History of the Omega 2505 “Jumbo”
Audemars Piguet has its Royal Oak Jumbo (5402 – 15202), Patek Philippe has its Nautilus Jumbo (3700-5711) and also Omega has one, their reference 2505 “Jumbo”.
The Word “Jumbo” does not refer to one model or brand within the watch world. It refers to a very specific type of watches. “Jumbo” timepieces are mostly time-only (Calatrava) models that have a significantly larger size than its contemporaries from a certain era. Let’s say that in the ‘30s 28-31mm was the size of men’s watches. So, if you found one that was 34-35mm you could consider that a “Jumbo”. Though as of lately we are calling watches that are above 36mm or so for “Jumbos”.
Based on this analogy, an Omega that first came out in the mid-40s and had a 38mm + case is a “Jumbo”. Not only a “Jumbo” but for many vintage Omega collectors it is the “Jumbo”. The one to go for if you are looking for vintage from the Biel brand with a contemporary size. Omega released the reference 2505 in 1946. To put it into perspective during the ‘40s the average size of a wristwatch was 33-34mm. Even the chronographs that people considered large at the time were not larger than 37-38mm. So to come out with a time-only watch in a 38mm case was pretty unusual. This was not the only timepiece with such a size but it clearly is the one that is more available then for example the references 2808, 2444, 2445 and 2609
As already mentioned above the “Jumbo” watch came out in 1946 as part of Omegas international collection under the reference CK 2505. It had a stainless steel case (hence the CK) 38.5mm, not including the crown. The thickness is 10.7mm and the lug tip to lug tip length of the case is a whopping 46.5mm. Other than the common steel watch, with some luck, you might also be able to find a gold plated version under the ref. BK 2505. Albeit the reference number is an interesting and important identifier of a watch the Omega reference 2505 is the fact that numerous different dial variation came out during its production run. We have seen the referneces from 2505-1 to 2505-30
The CK 2505 is a stainless steel case with a press-in case back. As such, the watch has no water resistance, pretty normal for timepiece from the ‘40s. The case is round and huge with relatively short but thick lugs. If you turn the Omega ref. 2505 to the side you can see the downward curvature of the lugs. This makes the watch sit on the wrist very comfortably. The only Achilles heel of the Omega 2505 “Jumbo” is the dial. More precisely, to find an original one.
Due to the case not being water resistant many of the watches have either badly damaged or repainted dials. The ones that are original often come with very high prices. All in all the dial design is fairly simple. Most pieces only had raised indexes. Some had painted or even applied numerals but that’s about it. Few examples have rarer sector, two-tone or waffle dials.
Finding a watch with an original dial can be challenging. Even to the trained watch collectors. As the watch was made for a number of years logos or fonts change. Some have painted Omega symbols, others have raised and so on. You really have to know your trade to pick the correct ones.
Now that we looked at everything on the outside, let’s look inside the large steel case. The movement inside the Omega reference 2505 is the caliber 265. It is a manual wind, sub-second movement with roughly 45 hours of power reserve, 15 jewels, and 18,000 Vph. The 265 is also the straight descendant of Omega’s legendary workhorse caliber 30T2. That one (the 30T2 that is) also has 15 jewels but no shock protection. The 265 on the other hand already has that and it’s antimagnetic. Back in the day often times a watch with a larger case was the indicator that it is anti-magnetic. The movement family the 265 belongs to went into production between 1939 and 1963 during which hundreds of thousands of movements came out of Biel.
When new, the CK 2505 was sold on a leather strap. Due to the long production run and the fact that there are still many different models on the market the reference 2505 remains one of the most interesting vintage time only Omegas known to collectors.
(Source https://www.fratellowatches.com/omega-reference-2505-aka-jumbo/)