Arizona state miner., 1925-06-13
BY JAMES e. CARTIER,
in New York HerSId-Tribune.

in New York Herald Tribune.
The construction Of seemingly diff
cult multitude radio receivers seems
to have been the stumbling block Of
many amateur builders. For this rea-
son the home constructor has been in
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 it 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 we'll 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:
Z by 12-inch panel.
Z 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 .00037 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.
CoiI-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 80
turns Of No. a wire, wound on a 2A-
inch form, and over this should be
wrapped a sheet Of insulating cloth or
waXed paper. This serves as an in
sulat0r 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 to be had.
The primary of the second coupling
transformer is slightly different in size.
c,fO ic q
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.
In order to make it possible for the
set to be mounted in as small 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. The
primary wires should be left discOn-
nected until the set is to 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 regeneratiye
receiver. The wiring diagram, as
shown, will aid the constructor in the
proper arrangement Of the apparatus
Will Not OscIIate.
A particular advantage Of this re-
ceiveP is tlNt it will neither Oscillate
nor radiate an interfering wave on the
air. One of the tubes employed in the
receiver acts as radiO-freQuency am
plifer and is refexed so as it acts as
radio and audiO-frequency amplif1el
at the same time, or in other words
does double duty. The detecting is ac
complished by means of a simple crys
tai detectOr
Such a simple receiver, although
seemingly small in size, ought to be
capable of receiving many stations
both local and distant with sufficient
volume to operate loud speaker.
Either loop or outdoor antenna may