Jeambrun 26D
Description
The caliber Jeambrun 26D, with a diameter of 11 1/2 lines, originates from Maiche in France.
It is based on the 10 1/2 line Jeambrun 23D and was used, among others, by Gruen in the USA under the designation Gruen 515SS.
base plate
The executiomn of this piece is flawless; one can immediately recognize the old-fashioned construction with a central minute wheel, which is mounted under its own bridge.
gear train
The rest of the gear train also reflects the state of technology at the time (1950s?):
The third wheel is driven by the central minute wheel, followed by the directly driven center seconds wheel, and finally the escape wheel.
A Swiss pallet lever escapement is used.
side view of the gear train
The Jeambrun 26D still uses a gold-toned Glucydur screw balance, beared in two French Antichoc 102 shock protection systems, and operates at a contemporary slow beat rate of 18,000 semi-oscillations per hour.
In the configuration shown, adjustment can only be made directly at the hairspring key.
balance spacer for height adjustment
What is otherwise only known from Russian movements is also used here: Between the balance cock and the main plate is the balance spacer, a very flat brass plate, with which the vertical play of the balance cock is adjusted to different shock protection systems.
Jeambrun 26D: Dial side
On the dial side, the beveled edge immediately catches the eye; it allows for a slight reduction in height, an important criterion at the time for fashionable, slim watches.
Otherwise, the cap jewel for the escape wheel bearing (which is also used on the movement side) and the yoke winding mechanism with its large screw are particularly noticeable.
In the lab
Timegrapher result
After many years of use, little remains of the “precision”; the readings on the timing machine show such a wide range that one must assume a defect or at least significant wear on the balance staff.| horizontal positions | |||
|---|---|---|---|
| dial up | +-0 s/d | 253° | 2.4ms |
| dial down | +-0 s/d | 271° | 2.1ms |
| vertical positions | |||
| crown right (12 up) | +27 s/d | 186° | 3.6ms |
| crown up (3 up) | -7 s/d | 195° | 3.0ms |
| crown left (6 up) | -33 s/d | 190° | 3.3ms |
| crown down (9 up) | -8 s/d | 195° | 3.5ms |
Technical data
| Manufacturer: | Jeambrun |
| Caliber: | 26D |
| Size: | 25,4''' (measured: 11 1/2mm) |
| A/h: | 18000 |
| Number of jewels: | 17 |
| Escapement: | Pallet lever |
| Balance types: | Glucydur screw balance (two legs) |
| Shock protection(s): | Antichoc 102 |
| Balance bearing / direction hairspring: | Clockwise |
| Moveable stud: | no |
| Adjust mechanism: | Hairspring key |
| Construction: |
|
| Construction type: | solid construction |
| Winding mechanism: | yoke winding system |
| Setting lever spring: | 2 holes |
| Attachment of setting lever: | screwed |
| Features: |
|
| References: | Flume: K3 38 |
| Inventory number: | 24054 |
Usage gallery
Gruen Precision gents watch (movement marked as "Gruen 515SS")