San Antonio light. [volume] (San Antonio, Tex.) 1911-1993, 1925-11-01
SLIGHT CHANGE
IN WIRING IS
NECESSARY
Home Builder, by Following
Directions May Cheat
Coil Shortage Delay.

Coils designed for the remarkably
successful Roberts Knockout receiver
will operate satisfactorily in a modi.
fled Browning Drake. Radio fans who
are unable to obtain the regular
Browning-Drak coil kit, on account
of the wide demand. may well sub
stitute the Roberts coil and proceed
with their construction.
The set, when completed, will differ
slightly from the conventional Brown.
ing-Drake in that two-circuit coil in
stead of a single circuit is provided in
the aerial tuning circuit, the primary
being tuned by a series of taps and
the secondary by a variable condenser
Just as in the Browning Drakc. There
is no connection between these coils.
the radio signals passing from one coil
to the other by induction. This has n
tendency to make the set even more
selectiye than the original Browning
Drake. and makes radiation of signals
to annoy ones neighbors practically
impossible.
WIRING rs SIMPLE.
The Roberts coils as commercially
marketed come in n number of forms.
Those. used by The Light in construc:
ton Of the receiver under discussion
were obtained at San Antonio de-
partment store and are shown in the
illustrations accompanying this article.
A glance at the schematic wiring
diagram will show the wiring Of the
antenna circuit as simple. The term
inal numbered 3 in the photograph
is the aerial connection. The terminal
and loops marked l are connected to
the six taps shown in the schematic
diagram. The switch arm of n small
tap switch connects with the ground
binding post of the set.
For the secondary coil, terminal
"4' is connected to the grid Of the
radio frequency tube and to the sta
tiOnary plates of the first condenser
Terminal 80" connects TO filiamcnt
+ negative, minus A" and to the rotor
plates of the first condenser.
WIRING THE TUNER.
The three circuit tuner is slightly
more complicated in its wiring.
The ticker, marked AZ" in the
photograph is simple enough, its two
terminals being, shown on q small in
sulating strip marked ~.
The secondary is the coil next to
the ticker, and its two terminals,
marked II" and 20" are connected
respectively to the grid of the dctector
tube and the stator of the second
condenser and to the POSITIVE A
battery lead and the rotor Of the
second condenser. BE sure it's the
positive lead.
Now for the primary, which en-
bodies the Roberts system of neutral.
ization, perhaps the most efficient
known to radio.
The primary coil is double wound.
In the commercial sample used by
The Light, two wires of different
colors, maroon and white, were en-
ployed to wind the coil, this to make
it simple matter to trace out the
connections. In the photograph,
terminals @ and tie lower terminal
marked three are white; terminal 2
md the upper terminal marked three
are maroon.
JOIN TWO TERMINALS. Il
FiHt: Join the two terminals
marked 3 Zone maroon and one white)
together. This connected wire is in
turn joined to the positive 90 volt 4
battery lead, and to one side of
.005 fixed condenser. The other side
of the fixed condenser is connected
TO the minus A battery lead.
The builder now Inns two terminals
on the primary left untouched. One,
marked 20" is to be connected to
the plate terminal of the radio fire.
quency tube socket. The other, mark
ed 2, goes direct to one end of the
small neutralizing condenser which is
employed ns in the Browning Drake
regular receiver-its other side is con-
nected to the grid of the first tube.
The remainder of the set. the nudi-
frequency amplifier. is built exactly
as in the original Browning. Drake.
ONE MORE CONTROL
Operation of the set is likewise the
same, excepting that there is one more
control to be handled, the ground tap
switch, which controls the primary
coil of the antenna circuit.
As the arm of the switch is rotated, |
more or fewer turns of the primary
coil IRE thrown into the circuit. Less
turns means greater selectivity but
less volume. More turns give more vol |
ume, less selectivity. The operator
can thus adapt his set to the neces- |
sites OF the moment, building I'D a |
IL -