Radio Broadcast - 1925, February - 113 Pages ... - VacuumTubeEra

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1
712 Radio Broadcast
template and ream out the holes in the fibre
with the No. 19 drill.
a strip of tin as shown in the sketch
Fig. 2 and bolt it to the center of one of the
fibre circles. Mark the spokes with it using
a scratch awl and not a pencil, then cut on
these lines with the tin snips and you will have
a perfectly good form. Sec Fig. 3.
The forms should be boiled in paraffin for
about ten minutes before winding or they
will absorb moisture. After they are wound,
the coils may be painted with a thin solution
of celluloid dissolved in acetone. HARDING
Cow, East Sound, Wash.
IN
A FILTER FOR THE
SUPER-HETERODYNE
PUTTING up a super-heterodyne
along the lines of Mr. McMurdo Silver's
set, using Acme 30 kc transformers, 1
found that the filter suggested, though not
recommended, caused considerable distortion
(due possibly to the cutting off of some of the
CIRCULAR PLATE
1600 TURNS IN EACH SLOT. OF FIBRE OR BAKELITE
f\ \
750 TURN H.CCOIL
October RADIO BROADCAST. F. S. WHITE,
Syracuse, N. Y.
A PICKLE-BOTTLE COIL
B
FORM
HERE is a stunt that you might pass
on to your readers so that picklebottles
will be not in such great demand
for coil-winding purposes.
In a circle, inscribe an octagon of the size
H
'INSCRIBE AN OCTAGON
WITHIN A CIRCLE'
FIG.
S
required for the
coil to be wound,
as in Fig. 5 .
Next, cut a strip
C of tin A-A' long
\ and about 2f"
I
wide. See Fig. 6.
Allow \" at each
end for a joint.
Bend and form
the joint first,
then fold ac B-
C-D etc., to obtain
the shape as
shown in Fig. 8.
Bend a piece of
tin for a clamp, or slot a thin-walled brass
tube so it will slip over the flaps as shown
in Fig. 7.
Small angles of tin
may
be soldered at one
A B C D E F G H A*
FIG. 4
side bands).
I then worked out a filter which
not only produced no distortion, but which
also brought about sharper tuning and more
volume.
I removed the primary of 800 turns and
placed the form bearing the two secondary
coils, as described in Silver's filter, inside a
750 turn honeycomb coil providing the necessary
mechanical support as shown in the
sketch Fig. 4.
Connect the small coil as an untuned primary
and shunt the honeycomb coil with a .001
mfd. variable condenser or approximately .0005
mfd. fixed condenser making this the secondary
of the filter. With this substitution and using
the Acmes in the two intermediate R. F.
steps I
could not ask for a smoother operating
set than McMurdo Silver's set as described in