1977 digital clock kit retrospective 

I recently came across a small electronic treasure from my youth. It is a digital clock kit, circa 1977. This was the first electronics kit I ever bought and built. It might have been bought from Dick Smith Electronics although there is no DSE branding — that may have come later.  I think it cost in the order of $25. I remember it being pricey enough that I had to put a few dollars aside for a while until I had enough.

Consumer electronic digital clocks were a novelty in 1977. You couldn’t buy them cheaply.  My dad had a digital clock, but it wasn’t a real electronic clock, it was a mechanical clock with rotating drums and lightweight metal plates with numbers on them that flipped over like the departure boards at an airport. My brother, who was also a keen electronics enthusiast in 1977, built a digital clock that used the same clock chip (MM5314) and red 7 segment displays (DL707s /704s). About that time, I built a single digit counter with 7490, 7447 and DL707 combination as an experiment with the new and exciting TTL logic. It sat on the bench endlessly counting. The TTL chips were power-hungry, and in the brief era before 7805 three pin regulators we used a 5 volt 400mW zener and a 2N3055 emitter-follower as a source of 5 volts at hundreds of milliamps. The first TTL digital frequency counters were appearing around this time. They drew an amp at 5 volts and got hot.

I loved the evenness of the red light coming off the LED display. In the era of 6v and 12v incandescent dial lamps, it was cool, pure and even light from a semiconductor diode junction, not physically delicate and never to burn out or expire like incandescent filaments.  By chance, my clock kit used a gas discharge display rather than solid state LED displays. I remember being a bit unsure that I would like the gas discharge display, being somewhat old fashioned tube technology. But when it was built it looked great — in fact the new gas discharge tube emitted so much light it lit up the bedroom at night. I resorted to placing a second piece of smoky perspex in front of it to attenuate the light intensity. How many nights did I fall asleep watching those seconds clocking over? Fifty eight, fifty nine, zero…

The clock reveals construction techniques of the time. The thru-hole board is light brown, possibly phenolic material (?). The parts are so strikingly big. The limiting factor was the width of the display, so there was no need to reduce the width of the board behind it. Instructions are screen-printed on the top. NPNs here, PNPs there. Kit builders in those days were less sophisticated, and there were no online forums in which to ask a question.

The gas discharge tube is a Japan Radio Corporation J4929A. Here is a page in japanese of old calculator displays, the J4929A is about half way down. It turns out it was an 8 digit (plus arithmetic sign) display made for calculators. This page in the Calculator Museum tells me it was released in 1973. and was used in the Canon L-811.

The brain of the clock was its National Semiconductor MM5314. This was a marvel of the electronic age at the time. It had no external crystal clock, rather, it counted pulses derived from the 50Hz mains. To the consumer, it kept near perfect time. Until the power dropped or someone turned off the switch at the wall. When powered up, it flashed 12:00:00 at one second intervals. Who can forget that. You can still buy the chip ($20), pulled from clocks like mine.   Even Aliexpress can’t do it any cheaper.   You can also still buy a ‘retro 1970s classic’ clock kit, although it uses retro LED 7 segment display, not a gas discharge device like mine, or nixie tubes.  It appears that people are using them to drive nixie tubes, to bring a bit of that hipster cafe vibe into the living room.

I turned it on, thinking I might run it agai in the bedroom. I don’t need another clock in the bedroom, but I thought it would be a nice  nostalgic piece, a token from my boyhood. On power up, it was dead. The mains transformer hummed slightly. But not a photon to be seen. I guess the gas discharge tube finally discharged itself after 40 years. Could I find a replacement? I googled it. Nothing, apart from museum pages. Then I tried eBay. Still nothing. You know you’re in trouble when eBay can’t find what you’re looking for. I’ll put it back in its storage box. Who knows, I might acquire some nixie tubes one day.

Postscript: Heathkit, America’s much loved kit electronics company, are back.  With digital versions of a few of their famous kit offetings. Their first clock kit in 30 years, the Heathkit Most Reliable Clock, has a lot in common with my old piece. 

