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Metamec, Diehl Type 726 Mantel Clock
(Impulsed; moving magnet; electronically switched)

Metamec/Diehl type 726
 


The moving magnet, transistor switched, balance wheel movement is probably the most common of the electro-mechanical mass-produced clock movements, and was made in many variations by numerous manufacturers. This clock was made by Metamec in England, but uses a movement by Diehl from Germany.

 

Metamec/Diehl type 726


Many movements used plastic or nylon parts to keep costs low but this example does use many metal parts.
Metamec/Diehl type 726

The electronics are contained within the small circuit board in the top right corner of the movement, with the trigger/impulse coil being mounted at one end of the board.

The principle of the movement is this. The balance wheel has a magnet attached to it, which passes over a coil with two concentric windings. One winding generates a small current as the magnet passes which is used to turn a transistor on, while the other winding is in the collector circuit of the transistor and has a larger current pass through it when the transistor turns on. This larger current generates a magnetic field in the coil which interacts with the magnet on the balance wheel and gives impulse to the balance. There is no mechanical switching of the current and therefore no switch contacts to fail. 

The balance drives the clock by an inverted Sully escapement.


Voltage: 1.5v
Battery type: one LR14/MN1400/C size cell
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Copyright  Text & Pictures - Martin Ridout.   Last updated Jan 2005.