How to Service and Set Up a Bulle Clock — Contacts, Coil, Balance, and Power Flow

Introduction

Bulle clocks use an electromagnetic impulse system rather than a traditional escapement. Their accuracy depends on clean electrical contacts, proper balance alignment, and a correctly functioning coil and armature. Because these clocks rely on extremely low power, even small mechanical or electrical issues can stop the movement. This guide explains how a Bulle clock works, how to service its key components, and how to diagnose common problems.

How a Bulle Clock Works

Electromagnetic impulse system

The balance wheel carries a small coil. As the balance swings, a contact closes briefly, energizing the coil and giving the balance a push.

Permanent magnet interaction

A fixed magnet beneath the coil provides the magnetic field needed for impulse.

Low-power operation

Bulle clocks draw very little current. Any resistance—dirty contacts, corrosion, or weak batteries—can stop the clock.

Suspension system

The balance is suspended on a delicate spring. Any twist or distortion affects timing and amplitude.

Electrical path

Power flows from the battery through the contact system, into the coil, and back to the battery. Clean connections are essential.

Servicing the Contact System

Cleaning the contacts

Use a fine burnisher or paper strip to remove oxidation. Do not use abrasive stones, which remove too much material.

Setting contact pressure

The contacts must touch lightly—just enough to close the circuit without dragging.

Checking alignment

Contacts must meet squarely. Misalignment causes intermittent impulse or arcing.

Preventing arcing

Arcing pits the contacts and increases resistance. Proper pressure and clean surfaces reduce this risk.

Testing continuity

Use a meter to confirm a clean, low-resistance path when the contacts close.

Balance, Coil, and Suspension

Inspecting the coil

The coil must be clean and free of breaks. Damaged windings reduce impulse strength.

Checking the armature

The armature must move freely without rubbing the magnet or frame.

Suspension spring condition

The spring must be flat, untwisted, and free of cracks. Even slight damage affects timing.

Centering the balance

The balance wheel must swing evenly. Off-center motion indicates spring or pivot issues.

Using a movement clamp

A clamp or support stand stabilizes the movement during service, preventing accidental damage to the delicate suspension.

Battery and Electrical Considerations

Correct battery type

Use the recommended voltage. Higher voltage increases arcing; lower voltage reduces impulse strength.

Clean battery contacts

Corrosion increases resistance. Clean contacts ensure full power reaches the coil.

Wire condition

Check for frayed or brittle wires. Replace any that show signs of fatigue.

Polarity

Bulle clocks require correct polarity for proper impulse direction.

Testing the circuit

Verify continuity from battery to coil and back. Any break stops the clock.

Troubleshooting Flowcharts

If the clock will not start

Check battery → Clean contacts → Check coil continuity → Inspect suspension spring → Verify polarity

If the balance amplitude is weak

Check contact pressure → Check coil → Check magnet strength → Inspect suspension → Reduce friction

If the clock runs intermittently

Check contact alignment → Check wiring → Check battery terminals → Inspect armature clearance

If the contacts arc

Reduce pressure → Clean surfaces → Check battery voltage → Inspect coil resistance

If timing drifts

Check suspension spring → Check balance centering → Verify contact timing → Inspect coil impulse strength

Common Mistakes to Avoid

Using abrasive tools on contacts

Abrasives remove too much material and shorten contact life.

Bending the suspension spring

Even slight distortion affects timing and amplitude.

Using incorrect battery voltage

Too much voltage causes arcing; too little stops the clock.

Over-tightening screws

Excess pressure can distort the frame or restrict balance motion.

Ignoring wiring condition

Old insulation or corroded wires cause intermittent operation.

Checklist for Final Verification

• Contacts clean and aligned
• Coil intact and properly positioned
• Suspension spring flat and untwisted
• Balance swings evenly
• Battery voltage correct
• Electrical path continuous and low-resistance

FAQs

Should I oil a Bulle clock?

Only the mechanical pivots receive oil. Contacts, springs, and electrical components must remain dry.

Why does the balance barely move?

Likely due to weak impulse from dirty contacts or coil issues.

Can the coil be rewound?

Yes, but it requires fine wire and careful technique.

Why does the clock stop randomly?

Intermittent contact closure or wiring resistance is usually the cause.

Do I need a special key?

Most Bulle clocks use a standard winding key for the motion works, but the electrical system provides the impulse.