BIFORA B11 ELECTRIC 1971
This is the only electric calibre invented inhouse by the German Bifora Uhrenfabrik in 1971. Based on the famous database by Pieter Doensen there were two different versions a ladies B10 and mens B11 which differed only with the diameter of the baseplate and dial. The vastly unoccupied baseplate must have been an advantage when designing ladies watches but they are nowhere to be found although even these mens sizes are extremely scarce...and I mean scarce. This transistorized electric is powered by a generic 357 battery applied negative side down and the circuit is simply closed with the caseback.
The build is typically German resulting in an ugly slightly overengineered design very similar in concept to Porta watches (PUW) but far smaller. On the other hand the mechanical gear train is simple with a pin-lever escapement activated by a balance with two coils that operates within a steel basket with magnets. This magnet assembly (composed of 2 layers of permanent ferrite magnets glued to 2 sheets of stainless steel) can be easily and quickly removed by sliding the basket away as pictured above. The electro-magnetic balance is equipped with a double hairspring on top and bottom that provides current from the battery through a transistor circuit on a ceramic substrate to the coils on the balance. The bottom hairspring closes the circuit with the baseplate that is connected with the case and caseback.
The movement has a double hacking function by means of the setting/clutch lever - upon pulling the crown a pin is moved by 1mm and disconnects the circuit on the ceramic substrate whereas the other longer end of the lever blocks the balance wheel (as pictured above). These overengineered movements have a few drawbacks in the sense that all parts must be perfectly aligned to work properly. First of all the pins, levers and hairsprings must either be properly insulated or connected in exact spots - otherwise the watch will not work! The same rules apply to the Bifora B12 Quartz developed from this B11 calibre.
Keywords: bifora, dugena
Market value: 10-150$ (brand, condition, box)