The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1926-02-19
BY CARLTON e. BUTLER,

by CNRI YIN Z. bO LEN,
Member American Institute of Electro
cal Engineers and Institute of Radio
Engineers.
Changing conditions make new
radio circuits necessary. A few years
ago the single circuit and ultra
audion receivers were satisfactory
and were capable of bringing in dis
tant stations with volume. Today the
same sets cannot be used, except In
isolated districts away from broad
casting stations, due to their broad
tuning qualities.
The receiver of the earlier day Is
no longer satisfactory for other rea-
sons, principally on account Of its
squealing and radiating qualities and
because it's tone quality is poor and
distorted. At the last radio confer
ence in Washington it was agreed that
in the near future the use of radiating
receivers would have to be ended, even
If it became necessary to pass a fed
eral law to accomplish that result.
Today, with modern laboratory
standard apparatus available, and
with sets of better design, the quality
attains the standard demanded by
lovers Of music.
The R-4 circuit, as developed for
use in a new receiving set, is a good
example of present day design. The
most popular form of circuit was
selected-the five tube tuned radio
frequency-and by the use of the lat
est type Of condensers, coils, and
transformers, together with improve
ments in the circuit, produced re-
ceiver that is capable of tuning
through interference, bringing in sta
lions from distance on the loud
speaker, and surprising many re-
ceivers for all around performance
and quality of tone.
To Shut Out Stray Currents.
Noteworthy of the improvements In
densers, between the primary of each
of the first two radio frequency trans
formers and the filament. This serves
to bypass and keep stray radio fire.
quency currents out Of the rest of the
wiring, and stabilizes the circuit. A
large condenser is placed across the
"B" battery terminals to reduce noises
and bowls due to long leads or low
voltage.
Refinements in apparatus include
the new square wound toroid coil,
with the new straight line frequency
cOndensers which provide shielding of
electromagnetic lines of force, as well
as keep the instrument dustproof, a
mighty important detail.
The toroidal coils eliminate the
spraying effect of magnetic lines of
force within the set proper, and re
move the principal bugbear that radio
engineers have been working for years
to solve The coils have self-con-
tanned fields that make pickup of stray
current impossible. Their use In the
RI receiver makes a set that will
tune through strong interference.
The variable condensers on the first
and second stages of radio may be
tuned by one control as in the manu-
featured receiver if desired. Three
condensers and three dials may be
used in the ordinary manner, how
ever, without lessening efficiency.
The Parts Needed.
To construct the circuit you will
need the following parts:
1 Square wound toroid coil, type
tt indicated on diagram as Ii.
2 Square wound toroid coils, type
To Indicated as LIZ and L3.
8 Straight-line frequency variable
condensers, preferably the All-Ameri-
can shielded type C35, indicated on
diagram as CT, CO, and Co.
Rauland lyric audio transform
ers. type R500.
0O2 mid. fixed condensers, in
Dictated on diagram as CA, CO and c.
/ .0OO25 mid. fixed condenser, in
Dictated on diagram as CO.
1 10 mid. fixed condenser, In
Dictated on diagram as CT.
The rheostats should each be of
six ohms capacity for the use of Nv
201-A or c 301-A tubes, and the grid
leak R3 should be two megohms When
using the new UX amplifier tubes,
break the grid return of the last
transformer and insert CO. battery of
voltage recommended by the manu-
facturer