The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1925-05-22
left-Circuit Diagram Which Is he Principle Of the Monophase. Riuht-
Details of Radio Frequency Coupling Transformers.

coils can be left untouched once they
are adjusted, so that the number of
tuning controls in the set is reduced
TO the three condenser dials and one
dial for adjusting the first feed-back
coll or compensation.
The idea is that the second stage of
RE. amplification is adjusted on the
long waves, so that, as the feed in
creaseS with the short waves, there
will be less tendency for oscillations.
That is, the set is tuned in on the
longest wave it is desired to receive,
say 600 meters, and the second and
third compensating coils adjusted
carefully to the point at which howl
ing just ceases. After this, they can
be left alone, for on all wave-lengths
shorter than this there will be less
tendency for self-oscillation to occur.
h amplification in these stages
will always be high. however; in fact,
it will be very close TO the amplitica-
ton obtainable at the critical point,
for exceedingly small adjustment of
n compenSatorS is necessary to start
or stop oscillations. After the second
and third c~ompensators are properly
adjusted they are to be left alone and
the circuits can be brought up to the
critical point by manipulating the first
compensation alone.
There is an interesting point In con
nection with the placing of the feed
back coils which deals with their posi-
ton with respect to the secondaries
of the tuning units.
Constitutional.
The first step in assembling this re-
ceiver Is to procure the best Of the
necessary materials. A u by 26-inch
panel and a Z by 24-inch Dashboard are
fastened together i'm the customary
manner, after the panel Is drilled
with the necessary holes.
The construction of the radio fire.
Quency transformers is not a difficult
one. Three bakelite or hard rubber
tubes PA inches in diameter and q
inches long are required. There are
wound 45 turns of No. % DEC. wire.
A 6-turn winding of the same size
wire composes a primary winding u
of an inch from the first winding. The
secondary winding is then continued
for another 40 turns. The compen-
sating coil Is next placed on the tub
ing and consists Of six turns of wire
wound in the opposite direction to
that of the other %windings. Two smah
brackets are used to fasten the radio
frequency transformers to the base
board.
The above description pertains to
two of the transformers, the third be-
ing slightly different in that the com
pensating coil, instead Of being wound
on the tube itself, is placed on a small
rotor at one end of the tube. This
rotor is a piece of bakelite tubing two
inches in diameter and one inch long,
at one end of which is placed the six
turn winding. 1t is not necessary that
the wire be wound in any specific d.
rection, since the coil can be readily
turned through $50 degrees and thus
change its polarity.
The wiring of the receiver is not
yery difficult, since there are no set
rules, except that careful work brings
good results. In case trouble is ex-
perienced from the beginning, the con-
nections to the compensating coils
should be reversed one at a time until
the undesirable oscillations are elimi-
mated. 1t will be found advisable TO
Mace two bypass ~condensers across
the "B" battery and also to use a
.OOO25 MID. condenser between the
grid and plate terminals of the last
audio-freuuency amplitier tube.
AS regards the selectivity of the set,
If is safe to say that it surpasses the
maioriy of those on the market today.
In sensitivity, too, due to the exacting
values of the apparatus used and the
correct engineering principles in
yolyed, the receiver stands as a big
step in the development of tuned radio
frequency sets.
AS will be noted, the coils are fully
6B inches apart, reducing to a mini
mum the tendency towards inter-stage
coupling with resultant oscillations.
Two stages of audio-frequency ampii-
ication will be found to give more
than sufficient volume, it being neces-
sary to incorporate a bypass con-
denser across the grid and plate ter
minals of the last tube.