The movements are characterised by:
- Balance Wheel
- A Transistor acting as a switch
- No Mechanical contacts
Sometimes the coil is on the balance wheel and the magnets are on the base plates, but it is more common to find it the other way around. Because a transistor can act as switch, these were the first battery-powered watchs that no longer needed a physical electrical contact. The days of worn-out, sparking contacts were over.
The voltage to steer the base of the transistor is generated by induction in the trigger coil; the visible coil in these watches is actually two coils side-by-side. As the fixed magnets on the balance pass over these coils, the trigger coil generates a voltage and the transistor completes the circuit on the impulse coil and the balance receives an impulse. When the balance swings back due to the spring, the trigger coil generates a reverse voltage and the transistor breaks the circuit to the impulse coil.
This system was invented, and patented, by Etablissements Leon Hatot (ATO) in the early 1950s. As a result, millions of watches carry the ATO or Lic. ATO mark either on the movement plates and / or on the dial. You can see this quite clearly on this Nivada dial.
In the early 1960s, Omega experimented with transistor controlled balance wheel watches, but none were ever brought to market. Very little is known about them but I have been sent a couple of scans of these unique movements; you can find them here in the Omega section of this website.
The movement below is the only Bifora electric / electronic movement to reach production. The same movement was used in both the ladies (B10) and mens (B11) watches; see the men’s watch here. It runs at 36,000bph and is characterised by two coils on the balance and four permanent magnets.
The Bulova Caravelle 12 OUCD movement is the same as the Citizen X-8.
These were not the first movements with a transistor; the Bulova Accutron can claim that but the ESA 9150 Dynotron, launched in 1967, was the first movement with a balance and a transistor.
Judging by the number of watches that are still around today, running quite happy with these movements, the Dynotrons must have been a very successful movement for ESA. In addition, many watch companies employed Dynotron movements in their watches. There were four main calibres:
- ESA 9150: 1967, the first electronically controlled balance wheel movement, date, running at 21,600 BPH.
- ESA 9154: 1970, date, increased to 28,800 BPH; 9150 and 9154 look very similar.
- ESA 9157: 1975, date, 28,800 BPH.
- ESA 9158: 1975, day and date, 28,800 BPH; 9157 and 9158 look very similar and do not have the quality of the earlier 9150 and 9154.
In addition to the four main calibres above, there was also:
- ESA 9156: from the balance side, identical to the 9154 calibre but turn it over and it has a complication involving 4 biorhythms disc. It was only ever used in the very rare Certina Biostar Electronic watch.
- ESA 9159: from the balance side, identical to the 9157/8 calibres but lacked hands. It was only ever used in the very rare Gruen Electronic Jump Hour watch.
- ESA 9176: a very strange movement that was used in the Jaz-Derby Swissonic
- ESA 9200: a small calibre that was often used in ladies watches (see Lukcom).
The Junghans 600 or “Ato-Chron” appeared at roughly the same time as the ESA Dynotron. It was the first German transistorised movement. Sheffield also sold these movements (below): this one came from the Wedgefield watch
The first group of photographs show some of the movements in the Citizen 7800 Cosmotron range: the 7802A, 7803A and 7804A. To change the date on these watches, you hold them with the dial facing downwards and press the button; to change the day, you press the button with the dial side up!
The 1971 West German Porta PUW 2001 (with date only) has the coil on the balance wheel, three fixed magnets with separate electronic components (3 transistors, 3 resistors and 1 capacitor). These rare watches were only produced for a very short time. There is also a PUW 2000 without day or date and PUW 2002 with date and day.
The Porta PUW 2500, 2501 and 2502 movements moved these individual electronic components into a single integrated circuit.
The Model 87 was introduced in 1969 and is a dated version of the Model 84 that was introduced in 1965. Both are similiar to the Model 40 but with the contacts now replaced with a transistor… this is a Moving Coil, Transistor Controlled movement.
More Timex electric watches here.
A rare Chinese transistorised movement from the 1970s. Read more about it on the main Xiang Yang page.