Telechrome was the first all-electronic single-tube color television
system. It was invented by well-known Scottish television engineer,
John Logie Baird, who had previously made the first public television
broadcast, as well as the first color broadcast using a pre-Telechrome
Telechrome used two electron guns aimed at either side of a thin,
semi-transparent mica sheet. One of the sides was covered in cyan
phosphor and the other red-orange, producing a limited color gamut,
but well suited to displaying skin tones. With minor modifications,
the system could also be used to produce 3D images.
Telechrome was selected as the basis for a UK-wide television standard
by a committee in 1944, but the difficult task of converting the
two-color system to three-color
RGB was still underway when Baird died
The introduction of the shadow mask design by
RCA produced a workable
solution for color television, albeit one with considerably less image
brightness. Interest in alternative systems like the
Geer tube faded by the late 1950s. The only alternatives to see
widespread use were General Electric's slot-mask, and Sony's
Trinitron, both were modifications of the
RCA concept. All CRT-based
methods have since been almost completely replaced by LCD television,
starting in the 1990s.
1.1 Mechanical and hybrid color
1.2 Fully electronic systems
3 Public demonstrations
Telechrome and the Hankey Committee
Telechrome and Trinitron
8 External links
Mechanical and hybrid color
Baird performed one of the earliest public demonstrations of color
television system on 3 July 1928 using an all-mechanical system with
Nipkow disk scanners synchronized with a single disk on the
receiving end and three colored lights that were turned on and off in
synchronicity with the broadcaster. The same basic system was used on
4 February 1938 to create the first color broadcast transmissions from
The Crystal Palace
The Crystal Palace to the
Dominion Theatre in London. Baird was not
the only one to experiment with mechanical color television, and a
number of similar devices were demonstrated throughout this period,
but Baird is recorded as the first to show a real over-the-air
transmission in a public demonstration.
In 1940 he introduced a much better solution using a system known
today as hybrid color. This used a traditional black and white CRT
with a rotating colored filter in front. Three frames, sent one after
the other in a system known as sequential scan, were displayed on the
CRT while the colored wheel was spun in synchronicity. This design was
physically very long, leading to deep receiver chassis, but later
versions folded the optical path using mirrors to produce a somewhat
more practical system. Again, Baird was not the only one to produce
such a system, with
CBS displaying a very similar system at almost the
same time. However, Baird was not happy with the design later stated
that a fully electronic device would be better.
Fully electronic systems
This live image of Paddy Naismith was used to demonstrate Baird's
first all-electronic color television system, which used two
projection CRTs. The two-color image would be similar to the basic
telechrome system. Note that the green in Paddy's blouse reproduces
very poorly as a dark, grayish cyan. Baird's two-color method can't
reproduce true greens or blues.
The basic problem facing designers of color televisions was this:
Sending each frame of the moving image meant sending three signals,
red, green and blue. The sequential systems, like Baird's earlier
efforts, sent the three images one after another. In order for motion
to appear smooth, images must change at least 16 times a second. To
reduce flicker, over 40 frames per second (fps) is mandatory. In
sequential systems, each color requires a separate field. For this
reason, very high refresh (field) rates were necessary. CBS' system
refreshed at 144 fps. (Peter Goldmark's
CBS team tried several
field rates. Within the 6 MHz allowable channel bandwidth, the most
acceptable rate was 144 fps. This rate made pictures incompatible with
existing systems working at 50 or 60 Hz.
A system sending all three signals at the same time at a conventional
refresh rate would be greatly preferable. Transmitting such a signal
could be accomplished by using three camera tubes, each with a color
filter in front of them, using mirrors or prisms to aim at the same
scene through a single lens. Each signal would then be separately
broadcast using three conventional TV channels, and using the
luminance concept, one of those could be received on a conventional
black and white set. This would use a considerable amount of
bandwidth, but this was a small cost in the era of only a few
The problem, however, was how to combine the three separate signals
back into a single display. The system used in the cameras, with three
separate tubes combined together optically, was not practical due to
the cost of a receiver set with three CRTs as well as the unwieldily
chassis needed to contain them. One such example was the RCA
Triniscope, which produced useful images but was extremely complex,
required constant adjustment, and was the size of a contemporary
refrigerator to produce a 10 inches (250 mm) display. A number of
experiments were carried out using more conventional tubes and then
filtering them, but the low output of the CRTs produced very dim
images that were dismissed as impractical.
