15-06-2013, 05:33 PM
Well today was another unpleasant cold, wet day down here in the 'sunny sarf'. I am reminded of my days spent on 'detached duty' in Preston in the early 1970s; usually cold and wet with the added misfortune of appearing like the set from the first series of Coronation Street complete with folk with cigarettes stuck to their bottom lips who seemed to buy all their clothes from jumble sales. Funny how nobody else wanted to go and being the youngest at work, I always drew the short straw.
I decided that after walking the dogs with a friend between the rain showers, I would get another clock to repair, so out came the box of junk and a Tempora mantle clock was selected for 'the treatment'.
This clock dates from the early 1970s and has the Smiths Sectric tuning fork movement fitted. The clock was not in too bad condition overall; someone had robbed the brass feet and although it was dirty, it ran for a few seconds before stopping.
This mantel clock was expensive to buy and to repair, and somewhat unreliable; they do not appear very often so I assume most were binned years ago.
This clock has a tuning fork movement similar in principle to the Bulova Accutron wrist watch. Whereas the Accutron drives the hands by a mechanical linkage from the tuning fork, this clock does so by means of a magnetic escapement (developed by C.F. Clifford in the 1940s). The tuning fork vibrates at 300Hz, which makes the second hand move smoothly, and look as though the clock is powered by a motor.
The electronics (one transistor, one resistor and two capacitors) are on a single board along with the coil assembly.
The 300 Hz tuning fork can be seen in the picture of the movement. It is fixed to the back plate at the centre of the curve at the left hand end. The right hand end of the lower tine carries a cylindrical magnet that vibrates within the coil. The coil has two windings; one generates current from the movement of the cylindrical magnet which turns on a transistor; a second coil which in the collector circuit of the transistor then gives impulse to the tuning fork, maintaining its vibrations.
The right hand end of the upper vibrating tine carries a small horse-shoe magnet which interacts with the mu-metal escape wheel and drives the wheel round in continuous motion. The escape wheel is not self-starting, but is spun into motion by the hand-setting action. Once rotating, the escape wheel's speed is locked to the vibrations of the horse-shoe magnet. There is no mechanical connection between this magnet and the escape wheel.
Some pictures of the clock before restoration are attached.
Pic1 and Pic2 show the unrestored clock.
Pic3 shows the tuning fork movement.
I decided that after walking the dogs with a friend between the rain showers, I would get another clock to repair, so out came the box of junk and a Tempora mantle clock was selected for 'the treatment'.
This clock dates from the early 1970s and has the Smiths Sectric tuning fork movement fitted. The clock was not in too bad condition overall; someone had robbed the brass feet and although it was dirty, it ran for a few seconds before stopping.
This mantel clock was expensive to buy and to repair, and somewhat unreliable; they do not appear very often so I assume most were binned years ago.
This clock has a tuning fork movement similar in principle to the Bulova Accutron wrist watch. Whereas the Accutron drives the hands by a mechanical linkage from the tuning fork, this clock does so by means of a magnetic escapement (developed by C.F. Clifford in the 1940s). The tuning fork vibrates at 300Hz, which makes the second hand move smoothly, and look as though the clock is powered by a motor.
The electronics (one transistor, one resistor and two capacitors) are on a single board along with the coil assembly.
The 300 Hz tuning fork can be seen in the picture of the movement. It is fixed to the back plate at the centre of the curve at the left hand end. The right hand end of the lower tine carries a cylindrical magnet that vibrates within the coil. The coil has two windings; one generates current from the movement of the cylindrical magnet which turns on a transistor; a second coil which in the collector circuit of the transistor then gives impulse to the tuning fork, maintaining its vibrations.
The right hand end of the upper vibrating tine carries a small horse-shoe magnet which interacts with the mu-metal escape wheel and drives the wheel round in continuous motion. The escape wheel is not self-starting, but is spun into motion by the hand-setting action. Once rotating, the escape wheel's speed is locked to the vibrations of the horse-shoe magnet. There is no mechanical connection between this magnet and the escape wheel.
Some pictures of the clock before restoration are attached.
Pic1 and Pic2 show the unrestored clock.
Pic3 shows the tuning fork movement.