Early Television How to Work 1928 ….!!!

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If you have not already experienced the thrill of tuningto
pictures, get out the soldering iron, the screwdriver, Me
hook-up wire and build this Television Receiver.
0NE cannot yet press a button
and cause to appear on the.
screen of his television receiver
a view ot a ball ga me. a
yacht race, or a political campaign.
All these things are bound to come
in time, but they are not here yet.
Television as we have it now is
something for the amateur, rather
than the layman who is interested
solely in the image received and not
in the fun of experimenting with a
new science.
The most certain method of
hastening the problems of television
is to have as many experimenters
as possible working on
the problem. Turn television
loose among the amateurs or those
who love scientific experimentation
and watch the important developments
take place, just as in radio
broadcasting.As the receipt of a bit of bldly
distorted phonograph music from
a well-worn record was considered
quite an event, only seven or eight
years ago, equally thrilling now to
the constructor of a home television
receiver is the reception of a
recognizable profile of one of the
technicians of a television broadcast
station in Boston, Schenectady
or Chicago, the silhouette of a
small girl skipping rope and bouncing
a ball in Washington, or a
page from some magazine held up
before the “eye” of a station in
California. While there are several
diferent television systems being
employed at present, they al)
have many points in common, and
an outfit designed to receive images
from one source. may readily be
altered to work from other transmitting
stations.Distant Reception Possible
The receiver described in this
article was designed for receiving
the half-tone broadcasts from station
WLEX of Boston and the
silhouette “movies” from iX K
the Jenkins Laboratories, in Wash-.
ington, D. C. Outfits made to
these specifications have given very
satisfactory results. Station 3XK
is over soo miles from Boston yet
its thrice weekly program was consistently
received throughout
August, even during local thunder
showers and other handicaps. The
same outfit, except for the subst;-
tution of a 24 aperture, 12 inch
diameter disk for the larger 48
aperture disk. was successfully used
at Long Beach. Cal.. last July to
receive the television broadcasts
of station WGY, Schenectady.
These instances show that while ,there are few television stations
on the air in the country at present,
the lack of great numbers
need prove no serious handicap
to the determined experimenter.
There is hardly a location in
which, if there is no local transmitter,
the signals for a distant
television transmitter cannot be
received with suficient intensity to
gi ve satisfactory experimental
results.
For sake of discussion a dotted
outline has been used to divide
the schematic diagram of the complete
receiver into its components
in Figure r They are: Short
Receiver; Audio Frequency Amplifier:
Kino lamp and Scanning
device. While any good radio
frequency receiver capable of being
tuned to the wave length of
the transmitting station may be
used, it has been found that a
receiver employing a stage of untuned
RF using the 222 high amplication
tube is general preferable.
Standard Set Used
The receiver ilustrated is one
we have been using and is a standard
kit set. All of the parts are
available in the open market.
It comprises several rather
unique features. One is the single
tuning control. Another is the
foundation unit design which permits
an eficient layout of parts
with but few connections to be
made by the assembler. As a
result of the 222 tube in the first
stage the sensitivity of the receiver
in general is materially better than
that of the plain regenerative detector
type of set formerly much
in use.
Circuit Non-Radiating
Furthermore, the use of the 222
tube ahead of the essential regenerative
detector prevents radiation
—a problem which would soon become
quite serious if all short
wave receivers were of the radiating
variety.
Another important advantage
secured by the use of the 222 tube
in this receiver is the elimination
of tuning “holes,” or dead spots
commonly encountered with plain
regenerator receivers. Heretofore
rather carefully placed shielding
h,c heen considered essential to a
receiver using the 222 tube, but the
use of the untuned antenna circuit
has been found to make shielding
unnecessa ry. Elimination of
shielding not only reduces cost and
simplifies construction work but
also makes it a simple matter to
change coils when going from one
wave band to another.
In constructing any type receiver,
especially for short waves,and more particularly one for television
where a motor and scanning
disc are located in the same room,
considerable attention mu st be
given to rigidity of construction.
This applies to the coils and their
mountings, as well as the wiring
and other parts of the set. The
radio frequency choke coil used in
the detector plate lead is of the
multisection slot wound variety
having very low distributed capacity
over a wide band of frequencies.
The other RF Choke,
or grid circuit impedance is one
especially designed for the purpose
and has an inductance of approximately
2 millihenries.
