeping batteries. There are 3 test points on 3 corners of the battery compartment, two for checking the battery voltage and one for (roughly) checking the timekeeping accuracy. Directly above the power cord is a .25A fuse. On the left side I have placed a label indicating that I replaced the tubes and calibrated the clock, along with the date.

Back Panel

In addition to the 7-06M model described in this article, other versions were manufactured with larger displays. I have one with a label reading 7-06 (no suffix) dated 1984 which uses 12 horizontal tubes per digit. I have photographs of one labeled 7-06K dated 1989 which has 11 tubes per digit. This may have been a reduction for cost reasons – more research is needed.

These clocks were manufactured between (at least) 1982 and 1991. The oldest clock I’ve seen has a 1982 date, while the instruction manual (which was supplied with a clock, as it has a serial number written on it) is dated 1991. Production may have started before 1982 or ended after 1991.

The Russian Wikipedia article referenced above states that the clocks were introduced in 1982 and that the K model suffix indicates that the clocks were equipped with a connector for radio synchronization of the time. However, my 7-06 (no K) also has this connector.

Modern versions of the Elektronika clocks are still being manufactured in Russia under the Vesta name. These are available with red or green LEDs or the more traditional VFD (but not with IV-26 tubes, which are no longer manufactured). This is apparently what the soda-can-sized ILC1-1/7 (ИЛЦ1-1/7) 7-segment displays are used for – there is a YouTube video of a 6-digit one in operation here.


Operation of the clock is quite simple. After plugging it in, the clock will display 00 00 (unless backup batteries were installed, in which case it should retain the correct time) and the colon indicator will be flashing once per second. There is a vertical row of buttons on the right side of the clock case. Refer to the following image for the functions of each button:

Function Buttons

  • МИН – Minutes – Press and hold to increment count 2 times per second, or press once to increment once
  • ЧАС – Hours – Press and hold to increment count 2 times per second, or press once to increment once
  • СТОП – Stop – Reset minutes and seconds to 0 and stop counting until released (latching button)
  • ЯРК – Bright – Dim display while pressed (latching button)

Setting the time involves pressing ЧАС to set the hours, pressing СТОП until your reference time shows 00 seconds and then releasing, and then pressing МИН to set the minutes. Changing the hours or minutes does not affect the (internal) seconds counter.

I obtained an instruction manual from WASP in Kazakhstan. With their permission4, the manual is available for download from my site here (PDF, 16MB).

Internal construction

The internal components are all mounted to a metal frame which has 4 metal “ears” which are attached to the cabinet with screws. Refer to this numbered picture to identify each major component:

Interior Components

Clockwise from the left side, the components are:

  1. Compartment for 6 Type 316 (AA equivalent) batteries for timekeeping (but not display) during power outages
  2. Hours decode / display circuit board
  3. 1/4A input power fuse
  4. Colon and minutes decode / display circuit board
  5. Buttons for setting time and dimming display
  6. Logic board
  7. Input power transformer (220V input; 23V and 3.2V outputs)
  8. KC402E (КЦ402Е) full-wave bridge rectifier (right) and D226 (Д226) diode (left)

Note the use of connectors on the logic board. I have seen clocks of this model which also use connectors on the two display boards, which was apparently done to make it easier to service the display boards. Strangely, this seems to have been discontinued. My clock has a late 1988 date code, white wires with black lacing cord, and no connectors on the display boards. Another clock of the same model has a mid 1986 date code, green wires with white lacing cord, and connectors on the display boards. The service manual the schematics came from is dated April 1991 and doesn’t show the connectors.

While getting ready to clean the circuit boards, I removed the inspection sticker that was tied to the wiring harness on the minutes board, shown just to the right of the “4” legend in the above picture. It has an odd mixture of dimples (both in and out), rubber stamp, and handwritten markings in both pen and pencil:

Inspection Sticker Front

Inspection Sticker Back

Eremeev Alexey wrote in to say: “I have just little note about “inspection sticker that was tied to the wiring harness…………. It has an odd mixture of dimples” actually its not odd dimples, it iss recycled paper from old books for blind people (Braille writing system). Suspect so it was because many disabled people work (often work in Soviet Union time) on electromechanical plants and they assembled more or less simple devices such wall sockets and switches. Such job may had in nearby worskhop in factory and they may had lots of useless braille paper documents.”


