May 1956 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
recent headline announced where a guy hacked his hearing aid to
listening to Wi-Fi signals as he walked around town. Why would
a person do that? I suppose now that the audible digital handshaking
tones of telephone modems and fax machines are all but gone from
everyday life, he must have really been missing the nerve-grating
melodies. I don't recall ever seeing a story about anyone picking
up Wi-Fi signals from a faulty metal tooth filling like used to
occur occasionally in the presence of high power AM transmitter
towers*. This article from a 1956 edition of Popular Electronics
reminded me of it. I think I've told the story of how while working
as an electrician in Annapolis, Maryland,
(mid 1970s) I sometimes used a pair of modified telephone
handsets to communicate with co-workers while working on circuits.
It was not unusual to be on the roof of a building working on an
HVAC unit and very clearly hear the
signal in the earpiece.
* Possible if dissimilar metallic junction
was created, but could just be a much-promulgated myth
See all articles from
Radios Made from Hearing Aids
This Acousticon hearing aid was modified by adding a
loopstick and a midget tuning capacitor.
With minor alterations and additions, you can make a radio from
a hearing aid
Radios that can be put in a pocket, worn on the wrist, or carried
in a purse are extremely popular these days. You can go out and
buy one of these pocket - or purse-size units, but you'll find it
rather expensive. Besides, who wants to buy something that you can
Here are two versions of a midget radio built around a hearing
aid. You don't have to be hard of hearing to build these devices,
but you will need a hearing aid in good working order. Perhaps you
can pick up a used model for a reasonable price at your local hearing-aid
In both cases, the hearing-aid is used as an audio amplifier
and is preceded by a simple tuned circuit to select various broadcast
stations. Range will depend on the power of nearby stations, and
on the length of antenna employed. In metropolitan areas, you will
probably be able to get quite a selection of stations without using
any antenna at all. For other places - or inside steel-reinforced
buildings - a wire three or four feet long will help.
In each of the units described, the major work is mechanical
rather than electrical, so you have plenty of leeway to use your
own ingenuity. Different hearing aids will present different problems
- the basic suggestions included here should enable you to convert
practically any of the hearing aids now on the market to a suitable
By Gary Edson
The first unit involves the conversion of an Acousticon hearing
aid. The tuned circuit consists of a Vari-loopstick with midget
tuning capacitor such as the Lafayette part No. MS-215 connected
in parallel with it. This capacitor is mounted in the space usually
occupied by the microphone grille, which is removed; to fill in
the extra space between the edges of the capacitor and the edges
of the hole in the case, solder in a piece of sheet metal previously
cut to shape. For other models, you can easily design a suitable
mounting system. Cut off the threaded sleeve on the capacitor unless
it is used for mounting purposes, and shorten the shaft so the tuning
knob will not stick out too much.
C1 - 10-365 μμfd. midget tuning capacitor (Lafayette
L1 - Vari-loopstick with mounting bracket (Graybourne
or equivalent) or the coil from a 456-kc. i.f. can (see
Schematic and parts list for the first unit.
C1 - 330·μμfd. subminiature ceramic capacitor
CR1 - Crystal diode rectifier (CK707, IN34, etc.)
J1 - Miniature closed-circuit phone jack (Telex or Switchcraft)
L1 - Slug·tuned loop antenna with threaded shaft (Walsco
PL1 - Miniature phone plug (Telex or
1 - Alligator clip
1 - Tuning knob
1 - Pen clip
1 - Plastic tube, approx. 1/2" i.d.
x 4" long
1 - Piece of Lucite, 2" square (for washers)
Schematic diagram and parts list for the second conversion
described in text.
Mount the loopstick by means of an L-shaped bracket bolted to
the side of the hearing-aid case. Mount a binding post for an antenna,
or merely solder a wire in place after you have determined the proper
Connect the parallel coil and capacitor combination to the microphone
terminals as shown in the schematic. You will probably note that
no detector is employed - detection of the radio signal takes place
in the grid circuit of the first audio stage. Volume and tone controls
on the hearing aid are undisturbed; they can be used to control
sound coming from the earphone. Adjust the coil slug for best performance
over the whole band.
A more compact receiver may be devised by using a coil from a
456-kc. i.f. transformer. The coil can be mounted inside the hearing-aid
enclosure (without the i.f. can, of course) but performance will
be inferior to that provided by the loopstick. An external antenna
is a "must" with this scheme.
By F. E. Bassett
The second conversion is somewhat more involved mechanically,
but has the advantage that you can unplug the tuned circuit and
use the hearing aid for what it was originally intended - a hearing
aid. Proper switching for this purpose is accomplished in the plug
and jack arrangement, as shown in the schematic diagram.
A glance at the photos and diagrams will give you a general idea
of the jack and plug assembly. The tuned circuit components, L1
and C1, and the rectifier CR1 are all mounted inside a plastic tube
about 3" long, having an inside diameter of 1/2". Suitable plugs
and washers for the assembly are cut from a sheet of 1/8"-thick
To reduce the size of the coil, remove the solder lugs. Then
carefully slit and remove the cardboard tube supporting the lugs.
Pry open the adjusting screw mounting slightly so that the screw
turns freely. This screw, with a suitable tuning knob made from
the cap on a can of lighter fluid or other suitable device, is used
for tuning the receiver.
Mount and solder the tuner components as shown in the pictorial
diagram, being careful not to overheat the rectifier. Cut washers
for the plug end and for the snap-in end of the coil, slip the whole
assembly inside the plastic tube, and glue the washers firmly in
place with plastic cement or acetate liquid. Be sure to bring the
antenna lead outside the case before final assembly. Mount a pen
clip as shown below.
converted unit mounted (left) in a
shirt pocket, and being tuned by adjusting the loopstick screw.
Pictorial diagram of the tuning unit. This assembly mounts inside
of a plastic tube.
Cross section of jack assembly (below) shows various connections.
Lead colors are optional.
Now wire up the jack as shown in the cross-sectional view, cut
suitable washers from the Lucite sheet, and assemble inside a 5/8"
length of plastic tubing - gluing the washers firmly in place. It
is a good idea to use color-coded leads to make certain that you
wire the plug to the hearing aid correctly.
Remove the hearing aid assembly from its case. Unsolder the microphone
input lead, and connect the three leads from the plug as shown in
the cross section, and in the schematic. Protect these three leads
with spaghetti tubing. Re-install assembly in case.
With the tuner unplugged, the hearing aid should operate normally,
Plug in the tuner, and clip the antenna lead to a metal lamp shade,
phone finger stop, or outside antenna. Then turn up the volume,
and hunt for stations by turning the coil adjusting screw. You should
receive several stations with good volume and clarity.
By eliminating the 330-μμfd. capacitor across the coil,
the author was able to tune in a number of ham stations. Try experimenting
with different capacitors to see how many short-wave stations you
assembly (left), including loopstick tuning unit and antenna with
clip, the hearing aid with jack added for radio operation, and the
Posted November 17, 2014