ARCTOS 375 PROVITA CHRONO QUARTZ 1972
This extremely rare Provita Chrono-Quartz features a unique movement developed in 1971 by Arctos Uhrenfabrik of Pforzheim, Germany. According to Pieter Doensen's invaluable database a limited series was released in late 1972 and mass production began in 1973. The mechanical parts were made by Durowe, whereas the huge 32,768Hz quartz by Siemens and microchip by Motorola. This unusual and akward caliber 375 is impossible to find due to the rapid technology progress during the Quartz Revolution which made this concept obsolete in a matter of months. Not many were produced and the brands that used this caliber are not widely known. This makes it difficult to source a 375 because these watches are so plain on the outside and do not stand out from the crowd in any way. The only hint is the caseback with battery hatch.
The Arctos 375 is a strange workaround typical for the early years of the Quartz Revolution when micro stepping-motors were not yet available or were extremely expensive. This hybrid contains an electromagnetic balance wheel and large ferrite magnets similar to that of other German electrics however it does not oscillate in the same manner. In comparison to other unique Quartz concepts like the Mirexal Golay µ-Quartz FB7743 or Luch 3055 the balance wheel in the 375 remains still and acts as a stepping-motor with only one beat/kick per second. Although it appears to be overengineered it clearly does the very same job as the far simpler electromagnetic pallet escapement on the Roamer Micro-Quartz or Omega MegaQuartz. There is also a safety pin on the center wheel that prevents backlash movement of the seconds hand.
The electronic module on top of the mechanical baseplate is one big question mark upon a first impression. Why does an electronic module need a hairspring?! Well, it becomes simple after analyzing the exposed construction and following the electronic traces on the pertinax substrate. The metal hairspring simply provides current to the insulated coil on the balance wheel and additionally acts as a retracting spring so that the balance returns to start position after each beat. The balance is additionally secured from excessive oscillation with two red plastic bankings. If you follow the traces on the underside of the substrate you will notice a deliberate gap that has been applied to disconnect the circuit upon pulling out the crown and provide a hacking feature. A post on the clutch has a pertinax disc which connects the traces.
The hairspring on the electronic module could have been replaced with something far simpler or more durable but it does the job nicely however it makes servicing far more complex as watchmaking skills are required when disassembling the movement. The only way to remove the electronic module is to pull out the brass taper pin that secures the hairspring in the raised post on the balance. This post is insulated in a ruby jewel as pictured to the right and the ultrathin wire from the coil is soldered to the tip. The 375 calibre is a unique concept but it has so many possible reasons of malfunction that it might require extraordinary patience to complete a task. While working on the electronic hairspring please remember that it must be true and must not short the caseback - hence the white paper insulation pad on the caseback.
Keywords: arctos, provita chrono-quartz, eisenhardt, 375
Market value: 250-500$ (impossible to find)