Chromatron is a color television cathode ray tube design invented
by Nobel prize-winner
Ernest Lawrence and developed commercially by
Paramount Pictures, Sony,
Litton Industries and others. The Chromatron
offered brighter images than conventional color television systems
using a shadow mask, but a host of development problems kept it from
being widely used in spite of years of development.
abandoned it in favor of their famous
Trinitron system using an
1.1 Color television
1.2 Shadow masks
1.4 Commercial developments
1.5 Sony's attempt
1.6 Limited sales
3 See also
5.4 Further reading
Color television had been studied even before commercial broadcasting
became common, but it was only in the late 1940s that the problem was
seriously considered. At the time, a number of systems were being
proposed that used separate red, green and blue signals (RGB),
broadcast in succession. Most systems broadcast entire frames in
sequence, with a colored filter (or "gel") that rotated in front of an
otherwise conventional black and white television tube. Because they
broadcast separate signals for the different colors, all of these
systems were incompatible with existing black and white sets. Another
problem was that the mechanical filter made them flicker unless very
high refresh rates were used. In spite of these problems, the US
Federal Communications Commission selected a sequential-frame 144
frame/s standard from
CBS as their color broadcast in 1950.
RCA worked along different lines entirely, using the
luminance-chrominance system. This system did not directly encode or
transmit the RGB signals; instead it combined these colors into one
overall brightness figure, the "luminance".
Luminance closely matched
the black and white signal of existing broadcasts, allowing it to be
displayed on existing televisions. This was a major advantage over the
mechanical systems being proposed by other groups. Color information
was then separately encoded and folded into the signal as a
high-frequency modification to produce a composite video signal – on
a black and white television this extra information would be seen as a
slight randomization of the image intensity, but the limited
resolution of existing sets made this invisible in practice. On color
sets the signal would be noticed, decoded back into RGB, and
Although RCA's system had enormous benefits, it had not been
successfully developed because it was difficult to produce the display
tubes. Black and white TVs used a continuous signal and the tube could
be coated with an even painting of phosphor. With RCA's system, the
color was changing continually along the line, which was far too fast
for any sort of mechanical filter to follow. Instead, the phosphor had
to be broken down into a discrete pattern of colored spots. Focusing
the right signal on each of these tiny spots was beyond the capability
of electron guns of the era. RCA's early experiments used three-tube
projectors, or mirror-based systems known as "Triniscope".
RCA eventually solved the problem of displaying the color images with
their introduction of the shadow mask. The shadow mask consists of a
thin sheet of aluminum with tiny holes photo etched into it, placed
just behind the front surface of the picture tube. Three guns,
arranged in a triangle, were all aimed at the holes. Stray electrons
at the edge of the beam were cut off by the mask, creating a sharply
focused spot that was small enough to hit a single colored phosphor on
the screen. Since each of the guns aimed at the hole from a slightly
different angle, the spots of phosphor on the tube could be separated
slightly to prevent overlap.
The disadvantage of this approach was that for any given amount of gun
power, the shadow mask filtered out the majority of the signal. To
ensure there was no overlap of the signal on the screen, the dots had
to be separated and covered perhaps 25% of its surface. This led to
very dim images, requiring much greater power in order to provide a
useful picture. Moreover, the system was highly dependent on the
relative angles of the beams between the three guns, which required
constant adjustment by the user to ensure the guns hit the correct
colors. In spite of this, the technical superiority of the
was overwhelming compared to the
CBS system, and was selected as the
new NTSC standard in 1953. The first broadcast using the new standard
occurred on New Year's Day in 1954, when NBC broadcast the Tournament
of Roses Parade.
In spite of this early start, only a few years after regularly
scheduled television broadcasting had begun, consumer uptake of color
televisions was very slow to start. The dim images, constant
adjustments and high costs had kept them in a niche of their own. Low
consumer acceptance led to a lack of color programming, further
reducing the demand for the sets in a chicken or the egg situation. In
the United States in 1960, only 1 color set was sold for every 50 sets
sold in total.
In 1951 Ernest Lawrence, a professor at University of California,
Berkeley best known as the father of the cyclotron, patented a new
solution to the color decoding problem. This system, the "Chromatron"
or simply "Lawrence Tube", used an electronic focusing system in place
of RCA's mechanical solution. The system consisted of a series of
thin metal wires or plates placed about 1/2 an inch behind the
phosphor screen. The wires were used to electrically focus the beams
and bend them onto the correct phosphors, which were arranged in
vertical stripes. The phosphor covered over 50% of the screen's area,
whereas the contemporary shadow masks covered about 25%. This led to
much brighter images using the same amount of power.
