rf - Free and Open Source Software

Economy
Ed Baker, W0EDO
993 7 Truman Road
Independence, Missouri
Chronometer
How would you like to have an illuminated
station clock for less than 55.00?
The unit described was built at a total
cost of 53.14 plus tax, but, with a wellstocked
junk box, this figure co uld be reduced
still further.
The secret of such a bargain lies in the fact
that most "electric" automobile clocks are
really mechanical clocks which arc wound
elect rically every two to five minutes. Since
this winding is done by a pulse through an
electro magnet, the clock doesn't care wh e­
ther this pulse is ac or de, thus making it a
sim ple matter to power the clock in the home
sta tio n.
These clocks are available from your local
salvage yard, and sell for 50 cents to 53.00,
depending on the condition a nd whether or
not you remove it from the wreck.
The major enemies of auto clocks arc
moisture and dust. The latter is the most
common but least damaging. In selecting a
clock, pick one which shows no sign of rust
on the fa ce, hands, or any other exposed surface.
and your chances o f restoring it to service
arc almost a certainty.
To remove the clock from the case pry up
the edges of the bezel which holds the glass
and remove these parts. Two or three small
scre ws or nuts in the back of the case will
now allow the clock to b e removed.
A large eye dropper or "ear" syringe will
su pply a low velocity air blast for cleaning.
Do not attempt to use a brush, as fragments
o f the bristles will catch in the gea rs.
The most common cause of failure is in
the winding mechanism. so a co mplete description
of this operation is in order. On the
back of the "works" is a rather large winding
surrou nded by a rotary armature. When this
armature is aligned with the winding, the
clock is wound. As the clock runs d own, the
armature moves away from the poles of the
winding, and, near the e nd of its travel, a pin
on the armature engages a Y-shaped yoke and
closes a pair of contacts. These contacts are
in series with the winding and the voltage
sou rce . so when they close , the winding is
e nergized and the armature is drawn toward
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the poles of the winding. This rewinds the
clock. This movement o f the a rmat ure also
opens the contacts b y the action of the pin
in the yo ke. This contact between pin a nd
yoke is where trouble develops. J ust befo re
the contacts close, the me chanism is at a point
o f ma ximum friction and minimu m spring
tension: so , with the co llection o f dust and
eva po ra tio n o f lubrication. the clock stops
just short of re winding.
After all traces of dust have been removed,
apply a drop of solvent/lubrica nt of the type
used for tuners and volume cont rols (Quietrol,
Spra Kleen, ctc.) to the yoke wh ere it
co ntacts the pin. Wind the clock by push ing
the armature, and start it by lightly pushing
the balance wheel. It will probably stop just
before the cont acts close. Without re winding,
start it again and let it run until the contacts
do clo se. Rewind and repeat until it runs
freely from rewind to point closure. Dry the
yoke and apply a mi nute quant ity of lubriplate
(a very light lubricant cre a m available
from hobby and gun shops) to the point of
co ntact wit h the pin. If desired a small amo
unt o f the solvent/lubrica nt ca n be applied
to the pivots and teeth o f each gea r. The
smallest drop you can get is slight ly too much
for each point. so if you wish to skip this,
the clock will probably run wit hout it for
years.
The points ma y be clea ned with a burnishing
tool, b ut avoid excessive filing.
Whil e the clock is " running in" the power
su pply ca n be prepared. The transformer ca n
be any, which gives the proper voltage. My
clock used 12 volts. so a 6.3 and 5 volt winding
were connected in series to give 11 .3
volts. This is plenty, since the winding is designed
to work o n 10-14 volts. The transformer
also ha s a 90 V winding which is not
used, so the leads arc ta ped to prevent shorts
and left hanging frce .
T o determine the required voltage. look at
the bulb in the so cket wh ich sits inside the
case . If the bulb is missing, apply 6 .3 ac between
the input terminal and fra me. and observe
the armature. If it moves toward the
poles of the winding (not necessarily all the
73 MAGAZINE