October 1952 Radio-Electronics
[Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Electronics,
published 1930-1988. All copyrights hereby acknowledged.
If you have never received
a major electrical shock, you might be tempted to be a little lax when working around
high voltage. However, once you get your first taste of the jolt, you will probably
never forget it and will be very mindful of safety in the future. I got my share
of 120 V and 240 V shocks during my days as an electrician. Minor shocks
feel like a vibrating twinge of pain that just scare the crap out of you, while
more severe instances feel like getting jabbed in the finger(s) with a pick - at
least that has been my experience. I got hit by 408 V once while working on
a 3-phase air compressor for an auto body shop - that was during high school while
electrical vocational program. While working on radar in the USAF, I saw a guy
get bitten by 10 kV from a CRT display circuit - it left a burn hole in the
tip of his finger. You might think after all that I would always be sure to turn
off circuit breakers before working on stuff, but unless I thinks there's a real
danger of getting shocked, I still will change out a light switch or receptacle
on a live circuit in order not disturb other things being powered by it. Some people
never learn ;-)
High Voltage Service Hints
By H. Leeper
Most of us enjoy seeing our names in print - but nobody wants to be featured
in the obituary column. Every so often a nasty reminder comes along that service
technicians - even the most experienced ones - are not shockproof. The most recent
of these was the death of a Chicago technician - electrocuted by the h.v. circuit
of a television receiver. (See Radio-Electronics for September, 1952, page 90.)
In spite of the obvious hazards of high-voltage circuits, a far greater number
of fatalities are caused by contact with that little old 117-volt line which many
of us regard with such contempt. And the B supply circuits of modern TV receivers
- with their extra-high-capacitance electrolytics - can store more death-dealing
energy than any present-day h.v. supply.
Remember, it takes less than 150 ma to kill a normal, healthy human being. A
quick look at Ohm's law (E=IR) will show you that very little voltage is required
to push that current through your body if its resistance is low enough.
Keep your body resistance as high as possible, and avoid any contact with the
live circuits of a receiver. At times, unfortunately, many of us forget the fact
that the live circuits may include the chassis, or any grounded object (even the
Every service shop should have a wooden floor. Where work must be done in homes
or other locations with cement floors, insulate yourself from the floor with rubber
mats. These mats are about 13 x 21 inches and are obtainable at any auto or department
stores - inexpensively. (Photo A)
Dry boards may be used for the same purpose. A few 1-inch-thick boards about
10 x 60 inches will provide a safe working platform. They should be stood on end
to dry when not in use.
When testing or repairing equipment near water pipes, radiators, steam pipes
or grounded electrical conduits and switches, wood or Masonite boards provide the
necessary margin of safety. (Photo B)
A long, dry, wood stick or plastic rod is the best tool for probing around wiring
near the picture tube or other live parts. (Photo C)
Where line-interlock switches must be held in the closed position with the receiver
back off a wood tongue depressor is a lot safer than a screwdriver. Even if you're
using only one hand inside the cabinet you might come in contact with the blade.
Always hold a high-voltage probe so that the guard ring is between your hand
and the high voltage. Keep your hand closed and away from the probe lead. (Photo E)
Don't depend on the wire insulation to protect you if the internal multiplier
resistor should break down or arc over.
High-voltage probes are easier to carry, store, and keep dry, if they are taken
apart. With the probe dismantled the multiplier resistor should be kept in a toothbrush
container lined with soft, dry loth. A small zipper bag is an ideal carrying case.
The outside of the probe should always be wiped dry before and after use. Moisture
inside the probe can be removed with a narrow bottle brush.
Wearing goggles while handling picture tubes is a common-sense precaution repeatedly
emphasized by the tube manufacturers themselves. They should know. Still, many technicians
refuse to wear them, especially if they already wear glasses. These impact-resistant
goggles weigh only about 3 ounces and can be worn comfortably even over ordinary
eyeglasses. They give unobstructed vision and cover considerably more of the face
than the usual type. (Photo G)
Some picture tubes rest loosely on the metal chassis when the set is removed
from the cabinet. An old bicycle inner tube makes a handy protective bandage. The
ends of the inner tube can be anchored to the chassis to hold the picture tube firmly
and safely in position. (Photo H)
Posted November 19, 2021