Baird had previously worked on a high-intensity CRT system known as
the "teapot tube" that saw some use in the UK and US as a projection
system in theatres. These were normally built with two such CRTs
side-by-side, with one acting as a hot backup in case the primary tube
failed. In 1941 Baird converted such a projector to produce a
two-color image simply by placing filters in front of the two tubes
and projecting them onto a smaller screen to improve the effective
intensity. He first showed this in 1941, and in 1942 the
the resulting color image as "entirely natural". The image, of Paddy
Naismith, is the first known image of color television to be
A projection system with two CRTs was better than three, but still not
practical for a home receiver. Baird continued to consider other
solutions. One used a single conventional CRT with the two images
displayed in a single frame, with the top half of the image containing
the image for one color and the bottom the other. Lens systems focused
on the display were positioned to see only the top or bottom image,
passed them through filters, and then recombined them on a screen.
There were drawings showing a similar system with three frames.
Like many similar efforts from other experimenters, Baird abandoned
Still searching for a single-tube solution that was bright enough for
direct viewing, in 1942 Baird hit upon the
Telechrome concept. His
solution was essentially to combine two tubes into one large spherical
enclosure. In the center of the enclosure was a translucent mica sheet
forming the display, covered on one side with cyan phosphor, the other
with an orange-red color, producing a limited but useful color gamut.
Two electron guns arranged on either side of the screen fired at it,
producing the two colors. The image was viewed from one side, seeing
one of the colors directly and the other being transmitted through the
screen from the other side. This was the first single-tube color
The earliest test models used screens only a few inches across and had
the guns arranged almost at right angles to it, making for a very
large tube. Later models were built inside very large
Hackbridge-Hewittic (H-H) vacuum tubes, which the company originally
designed for use as high-power rectifiers in power supplies. Arthur
Johnson, a glass blower who had previously worked for both Baird and
H-H, produced the new models. These had screens ten inches across,
comparable to monochrome screens of the era. The guns fired upward at
about a 45 degree angle. As in the teapot tube, the necks were very
The trick would be to introduce a third color. For two colors one can
aim at either side of the screen, but for three there is no "third
side" that can be used. Baird's solution used a variation on his
two-color system, using one side of the screen as-is, and patterning
the other side with a series of horizontal triangular ridges. One gun,
normally shown as red in most diagrams, fired onto the flat side of
the screen, as in the two-color model. The other two guns were
arranged above and below the ridged side of the screen, so they fired
onto one side or the other of the ridges. These were colored green and
blue. When all three guns fired, the image would be combined into a
The problem with this approach was that it was very difficult to focus
the electron guns on the ridges without the signal bleeding over to
the ridges on either side. This problem was compounded by the changing
angle between the gun and the ridges as the signal progressed down the
screen. Similar designs were attempted by a number of researchers, the
best known being the
Geer tube that used pyramid-shaped patterns with
three guns arranged around the back. None of these systems could ever
be made to work reliably, with focussing and alignment being continual
problems. There is no documentary evidence that a successful
version of the three-gun
Telechrome tube was ever built, although
images of Baird holding a prototype are widely duplicated. The
prototype that usually appears is the two-gun tube. The two-gun tube
actually had three necks. For this reason, people often mistake this
tube for a three-gun prototype. In fact, the third neck is the
original neck from the Hewittic envelope. This third neck holds not a
gun, but instead, supports for the two-sided target. Burns published a
typical photo of the two-gun, three-neck tube.
