In the 1960s and 1970s, Citizen produced both transistor controlled balance wheel movements (Cosmotron) and tuning fork movements (HiSonic).


The definitive guide on all things Cosmotron is Sweephand’s excellent blog here. Below, I’ll just summarise the key dates, calibres, names and show a few of my own photographs.

All of the calibres below are of the transistor controlled, fixed coil, moving magnet type.

  • 1966: Calibre 0801, 18,000 bph, ‘X8 Electric Watch’ on the dial
  • 1969: Calibre 0802, 18,000 bhp, ‘X8 Chrono Master” on the dial, remained in production until about 1972
  • 1969: Calibre 0840, 21,600 bhp, first models to carry ‘Cosmotron’ and ‘transistor’ on the dial
  • 1969: Calibre 0880, 18,000 bhp, first models to carry ‘Cosmotron’ and ‘transistor’ on the dial
  • 1969: Calibre 0820, 21,600 bhp, Officially Certified Chronometer, world’s first titanium cased watch
  • 1970: Calibre 4840, 18,000 bhp, first Cosmotron with a date
  • 1972: Calibre 78xxx series, 36,000 bhp, ‘X8’ dropped
  • 08xx movements were also used in the Caravelle Transitorised range of watches.

There is one oddity in the Cosmotron branded range. The “GX Cosmotron” branded watches contain a tuning fork movement rather than a balance wheel based one. It is a little strange that these GX watches are not branded “HiSonic” along with Citizen’s other tuning fork watches but see below in the HiSonic section….

There was great variety in watch design in the Cosmotron range; some were very conservative, while others were hideous colours with large faceted crystals! Some had a button at the 8 oclock position; when pressed, it zeros the constant second hand — maybe a doctor’s watch for taking a pulse?

And since many people have asked me, on the 78xx series watches, you set the date and day in the following manner: Hold the watch upright in front of your face with 6 pointing to the ground and 12 pointing to the sky. Pressing in the crown will advance the date. Now turn the watch so that 6 points to the sky and 12 points to the ground. Pressing in the crown will now advance the day.


The Citizen HiSonic range of tuning fork watches uses movements made under license from Bulova. They are based on Accutron movements and, in some cases, are exact copies with interchangeable parts.

Having looked at both Bulova and Citizen tuning fork calibre numbers, the correlation seems to be:

  • Citizen 3701A = Accutron 2181 (day)
  • Citizen 3702A = Accutron 2182 (day/date)
  • Citizen 3701B = Accutron 2191 (day)

So the “A” on these HiSonic calibre numbers appears to indicate that they are based on the Accutron 218 Series while the “B” calibres are based on the Accutron 219 Series. The last numeral appears to be used in the same way on both Accutron and HiSonic with “1” indicating a date only model and “2” a day and date model etc.

The “A” Series is infact an exact copy of the 218 Accutron and all parts are interchangeable. The “B” Series is based on the design of the Accutron 219 and some parts, such as the index wheel, are interchangeable, but Citizen have altered the layout of the single tuning fork cup and moved it to the opposite side and turned it through 90 degrees (see photos below) — it would be interesting to know why they did this? Was it patent related or were there some genuine improvemnts over the Accutron 219 movement? Is this the reason that the “B” Series is branded as GX Cosmotrons rather than HiSonics? I’m sure Sweephand will find out and let us know!