As mentioned above, the clock uses IV-26 tubes for the display:

IV-26 Tubes

IV-26 tubes were manufactured in 3 variants. The Type 1 has individually-addressable dots while Type 2 has internal connections between dots 1-2, 3-5, and 6-7. Type 3 has internal connections between dots 2-3 and 5-6. Type 2 was used to create numeric displays from horizontal tubes and Type 3 was used to create numeric displays from vertical tubes. This was presumably done to reduce the amount of assembly labor, as a clock with 16 Type 1 tubes would have 144 soldered connections, while a clock with 16 Type 3 tubes would only need 112 soldered connections. That isn’t a huge savings, but on the 12-tube-per-digit 7-06 version (to be discussed in a later article) the connection count drops from 432 to 240. (The percentage saved varies because a Type 3 tube has 7 pins while a Type 2 tube only has 5 pins.)

After operating for over 20 years, the various dots within the tubes have faded from use. This varies depending on how often a particular dot is illuminated, and the fading of the dot is accompanied by a darkening of the phosphor material. This does not correspond exactly to the fading of the dot as you can see in the following two pictures of the same tubes when off and lit:

IV-26 Tubes (off)

IV-26 Tubes (lit)


Given the somewhat bizarre use of IV-26 tubes to create a pseudo-seven-segment display, I assumed that the circuitry would be equally Byzantine. It is actually very elegant. The same circuit board is used in multiple clock models, since the timekeeping is separate from the display decoding and drive. It has features not used in the 7-06M – for example, connectors for a daughterboard to process an external radio synchronization signal.


The circuit board contains 6 integrated circuits which operate at 9V (not standard 5V TTL levels). They are:

  • K176IE12 (К176ИЕ12) – 15-bit frequency divider with 1PPS and 1PPM outputs
  • K176IE4 (К176ИЕ4) – Modulo 10 counter with 7-segment output (2)
  • K176IE3 (К176ИЕ3) – Modulo 6 counter with 7-segment output (2)
  • K176LA7 (К176ЛА7) – Quad 2-input NAND gate

The timebase is generated by a 32KHz RK-72 (РК-72) crystal, known colloquially as a “boat crystal” due to its shape. A trimmer cap provides adjustment of the frequency for accurate timekeeping.


[Click on the schematic for a full-size version.]

The display boards use a series of KT209 (КТ209) PNP transistors to switch the 25V drive to the tube dots on and off, controlled by the 9V logic levels from the main logic PCB. The 1’s of hours and 1’s of minutes each use 7 transistors, one for each of the emulated 7-segment display elements. The 10’s of hours only uses 5 transistors as this digit only needs to display 0, 1, or 2. The 10’s of minutes uses 6 transistors as the possible digits are 0 through 5. There’s a bit of a clever trick with four diodes on the leftmost tube on the 1’s of hours and both minutes to complete the 7-segment decoding. The 7-segment tube used as the colon display receives its voltage from a KT209 transistor located on the main logic PCB. I’m not sure why this was done – there is certainly enough room on the minutes display board for an additional transistor. Refer to the complete schematic set (PDF, 13MB) for additional information.


Since this clock comes from Russia, it operates on 220V 50Hz power. Fortunately, it doesn’t rely on the AC line frequency for timekeeping so the 60Hz power in the US is not a problem. However, it does require 220V and won’t work on regular wall power here. For testing, I have a Goldsource STU-300 (Amazon link) power converter. This is a true transformer-based voltage converter and not a simple adapter plug (which wouldn’t work). 300 Watts is massive overkill for this clock (the manual says it consumes 20W). However, this is a nice adapter to have around as it has a regular US 5-15P plug on it and has universal receptacles on the front.

STU-300 Adapter

[Stock photo from]

After I finished restoring the clock, I plugged it into a large Symmetra UPS I have in my server room. That UPS has 220V outputs as well as the normal 120V ones.


