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

748 Radio Broadcast
and will not be repeated here.
RADIO FREQUENCY AMPLIFIER NEUTROFORMERS CRYSTAL DETECTOR
'
P S UV 201 A PS UV 201 A P
The
- S
P S UV201A
suggested circuit is shown in
Fig. 6. Any standard type of
tubes may be used in a unit of
this kind but of course uv-2Oi-A's
or better still, power tubes such as
the 202 or the w. E. 2i6-A will be
more suitable for this type of work.
The value of C battery will vary
in proportion to the amount of B
battery used. A table of C battery
voltages was included in THE GRID
for January, 1925. For the tubes
-
-
A + B
suggested
FIG. 120 to 150 volts B battery
will be sufficient.
as explained in the April, 1924, RADIO BROADCAST,
CALIBRATION CURVES
3
The radio-frequency transformer T2 is of the untuned
type and covers a wavelength range of 200 to
any type of receiver may be charted
5,0 meters. Much
and calibrated so that a
of the instruction as outlined for
the three-tube circuit of Fig. 3
ALMOST
graphical curve is
may be followed in
produced that may be used for reference
the construction of this receiver. Especial care purposes. Instead of rumaging through numerous
should be exercised in the selection of a suitable papers having dial settings numerically listed, it is
audio-frequency transformer and much easier and more efficient to refer to the s.hipshape
wavelength curve that also helps you to locate
crystal.
JACKS, AND HOW THEY ARE USED
new station positions on your tuning dial. Neutrodyne
and tuned radio-frequency receivers, superhetrodynes,
and crystal reflex receivers furnish the
are as many types of closed circuit
jacks as there are manufacturers of them.
most
THERE
It should be remembered that jacks are used
accurate curves. In the regenerative type of
for the sole purpose of receiver, several combinations of inductance and
providing a mechanical cutin
on any part of a radio circuit. In the natural
capacity will tune to the same station and the curve
progress of system
things, jacks came to be used in more
of tuning is not so dependable or reliable.
A specimen of a wavelength graph curve is shown in
elaborate ways. One manufacturer produces 14
Fig.
different kinds of jacks. Not all of them can 8. The several points marked on the diagonal
be
line indicate station positions. For instance 492
explained here but several of the more well-known
meters, WEAF, is located on the vertical border to the
type are illustrated in Fig. 5, A and B. In A, the
left; running
several styles are outlined and rcross horizontally on the 492 line we
their use is depicted
in B. For the output jack in the stage of an note where it is intersected by the diagonal line.
amplifier
or a plain detector circuit we have that as shown
Then, coming down vertically, it is found that this
position is equal to 81 on a 100 segment semi-circle
in i . This is called the single open-circuit type.
I n
of the dial. This base line is comparative to and
2 is shown a single-closed circuit type permitting indicates the
the throwing in or markings on the dial. To
out, automatically, of the prepare a
primary wavelength
of a transformer. Another method curve it is well to have commercial graph
of performing paper
the same operation
is shown in 3. That shown that is obtainable in most stationery shops.
in 4
is
fundamentally the same as that shown The dial markings are laid off at regular, equal intervals
along the base line and the wavelength
in i except
that a filament control is included which breaks the
filament circuit when the range, usually from 200 to 600 meters is hid off in a
plug
is withdrawn from
the jack.
UNTUNED
In 5 we have practically the same as that shown
RFT
in 2 with the addition of the filament control as
explained. The method of controlling one or more
V T I
T 2
filament circuits by means of jacks is shown in 6.
A PUSH-PULL POWER AMPLIFIER
THE construction of a push-pull amplifier,
the selection of satisfactory parts plays an im-
role. In fact, the ultimate successful
INportant
operation of the unit depends upon this consideration
more than anything else. The input stage audio
transformer should have a low ratio, say 2 to i, so
that the voice and music is not unnecessarily distorted
before it reaches the push-pull transformers.
The action and theory of operation have already
been explained in past issues of RADIO BROADCAST