In the early days of television, what we today refer to as cathode
ray tubes were called kinescopes. The kinescope on the
receiving end displayed images generated by a tube called an
iconoscope on the transmission end. Kinescopes had round
faces onto which a rectangular picture was electronically drawn.
Once manufacturing technology evolved sufficiently, it became
possible to make them rectangular in order to save on material
and to fit a larger picture in a smaller area. The real story
in this article from my perspective is appreciating the ingenuity
of the manufacturing engineers for an ability to develop machines
that handle very complex operations. They were wonders of electromechanical
manipulation. There were still some operations that needed human
dexterity and decision making.
Television Tubes by the Thousands
By Frank E. Butler
A modern miracle of mass production is typified by the ingenious
wedding of automatic machinery, technical skills, and quality-controlled
Fig. 1 - Completed 10" kinescope at
left. Center unit is bulb blank in which the "button" has been
sealed. In front of tube are the stem and completed tube element
assembly. Right hand bulb shows fluorescent coaling and colloidal
The Age of television is at hand and to speed its progress
toward perfection, groups of technical experts in widely divergent
professions such as electronics, optics, and the glass industries
are contributing their share of scientific knowledge and experience
to this end.
The technological advance is so rapid, both in monochrome
and color television transmission and receiving equipment, that
pictures by both systems are now being shown with surprising
realism and clarity. Only very little of this advanced development
remains in the laboratory stage and this is sufficiently developed
to insure its appearance in homes much sooner than most of us
Fig. 2 - Flare machine in which G12 glass
tubing is cut off and pre-formed to provide a flat pressed stem
for the tube. Glass parts are heated at various stages from
The rapidity and skill with which this progress has been
made by television laboratories and their confidence in the
future of television is evidenced by the building of new plants
and the designing of special machinery for the manufacture of
equipment. Therefore a peep behind the scenes of television
activity should prove of unusual interest at this time.
The heart of television is the iconoscope - the electronic
device capable of detecting the image or scene of action that
is to be televised through space, then subsequently translating
the reflected light into electric impulses.
The kinescope is a similar electronic tube which reverses
the above action whereby the televised impressions are transformed
back into light to form a reproduced image or "picture" on the
sensitive face of the tube. To create these two companion tubes,
which must combine delicateness, ruggedness, and utmost sensitivity,
requires the use of nimble fingers, keen eyes, highly developed
skills, modern automatic machinery and the best techniques that
can be devised by the several different industries involved
in the manufacture of tubes.
Fig. 3 - Hundreds of 10-inch kinescope bulbs
lined up ready for the application of the fluorescent coating
to the inside. .Each tube receives a measured amount of solution.
The factory where these tubes are . produced must be fully
air conditioned and the humidity level must be maintained at
a predetermined level. In addition, the factory must also be
equipped with dust filters in order to eliminate impurities
which might affect the sensitive tube elements.
There are two kinds of kinescopes produced - one known as
the electronic direct view type, and the other as the projection
type. From the small kinescope which produces exceptionally
brilliant images which are subsequently enlarged optically for
projection on a viewing screen of a 7 1/2 x 10 or 18 x 24 foot
theater size, to the largest kinescopes which have a 10 or 12
inch face from which the image is viewed directly (without enlargement),
there are many precise and intricate operations which must be
performed on both the tube elements and the glass bulb.
Fig. 4 - Operators prepare the fluorescent
solution which is used in the kinescopes to form the picture
screen of the video tube. Quality control of the solution is
vitally important here.
One of the first glass operations in the production of kinescopes
or iconoscopes is to make the flare of the stem which holds
the elements. This is done on the flare machine shown in Fig.
2. Here gas fuel is used to heat the glass parts as they index
around the automatic machine, in various stages, to temperatures
rangng from 600°C. to 900°C. After a small section has
been cut off and the end flared, the bottom portion is heated
by a special gas flame pattern which places the heat exactly
where it is wanted at the proper temperature for flat pressing.
Heating time is controlled by the speed at which the machine
indexes from station to station.
Fig. 5 - Fluorescent coating, in solution,
is carefully poured into a prepared kinescope bulb.