Audio System Important
The perfection of the picture received
depends upon how good a
signal is transmitted in the first
place and upon how well it is reproduced
at the receiving end.
Here the amplifier used following
the detector plays the important
part. If the signal to be received
contains frequencies of from 18 to
20,000 cycles, then it is important
that the audio amplifier be able
to amplify al frequencies within
these limits. The diagram of the
audio amplifier in Figure i is one
that has a much higher frequency
range than the average, giving picture
reproduction with ample de tail for recognizability of persons.
This amplifier is essentially resistance
coupled. The first tube
is a 240 or 340, high-mu tube. The
second is a 12, and the third a
171. The values of the coupling
resistors, grid leaks and coupling
condensers are marked on the diagram.
The grid leak is replaced
in the case of the 171 by an audio
frequency choke in series with a
radio frequency choke. In the
output circuit two 3-henry, choke
coils are connected in series.
Spring suspended sockets should
preferably be used in building the
amplifier to reduce the possibilities
of microphonic tube noises when
motor and disc are located close
by. An important point to keep
in mind is the necessity for employing
high-grade resistors in the
grid and plate circuits.
Noise does not present the same
limitations in a television receiver
that it does in a broadcast receiver.
Any noise is bothersome
if you must listen to it, but in a
picture it is represented by black
spots and streaks that appear in
a continually shifting position unless
it is a periodic noise. Poor
coupling resistors and vibration
are the two most common sources of noise in the receiving amplifier.
If in an early stage of an amplifier
a plate coupling resistor is
defective it will introduce noise
that is amplified. A pair of ear
phones connected to the output
terminal will reveal this noise.
Some noise is to be expected in a
high gain amplifier but one can
easily judge the amount of noise permissible by tapping the tubes
and comparing the microphonic
noise with the amplifier noise.
In three stages of amplification,
as a rule, the amplifier noise will
not be appreciable. Unless there
is a poor or defective resistor in
one of the plate circuits the amplifier
will be quiet. Vibration from
the receiving disk or its motor,
transmitted to the amplifier or
detector tube, will introduce periodic
noise which will cause a black
streak across the field of the picture.
Other periodic interference
such as sixty cycle hum may get
into the signal and cause streaks
across the picture. These will not
remain stationary but will move
upward or downward across the
field of the picture.
Neon Lamp in Output
The Output Circuit is so arranged
that the neon or Kino-
Lamp is always iluminated. When
a signal is received the brilliancy
of ilumination merely varies in
accordance with the signal. The
construction of the tube is quite
simple. There are two flat metal
plates placed parallel and very
close together. The plates are one
and one-half inches square, and
present an area of two and a
quarter square inches. Either
plate can be used as the anode.
The plates are in a space containing
neon gas, hence the name, neon
tube.When the current through the
tube is changed, due to a change
in impressed voltage, the amount
of light emitted is changed. This
fact is made use of to reproduce
the picture. A resistance must be
connected in series with the tube
because, like all gas conductors, it
has a negative resistance coeficient.
A good picture background will
be obtained if the current through
the neon tube is limited to 10 or
20 milliamperes. More current will
cause the lamp to glow brighter
and brighter, but there is no advantage
in this so far as the picture
is concerned and it only
serves to shorten the life of the
lamp. Accordingly, care should
be taken to adjust the current to
the minimum satisfactory value.
A Clarostat has been found just
right for such use and may be
conveniently mounted on the front
of the frame supporting the scanning
apparatus.
For iluminating the kino lamp
either a standard high grade “B”
eliminator, using a filament type
rectifier tube such as the UX28o,
or heavy duty “B” batteries may
be used. If the back plate glows
instead of the front one when the
lamp is turned on the dificulty
may be corrected by reversing the
leads to the power supply.
Accurate Disk Is Necessary
Several diferent concerns are
manufacturing scanning disks suitable
for use with signals now on
the air. The better grade disks
are well made mechanically, so as
to run true and require little
power. The holes in the disks
must be punched to the necessary
degree of accuracy if the received
image is to be free from black
lines and streaks. A feature of
the National disk is radially
shaped holes, rather than round.
By making the holes this shape the
“lines” across the image are much
less obvious than the use of a
disk with round openings.
