■ PHOTO 3.
■ PHOTO 4. PVC
J1 RCA Jack
9V Battery Snaps
■ TABLE 1
■ PHOTO 5. Search coil
assembly with bracket.
pins of the adapter can be bent to
90 degrees for top adjustment. The
volume control (R16) pin designations
are shown in Figure 4. Break off the
keying post of R16 with a pair of
pliers. Instead of soldering the
connecting wires directly to the PCB,
.100” male headers are used. These
headers are installed for the search
coil, volume, S1, earphone, and 18
VDC. Female crimp housing connectors are used to make the twisted pair
cable assemblies shown in Table 1.
Be sure to note the ground pin on
the COIL, VOL, EAR, and 18 VDC
connectors. An easy way to do this is
to make the ground connections with
a black wire in the cable assemblies.
■ PHOTO 6. View of open case.
Keep the cable to
the RCA jack as short
as possible to reduce
To construct the
search coil, obtain a 1X
copy of Figure 2
(Search Coil Form).
Use the template to cut
a form from the wood
slat given in the Parts
List. Drill the six holes
5/32“ in diameter.
Now construct the
wire coil. Wrap 21
turns of 22 gauge solid
magnet wire around a
4“ diameter tube (an oatmeal container works nicely). Once the coil is
wound, wrap it in electrical tape (see
Photo 2). Wrap 1” strips of aluminum
foil around the coil, leaving space for
the two magnet wire leads. Strip three
inches of insulation from a six inch red
22 gauge solid wire. Wrap the three
inch bare end of this wire around
the aluminum foil (see Photo 3).
Wrap the whole coil assembly with
Make the search coil strain relief
bracket from a piece of aluminum
sheet (Figure 3). A 1/4” grommet is
installed in the 1/4” hole. Cut off one
end of the RCA cable and feed it
through the grommet. Remove 1” of
insulation from the end of the RCA
cable. Cut the red wire from the
search coil to 1/2” long and strip the
insulation to 1/4“. Scrape the enamel
from the magnet wires with a razor
knife and tin with solder.
Solder the magnet wire adjacent
to the red wire along with the red wire
to the shield connection of
the RCA cable. The other
magnet wire is soldered to
the center conductor of the
RCA cable. The solder
connections should be less
than 1/2” and carefully
wrapped with electrical tape
or the output of the mixer
Next, mount the strain
■ PHOTO 7. Front panel view.