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Telechron Coil Assemblies:

The Telechron coil assembly powers the rotors via magnetic induction. They are self starting by way of a shaded pole affect. Telechron Coils are generally matched to the series of rotor they power. (ex: S, H-3 and B).  These coils are amazingly reliable.  I've never seem one burnt out from normal operation even after decades of use.  The single biggest failure mechanism is the connection to the electrical cord.   The outer layer of insulating paper on the coil is usually brittle from time and heat.  Flexing or stress from the power cord can cause the connections to the tiny coil wires to break off.

If the coil hums, gets warm (not hot), has magnetic attraction on the iron lamination then the coil is generally electrically OK.  Most coils measure about 600 -1000 ohms but it can vary depending on the style of the coil.  The insulating paper on coils can be reinforced but don't use electricians tape.  My preference is 3M ©  #27 Glass Cloth insulating tape.

Note: Telechron rotors are easy to replace but any work on the electrical portion of a clock like the coil assembly is best left to a clock repairman experience in electrical repairs.

Here are the common Telechron Coils:

Telechron B Coils:

These coils measure about 2-1/4" X 1-3/4" at the frame. They are about 1/2" thick and have 10 layers of iron laminations.The mounting holes measure 1-7/8".

Most B coils have electrical leads vs. solder terminals.  

Some B coils also powered the small low voltage lamp in early Telechron clocks.  (note the 4 wires)

Telechron H-3 Coils:

These coils are the same dimensions as B but they are 3/16" thick and have 6 iron lamination layers.  They almost always have terminal strips vs. leads.  Some of these coils have small brackets to support knob shafts and alarm features.  These brackets can generally be easily transferred to other coils.

Telechron S Coils:

The Telechron S coils came in different form factors.  The most common, (bottom image), has the same dimensions as the H-3 coil but the terminals are on the end.

There's also a small frame S coil that's typically used in stove and range clocks.  The coil measures 1-1/2" X 1-3/4" frame with 1-3/8" mounting screw spacing (middle).

Telechron also producing other form factors depending on the application.  The top image is a coil used in flip clock radios.