Evening star., 1922-06-02
Expert Advice on Radio
No. 17.-To Make Two-Circuit Crystal Set.

through the bare ends Of the tube,
but care must be taken that they do
not project inside the tube. The next
thing is to wind the secondary coil.
This is slightly difficult. For the
secondary, use No. "a or 26 insulated
hole through the coil. Take tap
from the wire. leaving loop as al
ready directed, and to this loop attach
q piece of flexible insulated wire at
least a foot long. Wrap the spot
where the tap and flexible wire join
the hole In the tube.
Dull the tap down tight to the
surface. Then continue winding and
making taps in the same way until
the end of the coil is reached.
You ,S VIII IN need some one to help
easy to hold the wire in place while
making the taps and connections.
but IL you are q careful worker a
lot of trouble will be avoided by
measuring the distance from the first
turn of wire to the first tap, then
same distance apart, and making
your holes in the tube, before you go
on winding.
When all the taps are completed
and the tube wound. you should fit
two wooden disks in the ends OF the
however, clamp together in a wise
and bore two one-quarter-inch holes
through both disks little above
the center. Then bore a third hole.
large enough to ADMIT all the wires
from the taps and the end wire of
the secondary coil, in one of the
disks. Slip the disks in the ends of
the coil and thrust two brass one
quarter-inch rods through the one
quarter-inch holes. letting the rods
\
Carefully move and slip the disks
about until the rods are perfectly
parallel with the axis of the tube.
AS soon as this position is found
mark discs and tubes Fasten the tube
to the disks with tracks or screws
the tap wires through the hole made
for them. Wrap several layers of
heavy paper around the coil until it
can be slipped inside the primary
tube and 'fit snugly.
Have two pieces of wood. large
enough to form supports for the Sec
ondary coil. and place one of these
at one end upright of the primary
coil. marking a line around it on
the primary. Dip the ends Of
the brass rods in paint. or rub
them with colored chalk and thrust
ondary coil ends. While holding the
piece of wood in position against
the end of the primary, turn the
rods and bear upon them until they
have left marks of paint or chalk
upon the piece of wood. Clamp this
piece to it's mate, using the paint or
chalk marks as guide.
Sealing Wax Used.
Bore one-quarter Inch holes through
both pieces. Secure the piece to the
end Of the primary coil and support
with the rods, through the holes.
using the pencil mark you made
as a guide. Then slip the other
piece over the opposite ends of the
rods and mark around 1t where 1t
rests on the panel. leaving a space
equal to the length of the secondary
coil between it and the primary coil
end.
Secure this piece in position. Then
slip out the rods, draw the secondary
from the primary and remove the
paper wrapping. Slip the rods back
disks of the coil. Cut them of SO
they will not come quite to the sur
face Of the supports and secure them
by filling the space between their
ends and the surface of the wood
with sealing wax. as illustrated.
Place multiple point switch on
the support. Lead the wires from
the secondary coil to the points as
shown. For the next step make the
sliders and slider rods for the pri-
mary If the coil 10 wound with bare
wire 1t will make no difference as