Baird also demonstrated the use of the two-color tube as the basis for
stereoscopic 3D television. In this use, the two color-filtered
television cameras were separated to produce a measurable angle, and
then broadcast normally. Viewers wore colored glasses to re-separate
the images into the left and right eye, in a fashion identical to
Anaglyph 3D movies. However, Baird also described a system using
the ridged tube that eliminated the need for glasses. In this case the
tube was rotated so the peaks ran vertically instead of horizontally
and the red gun was removed. The guns formerly used for green and blue
were now used for left and right images. The basic concept is
identical to the lenticular printing system used on magazines and
other printed materials to produce 3D images.
Notwithstanding the above: Lenticular color with
Telechrome is a
matter of speculation. No Baird lenticular tube for direct,
autostereographic pictures exists today. Ray Herbert's 1996 book
refers to 3D pictures with Telechrome, but only with anaglyphic
glasses. (See p. 26.) Baird's British
Telechrome patent #562,168 never
mentions any use of
Telechrome for lenticular 3D. The 1944
Wireless World article  (see bibliography) also neglects to mention
lenticular color with Telechrome. Further, the ridges in Telechrome
allow viewing by both eyes simultaneously. The obvious intent is to
combine two color images into one. A lenticular system would operate
differently. It would substitute lenticular lenses for Baird's angular
ridges. (The cross section of a lenticular lens is rounded, not
angular.) The lenses would separate the colors so that each eye
would see only one color.
Telechrome operates in a different
manner. Further discussion of this topic appears at the Early
Television Museum site.  (The
Telechrome patent is available at
Baird gave a number of demonstrations of the two-color system
throughout the war, and held a full press demonstration on 12 August
1944. These were generally reported in glowing terms, notably an
October 1944 report in Electronics that described the images as bright
and the 3D effect "excellent".
Not all reports were so positive. One concluded that Baird had "done a
real service in demonstrating the value of colour television", but
suggested that the two-color system would ultimately have to be
replaced with a three-color system. They went on to note:
Apart from the coated mica screen, we do not think any new invention
has been demonstrated, and we consider that development on a scale far
beyond the capabilities of Mr. Baird's present organisation is
necessary for successful results.
They also dismissed the 3D work, which Baird had apparently ended by
this point, as a "stunt".
Telechrome and the Hankey Committee
In 1943, with the war clearly turning in the Allies favor, Winston
Churchill formed a series of committees to consider post-war
redevelopment. Among these were plans to re-open the Alexandra Palace
broadcaster, and more widely, nationwide television. To consider this,
in September 1943 Churchill formed the Television Committee, better
known to history as the Hankey Committee.
The Committee met numerous times during the next year, and asked Baird
to prepare a number of papers on the topic of post-war broadcasting.
Among his suggestions, he stated that the BBC's monopoly should be
ended and independent broadcasters should be licensed, which was
delivered along with a request to start such a service. The Committee
agreed with this position. He also described the
and this appears to have had a great impact on the Committee.
In his comments to the Hankey Television Committee, Baird suggested
two-color, 1,000-line pictures. Such pictures would have required
considerable radio bandwidth. The pictures would be incompatible with
the pre-war, EMI / BBC, 405-line system. Before the Hankey Committee,
Baird also considered the possibility of compatible color systems.
 We can imagine two ways to adapt
Telechrome as an EMI / BBC
compatible color system. Method 1 would use one field of the EMI / BBC
interlaced image for red. The other field would convey cyan picture
information. Yet this method would reduce the effective resolution
from 405 to 202.5 lines. The video field rate would drop from 50 to 25
Hz (40 mS). In areas of solid color, flicker would increase. Method 2
would broadcast full, 405-line images. But in this method, frame rate
would fall to a mere 12.5 fps (80 mS). Flicker would then be
Telechrome Color Method, BBC-Compatible (Hypothetical)
Red, 202.5 lines (sequential)
Red, 202.5 lines (odd)
Cyan, 202.5 lines (sequential)
Red, 202.5 lines (even)
Cyan, 202.5 lines (odd)
Cyan, 202.5 lines (even)
Total, Time Per Frame
In December 1944, the committee delivered its preliminary report. The
report called for a system that had "on the order of 1,000 lines" of
resolution. The system would optionally be capable of color and 3D
displays. The system also be able to run beside the pre-war 405-line
system by Marconi and EMI.