As I mentioned above, the tubes had become dim with age and for the best appearance I decided to replace them with NOS (new old stock) tubes. I used the same Type 3 tubes that were used originally in order to keep the wiring identical, and I also re-used the original insulating sleeves. There were strips of orange-brown open cell foam which were used along the tops of the IV-26 tubes to prevent damage during shipment. Like most foam from that era, it had denegerated into a sticky goo that would not spring back once pressed. The same foam was used on the inside of the battery compartment cover. I replaced all of this with a modern grey open cell foam trimmed to the same dimensions, after cleaning off the residual goop from the frame. Since I was replacing all 16 IV-26 tubes, I decided to replace the IV-6 colon tube for completeness. I was concerned that while it originally looked fine, it would appear dim when contrasted with the new IV-26 tubes. While the tubes were removed, I carefully cleaned the black metal plate behind them.

I decided to replace the tubes 8 at a time (one board’s worth). In addition to giving me a good reference for what the positioning should be, this also allowed me to take the following photograph, which shows just how badly the tubes had deteriorated over 20+ years of operation:

Half Tubes Replaced

I noted with interest that both the original IV-26 tubes and the replacements I installed were manufactured by Orzep, not Reflektor, despite the two companies being competitors (or at least as much as there was competition in the Soviet system). Both the original IV-6 colon tube and its replacement were manufactured by Reflektor. A search on eBay (which certainly isn’t definitive) doesn’t show any IV-26 tubes made by Reflektor. In all cases where a logo is visible, it is the Orzep logo. Perhaps Reflektor never manufactured the IV-26 tube type.

If you decide to replace the tubes on your own Elektronika, be very careful as the circuit traces can de-laminate from the PCB. Use the lowest wattage soldering iron and the minimum temperature that will do the job. When inserting the tube pins, watch out for the pins getting stuck on the circuit pads and trying to lift them off the board.

I also blew all of the loose dust out of the internal components. As I worked on each board, I carefully cleaned it with board cleaning fluid and an assortment of hog bristle brushes to dislodge any debris that remained on the board after cleaning with the compressed gas duster.

Next, I used contact cleaning spray to clean the switches that protrude through the side of the case. I also wiped down the buttons with an alcohol pad to remove decades of cigarette smoke, grime, and other things I don’t want to think about that were deposited on the buttons over the years.

Having completed the innards, I turned my attention to the case. My first step was to use a spray on wood cleanser / polish to remove the decades of built-up gunk. After several coats and buffing the wood to a nice finish, I moved on to the inside of the case. Again, I used the duster to blow loose material out of the inside. I gave the interior wood a quick wipe to remove some more of the dust, but concentrated most of my efforts on the front glass5. Using a streak-free cleanser I removed an amazing amount of grime from the inside of the glass. If you do this on your own Elektronika, please use caution as the black paint mask on the inside of the glass is relatively fragile. You don’t want to either dissolve or chip it. I then repeated the glass cleaning on the outside. The caution about being gentle applies doubly here – the Электроника 7 lettering on the front is also quite fragile. Once I had a perfect streak-free glass, I cleaned the plastic surround with alcohol wipes and cotton swabs to get into the crevices and seams.

The bezel for the control buttons had been removed as part of the procedure for extracting the internal frame from the case. It received the same alcohol cleaning that had been used on the buttons and the display surround.

The remaining case components were the rear metal panel and the battery box cover. These received a quick wipe-down to remove any surface crud, being careful to not damage the serial number / warning sticker any further (the model and serial information had been defaced at some time in the past, presumably to keep the source of the clock secret if it was found in an unauthorized location).

My last step was to replace the taped-on power extension cord with a 2-wire Europlug cord. As these clocks were designed to hang on walls, the orginal power cords were probably quite short – I’ve never seen one with an original cord longer than a foot or two. Normally the people who salvaged the clocks would attach a power cord to the original cord, using varying levels of skill and safety. When this particular clock was delivered to me, it had an original 1 foot power cord and another 10 feet of power cord attached with electrical tape. There was no plug on the end, though, just some bare wires hanging out. This needed to be cleaned up for both safety and aesthetic reasons.