Each focusing element consisted of a pair of wires, and a conductive
aluminum coating on the back of the phosphors. The screen was normally
charged with a potential of 3000 to 4500 V between the wires and the
aluminum, resulting in a curved electric field between the grid and
the screen. When the electron beam from the gun entered the region
between the grid and the screen it was accelerated and focused down to
a tiny spot, normally impinging on the green phosphor. By varying the
relative voltage between the two wires in each pair, the beam would be
bent one direction or the other, allowing control over the color.
Unlike a shadow mask, all of the signal eventually reached the screen,
further reducing power requirements.
If the chrominance signal was missing, or deliberately ignored, the
focusing system was disconnected and its power added to the gun. This
produced a slightly stronger and unfocused beam, which hit all three
colored strips and produced a B&W image. The spaces between the
stripes meant the overall image would be about as bright as a
conventional B&W set. A shadow mask set required all three guns to
be powered to produce a B&W image, and since the color spots were
small, their power had to be very high.
Yet another advantage of the near-screen focusing was that the
electron beam was bent to hit the phosphors on the tube's faceplate at
right angles no matter what the angle of the beam was behind the
focuser. This allowed the tubes to be built with much higher
deflection angles than conventional tubes – 72 degrees as opposed to
a more typical 45.
Chromatron tubes thus had much less depth for any
given horizontal size.
Chromatron also had several disadvantages. One was that there was
a fundamental ratio between the acceleration provided by the grid and
the electron gun at the back of the tube; in order to ensure that the
grid could successfully control the beam, it had to have a significant
proportion of the overall power. Unfortunately the mechanical layout
of the grid limited it to voltages of about 5000 V or less, which in
turn limited the electron gun to relatively low voltages around 8000
V. Thus the overall power in the
Chromatron was less than in
conventional tubes, offsetting its natural brightness to some
The more pressing concern was the mechanical layout of the grid.
Getting the fine wires to stay aligned with the strips of color on the
screen proved to be the design's Achilles heel.
University of California, Berkeley
University of California, Berkeley set up "Chromatic Television
Laboratories" to commercially develop the system, in partnership with
Paramount Pictures who provided development funding. They started
producing the PDF 22-4 22 inch prototype tubes in 1952 and 1953,
with a display area of 14 by 11 inches.
In practice the design proved to have serious problems. Since the
focusing system had to quickly move the beam to generate the correct
colors, very high voltages and powers had to be used, leading to
arcing problems and radio frequency (RF) noise. The latter was
particularly annoying when used as the basis of a television, as the
noise interfered with the radio receivers that picked up the
broadcasts. The University eventually abandoned their interest in
Chromatron, but Paramount continued development as a system for
displaying film during editing, which meant that the RF noise did not
present a problem. Development was still continuing in the early 1960s
when their work was bought by Sony.
In spite of these problems, the promise of the
Chromatron system was
so great that a number of companies continued development of the
system throughout the 1950s. The
Chromatron design was also licensed
for a variety of other uses;
Litton Industries used the Chromatron
with a two-color display (blue-red) as the basis for an Identification
Friend or Foe system.
Sony was a major Japanese manufacturer of black and white
sets, but had no color television technology at all.
Sony dealers were
asking when they could expect a color set, and the sales division
started putting pressure on engineering to simply license a shadow
mask design from another maker and start production. Masaru Ibuka
refused, apparently displaying an intense personal feeling that the
shadow mask design was fundamentally flawed.
In March 1961 Ibuka,
Akio Morita and
Nobutoshi Kihara attended the
IEEE trade show at the New York Coliseum. This was Kihara's first
visit to the U.S., and he spent considerable time wandering the show
floor. At the small
Autometric booth he saw the
displayed, and hurried to find Morita and Ibuka to show them. When
Morita saw the display he immediately started negotiating a meeting
for the next morning to visit the Chromatic labs in Manhattan. By
the end of the meeting the next day, Morita had secured a license to
Chromatron tube and color television receiver utilizing
In early 1963 Senri Miyaoka was sent to the Chromatic labs to arrange
the transfer of the technology to Sony, which would lead to the
closing of Chromatic. He was unimpressed with the labs, describing the
windowless basement as "squalor". The American team was quick to
point out the flaws in the
Chromatron design, telling Miyaoka that the
design was hopeless. By September 1964, a 17 inch prototype had
been built in Japan, but mass-production test runs were demonstrating
Ibuka remained a staunch supporter of the technology, and pressed
ahead with the construction of a new factory to produce them at Osaki
Station in Tokyo. This proved unwise, and in early runs only 1 to 3
tubes would be usable out of every 1,000 produced. The rest suffered
from alignment problems, with the colors fading from one to another
across the screen, impossible to fix after the tube was sealed. Usable
tubes were quickly rushed to
Sony showrooms in spite of the low
yields, and Ibuka make the product Sony's top sales priority. This too
proved unwise; the low yields meant that the production cost was about
400,000 yen, but
Sony was forced to sell them at 198,000 yen ($500) in
order to be competitive.
