Latest Arrival – Cosmotron 7800

I have a soft spot for the Cosmotrons – these were electro-mechanical hybrid watches with a limited production life since their new technology was almost immediately superseded by quartz technology. The fact that they were doomed almost from day one seems a good reason to collect a few! 🙂

I also realised that I don’t have many square, or square-ish watches so a ‘tank’ case Cosmotron was a nice find:

This one, from 1973, is on a good solid link bracelet, and since it has a chunky case it has a nice heft about it. It’s also a Cosmotron ‘Special’ with a button at 8 o’clock which zeros the second hand – it also zeros the minute hand when close to the 12 o’clock position. See this video of another model with this movement:

The bracelet is in good condition (the same design can be seen on some of the Challenge Timer Chronographs) and is just the right size for me.  Time keeping is very good from this 36,000 beats per hour movement , requiring no adjustment over a week or so 🙂


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11 Responses to Latest Arrival – Cosmotron 7800

  1. Kevin says:

    I have 2 new citizen Cosmotron for sale
    R1000.00 each

  2. Jeff Ferguson says:

    Hi sweephand- I have a 7801A and was wondering about the balance adjustment. Do you simply turn the screw or do you move one of the arms? If it’s the screw do you know how many seconds one notch is? Sorry to post this here I wasnt sure how to contact you via a new post. Thanks

  3. Jeff Ferguson says:

    Actually my mistake, there are no lines near the + or – …..

    • sweephand says:

      Hi Jeff, thanks for visiting my blog. No problem about using ‘comments’ for your question, it’s the best way in fact since only I can create posts. The screw on the balance:

      This screw is a fine adjuster typically used on high beat watches – the 78 Cosmotrons run at 36,000 beat per hour – which are capable of being finely tuned for very accurate time-keeping. Only a small movement of the screw will adjust by a few seconds or even less if you move it very carefully once the watch is already running fairly accurately. I can’t say that a certain amount of movement results in x amount of seconds – it’s a case of trial and error, so can require patience if you want to get very accurate timing. If your watch is currently running minutes out, say more than 2 minutes, then this adjuster is unlikely to provide enough adjustment, and I’d recommend getting the watch serviced first to make sure it is clean, oiled and checked for worn parts, so that it is in the best possible condition to get the most accurate time-keeping.


      • Jeff Ferguson says:

        Thanks for the response Stephen. I suppose I’ll turn the screw all the way in one direction and then all the way the other direction, compare the results, then adjust accordingly. I have 6 Cosmotrons and they are among my favorite electronic watches. All except 1 are accurate and I haven’t had to adjust until now.
        Someday I’d like one of those IC-12’s with the 5800 movement or a GX with the 3701B movement. The Hisonics are too expensive!

  4. Binh Nguyen says:

    Hi Stephen
    I recently acquired an cosmotron 7804 with movement inside but it little too fast so i try to fine tune it but without knowledge i accidently moving the hand instead of the screw, i managed to slow it down to -19s/d but now it have pretty bad beat error, is there any chance or advice for me that i can undo my mistake, i’m pretty much screw rn

    • sweephand says:

      Hi Binh Nguyen, sorry for my slow reply. I’m afraid I can’t help much – I’m not a watchmaker, and I’ve never tried to adjust the timing/beat on a Cosmotron. You’ve no doubt tried to carefully return the part you’ve moved on the adjuster to where it was before, and then tried to adjust accuracy using the fine adjuster. Other than that I can only suggest taking it to a reputable watchmaker if you know of anyone local to you for advice or a fix. This pic of the movement and might help to get it back to where it should be:


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