Here I would like to introduce you to an electromechanical movement, which I only understand to some extent, but this is also a self-development of Zenith.
It all started with a meeting of watch collectors in my region at the beginning of November. A participant who knew my fable for old Zenith clocks brought a Zenith shop-window clock of the 1970's to the meeting.
The decorative clocks around it are then my playground and I was completely overwhelmed. But I found a similar model in the bay in a disgusting truck clock. A specialist, who in the meantime had come into possession of the "Exact hour", did not want to believe this. Since I know a collector of on-board clocks of all kinds, where I had something open, a curious specialist on hand and myself was so curious, the truck clock was fished spontaneously out of the bay. Therefore I can introduce you to the unconventional caliber here.
The Zenith movement E 61 is, as the letter E suggests, an electrically driven movement. It dates from the period shortly before the invention of quartz watches. The idea of periodically driving balances or pendulums by means of electromagnetic force is very old. It was first realized in the form of a magnetic pendulum clock patented by the Scot Alexander Blain in 1841. The inventions of Léon Hatot / ATO (1883-1953) were groundbreaking for today's quartz clocks and also for the realization of electromechanical clocks. As early as 1920, he produced ATO magnetic pendulum clocks in three variations as a serial clock, which he had invented in 1919. Marius Lavets, the ATO workshop manager, developed the Lavet motor named after him in 1936, and after several preliminary patents, Lavet was granted a basic patent for transistor control of electromechanical clocks in 1950. The royalties for this patent were high, as every electromechanical or quartz watch with an analogue display contains the Lavet motor. (The Léon Hatot brand has been part of the Swatch Group since 1999).
Therefore, on some E61 movements, the serial number is accompanied by the indication LIC. ATO
As the photo already reveals, the E61 is a slightly larger movement of about 6x6x6 cm. Since the production of this movement probably overlapped with the rapid conquest of the market by quartz watches, it was not produced in large quantities. The planned applications of this complex movement can only be guessed. It should probably be used in table and ship chronometers. At least as a table clock and as a shop window clock, it was listed in the brochures as successor of the mechanical "Exact Time" until the 1970's. On request, the dials were also marked with the name of the concessionaire (see above). Here a picture from a brochure:
Let us now come to the movement. Here a view at the front:
One recognizes a large black balance wheel, Breguet hairspring and an Incablock shock protection system. The regulation of the hairspring length is done by a screw, which is sticking out of the protection cover of the movement, which is removed here, and moves the regulator arm. On the left side, in the red protection cap, there are the coils, which drive the balance wheel by magnetic induction and control the pulse length.
On the side you can see the four connections of the coils:
Two serve the balance drive. For this purpose, the hoop has two magnetic bars arranged opposite each other, which are pushed on or off depending on the load. For this purpose, the red coil module must be adjusted exactly in height, inclination and distance, so that the magnetic cylinders attached to the balance wheel run exactly "in the middle". For this purpose, there are several adjusting screws on the XYZ axis of the coil module. The most important element of this drive, however, is the control of the pulse length. The measurement of the amplitude of the balance wheel is done by means of another one-sided pickup at the hoop. It runs ferromagnetically (?) passively on the balance wheel.
This feedback system keeps the amplitude of the balance wheel always stable. It is independent of the battery voltage. If the system needs more energy, e.g. due to resinification, it will be supplied. So, an electromechanical watch of this design won't show any deviation of rate, if there are signs of need for revision, but simply consumes more power. In the worst case, when the system is mechanically blocked, so much energy is supplied until the cell is quickly discharged completely. In the case of the E 61, with a frequency of 28800 half oscillations, it is already a "fast oscillator" of its time. Instead of a typical Swiss lever escapement, the E-61 has a plastic ratchet wheel. Since the coils can be adjusted exactly and the length of the spiral can be changed, the measured values are excellent: 0.1 sec/day
The electrical part takes over the drive and the amplitude stabilization of the balance. The electronic module can be seen in the rear view above. The two transistors mounted in the board are the only active elements.
The electricity feed-in was built in two variations by means of appropriate rule technology. In the case of the table and display clocks, two Mallory type Z12 cells (1.4V 3600mAh) connected in series were simply integrated into an easily accessible battery compartment. The movement was powered by 2.8VDC. The table and window clocks consumed very little energy in maintained condition. The measured values are about 400 μA. In general, it is important not to use nickel/metal hydride or alkaline manganese batteries in electromechanical table clocks. If, for whatever reason, these batteries run out, vapors develop in the relatively closed cases, their metallic "precipitation" and acid rain is completely distributed on the movement and destroys it irreversibly.
This exciting and complex electro-mechanical movement with chronometer characteristics was now developed at Zenith and was overtaken by the rapidly advancing technological development to the point where it was ready for series production. What to do? The fact is that all four movements known to us have four-digit serial numbers and can probably be assumed to have been produced "only" a few thousand pieces. In times of quartz technology, not all of them could be sold as table clocks, especially since the quartz was also protected by the Zenith company in the 1970's. Under the American Zenith Radio Cooperation, which acquired Zenith in 1972, the production of mechanical movements was completely stopped in 1975. Fortunately, this changed again in 1984.
The fact, that a surplus stock of the E 61 was sold in the sense of a recycling is for us at least the only explanation, why you can find this movement in truck clocks, even without the second hand, which disturbs the overview. These movements only differ in their oil plan and the adapted power supply by the truck battery. The Bord watches were powered by 12 to 24VDC and were internally stabilized to 6.2VDC by a diode.
The luminous mass of these truck clocks shows no radioactivity. This is also a clear sign that the complete watches were made after 1970. A standard Li-Ion 9V battery can run these watches for 70 - 80 days until the voltage of the battery falls below 6.2 VDC. As board clocks have no direct second hand and no pointer setting mechanism directly at work. The time is set by a steel shaft integrated in the dashboard of the car.
The oil plan was much rougher. Generously tougher oil was distributed on the bearings. This made sense, because with these clocks one could not assume regular maintenance. Since a somewhat sluggish movement is completely compensated by the pulse length at the balance, they were almost maintenance-free truck watches, which did not need to be set or wound.
All's well that ends well. "My" truck watch is modified to be powered by a standard Li-Ion 9V battery. This battery can run the watch for 70 - 80 days until the voltage of the battery is below the 6.2 VDC limit. It has been passed on to a suitable delighted friend and new owner, Theo, the specialist for this stuff now has both versions and thanks to another collector, who also owns a table clock, characteristics such as the different oil plans have been confirmed, as such changes may well be changed after a revision.
Even if I do not understand everything I am fascinated. A big thanks to Theo who gave me an insight into the electromagnetic world, restored the watches and edited the text.