Atmos clocks, due to their unusual design and very delicate construction, should only be repaired by a specialist.
The latest model in the Atmos range is the cal 540, (the cal550 series is based on the 540's design). Some collectors are not too fond of this model because they consider that the changes brought about by Jaeger LeCoultre are too radical and therefore the design is now a bit too far from the original.
In theory, nobody can deny that the changes made by Jaeger LeCoultre are of great benefit to the performance of this clock.
Atmos, cal 540(left) and cal 528(right). Comparing the construction of the latest Atmos cal540 with the earler 528 model.
The construction is much lighter, the wheels are lighter and the new mainsping is a major improvement.
The new mainspring goes some way to ease the problem of variation in power, found in earlier models.
The bellow is smaller and seems more flexible. The bellow housing is stronger, therefore more efficjent and reduces the likelyhood of cracked bellow housing.
Technically, the benefits outweight the need to mantain "originality", as it produces a much more reliable balance amplitude.
Alhough I believe, that there could be another aspect to the cal540: Maybe this new model requires to be serviced more often. I have personally come across quite a few examples where this model needed servicing after 10years only or even after 5 from new. This was to much surprise of the owner expecially if they also posses an older caliber Atmosl which has not needed any attention for 30-40years. Of course, I do not know how many there are in uk and what is the average service-gap, I can only speak from the repairs that have come to me.
A good service and fault-correction, with great attention to details, should give this model the longer trouble-free period that it is capable of.
Recently, In the second-hand market, the cal540 has become much more in demand than any other ordinary model.
They regularly fetch a higher price than the older calibers. I would logically attribute this to two factors: first, the lure of the better exterior condition and second, the unlikelyhood of needing expensive repairs....... they are much newer, after all.
W. Churchill, J.F.Kennedy and C. De Gaulle with Atmos clocks
Article found in an old magazine
Comparing Atmos Cal540 with Cal528 movements
From the pictures you can clearly appreciate the differences. In the cal528 (right), the extra plate accomodates the heavier barrel and the first intermediate wheel.
All the dimensions in the cal540(left) are smaller: the movement, the "winding" spring, the bellow and all the case dimensions are all about 1cm smaller.
When an Atmos stops working, in 95% of the cases the failure is readily blamed on a faulty bellow, while I find that in less than 20% is the bellow at fault.
An Atmos specialist will correctly diagnose the likely cause of the stoppage.
Bellow comparison: Atmos cal540 (left), Atmos cal528 (center), Atmos cal519 (right)
The cal540 bellow case has a bayonet fitting and measures 120mm dia.
Cal528 and cal519 have larger bellows, 130mm dia. They are attached with two and four nuts respectively.
~~We have replacement Atmos bellows in stock, if required~~
Bellows can vary: the image below shows two similar ones which have different dimensions when fully contracted.
Below, LEFT AND CENTRE IMAGES illustrate how a faulty bellows would look like at room temperature, flat or half deflated.
RIGHT IMAGE: bellow in good condition.
Of course, bellow expansion will also vary according to temperature and air pressure, .
I am interested in purchasing any Atmos clocks for spares,
If I can, I will supply second-hand Atmos parts to other repairers, when available.