A battery of automatic flare machines is used in making the
glass stems in which the tube element supporting the lead-in
wires are sealed. Specially designed gas burners, emitting predetermined
flame patterns heat the glass tubing to various stages of viscosity
in order that it may be flat pressed into a stem. All of the
equipment that utilizes heat in any form for processing is efficiently
hooded and ventilated to carry off excess heat and the products
Fig. 6 - Next step is the insertion of the "button" in the
side of the bulb by means of a gas-fired torch. Operator softens
the glass, punctures a hole, and inserts button.
When this part has been formed, the lead-in wires to the
tube elements are inserted and the assembled element units are
placed on another automatic gas-fired machine where special
flame patterns heat those parts of the stem to just the proper
temperature and for just the correct time to effectively seal
the wires into the glass stem. Annealing takes place immediately
after the part has reached the last position on the machine.
The unit is then ready for mounting the tube electrodes, after
which it is prepared to be sealed into a bulb-blank, which resembles
a large glass funnel with a long stem.
Fig. 7 - Baking on the colloidal graphite coaling requires
approximately one and a half hours at 400°C in a gas-fired
oven. A specially designed oven is used in this operation.
The bulb or kinescope blanks are subjected to many processes
and operations; the first being a thorough washing, inside and
out, after which they are placed in specially constructed racks
in the "settling-room" Fig. 3. This room is constructed on its
own foundation and the floor is composed of a heavy concrete
slab floating on a layer of cork. There is no physical connection
to any other part of the building, thus eliminating any transmission
of vibration. A measured quantity of liquid containing a fluorescent
substance is then placed in each tube. The preparation of this
fluorescent solution requires a high degree of skill and accuracy.
The operation is shown in Fig. 4.
Next, the coating, in suspension, is carefully and accurately
poured into the kinescope bulb. See Fig. 5. Slowly, the solid,
active fluorescent material settles on that part of the tube
face on which the electrons react to produce the image. When
the settling process is complete, the remaining liquid is carefully
Fig. 8 - A non-reflective carbon coating,
designed to keep stray electrons from the picture screen, is
next applied with a long-handled brush.
The next step in the manufacture of the tube is the insertion
of a "button" in the side of the bulb. This operation, which
is illustrated in Fig. 6, is performed by means of a gas-fired
torch. The operator softens the glass, punctures a small hole
and inserts the "button" or electrical contact which is then
hermetically sealed in the tapered section of the bulb. The
tube is then annealed at 450°C. by means of a continuous
gas-fired radiant tube glass lehr where the cycle of passing
through the heated air ranges from four to six hours, depending
on the size of the tube.
Fig. 9 - The operator is shown installing
the cathode-ray gun in a modern type image orthicon camera tube
which is used for video pickups.
The inside of the bulb is next coated with a colloidal graphite
mixture which serves to carry off the electron charges after
they bounce back from the screen. The grounded electrical circuit
is through the "button" previously described. Next, this inner
graphite coating is subjected to a baking cycle which is performed
at temperatures of 400°C. for approximately one and a half
hours. This operation is shown in Fig. 7.
The operator now applies a coating of non-reflecting carbon
to the interior of the tube by means of a long handled brush
(See Fig. 8). This coating keeps stray electrons from the picture
Fig. 9 shows the operator adjusting the delicate electrical
components that are to be inserted in the tube. At this stage
of production, the prepared bulb is ready to be sealed to the
glass stem which supports the internal elements, or electron
gun. This operation takes place on a completely automatic gas-fired
sealing machine (Fig. 10) where the elements are set in the
tube, the flare and bulb are sealed, and the collet cut off.
These operations take place as the tubes index around the machine
to their respective stations where varying patterns of gas flames
perform the successive operations on the glass. At the final
station the excess neck of the bulb, or collet, is cut off when
the No. 6 lime glass of which the kinescope blanks are made
is heated to 1050°C. by a needle flame which produces a
clean, sharp cut.
Fig. 10 - Automatic sealing machine where
elements are set in tube. The flare and bulb are sealed and
the collet is cut off.