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38 thoughts on “1977 digital clock kit retrospective 

  1. Anonymous says:

    Nice, thanks for posting. I am into these kit clocks now and I am collecting similar vintage units on the 60 Hz side of the world. I like the mm5314 clocks of that time and have a few (6 or 7 and growing). Maybe put in a saved search into ebay and it seems as if you know that a calculator used that display, put that in as a saved search also. You may get an alert one day! If the high voltage is already there, it may be possible to neatly upgrade your clock to 2 pieces of beckman sp-353 panaplex displays in the mean time in a clean, reversible way. I am starting to document a few clocks on youtube at JIMO415 …enjoy, Jim


    • Paul Taylor says:

      Thanks Jim. There are quite a few contemporary updates on clocks using Nanos and RTCs. I built a GPS clock which is a fun take on the classic digital clock.
      Dave at EEVBlog recently posted a 1970s Nixie counter teardown. The Nixies and slow counting speed look amazing. Its here, if WordPress doesn’t strip out the url

      Your 1977 Numitron clock is a pearler! And a crystal time base, a top shelf design in its day I subscribed to your channel, keep the retro clocks coming!.


      • Anonymous says:

        Paul, thanks, I did see that video. I think he is a brilliant individual and I currently have no way to even keep up with his mind. I love his funny little comments along the way in his videos. Along your way, I have to that HAM radio stuff has not grabbed me yet but it has recently grabbed my cousin. He and his son are getting into it. thank you for the reply and comment on youtube.
        Be well,


      • Paul Taylor says:

        Thanks Jim. I got back into ham radio mainly for building. Arduino, the hundreds of digital and analog IO devices now available, and the dirt cheap parts and cards available as a byproduct of the consumer electronics revolution coming out of China’s surplus markets, have made high quality home made radio projects achievable for the home experimenter. And the internet maker communities have exploded with activity and support. I find the Summits On The Air (SOTA) competition is a great way to combine designing and building small simple radios, what we Aussies call ‘bushwalking’ , and being in an active radio enthusiast’s community a good combination. Cheers and keep building.


  2. Peter Seed says:

    I Have one display that is! no idea if it works. How could I test it? if it works would you like it?


  3. Anonymous says:

    Paul, thank you for considering especially since the clock has a long history with you! It would be great if Peter is on board. I will stay tuned.


    • Anonymous says:

      The thread had been quiet and it looks like it may not work out with the above mentioned display. I just wanted to let you know that I am still interested if you are putting the clock on the “not going to get to it list”. I am not sure as to how to give you my direct contact info as I am not sure if I want to list it here (not sure how to delete it after). Maybe you can reach out via my youtube or if you have another idea… Thanks, Jim


  4. Anonymous says:

    The email address seems to be not working. It is kicking back.



  5. Anonymous says:

    Thank you Paul, I reached out to Peter with address. Talk soon, Jim


  6. Anonymous says:

    Hi again, I just wanted to touch base and I hope all is well. I was thinking….since it seems that you both are somewhat close to each other, would it be better for Peter to send the display to Paul first so that at least the display is with the clock? then send it over the pond? Either way is ok , You have my info. I hope all is good, Jim


  7. Anonymous says:

    Paul, Thank you for the very generous transaction!!! It has a great new home with 22 or more siblings!


  8. John Lowe says:

    Paul, Hi. I have one of these – also built into a metal case just like yours. I bought it in 1977 from Dick Smith Electronics at the Artarmon head office/warehouse, where I worked as a storeman all those years ago. It has been running faithfully almost to this day. I noticed only a few weeks ago, that it was losing time. Right now, it has lost about 4 minutes in about a week or so. I was planning to crack it open and look at why it is losing time. The displays still function, although one or two digits occasionally go a bit faint.

    I was just google’ing for “dick smith 1977 digital clock kit” and came across your article – I will certainly let you know how I go with this. Also it may be the high voltage that is failing in your clock. Worst case, it should be possible to upgrade this to use 7-segment LED displays – which was what I was thinking of, if the display eventually failed.

    Liked by 1 person

    • Paul Taylor says:

      Hi John

      That’s a great story, we are most likely of similar age. As I wrote in the post, this was one of the first kits I ever attempted to build and I was incredibly proud of it, it ran for years and years, and after I boxed it up for about 4 decades, I could not decide to get rid of it. When I blogged on it over 3 years ago, a clock collector named Jim on the USA contacted me. After a bit of chatting, I sent it to him, he collects MM5314 and Nixie clocks, he was very happy to receive at and it will get a lot more care with him that it would have with me.

      His YouTube is here: https://www.youtube.com/user/JIMO415/videos

      Thanks for commenting, as these clocks count the mains, I assume that its losing time is due to consistent fluctuations in the 50Hz mains frequency. But that’s just a guess, 4 minutes is a lot to lose. Please let me know if you find the issue, and if your clock gets a new display.

