The Challis messenger. (Challis, Idaho) 1912-current, 1925-06-10
BY JAMES E. CARTIER,
In New York Herald ribune.

clined to build sets along simpler lines.
Although a two-tube receiver does not
seem capable Of receiving signals like
one of its bigger brothers IL is sur
prising just what results may be OBJ
tanned with such set If properly con-
structed.
The Air Service two-tube reflex re-
ceiver employing the well known Hark-
ness circuit seems to be one Of rea-
sonably simple design. The list of
parts for the construction of this re-
ceiver is as follows:
by 12-inch panel.
by 11-inch Dashboard.
Two standard sockets.
Two audio-frequency transformers.
One rheostat (six ohm).
Battery switch.
Crystal detector.
Double circuit jack.
Single circuit jack.
Set Of six binding posts.
Two .0O037 mid. condensers.
Two radio-frequency transformers.
OF the aforementioned parts the
two radio-frequency transformers may
be easily constructed by the handy
radio builder, or may be bought In kit
form ready to assemble.
Coil-Winding Data.
For the benefit of those who desire
to construct their own radio-frequency
transformers the data will be given
herein.
The secondary of both Of the coup
ling transformers is the first to be
wound on the tube form. The sec
ondary of the transformer coupled to
the antenna circuit should have 60
turns of No "a wire, wound on "a
inch form, and over this should be
wrapped a sheet of insulating cloth or
waxed paper. This serves as an In
sulator between the primary and sec
ondary coils. The primary should con-
sist of ten turns of the same size wire
wound over the insulation cloth and in
the same direction as the secondary
1t is absolutely necessary that both
coils be wound in the same direction
if best results are 10 be had.
The primary of the second coupling
transformer is slightly different in size.
This transformer is wound on the
same diameter tube and assumes the
same physical proportions as the trans
former just described, the chief differ
ence being that the primary consists
of 80 turns instead of 10.
l.
set to be mounted in as small a space
as possible the coupling coils may be
mounted directly on the back of the
condensers with the secondary wires
connected TO the two terminals. Inc
primary wires should be left discon-
nected until the set is 10 be wired.
Then they may be connected to the
respective places in the circuit.
The two transformers should be
mounted at right angles to each other
In order to minimize coupling between
the two.
The drilling of the panel and the
wiring Of the set is no more difficult
than the ordinary simple resenerative
receiver. The wiring diagram, as
shown, will aid the constructor in the
proper arrangement of the apparatus.
Will Not Oscllate.
A particular advantage of this re-
ceiver is that it will neither oscillate
nor radiate an interfering wave on the
air. One of the tubes employed in the
receiver acts us a r.dlo-frequency am |
nlifier and is reflexed so as it acts as
A radio and audio-freQuency amplifer
at the same time. or in other words, |
does double duty. The detecting is ac-
by means of simple crys-
tai detector.
Such SIM. lie receiver. although
small in size, ought TO be |
capable of receiving many stations.
both local and dstan. with sufficient
volume to operate lond speaker
Either loop or outdoor antenna may
be- used on such Il reflex receiver. al
though the latter will give better re-
suits on distant stations.
Mounting the Apparatus.
The two variable condensers are
on the extreme ends of the
panel with the rheostat and crystal
ictecror in the middle. This arrange
nent allows the operator to control
lie set with ease. all controls being
within easy reach.
When wiring the ampliiier hest re-
suits will he obtained By having the
io-frequency transformers piaceu
n right angles TO each other. This
Toes AWAY with the possibility of
rowling.
Particular care should he exercised
n VIKING the system. Make sure the