Fig. 11 shows a close-up view of the six needle gas flames
which concentrate on the bulb neck where the collet is cut off
as the tube revolves in the flame. The large gas burner, shown
at the right of the photograph, performs the annealing operation.
When the vacuum process has reached its final position, the
tube is "tipped off" - an operation w h i c h seals the tube
permanently and severs its connection to the vacuum pump.
After sealing, the tube progresses to an exhaust machine
where an extremely high vacuum is developed. While on this machine,
the glass bulb is heated by radiant heaters to its softening
point to assist the vacuum pump in removing occluded moisture
and gases. The electron gun and other internal elements are
heated by high frequency induction methods and, at another stage
in the process, working voltages are applied to the tube elements
Fig. 11 - Close-up view of operation in which
collet is cut off. The gas burner shown at right performs the
After the tube has been evacuated and severed from the exhaust
machine, the operator threads the lead-in wires into the socket
base of the kinescope. This operation is shown in Fig. 12.
Final tests are then run on the complete kinescopes. The
operator (Fig. 14) uses a special chart as a reference standard.
Following this testing, the tubes undergo a 500-hour operational
test (Fig. 13).
Fig. 12 - Operator threads lead-in wires
into socket base of a kinescope after the air has been exhausted
from the tube envelope.
Larger television pictures obtainable in the projection system
are the result of an optical development which is an outgrowth
of a discovery revealed in 1932 by Bernard Schmidt, a research
assistant in a German laboratory. At that time astronomical
photography was unsatisfactory, due to spherical aberrations
caused by the mirror used to reflect light from the stars and
planets to the camera. By placing a "correcting lens" (corrector
plate) between the mirror and the camera, Schmidt discovered
that he obtained much clearer pictures. These plates, however,
had to be ground by hand, and prior to the war there were only
a few in existence because of the extreme difficulty of their
manufacture. During the war, American scientists developed a
new method for mass producing these "corrector plates" which
were used in infrared viewing devices. Now, tens of thousands
of these plates, embodying the same technique are being used
for television reception. They are made by heating a flat piece
of glass until it flows into the specially curved surface of
a refractory on which the glass is placed. This mold is made
of special composition that does not adhere to the glass and
yet permits it to assume the desired curvature. One side of
the glass is then ground and polished to a plane surface.
Fig. 13 - Technician checking kinescope picture
tubes during a 500-hour continuous performance test run at the
The mirror is aluminized in such a way that the reflectivity
will be as high as possible. The problem of aluminizing large
surfaces and producing an aluminum surface of the required durability
was not simple, but it was solved .
Another contribution to the development of television receiving
sets was the result of a war-time invention for producing glareless
glass. This process makes possible the reception of clearer,
sharper television pictures. The successful removal of light-consuming
reflections from a television tube's glass face, which serves
as the screen of a direct-viewing home television receiver,
has been obtained through a new glare-removal technique which
also produces images of greater clarity when applied to the
optical system of the projection type. The technique was developed
during the war to increase the efficiency of such military optical
instruments as binoculars which gained over 60 percent in light
transmission when reflections were reduced. Reflections are
removed by directly coating the face of the television tube
with a secret chemical composition. It is not necessary to disassemble
the tube for the coating process or to apply the coating in
the vacuum chambers used in earlier glare-removing techniques.
Fig. 14 - One of the test procedures used in checking the
performance of kinescopes used in home television receiving
The coating improves the reception of television pictures
by: (1) Reducing reflections in the glass face of the tube caused
by light sources in the room housing the receiver. (2) Reducing
the intensity of false images caused by reflections from the
outer surface of the image-producing fluorescent screen in the
tube, thus increasing the sharpness of the images. (3) Reducing
light losses from reflections, thus increasing the amount of
It is a tribute to glass craftsmen, machine designers, optical
technicians, skilled operators, and electronic engineers that
these relatively high temperatures, automatic operations, accurate
optical amplification, and extreme electronic sensitivity can
be used effectively in such narrow confines as the interior
of television tubes - the iconoscope and the kinescope - an
accomplishment which has been due to the efforts of these men
of vision and still working in close cooperation.
Posted September 8, 2015