      Regards Paul Taylor.

      PS: I’ve followed your blog. I love repair, it is an underappreciated skill and and overlooked joy.

      Liked by 1 person

    • Anonymous says:

      Hi John,
      As Paul mentioned, I now have that clock. He was very kind to set me up with it (thanks again Paul). I have been on a search for a new display as I want to try to keep it original. The display in said clock looks a bit toasty and is very dim. You brought up a good point. I should recheck the HV and I have to take another look as it just may be failing caps. As far as yours loosing time, it does use the 50 hz as a reference and there is really nothing in the conditioning section but a disc cap, a small signal diode and a resistor. If you are checking against a quartz or other more accurate source, you may find that if you just watch it and wait longer, it may seem to “come back in correct time”. I have seen this over here albeit only 40 to 50 seconds over a month and then correct in a day! The power company does adjust over time. 4 minutes may be excessive so I don’t know.


      • Paul Taylor says:

        Hello again Jim, thanks for commenting, nice to see appreciators of MM5314 seventies digital clock ICs united in a conversation across the globe. The gas discharge display in my clock was always bright, in fact too bright. I used to attenuate the brightness with smoky perspex. I now wonder if I could have increased a dropping or current limiting resistor to reduce brightness, and as well, extend the life of that display. Maybe it might not have burned out. Just a thought.

        Regards to you both. Paul VK3HN.


  9. John Lowe says:

    Paul, yes, I am getting along in years, lol. I just opened up the clock. My clock is a little different in that my MM5314 is socketed – I actually remembered doing this when I saw it. At the time I was able to get socket strips that we cut to the right number of pins, solder them, and then bend the tab back and forth until it broke off and left the separated socket pins. In addition, my display is socketed as well.

    There is what appears to be a 120V high voltage line that drives the display and a fuse. My clock is covered in a fine layer of dust which I will remove. The time has been very reliable – I only change the time if we lose power, or for daylight savings changes and as has been mentioned, there is really nothing in the circuitry that could affect the time keeping. I will remove the dust for now and put it back in operation. I wonder whether the predominance of solar power may be a factor. I also have this running from a small UPS, so possibly we have been getting small outages where the UPS output frequency may be a bit low, but for losing minutes – this seems very unlikely. Anyway, i will set the clock using my Garmin GPS and keep an eye on it.

    BTW: I was VK2BZJ but I let my license lapse for many years.


  10. Paul Taylor says:

    Thanks John, let us know how your 1970s clock pulls up after its clean up. UPS and solar could I guess create the occasional spike on mains that might be xiubted by the MM5314, the mains is certainly not as untampered with as it was in 1977. Cheers!


  11. John Lowe says:

    Paul, sorry for the delay in coming back. Part of Covid madness, I guess. The update was that once the clock was plugged straight into the power point, bypassing the UPS – it keeps time again. I got reminded of this as the display is now flickering very badly – some days it is quite dim, so I will look at replacing the display with a LED panel one of these days.

    Liked by 1 person

    • Paul Taylor says:

      Hi John, no problem, this MM5314 clock has a long story to tell. The fluorescent display was seriously deteriorated from back in the late 80s from memory. It was radiant for the first 5 years, so bright I had to turn it away from my bed. Replacing the display with 7 segment LEDs would be the best idea as I don’t think you have a chance of finding another of those displays from the mid 70s. There will be schematics online for interfacing MM5314 to six DL704 or 707 style displays. It’s good that you have the board still working. Thanks for the update. Good luck with it. Cheers from Melbourne.


  12. Anonymous says:

    Paul, I did have a question about your old clock since this has once again come up. I was wondering what your average mains voltage is in your area. I have been playing with some 1980’s soviet clocks and they are said to be designed to run at 220 v. I run them at 220v. Now your old clock, I was just wondering if it was designed to run at 220 or 240 v. In playing with the clock, it seems as if the display is flat dead at 220v but wakes up with it’s weak flicker near 240v. Thanks. I hope all is well. Jim


    • Paul Taylor says:

      Jim, this page from 2012 explains it. I would have said 220 to 240 but turns out it is 230v. When plugging my multimeter into a power socket I expect to see close to 240 from experience but that all depends on load and other factors. So run the clock on 240v if you like, or probably 250 if you can generate it, it should be fine.


      Thanks for the question, I now know about the Australian standard.


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