[Hallicrafters] Isolation transformers

[Duane Fischer, W8DBF]

Excellent advice, Kevin. Especially for those with less experience and
knowledge, hopefully to profit from and avert a possible tragedy. 	
	
People do not understand the difference between AC and DC sets. Perhaps I am
among them. However, I think it is something like this. One plugs into the wall,
AC. The other uses batteries, DC. Not necessarily so! The old sets did not have
a power transformer and would operate on either AC or DC, same voltage,
different source. Many of those sets had insulators that kept the 'hot' chassis
away from the radio cabinet. Especially hazardous if the cabinet was made of
metal! You did not need a screw through the plastic or wood cabinet making
contact with the metal chassis to get a shock. Many have eliminated this problem
by the installation of a three wire line cord to insure proper grounding. It
does not reduce the economic value of a rx or tx necessarily. Maybe to the
absolute purist, but they are generally impossible to satisfy anyhow!	
	
The isolation transformer does what the name suggests. It goes between the AC
wall outlet and the rx/tx and isolates the rx/tx from electrical shock danger.	
	
DBF 	


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From: Kevin J Ward <kevin_ward at juno.com>
To: hallicrafters at mailman.qth.net
Subject: [Hallicrafters] Isolation transformers
Date: Saturday, December 28, 2002 7:48 PM


Many of us are restoring, not only old ham radio gear and general
coverage receivers, but things like vintage table model radios, many of
which are AC/DC.  The importance of using an isolation transformer cannot
be overemphasized.  The dangers of AC/DC radios and such was brought to
my attention in a shower of sparks as a teenager.  

In 1957 I was fifteen years old and eagerly awaiting my Novice ticket. 
KP was my exclusive privilege (?) which I seldom performed to the
complete satisfaction of my working mother.  There was always some
implement I overlooked or some spot on the counter that didn't get wiped.
 On the narrow counter area between the range and the refrigerator was my
mother's kitchen radio, a Philco 5-tube set in an ivory colored plastic
cabinet; AM only, of course.

One day, my mother was fed up with my lack of attention to detail and
began to bring some of these things to my attention, in rapid fire
manner, seemingly without end.  She was HOT under the collar, as the
saying goes.  One of the complaints was that I never moved things on the
counter and cleaned under and behind.  She grabbed the toaster and
pointed out the dust and crumbs underneath.  Then she picked up the
radio, pointed out the dust under it, and (so I would clean there) set
the radio on the nearest surface, a heating element on the range.

A huge shower of sparks blasted out from between the radio and the range,
then smoke, then the lights went out!  I think we both had in
instantaneous laundry problem.  As soon as Mother got her heart started
again, we got a light on in the next room and got the front and back
doors open.  We determined that the house wasn't going to burn down just
yet.

Of course it was an AC/DC set and one of the sheet metal screws in the
bottom of the radio, which held the radio in the cabinet, had contacted
the element.  As luck would have it the plug for the radio was in the
wrong way and the chassis was hot.  The screw was welded to the burner,
and we actually had to turn the radio around several times to free it
from the range.  The plug only came out of the outlet when we applied the
pliers.  

The radio survived; the line cord had to be replaced.  The range heating
element was ruined, as was the duplex outlet.  The miracle was, in all
the years that radio sat next to the range, my mother never touched both
the radio and the range.  We never again had a radio in the kitchen.

If you don't have an isolation transformer on your workbench, get one.  I
have a huge Westinghouse unit for the Wiremold plug strip I plug UUTs
into.  Also, the Weller soldering station.  Remember, the tip is
grounded.

Kevin  N2IE

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