The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1924-07-04
BY FRANK D. PEARNE
Chief Instructor, Department of Elec
tricity, Lane Technical High
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SHiSf iHSkTuStorp bSPaTthSII VI 6iSS-
tricity, Lane Technical High
School, Chicago.
Having constructed the single tube
reflex circuits, many fans are request
Ing information showing how their
sets can be improved by adding more
application The circuit shown here
is the standard two.tube Erla duo-re-
fiex, best of the reflexes. This will
also enable those who did not happen
to see the single-tube arrangement to
construct this set from the beginning.
1t consists of a stage of straight tuned
radio frequency application added to
the one-tube circuit.
Before going into the wiring details
one should understand that In this,
as well as any other reflex arrange
ment, the condenser values and the
transformer ratios have been carefully
worked out and any deviation from
the values given may be disastrous to
the proper working of the set after
completion.
The wiring should be done in care
full, workmanlike manner. 1t will be
noted that a selectoformer is used as
a coupler. This novel and efficient
coupling device permits of very loose
coupling and the transfer of energy
from the antenna to the input circuit
with very low losses, due to the cor
rect coupling coefficient and low loss
windings employed. 1t also does away
with all coupler adjustments, switch
taps, etc.
The aerial is connected directly to
the IAN" binding post of the selecto-
former The ground connects to the
"GR" post of same and thence to the
rotor of the 23-plate condenser, con-
tinuing on to the negative filament
lead. The &c" binding post is con-
nected to the stator of the 23-plate
condenser and also to the grid side of
the first tube socket.
The post marked "P" on the first
tube socket is connected to the "P"
On the No. 2 reflex transformer, pass
ing through the primary winding to
the positive binding post of the plate
battery.
The &c" post of the same trans
former is connected to the grid post
on the No. 2 reflex transformer,
which is the return side of the secon-
dairy, and is also connected to the
CO. post on the audio frequency
transformer.
The up" post on the second tube
socket is connected to "P" of the No.
/ reflex transformer. The "B" of this
transformer Is connected to one spring
of the open circuit jack, the other
connection from this jack being made
to the positive "B" battery binding
post.
The fixed crystal detector Is con-
nected between the "P" binding post
of the audio frequency transformer
and &c" of the No. l reflex trans
former. "a binding post of the No.
reflex transformer, which is the re-
turn side of the secondary, is con-
nected to the "B" of the audio trans
former.
One side of each rheostat is con-
nected to the negative "a" binding
pOSt eihd liC OliiCI Sluc VI Ceieh 40
wired TO the "a" minus of the tube
sockets. The "F' positive binding post
on each socket is connected directly
to the "a" positive binding post.
A .001 fixed condenser is connected
across the primary side Of the audio
transformer and .00025 fixed con-
denser is set across the secondary of
the same transformer.
Another fixed condenser, .O02, is
connected between "B" of the No. 1
reflex transformer and the "B" minus
binding post. All of these fixed con-
densers should be solidly made and
insulated between the plates with mica
and plainly marked tested capacity"
All parts should be mounted as
close together as possible without In
terfering, SO that the connecting wires
will be very short. This wire should
be No. II or IA timed copper. The
entire apparatus should be mounted on
bakelite panel Ia by 6 and a base
| board which will fit in the cabinet to
be used.
The material required for the con-