Tab broken off cardboard support. Cause of short circuit
Note the fine wire from the coil
Fine wire joined to ‘thin’ wire. Heat shrink tubing is used to cover all connections
Thin wire is knotted before and after iron bracket holes.
All wires are secured with zip ties
Vintage 1940’s Electric Clock Repair
General Electric “The Rapture” Telechron
60 cycles per second X 60 seconds = 3,600 revolutions per minute
Recently this clock was plugged in after years of storage. Surprisingly, a sharp
white spark and noise emitted from inside. This short circuit shut off the power
from the breaker box. Thankfully no one was injured or property damaged.
The Rapture line of clocks were generally made from the late 1930’s until 1942
when war efforts required the attention of companies like General Electric. These
clocks operate on the regular United States electrical line of 120 volts alternating
current @ 60 Hertz. Interesting to me is that the rotor (motorized component that
turns the drive gear) is set to turn at precisely 3.6 Revolutions Per Minute. At
first I thought this to be an odd number to set a motor to but I now see why this
motor is calibrated to run at precisely the correct rate because it is governed by
the 60 Hertz rate of the power grid.
1000:1 Gear Reduction Ratio
= 3.6 revolutions per minute
The cause of the short was because one of the wiring tabs had broken off of it’s
cardboard base that is wrapped around the electromagnetic coil. The original wire
had been replaced many years ago (the white appliance wire) with poor consideration
for normal cord movement/agitations. This eventually let to the tab breaking off
and touching the other wire.
To make the repair I needed to somehow connect to the fine wire from the coil
and keep it safe from agitation strain. The coil wire is only about the thickness
of a human hair. I decided to first use a thinner wire to connect to the coil wire
and secure it to the iron bracket. At the other end of the thinner wire I attached
a new appliance wire. I decided to make all wiring secure by using a zip tie to the
iron bracket. This approach should stop all strain from reaching the delicate coil
An interesting aspect to note is that the rotor is easily removable and operates
on the electromagnetic inductance transmitted from the coil through the iron bracket.
The resistance of the coil measures to be around 749 Ohms.
Also featured on many of these clocks is the red indicator “eye”. This was to
signal to a person that electrical service had been interrupted and so the indicated
time should be placed in question. Early electrical service was more prone to blackouts
and people couldn’t simply turn on a television or check the internet for the time.
This was an era where a lot of clocks were still spring or weight driven. The indicator
on this clock works fine and the rest of the clock is functioning perfectly after
reassembly and some oil to the moving gear pivots.