The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1925-10-02
Wiring Diagram
Inures Operation

'ODS~1 ~ thdl TIC ScleCIlNlLY OIL IHo
set Will not be impaired IL made at
home the primary L0 may consist of
ten turns and the secondary Ii Of
forty-three turns, wound ON a length
of composition tubing three inches n
diameter with about No. 20 double
silk-covered wire. There should be at
least quarter of an inch separating
the two windings The two tuning
condensers CT and CO should each be
of COOS microfarad capacity, and they
should be of the lest construction
The coil L3 may be similar to IL as
to lumber of turns, size of wire and
diameter.
Coil L2 is choke coil for radio fire.
quencies, consisting of $50 turns
No. 40 enameled wire wound on o
wooden dove, one inch in diameter.
The coupling condenser CO may be
one of .001 microfarad capacity. The
resistance r should not be greater
than one megohm. A half megohm
should prove sufficient. The bypass
condenser CA should be one of large
capacity. 1t is used mainly for the
purpose of bringing the rotor plates
Of condenser CO as nearly to ground
potential as possible, and thereby re-
ducing hand capacity effects. Any
value between .005 microfarad and l
microfarad may be used
The crystal detector Or is one of
the new type carborundum crystals.
These are sensitive and rugged and
will stand up under heavy loads. They
are also of the fixed type, so that the
cat whisker nuisance is eliminated.
Simplicity of Operation.
Simplicity of operation was one Of
the main considerations in building
the set. Thus there are only two main
tuning controls in 1t, the two tuning
condensers. Then there is the ticker
control for varying the sensitivity Of
the circuit. The inductive switch s
and the taps on the second tuning coil
are not brought out on the panel. A
short, flexible lead running from the
crystal terminates in a small connector
clip, which may be connected to any
one of the taps located on the tuning
coil. AS a means of simplifying the
filament circuits, self-regulating rheo-
stats (A) are used throughout in place
of adjustable rheostats. This is feas-
ible, since all the tubes operate as
amplifiers. One rheostat, however, is
used in the filament circuit of the first
tube, and this is for the purpose of
securing an additional volume contro'
This rheostat should be one of from
six TO ten ohms, either of which gives
sufficient control of the output of the
first tube.
This set has not been tried with dry
cell tubes, but no doubt it will work
with these as long as the volume is
kept down to moderate Intensity.
Since the first tube is operated as /,
voltage amplifier by virtue of tn i'm
pedance coupling, better results should
be obtained if high MI tube is used
in this stage. If, however, high MU
tube is used, it is of great importance
that the impedance of IL be high, be-
cause a tube Of this type has a plate
resistance il the neighborhood of
10000 ohms, and If the impedance of
LIZ is much less than this no advan-
tage is gained by the high MU.
List of Parts.
One radio-frequency tuning coil with
two windings. One radio-frequency
tuning coil with one winding and taps.
One ticker coil, as described. One
radio-frequency choke coil, five MILL
henries or greater. Two audio-fre-
quency transformers. Two tuning con-
densers, COOS mid. Four automatic
filament resistances. One six or ten
ohm rheostat. One coupling con-
denser, .001 mid. One bypass con-
denser. .005 mid. or greater. One
grid leak, 5 to- 1 megohm One crys-
tai detector. fixed carborundum. Four
standard sockets and four tubes. One
filament- switch. One double pole.
double throw Jack switch. Nine bind
ing posts. Two condenser dials and
one ticker knob. One panel. 7x21
inches, and one Dashboard, 7x2O inches.
One cabinet to match.
Since the tubes in this cabinet are
all working as amplifiers, all the grid
return leads should be connected to
the negative c battery terminal, and
the c battery should be given a value
consistent with the plate voltage en-
ployed. The plate voltage should pref
erably be 675 or more All the tubes
are more efficient when high plate
voltages are used, and this is particu-
larry true of the first.