Baird was called to a 29 February 1944 meeting of Cable and Wireless
(C&W) to discuss the formation of a color television studio. After
some discussion, C&W chairman
Edward Wilshaw noted that there was
an agreement in place that precluded Marconi from entering the market
until 1949, which would place them at a significant disadvantage
compared to other companies. He suggested that the matter be deferred,
as any immediate changes would produce friction between C&W, the
General Post Office
General Post Office and the BBC. The matter was dropped, and it would
not be until the
Television Act 1954
Television Act 1954 that the possibility was again
From 1944 Baird was suffering from increasingly poor health, and late
that year he suffered an attack of fever that left him almost invalid.
Nevertheless, he formed a new company,
John Logie Baird
John Logie Baird Ltd., with
offices and labs in a downtown
London house. Baird visited the lab
less and less frequently over time, and his wife noticed why in a
November 1945 visit when he was seen to have to stop and pant after
climbing every stair of the building's four stories. He caught a
cold over Christmas 1945, and suffered a stroke in February 1946. He
was ordered bedridden but refused to stay there, and continued to
deteriorate until his death on 14 June.
Telechrome died with Baird, but the company by this time had
introduced its first truly successful product. This combined a 27
inches (690 mm) black and white television, a radio receiver and
a record-changing record player in a single large cabinet. The company
was purchased in 1948 and switched hands several times, eventually
being used as a brand name by
Thorn Electrical Industries for a
Telechrome and Trinitron
Many years later, former Baird employee Edward Anderson was quoted as
saying that they "had the equivalent of the
Trinitron tube on the
drawing board". This has been used by a number of non-technical
authors to suggest that the
Trinitron is in some way technically
related to the
Telechrome in spite of the two systems having nothing
in common. This article discusses flaws in attempted
comparisons between the
Telechrome and Trinitron.
UK 562168, John Logie Baird, "Improvements in Colour Television",
^ a b c Colour 1941.
^ Abramson, Electronic Motion Pictures, 94-95.
^ a b "Early Color Television". Early Television Museum.
^ Reitan, Ed (24 August 1997). "
CBS Field Sequential Color System".
Archived from the original on 5 January 2010.
^ Burns 2000, p. 376.
^ a b c Stereoscopic 1944.
^ a b c d TwoSided 1945.
^ a b Media.
^ a b c Burns 2000, p. 378.
^ Herbert, p. 26.
^ "Teacher's Tube". Time. 20 March 1950.
^ Burns 2000, p. 379.
^ a b c d e Burns 2000, p. 380.
^ Baird, John Logie. "Improvements in Colour Television," G.B. patent
562,168, filed July 25, 1942, and issued June 21, 1944.
^ Burns, 380
^ a b Burns 2000, p. 381.
^ Burns 2000, p. 406-7.
^ Burns 2000, p. 383.
^ Burns 2000, p. 386.
^ a b Burns 2000, p. 388.
^ Waddell, Peter (11 November 1976). "Seeing by wireless". New
^ "Baird". Journal of Economic and Social Intelligence. 1992. All
modern T.V. receivers can be traced directly back to the TELECHROME of
^ Hawes, James T. "Did J.L. Baird Invent the Trinitron® Tube?" 2014,
access on February 28, 2018.
Abramson, Albert (1974). Electronic Motion Pictures. Arno.
Burns, R. W. (2000). John Logie Baird, Television Pioneer. IET.
Herbert, Ray (1996). Seeing by Wireless: The Story of Baird Television
"Television in Colour". Journal of The Television Society. September
"Baird 'Telechrome'". Wireless World. October 1944.
Telechrome tube". National Media Museum. 1962.
"Television in Color With a Two-Sided Screen". Popular Mechanics.
Telechrome tube, the only remaining Telechrome, the orig