Bulle info needed
Mike, thanks for the serial number info. By my research, that clock would have been made in 3rd quarter 1930. I checked Martin's site and could not find a dating table on Bulles, maybe I'm looking in the wrong place?
http://www.mridout.freeserve.co.uk/index.htm#moving%20coil. The one example shown on his site (a Clockette that probably is very much like the one you are working on) has serial number 295552, which he mentions is ca. 1934, my research shows early 1932. If he has something more on dating I would like to see it.
Regarding the pics, I can wait until you have it up and running.
As far as batteries are concerned I have to side with Les that only dry cells should be used, or a variable voltage power supply. When I find a clock that someone is running on 3v (or more), generally a good cleaning and adjustment will set it to running fine with 1.5v, usually to the amazement of the owner.
However: There are also some caveats that go with this.
1) The magnet must be in good condition. I use a Gauss meter to check, if the reading is less than 20 Gauss at any pole position on the magnet I will remagnetize it before going further. A weak magnet will require higher voltage to run.
2) The coil resistance should be 1200 ohms (all models). I have rarely found one with more, but fairly frequently will find one with less (maybe one in 20). The lower resistance could be from the coil being rewound by someone not knowing the correct resistance, or it can be the result of a short circuit within the coil that shunts current around a section of the windings. Either one gives the same result, a weak swing.
There are only two remedies for low coil resistance: Rewind it, or raise the voltage. You can roughly approximate the voltage required to get a normal swing by this quick calculation:
Divide normal resistance by actual resistance, square that result, and multiply by 1.5. For example, a coil with 1000 ohms requires 1.2(squared) X 1.5 = 2.16v to run normally.
OK, then what do you do? You can put in two batteries to give 3v, but as Les says you must also adjust the isochronous spring to compensate, and on the Clockettes there may not be enough adjusting length on the pendulum to do the job. You can also decrease the impulse by slightly raising the contact pin on the pendulum, to reduce the length of time it is touching the contact point on the yoke. A combination of doing this and adjusting the isochronous spring "can" get you in the ball park, problem is that the wear on the contact pin and yoke will be enough that this fix may not last more than several months.
My preference to solve this is to put a resistor in the circuit to reduce the voltage to the required level. Easy to do, resistors are cheap and available at Radio Shack or any commercial electronics shop. You can calculate the resistance needed based on actual coil resistance and applied voltage needed using Ohm's Law (E=IR). In the above example, the current through the 1000 ohm coil will be 0.00216 amps at 2.16v. To reduce 3v to 2.16, a resistor of 388 ohms is required at the same current flow. I would put in a smaller one, probably 350 ohms, to compensate for the battery discharge in time.
Hope this will help anyone working with these clocks.
John Hubby dba Pas-Times
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