Successful results have been obtained
with a number of diferent
types of small motors for driving
the scanning disk, but the one being
used at present is the Baldor Vs
horsepower, YIV variable speed
condenser type, for operation on
Tic) volts (single phase) 6o cycles AC. This is a ball-bearing motor
that operates very smoothly and
quietly. The swish of the disk
through the air, constituting the
major portion of the noise, is quite
insignificant. Special rubber vibration
absorbers are supplied with
the motor for mounting purposes.
The diagram, Fig. 1, shows the
method for speed control. For
the variable resistor “R12,” a 75-
watt, 4 to Ioo ohm wire wound
resistor with sliding contact is
used. The other resistor may be
a 10 ohm io watt resistance.
This is labeled “RI 1” in the diagram
and is shunted by the push
button speed control leads.
Push Button Controls Speed
The resistance “R 2” is so adjusted
that with the push button
released the motor runs at slightly
below proper synchronous speed.
When the push button is depressed
the disk tends to speed up.
Do not mount the television receiver
in the same cabinet with
the disk. Vibrating of the motor
will introduce a synchronous noise
that will result in a series of horizontal
lines being drawn across
the picture. Keep the receiver
and amplifier on a support separate
from that for the disk.
The following convention has
been adopted by the Raytheon
Company in regard to neon tube
mountings. The tube is fitted with
a standard UX base. The plates
inside the tube are placed in a
plane at right angles to the axis
of the “Pin” of the base. If the
pin, therefore, is pointed toward
the disk when inserted in the
socket, the plates inside the tube
will be parallel to the disk. Mount
the tube at the proper height to
cover the inch and a half square
scanned by the revolving disk.
The tube plates are connected to
the “plate” and “filament” prongs
of the base.
Phones Used to Tune in Signal
The first step in the reception of
a television is the locating of the
signal on the receiver dials. This
is best done with the aid of headphones
or a loud speaker connected
in place of the neon lamp.
However, do not fail to have a
fixed condenser of about one microfarad
capacity in series with the phones when connecting it in
place of the neon lamp or across
the neon lamp terminals.
Television signals have a very
distinctive sound but unfortunately
the short waves contain signals
which may easily be mistaken for
television. For instance, the high
speed code and picture transmission
of such stations as WIZ and
W QO are much like a television
signal because of a flutter, or what
may be called a group frequency.
A good wave meter will be of
great help in tuning television
signals. It will prevent mistaking
an automatic code station for the
picture station.
The television experimenter may
be puzzled to find his received
picture either turned upside down
or else reversed, as looking
through a photographic negative
the wrong way. Both of these
faults can be corrected quite easily.
Image May Be Inverted
When an image is upside down
and the correction of this fault is
obvious. The subject before the
transmitter at WLEX is scanned
from top to bottom during one
revolution of the disk. Accordingly,
if you rotate your receiving
disk so that the plate of the neon
lamp is scanned from bottom to
top the picture will be inverted.
To reverse the manner in which
the neon lamp plate is scanned
vertically, it is necessary to reverse
the direction of rotation of the
disk or remove the disk from the
shaft of the driving motor and
turn it around. The latter operation
may involve the removal of
the hub and remounting on the
opposite side of the disk.
The received image may be reversed
horizontally. For example,
one of the objects often placed before
the transmitter is a microphone
stand with the microphone
and the station letters mounted
on it. If you receive this object
erect, but reversed, so that the
letters are backwards your disk is
so rotated that the holes pass the
neon plate in the wrong direction.
• The correction of this fault is
not so obvious. It is plain that
whether you scan the plate from
top to bottom or from bottom to
top makes the diference between one another. Now, without disturbing
the perforated tinfoil, slide
the lens back carefully in its own
plane to its original position. As
this is done and the rays passing
through the various apertures
picked up by the lens, one by one,
the corresponding images on the
screen will fall together in the
most striking way, until, finally,

when the lens comes to its final
position covering all the apertures,
only one central image will be
found on the screen. Now prick
more holes until the whole of the
tinfoil in front of the lens has been
removed. Nothing further happens
except that the single image
becomes brighter and brighter.
This experiment shows us then,

the picture being right side up and
upside down. Similarly, whether
you scan the plate from left to
right or from right to left makes
uhe diference between seeing the
image correctly or reversed.
