This example of a T&N (Telefonbau und Normalzeit) electric master clock could have been manufactured in the 1960s or 70s. It has a blue enamelled steel case with a fully glazed door. The clock will drive a number of alternating polarity, one minute slave dials.
The escapement is a good quality dead-beat, and the 3/4 second pendulum rod is of wood with a spun brass bob. There is a seconds subsidiary dial.
The electric rewind mechanism consists of a large flywheel and a small weight suspended on thread, all mounted on a plastic (possibly bakelite) back plane. The rewind impulse arrangement consists of a pair of coils mounted parallel to the back plane, with an armature moving across the ends of the poles. One electrical contact is on that armature and the other is on the flywheel. The rotary switching mechanism for deriving alternate polarity pulses to drive the slave dials is to the lower left.
Alternate polarity slave dial pulses are triggered by means of a cam on the seconds arbor behind the dial, and extra wheel work between the front plate and a small third plate.
Power is transferred from the the flywheel to the movement by a short helical spring which also acts as maintaining power. Power is then divided between the main drive to the dead beat escapement and the slave switching by the differential shown in this picture.
Some T&N Master clocks were produced with a programmer mounted below the dial to switch other functions such as bells or lamps. The programmer allowed these functions to be set at 5 minute intervals over a 24 hour period, and to be suppressed on certain days of the week. The large wheel under the dial in this photo is the 24 hour programmer wheel into which small pins were inserted for each event.