The production problems were never solved, and led to increasing
tension between Ibuka and Morita. In November 1966 Kazuo Iwama told
Susumu Yoshida that the company was close to ruin, and that the team
had to improve the yields by the end of the year, or the product would
have to be cancelled. Meanwhile,
RCA was making great progress
improving their shadow mask technology, and new entrants like General
Electric's "Porta-Color" offered other advantages.
Sony was clearly
falling behind the rest of the market by following the Chromatron
Ibuka finally announced that he would personally lead the search for
an alternative system. His team of 30 engineers and physicists
explored a wide variety of approaches in the search for a uniquely
Sony system. After reading several of the reports, Ibuka called
29-year-old physicist Miyaoka into his office along with Yoshida, and
asked him if his single-gun approach could be made to work. Miyaoka
was attempting to leave work for a cello rehearsal, and rashly stated
that it would work. The result was the famed
Trinitron system, which
went on sale in 1968 to wide acclaim.
In spite of Sony's move to Trinitron, a limited number of 7-inch
Chromatrons were built and offered for sale in the United States
starting in April 1968 as the KV 7010U. These were replaced three
months later by the KV 7010UA using a
The basic concept that defined the
Chromatron was the near-screen
focusing system, which provided the beam resolution needed to
accurately hit the individual colored phosphor strips. The grid both
focused the signal as well as guided it to the correct colors.
The phosphors were silk screened onto the back of the tube in strips 2
mils wide with 2 mil wide gaps between them, and then coated in
aluminum to make the screen conductive. Since the grid had to be
charged to relatively high voltages, the aluminum coating was fairly
thick, which dimmed the image to some extent.
The phosphors were patterned in an RGB-BGR-RGB pattern. The focusing
grid was aligned so the beam would normally focus down onto the green
strips in the middle of each pair of wires. To produce different
colors, say blue, the beam would have to be pulled to the right for
one pixel, and then to the left for the next. Since the adjacent
stripes of phosphors shared one of the wires, this meant that a single
voltage setting would produce the blue color on two adjacent pixels.
Since a single frame of color television does not consist of a single
color, the deflection system had to be continually varied as the beam
moved across the screen.
Geer tube, another early color television CRT that is no longer used
^ In January, 2013, a working
Sony KV 7010U was found by this editor,
currently in his possession and confirmed to be a hybrid
inch CRT. The television was opened and among other things, a label
was attached to the CRT bell reciting "SONY CHROMATRON Licensed under
Paramount Pictures Corporation".[original research?]
^ Ed Reitan, "
CBS Field Sequential Color System" Archived 2010-01-05
at the Wayback Machine., 24 August 1997
^ Ed Reitan, "
RCA Dot Sequential Color System" Archived 2010-01-07 at
the Wayback Machine., 28 August 1997
^ Jack Gould, "Television in Review: NBC Color", The New York Times, 4
^ a b Sony, p. 42.
^ Cathode Ray patent.
^ a b c Summary.
Sony refers to Chromatic Television by the name "Autometric
Laboratories", although no other reference mentions this name.
^ Sony, p. 43
^ a b Sony, p. 44.
^ Sony, p. 45
^ Sony, p. 48
John Nathan, "Sony: The Private Life", Houghton Mifflin Harcourt,
2001, ISBN 0-618-12694-5
Sergey Shewchuck, "Summary of Research Progress Meeting of September
27, 1951", UCRL-1563, Radiation Laboratory, University of California,
14 November 1951, pp. 2–4
Milton Kaufman and Harry Thomas, "Introduction to Color TV", Taylor
Edward W. Herold, "History and development of the color picture tube",
Proceedings of the Society of Information Display, Volume 15 Issue 4
(August 1974), pp. 141–149
U.S. Patent 2,692,532, "Cathode Ray Focusing Apparatus", Ernst O.
Lawrence, University of California/Chromatic Television Laboratories
U.S. Patent 2,866,094, "Symmetrical to Asymmetrical Signal Conversion
Circuit", Hoffman Electronics
U.S. Patent 3,368,105, "High Voltage Power Supply System for Cathode
Ray Tubes Employing Protective Time Delay Means", Sony
"This is Color TV: A Look at the Record To See What's Ahead", TV
Guide, June 26 to July 2, 1953, pp. 5–7
Mark Heyer and Al Pinsky, "Interview with Harold B. Law",
Center, 15 July 1975
Chromatron KV 7010U
"Model PDF-22-4", Chromatic Labs brochure
"Lawrence Experimental type CH-22", Thomas Electronics brochure (also
has the 15GP22)
"Model PDF-10-1X", Litton I