How can we make the holes
pass the plate in the opposite direction
and still progress from top
to bottom? Reversing the rotation
of the disk alone will turn the
image upside down. You must
also turn the disk around on the
shaft of the motor. Thus, if your
image is right side up but reversed,
you must reverse the direction of
the rotation of the disk and also
remove the disk from the shaft
and turn it around with the other
side out. These factors make several
incorrect combinations and only one correct one, but the incorrect
combinations provide perfectly
recognizable images whose
worst fault is to be upside down.
Should the image obtained be a
negative instead of a positive AC
connections to the Kino lamp. Interchanging
these connections will
correct the trouble.
TELEVISION MOTORS

running just under synchronous
speed to be slightly accelerated by
pressing the button. When the receiver
scanning disc is just in step
the image will appear to stand still
on the screen. A moment longer
of pushbutton depression and the
image moves slowly of the screen that one of the primary functions
of a lens is to allow of the use
of a large aperture with its great
light-collecting power for imaging
purposes. Later we shall find that
this larger aperture is also necessary
for the definition of delail
structure in the image.due to the motor running a little
too fast. By releasing the button
the motor slows down slightly, and
so the image is kept “framed. –
A rheostat of i6o ohms divided
into ten steps, and a separate 25-
ohm resistor shunted by the pushbutton
will be found ideal. The
two resistors are connected in series.
Both should be capable of
carrying the required current without
undue heating. If the motor
is running too slow for the shortcircuited
resistance of the hand
resistor to overcome, move the
adjustable arm on the ten-stop resistor
one step further in advance.
The motor will then speed up
slightly and can be brought
“down” to synchronism, instead
of “up” to a state of perfect step
with the transmitter scanning disc.the drum. Between the lamp and
the periphery of the drum are tiny
quartz rods, each rod ending under
its particular minute aperture
in the drum surface.
Quartz Rods Carry Light
A quartz rod has the peculiar
property that light flows through
it like water flows through a pipe.
The use of quartz rods avoids
light loss. The tiny holes in the
drum are arranged in a plurality
of helical turns like a coarsethreaded
screw. The number of
helices determines the size of the
picture with a given size drum.
Increasing the size of the drum
also increases the size of the picture.
The number of glow-spots
in the lamp correspond to the
number of hole helices in the
drum. The glow-spots in the
lamp are lighted one at a time
by the current from the plate of
the last tube of the amplifier of
the radio set.
The adoption of quartz rods
for conserving the light, and dividing
the neon glow target into
small sections, lighted one at a
time, has enabled us to obtain a
large picture with a relatively
small current. The receiver is not
bulky and its operation is simple.
The motor cord is attached to the
house current and the lamp cord to
the radio set.Simple Device Gets Images
To get the pictures attach a correctly made picture receiver to a
suitable radio set, and tune in the
station broadcasting the pictures.
Surprisingly simple apparatus
can be put together to get the pictures,
namely, a neon lamp, a
scanning disc, and a small motor
to rotate the disc. A 12-inch
scanning disc with 48 scanning
apertures gives splendid definition.
The disc may be made of card board, bakelite, iron or aluminum.
The only real dificulty is getting
the tiny holes correctly laid of in a spiral. A Neon lamp suited to
this 12-inch disc costs one dollar.
Mount the scanning disc in a
bearing so that it turns freely.
Rotate it by any small A. C. induction
or D. C. motor of 1/20th,
1/16th, or 1/18th h.p., mounted
on a board between guide strips
so that it may move to and fro,
parallel to the scanning disc. Cut
from the inner tube of an automobile
tire a disc 2  ,1/2 to 3 inches in
diameter. Put this disc between
2-inch flanges on a hub to go on
the motor shaft. Locate the motor
so that the rubber driving disc
bears against the back of the
scanning disc.
To bring in the picture synchronism
is attained by shifting the
location of the motor with respect
to the disc axis. Support the lamp
behind the top of scanning disc so
that you can look at it through
the flying holes in the whirling
disc, and the picture receiver is
ready. The motor wires are attached
to the house current and
the lamp leads to the output of
your radio set, like a loudspeaker
is attached. A resistance-coupled
audio amplifier set produces the
best and sharpest pictures. The
picture is about the size of a picture
on a movie film, but appears
larger through a reading glass.
Tune in the station, adjust the
position of the motor, and out
flashes a picture in al its mysterious
fascination.

 

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පෙර ලිපියෙන්JACK PEARL 1929 Radio Star
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