I wasn’t able to locate a new power cord with an attached plug in the same off-white color that was originally on the clock. However, I did find a nice 6′ 2-wire Europlug cord in black, in the same flat style as the original cord (most power cords these days are round). It is a model 10W1-13306 (Amazon link), intended for use with notebook computers. A quick removal of the receptacle and some soldering gave me a nice new power cord for the clock. While this isn’t the exact same type of plug that was used in the Soviet Union, it still allows the clock to be plugged into a Russian outlet and operate.

After all this, I felt that the clock deserved a label indicating that it had been restored to as-new condition, so I made one up (in Russian, of course) and attached it on the left side of the back panel:

Service Label

Timekeeping accuracy

As received, the clock gained about 2 seconds per day. I mentioned earlier that the timing source is a 32KHz crystal and adjustable capacitor. These were never terribly accurate, and this clock is well over 20 years old and has probably never been adjusted since it left the factory.

I used a frequency counter to adjust the timing with the capacitor. I had some concern that the capacitor would fail during the adjustment due to dust or other stuff getting between its plates. I’ll monitor its accuracy over the next month or so, and if it still gains or loses time (particularly with changes in temperature), I’ll probably design a board to plug into the clock’s unused external timing input. A DS32KHZ temperature compensated timing IC will provide a clock with an accuracy of 1 minute per year (better than .16 seconds / day).


Look for an upcoming article on this clock’s big brother, the 48-tube Elektronika 7-06:

48-tube Elektronika


[1] Pronounced ee-lec-TRON-ee-kuh. Not uh-lec-… or eh-lec…

[2] Each time I first reference a Russian part number, I enclose the Cyrillic spelling in parenthesis. This is mainly to help search engines locate this page.

[3] The colon tube is actually an IV-6, not an IV-8. This has been confirmed on both my clock and the schematics – the Russian Wikipedia article is wrong.

[4] The WASP site states “I don’t mind when my articles are used on other web resources [in] the Internet community, certainly an indication of the author and links to my site are very welcome. The use of my material in the paper press or advertising material is different and requires permission from the author – write [to me], [as I] reply to all [inquiries].”

[5] An original Elektronika 7-06M will have a sheet of green glass (not plastic) with black paint on the inside to mask out everything but the tubes. If you see an Elektronika 7-06M with plastic or clear glass, it has been modified at some point in the past. The same is true of most other Elektronika 7 models, though some were built with MTH90 (МТХ90) thyratron displays which would need an orange filter.

My goal is for this blog to be the most complete source of information about the Elektronika 7 in any language. I welcome comments / suggestions on how to improve this article.

The GEN II MOD-6_7971

H Carl Ott and Michael Barile recently released the GEN II version of their fabulous MOD-6_7971 Nixie clock, and I ordered several kits from them. The new version adds GPS time synchronization, either via a GPS receiver plugged into the back of the clock, or by using an RF-Link repeater module which talks to the clock over short-range 2.4GHz radio. This clock uses the B-7971 Nixie tube, which displays alphanumeric characters 2½” tall.

The RF-Link lets you completely avoid the problem of needing to position the clock within a few feet of a window or resort to using a bunch of PS/2 extension cords. Now you can put the clock exactly where you want it. The RF-Link remote also includes an indoor temperature sensor and a pushbutton which can be used to remotely turn the clock display on and off.

I have a separate page here describing the clock, but I’m adding a link here so people can find it, and also to facilitate comments (while the actual clock page doesn’t support comments, you can comment here).

Here’s a couple of teaser pictures – click either picture for more info:

MOD-6 Nixie clock

MOD-6 RF-Link

For more info or to order a kit or assembled clock, visit the MOD-6 page at

The MOD-6_7971 Nixie tube clock

I haven’t mentioned it before, but I’m a bit of a clock geek. The technical term for that is “horophile”. I have quite a few oddball timepieces around the house, including the first QLOCKTWO delivered to the US, a pair of Bulbdial clocks, and many Nixie tube and VFD clocks.

However, last week I received the largest clock kit ever – the MOD-6_7971 by by Carl Ott and Michael Barile. The completed clock is over 20″ wide and 6″ high, with digits 2½” tall.

I have a separate page here describing the clock, but I’m adding a link here so people can find it, and also to facilitate comments (while the actual clock page doesn’t support comments, you can comment here).

Here’s a teaser picture – click the picture for more info:

MOD-6 Nixie clock