The HMT 6906 (sometimes also referred as HMT 6902) is a unidirectionally winding automatic movement from India, which is a direct relative of the Citizen 6501.
On the base plate you see, that all bearings, including those of the minute wheel and mainspring barrel are equipped with rubies. Perfect!
The gear construction is a bit old-fashioned, since a central minute wheel is used, which is beared under an own bridge and directly driven by the mainspring barrel, At 3 o’clock beneath the center second ruby bearing, you can see the pivot for carrying the breguet clutch of the selfwinding mechanism.
On the HMT with its classical gear train, not only center second wheel, third wheel and escapement wheel are beared under the large gear train bridge, but also the mainspring barrel and the two reduction wheel of the selfwinding mechanism. This is not really service friendly…
The lower wheel of the breguet clutch is attached with a spring to the upper wheel. In the side view of the gear train, you can see this quite well.
The Glucydur anular balance of this classical pallet lever movement beats with 21600 A/h and is beared in two Citizen Parashock 1 bearings.
The two clutch wheels are a Breguet clutch. It ensures, that the oscillating weight winds unidirectionally, while in the other direction, it spins free. For the ratchet, a simple spring is used, which blocks the second reduction wheel, at 2 o’clock at the outermost side of the movement.
The upper clutch wheel is secured by a spring on the axle, an efficient, but not really matchmaker-friendly solution.
On the empty dial side, you can see the yoke winding system. In its middle position, the date ring can be quicky advanced by a riveted finger with wheel, which is driven by the inner one of the two(!) gears on the winding stem. An unusual, but efficient solution.
The date indication mechanism has got a driving wheel with a plastic finger to ensure, that the date ring only advances but never turns back. This is important, as this is the only way to adjust day and date, since the day disc can be turned back and forth.
The weekday is driven by a switching star, which is driven by the date switching wheel. Date ring and weekday disc are both fixed by one spring (at 6 o’clock) and one lever (at 8 o’clock in the center).
Of course, there’s a cover for the date indication mechanism, which fixed the spring and the date ring.
The large weekday disc is only printed in one language. Date and weekday advance slowly and synchonously in a period of 90 minutes.
In the lab
|Number of jewels:||21|
Nickel anular balance|
Parashock 1 (Citizen)|
|Balance bearing / direction hairspring:||Counterclockwise|
|Adjust mechanism:||Hairspring key|
|Construction type:||solid construction|
|Winding mechanism:||yoke winding system|
|Setting lever spring:||3 hole(s)|
|Functions:||hour, minute, second, day, week day, selfwinding|
|Size:||10 1/2''' (measured: 23,55mm)|