is hand-wired rather than using a printed circuit board.
Don’t worry; I will lead you through each and every step.
First, we will construct the chassis. Traditionally, radio
chassis are constructed from aluminum or steel. Metal
working has its own set of challenges and requires
specialized tools, like expensive chassis punches. I chose
instead to use tempered hardwood as a base for mounting
components. Interesting, some
of the earliest radios were built
this way. (Refer to the image at
Start with a 2’ x 4’ piece of
1/8” tempered hardwood. Cut a
7-1/4” strip across the 2’ width,
then cut this piece at 7-3/4”,
again at 4”, and finally at 3”
(see Figure 2). These pieces are,
respectively, the base, front, and
rear assemblies of the chassis.
To locate holes simply to be
drilled, trim quad-ruled graph
paper (four squares per inch) to
fit each chassis assembly. Spray
the reverse side of the graph
paper lightly with spray
adhesive and place the graph
paper so that it lines up exactly
with edges of the finished side of
the hardboard. Press the graph
paper down from the center out
to remove an air bubbles and
obtain a smooth result.
Use the layout drawings
(Figures 3, 4, and 5; files are
available at the aticle link.
Graphics shown here are for
reference only.) to mark the drill
locations and drill sizes on the
graph paper. Note that holes for
the audio module LN1, V1, C2,
and binding posts J3 and J4 are
located using the actual
component to ensure correct
hole location. Use an awl or ice
pick to precisely locate where
each hole will be drilled. If you
plan to use an electric hand drill,
pre-drill 1/16” pilot holes, then
use the drill size specified. Clean
up the holes by rubbing gently
with medium sandpaper.
The circular hole for the speaker will require a hole
saw. Cut a 2-1/2” diameter hole first, then widen as
necessary by sanding the circle edges so that the speaker
rim gasket fits snugly into it. With the speaker in place,
mark and drill its mounting holes.
Variable capacitor C2 also requires special handling.
Place the shaft rim in the 1/2” drilled hole and note the
two threaded holes on the front of the capacitor. From
inside the capacitor frame, use a sharp pencil to mark the
holes. Drill the holes and check that they line up correctly.
May 2015 29
■ FIGURE 4.
■ FIGURE 5. Rear panel drilling template.