The 1954 version was offered in two dial patterns; on with numerals at 12, 6 and 9 and the other with numerals at the even number hours. Only the even numbered pattern was offered in 1955, so if you come across the dial with numerals at 12, 6 and 9, you know it's a 1954 model.
Like the K-575, the Datomatic A came in a stainless steel case. It's purely a guess, but the material choice of stainless steel makes me think that Hamilton executive may not have been sold on the idea that buyers would be interested in a watch that could tell the date, in addition to the time. As such, they limited their risk by pricing the watch at the lowest price point possible... a stainless steel case.
The Illinois-branded movements were the first time that Hamilton "stooped so low" as to use Swiss-made movements. Up until this point, every Hamilton movement was made in the USA, and mostly in Lancaster, PA. The exception being some of the movements that came as the result of the acquisition of Illinois Watch Company in 1928.
The Datomatic A used a variation of the ETA 1258, made by the Swiss ébauche maker, ETA - who still makes Hamilton's movements today, by the way.
I recently made a run at a Datomatic on eBay and missed out. However, the eventual winner contacted me about the watch so I got to see it after all. As received, it was running but it was very dirty and in need of a new crystal for sure. It interesting to note that the date wheel is red on these older calendar models.
The back of the case is marked Illinois and stainless steel. The Illinois models are pretty spartan and lack some of the finer details that the Hamilton-branded models had. For example, there is no serial number on the case or the movements.
The case back unscrews to reveal the classic shape of an ETA rotor. You'll see this same rotor shape in some of the Hamilton automatics, like the Kinematic.
With the dial and hands removed you can see the business end of the movement. This is a new setup for me and it's actually much simpler than the other ETA calendar models like the 694A that I've seen. The jumper is a small wheel near the 26 date and the index is spring-loaded wheel at the 2 date. This date wheel sort of eases on in to the next date rather than pop into the next date at midnight. Also, you need to set the time forward, and forward, and forward, until you get to the date you want, as there is no quick way of changing the date on this model.
All of the main calendar parts are removed and it's starting to look like a plain old ETA 1256 movement now.
With the oscillating weight removed, you can see the movement looks like any other ETA grade. I like the Inca-shock jewels - they are easy to open to clean and lubricate.
While all the parts are being cleaned, I will polish the case and prep a new crystal for installation. I got a question on what prepping a crystal means so I'll answer it here. For round crystals, it's a piece of cake. Glass crystals is a different story.
First I measure the old crystal and the bezel opening and pick a crystal that has a profile high enough to accommodate a sweep second hand and a diameter just larger than the bezel opening. A 29.8mm GS PHD (high dome) crystal will do nicely.
I clean the crystal and put it in my Bergeon holder so that when I use "the claw" it will grip it in the right place.
The trick with these crystals is to get the tool to grasp the crystal with enough material to hold but also to allow the crystal to go into the case. Tightening the tool compresses the crystal enough that it will fit into the bezel and when you loosen the tool the crystal expands and tightens into the bezel.
There should be just enough material to go into the bezel.
Now I put the bezel onto the crystal and loosen the tool.
There... good as new.
Everything is cleaned, dried and ready for reassembly. I'll also relume the hands the dial.
The movement is back together, just need to add the balance.
The balance is ticking away, even without a balance jewel. It will be even smoother once it's supported by it's jewels.
Ah, purring like a kitten. If you have good eyes you might be able to see TXD on the balance cock. That's the import code for Illinois branded movements and all of the Illinois movement have TXD on the balance cock.
According to the timer, it's running a little fast but a tweak to the regulator will slow it down.
There... that's much better, good amplitude and the beat error is on the high side of acceptable. These older ETA grades have fixed hair spring studs so they're a pain to adjust the beat error. I'll leave it as is rather than risk goofing up and otherwise fine hairspring.
All of the parts on the front of the main plate get reinstalled and I can confirm that the date changes when it gets to 12:00. Now to install the dial and hands.
The finished watch looks really good with a new crystal and fresh lume on the dial and hands. I also installed a period-correct vintage gray strap like most of the stainless Illinois models often got. Looks pretty sharp, I think.