Radio Broadcast - 1925, February - 113 Pages ... - VacuumTubeEra

How to Build a One-Dial Reflex 729
enough to light the filament
or the tube will be burned
out
Ȧ negative C battery
is used
to cut down the B battery
consumption and to improve
the quality of signals through
preventing distortion.
To operate at its best efficiency,
the set should oscillate
or be very near the oscillating
point over the entire range of
broadcasting wavelengths,
when the balancing condenser
is at- its minimum. At this
point the dial controlling this
condenser should read 100 degrees.
When this dial reads
near zero, oscillations should
not occur at any wavelength.
TUNING
THE method of tuning this
set is
very simple and can
be mastered in a few minutes.
It will be observed that the large dial at the
left is labelled "Tuning." The next dial to
the right is labelled "Volume." To the right
of the dial controlling volume are three rheostat
knobs, which control the current in the
filaments of the first, second, third, and fourth
tubes. Immediately below the volume control
dial is the filament current control switch.
Continuing to the right of this switch and
below the first rheostat knob is a jack for use
of phones with only one stage of amplification.
Then there is a second jack for the speaker,
using both stages of amplification and the last
jack employs all four tubes.
At first it will probably be best to try to
tune the set with powerful near-by stations.
To do this you set the volume control dial
near zero and slowly rotate the tuning dial.
Then having picked up a local station, by
increasing the reading of the volume control
dial, the signal should come in loud and clear.
The setting of the tuning dial should be recorded
and thereafter that particular station
should always be found at that setting.
To obtain maximum volume on distant
station reception the procedure is slightly
different. In this case it is best to set the
tuning dial approximately at the desired
wavelength and for each of these settings increase
the volume control dial until you get
a hissing noise. If you go beyond this point
you will get an audio note and the volume
dial setting should be reduced. Generally
THE BALANCING CONDENSER
When fully opened as shown has a minimum capacity reading. The
distance between the edges of the two plates is | inch. The semicircular
movable plate and the narrow \ inch wide plates make up
the full circular form if inch in diameter. The fixed plates are
spaced \ inch apart and one semi-circular plate rotates between
them. The plates are mounted on a bakelite base by means of bolts,
spacers, and a shaft of the required thickness. All these parts may
be secured from a radio shop with average stock
speaking, for every setting of the tuning dial
get the maximum setting of the volume dial.
The rheostats should be adjusted on a moderate
signal until maximum volume is obtained.
At the same time, for the sake of economy the
tubes should be run no brighter than is necessary
to give satisfactory performance.
The following is the list of parts for the
four-tube circuit.
It is entirely possible to use any standard
type of condenser, tube socket, jack,
rheostat, etc., when building this receiver,
and for that reason, no especial
make has been listed. However, for
the tuner and radio-frequency transformer
units, it is well to use the same
in the article and used
parts as specified
in the construction of the receiver described.
If the reader wants to construct
his own components, he can readily do
he follows the constructional data
so if
given.
From the data given about the radiofrequency
coil, it will be observed that
this is no ordinary radio-frequency transformer,
such as is
used for the common
but must be
radio-frequency amplifier,
especially constructed and connected in
the circuit as shown in Figs,
i and 3.
THE EDITOR.