December 1934 Radio-Craft
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
In the 1930s, electricity and electronics were mysteries to most
of the population. The concepts were relatively new and few had
a firm grasp on the technology. That reality was exploited by Hugo
Gernsback during the 1934 Electrical Exposition to challenge attendees
to discover how the radio receiver sitting on the top of an empty,
clear glass case was being powered. It was a clever ruse that
reportedly stumped most people. The secret is revealed here. BTW,
my guess is that an even smaller proportion of our current citizens
would be able to figure it out, or for that matter even realize
that maybe there should be a power source of some sort.
The Mystery Set
you like to build a radio novelty that will help you mystify your
friends and neighbors? This intriguing device caught the eyes of
many visitors at the recent radio exposition in New York City. It
will make an interesting and arresting window display for dealers
or Service Men.
No apparent light socket connection, yet the set, mounted on
a plate glass box, lights and plays!
Read how - below.
At the recent national Electrical Exposition which was held in
New York, September 19th to the 29th, Radio-Craft and associated
Gernsback Publications had a large booth where not only magazines
but radio sets constructed by Radio-Craft, etc., were exhibited.
In order to arouse interest for the 270,000 odd people who attended
the show, a number of novel devices were exhibited, and among these
was a Mystery Set designed by the writer, which created no end of
discussion, and which had many radio people and radio engineers
guessing for quite a while.
The set, as shown in the illustration, comprises a grooved wooden
base (about an inch thick), in which grooves are mounted, edgewise,
four pieces of plate glass; these in turn fit into grooves on the
underside of a second (three-quarter-inch thick), piece of wood,
which constitutes a top or cover. Inside the glass box thus created
there is a sign, "The Mystery Set - How Does It Work?" Placed on
top of the cover is the open chassis of a 4 tube, stock model Emerson
radio receiver. An aerial about a foot high is also provided, and
to make the display a bit more humorous a flower pot containing
actual earth is cemented in position on top of the audio transformer.
The ground wire is soldered to a nail, which is driven into the
"ground." A sign proclaims the fact that the flower pot is the "Ground."
The set was placed so that it could be conveniently handled by
individuals in the crowd. You could switch the set "off" and "on,"
whereupon the pilot light would light and you could tune to your
heart's content and also get the various stations. The power cord
and plug were in plain sight, hanging loose at the left side. Everything
was open and above board. You could walk around the set, look through
the glass, in fact nothing was hidden.
How then could the set work? Plainly, it could not work by induction
because you cannot work a radio set in this manner. The closest
scrutiny of the set did not reveal any hidden wires. As no cement
was used in joining together the panes of plate glass all corners
were visible, and revealed - nothing! How is the mystery explainable?
The answer is: Ohm's law. Not so long ago, I did a little calculating,
and found out that two No. 36 or even No. 38 copper wires connected
in parallel, (or four wires, total,) were sufficient to carry the
full load of a small radio set, such as the one shown, which only
consumes approximately 40 W. The problem, therefore, resolved itself
into hiding the wires in such a way that the closest examination
would not reveal them. Since there are four corners to the cabinet,
this was easily accomplished as follows:
The 110 V.A.C. power supply was split up into its two component
lines. Then, green silk covered wire of No. 36 B. & S. gauge
was fastened, by means of transparent cellulose cement, against
the inside edge of each of the quarter-inch thick plate glass panes.
Now it should be remembered that the edge of plate glass is green,
and green silk wire against green glass is quite invisible, particularly
when the wire is as fine as the one that was used. Unless you had
a pretty good magnifying glass you could not possibly see the wire.
To make the job perfect, the wire was run very close to the edge,
and for this reason the wire was mistaken, by even the keenest observer,
as the real edge of the glass. As no cement was used to cement the
four pieces of plate glass together, there was actually an open
space at each of the four corners, through which you could slide
a card or piece of paper. Yet, with all this, the wire cemented
on the inside edge of the plate glass remained undetected.
The four hair-fine wires were then run through needle-like holes
and sealed info shallow (1/32- inch deep) grooves in the underside
of the lower wooden board. The four grooves converged to the center,
where a standard plug receptacle was recessed into the baseboard.
Two of the No. 36 wires were soldered to one terminal, and the remaining
two leads to the other. Thus, the set could be plugged in from underneath
the table (through which a hole was drilled) and the connecting
wires were thus concealed. Needless to say, the A.C. connecting
cord (and plug) which hangs at the left was disconnected from the
chassis so that the plug would not be "alive" - it then was nothing
but a dummy.
Now, as to the radio signal pick-up, the set in question is rather
sensitive, and actually does pick up on the small one-foot aerial.
In order to get more wire into the limited space available for an
aerial, the wooden uprights (which are about a foot high) were wound
with black wire which was then connected to the respective ends
of the aerial, one black wire serving as part of the lead-in. This
gave a small but efficient, concentrated antenna which was sufficient
to pick up the programs of a few of the more powerful stations.
(In locations where the pick-up is not so good, a superheterodyne
five or six tube set would, of course, be preferable.)
This Mystery Set can be easily built, by Service Men and others.
It can be exhibited in windows or counters, and will create no end
of discussion by the average onlooker or customer who will not understand
as to how the set functions. The design is so simple that the cost
of the entire device, outside of the inexpensive radio set, comes
to less than $4.00.
A few important constructional details should be noted. The grooves
in the top of the wooden base and the underside of the wooden top
must be deep enough - at least 1/2-inch in the upper, and 5/8-inch
in the bottom board - to securely hold the plate glass. After the
set has been completely assembled cement can be placed in the bottom
and top grooves. The wooden top and baseboard will thus hold the
plate glass firmly - so firm in fact, that you can pick up the entire
set by grasping the upper board, although I do not advise that this
be done as a routine thing. The method of running and connecting
the top ends of the fine, green wires is as follows: exactly at
the top edges of the plate glass panels where the green wires run
off, drill a hair-like hole, for each lead, at an angle so that
the fine wire will come through the top of the top board inside
the boundary of the set chassis (out of sight). The same two fine
wires connected to one socket terminal under the baseboard are also
connected together underneath the chassis and to one of the two
power connections from which the power cord was previously soldered.
The remaining two fine wires solder to the second power connection
under-neath the chassis.
You will have a lot of fun in building this set and mystifying
the local radio wiseacres.
Posted September 16, 2014