Evening star., 1922-06-02
BY A. HYATT VERRILL.


The single circuit crystal set may
be improved upon by adding better
detectors, tuning devices and variable
condensers. ETC.. but they are never
as efficient as the double circuit set.
The chief difference between dou-
BILE and a single circuit set lies in
the fact that in the single-circuit set
a single or primary coil Is used as q
tuner. whereas, in the wo-circuit set.
double coil is employed; in other
words. a coil consisting of primary
and secondary winding: In such coil
the vibratory currents from the aerial
are carried through the primary coil,
while the currents to the. detector
and phones are from the secondary
coil and are induced currents. That
is. there is no connection between the
rents passing through the primary
start induced currents or vibrations
in the secondary. As such induced cur
rents are always stronger, or more
intense than the original primary cur
rents, the waves. passing through the
waves of greater intensity in The sec
ondary coll. Hence the music or sig
nails will be louder and sharper.
In such a set. the original vibrations
in the primary coil may be tuned as
finely as possible and then the induced
currents may be still further tuned,
so that, as q result, vast amount of
interference may be eliminated which
would be impossible with a single
circuit set. Aside from the coil. there
is practically no difference between
the two types of sets-one Is as sim
Pile as as the other.
Two-Circuit Set.
he
wiring arrangement of a two-ctrcuit
set is shown with loose-coupled coll
or loose coupler as tuner. If YOU
have already made the single-circuit
set, and good detector. you can use
the same set and same instruments
of the ordinary coil. You will then
have very effective and good double
circuit set.
The only additional thing you need
make is the loose coupler. and while
this Is a bit more difficult than the
coils already described, it is not
really complicated. The primary coil
may either be a tapped coil. like the
one described; a coil with finger-like
contacts. or a slider coil. In making
the loose coupler, you should have
two tubes. that for the primary about
and one-half inches in diameter. and
the secondary should be of the same
length, though small enough to slip
inside the other and leave space of
one-Quarter inch all around. -*
Wind the primary with bare or In.
sulated copper wire, No. 18 size, start
ing and fastening the ends as de-
scribed for the other coils. Mount 1t
upon two uprights, as illustrated. If
you use bare wire, which Is advisable.
wind 1t on with twine between the
turns. II you have used insulated
wire, mark two lines with pencil and
ruler along the coil from end to end.
parallel with the axis of the coil. and
about one-quarter inch apart. Mark
two more parallel lines one-quarter
inch apart at 80 degrees from the
first, as shown in the cut. You can
determine the point at 30 degrees
by drawing two lines across the end
of the coil at right angles and cross
ing in the center. Then, with a red
hot iron or a knife, clean the insula-
ing in the center. Each of these viii
be 90 degrees from the other Then,
with a red-hot iron or a knife, clean
the insulation from the wires along
the one-quarter-inch spaces between
the pencil marks. If the barred wires
are loose or slip, wind twine around
the coil between the turns.
Winding Coil Dimcult.
In mounting the coil 1t may be at
tached to, the uprights by tacks