Re: Bulle Model D
John
Many thanks for responding and for shedding further light on the dating and model type. I have not come across this particular model before.
It certainly makes sense that the clock was manufactured some time before the sale. It presumably took a while for the UK market in Bulles to be established, and at 5 1/2 Guineas (1 Guinea = £1.05) the cost of the clock must have made it quite a luxury.
Its a shame that the clock that was so dearly cherished and looked after from the outside, was so poorly treated on the inside. When I received the clock it had a home made 1.5 volt holder. I cleaned the contact pin and the pendulum did move (albeit erratically). On closer inspection, the contact pin was very badly scored (see photo). There wire that bridged the suspension was very thick and stiff, and there was an extra weight added to the pendulum. You can also see from the photo of the coil, that the wire out is incorrectly routed behind the pendulum. The contact spring was absent - and the post which should hold the contact spring had the battery lead soldered directly onto it !!
Once I cleaned the movement, replaced the bridging wire with a strand of silver wire, and fitted a new contact pin, the pendulum raced away with 1.5 volts. So i suspect that the "original" stiff bridging wire and pendulum weight were an attempt to reduce th pendulum swing ?
I have double checked my resistance reading with my best ohm-meter. I get an astoundingly low resistance of 127 ohms for the coil ! I have calibrated the meter against a know resistance, so am confident that it is reading correctly. I have added a 200 ohm resistor in series and the clock is running very well with an input voltage regulated at 1.48 volts. I am fortunate that I own 2 Bulles with similar movements, so I have been able to judge by eye the required pendulum amplitude. This gives a good starting point for regulation, with fine tuning achieved by adjusting the rating nut.
I was amazed that the clock runs with such a low coil resistance, and like yourself would have assumed it would require a much higher current to get it to run ? I know that some of the very early Bulle models had lower coil resistance and that some had resistors fitted in series to control the pendulum swing. But these coils were around 800 ohms and certainly not as low as 127 ohms !! I haven't taken the coil apart to determine whether it is incorrectly wound, or whether there is a partial short.
Clearly the downside with the existing set-up is that the lower resistance will mean power consumption will be higher. Not sure that this will be a major issue. But if it causes a problem, then I will just rewind the coil. It will also be interesting to see whether the regulated power supply will help overcome the absence of the iso-spring. I will continue my search for a lower bobbin assembly and for an arbor with the damping arm. I am not sure that the damping arm is really necessary, so it would be more for looks rather than functionality.
Finally, I did mis-post my original submission in a new thread. Might be better to move the entire piece to the "Post Your Bulle Clocks" thread. Unfortunately I am not sure how to do this.
Best regards,
Peter