ETA 2390

Description

In 1954, the swiss ETA launched a completely new and modern constructed series of windup and selfwinding movements, whose base caliber is the ETA 2390 with a diameter of 10 1/2 lignes. For the first time, its gear train lacks the center minute wheel to reduce the clearance of the minute hands, which was caused by the low-numbered toothing of a central minute wheel. This mechanism, called “System ETA”, invented by Heinrich Stamm was also patented under the swiss patent number CH297900A.

Another nice effect is, that more space was available for the mainspring barrel and the balance wheel.

As ususal that time, it was available in different versions. Depending on how much the customer was willing to pay, there were different types of balances, different shock protections and different numbers of (cap) jewels.

The base plate not only shows the good quality of the movement - all important bearings use rubies, but also that the gear train was constructed in a very modern way with the lack of a directly driven center minute wheel.

The mainspring barrel drives the large driving wheel, followd by third wheel, direcly driven center seconds wheel and finally the steel escape wheel.

The large driving wheel must use a large axle and a stable pinion, since the full force of the mainspring barrel acts on it.

The minute and hour hands are both driven on the dial side by the third wheel.

As regulating device, a screw balance (in later versions there were also screw-less anular balances) and a swiss pallet lever were used.

The balance wheel is of course shock protected and beats slowly with 18000 A/h.

The effective length of the fix mounted hairspring can be adjusted with a long regulator arm.

The ratchet, below the ratchet wheel, is a genious and space-saving construction, which is also visually pleasent.

On the empty dial side you see, that the minute wheel is plugged onto the center axle and driven by the third wheel at 8 o’clock. This construction principle of ETA is used until today.

The center minute wheel is with its other toothing engaged with the third wheel. Its cannon pinion in mounted on it with a skipping clutch. As usual, an exchange wheel followes, and finally the hour wheel.

The fact, that the construction principle of this movement is used until today, practically unmodified, on the modern ETA automatics, shows, how revolutionary it was at that time.