Cal. 5206A is an automatic movement with day and date produced by Daini Seikosha for use in Seiko Lord Matic watches from 1970 through 1972. It was superseded by Cal. 5216A, which featured an improved spring-loaded date quickset pawl. The first movement in the Daini Seikosha 52 stream, Cal. 5206A was the foundation for Vanac, Special, and Chronometer movements in the classic period as well as the updated Seiko 4S series that powered most high-end mechanical watches from Seiko in the 1990s.
Some examples of Cal. 5206A feature an outside micro-adjusting device. A screw located between the lugs moves a micro-adjuster plate which repositions the regulator on the balance cock. Models without this feature use a conventional screw or “tadpole” type micro-regulator.
This was a modern movement with bi-directional automatic winding (using a conventional reverser rather than Seiko’s Magic Lever technology), hacking seconds, hand winding capability, quickset day and date using the crown, and a bilingual day wheel. It operated at 8 Hz (28,800 A/h), considered “Hi-Beat” at the time, and was capable of high levels of accuracy. The movement measured 25.60 mm in diameter and was 3.95 mm thick. A “tadpole” style micro adjuster was used, along with Diashock anti-shock and Diafix oil lubrication.
Because it was just the second automatic movement family designed by Daini Seikosha, the 52 stream had some quirks. Notably, the hand winding mechanism remains engaged when setting the date, causing drag on the crown. The date pawl on Cal. 5206A and 5246A was also prone to breakage when the watch was adjusted near midnight. This was fixed in the similar Cal. 5216A and 5256A, which replaced these movements in 1972 and 1973.
Seiko 5206 Operation
The movement can be manually wound with the crown in position 1. Rotate the crown clockwise to wind the mainspring.
The day and date wheels are advanced with the crown in second position (one notch out). Turn the crown clockwise to advance the date wheel by one day. Turn the crown counter-clockwise to advance the day wheel.
The time is set with the crown in second position (pulled all the way out). Rotate the crown clockwise to advance the minute and hour hands and counter-clockwise to turn them backward.
Daini Seikosha 52 Stream Family
| Date Only | Day-Date | |
|---|---|---|
| Standard | Cal. 5206A Cal. 5216A | |
| Special | Cal. 5245A | Cal. 5246A Cal. 5256A |