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Early Color Television

DeForest Mechanical Color System

The following is a description of Lee DeForest's mechanical color system, developed about 1948, courtesy of Ralph Baer:

While I was a student at American Television Institute of Technology in Chicago in 1947-1949 on the G.I. Bill of Rights, I was introduced to Dr. Lee DeForest who was then one of the directors of ATIT.

DeForest is, of course, the man who put the control grid into the vacuum tube in 1905, thus creating the first signal amplifying device.

I was a senior TV engineering student in 1949 and already had  a decade of radio and TV technician experience behind me.

DeForest (a tall, white haired dignified-looking gentleman then about 72 years old) had asked for a student who might want to work with him on resurrecting his pre-WWII medical diathermy machine production company. Someone in the faculty picked me and sent me to his office.

After a brief but congenial interview DeForest and I went into his private lab. He sat down at the bench and showed me an electro-mechanical color TV display device he was working on. It consisted of two plates: One was a fixed, thin plate about 6 x 8 inches with an array of horizontal and vertical apertures (small holes) in a rectangular grid. The other plate was supported at each of its four corners by a four rotary joints which allowed the plate to be rotated through the vertical plane by a very small amount. The diameter of the circle described by any spot of the rotating plate was approximately the same as the center-to-center distance between the apertures on the stationary plate. I do not recall exactly of what material the rotating (gyrating) plate was made. It may have been a glass plate screened with black opaque ink. That black opaque surface was pieced by a rectangular pattern of tri-color, transparency  spots (RGB). I assume that there were about 400+  vertical  RGB group transparencies and perhaps 500+ in the horizontal direction  (for a 400 V by 500+H pixel display in today's terminology).

When the gyrating plate was set into motion, light from behind it would sequentially pass through one color filter at a time and then through a corresponding stationary aperture in the fixed plate. Hence a field-sequential color display was generated when this mechanical array was placed in front of a B&W CRT with a standard NTSC 441-line raster displayed on its screen. Thinking about the details of this scheme, the color apertures must have been 120 degree segments  and progressively rotated (in the process of making the artwork that was used to produce the screen with which these transparent dye colors were probably screened on) so that a portion of the the same color "triangle was still passing over the fixed aperture, depending on which "horizontal line" of aperture the CRT's illuminating spot was located.

I never saw this apparatus actually working. It was clearly intended to solve the problems generated by the huge scanning discs or drum such as those used on earlier mechanical systems and later in the CBS field-sequential system. Clearly, moving a thin plate at 60 RPS through a very small circular motion required very little mechanical (motor) power.  However, one look at the hardware and it appeared to me that the optical inefficiency of DeForest's ingenious mechanical color-wheel substitute had to be such as to doom this approach. I don't remember whether I had the presence of mind (or the nerve) to question the walking legend about just how he expected to overcome that problem. Perhaps I figured that an extra bright CRT might just have enough light output to make this system work.

I would be interested to learn if anyone (perhaps an old-timer such as myself)  knows of Dr. DeForest's color display device and what happened to it.  It would be interesting to know whether it was ever publicly demonstrated and whether of the unit that I saw in the lab that day in 1949 had survived and found a home in some collection or museum.

[The above photo shows] DeForest sitting at a lab bench at American Television Labs along with (I believe) John Sanabria (on the right), the brother of ATL & ATIT president Ulysses A. Sanabria and another engineer.

And what are they working on?  The color TV  scheme, of all things!  If you will look at the attached photo and blow it up, you will see that the engineer on the left has his hand inside a open (no case) TV monitor with what looks like a 10" or 12" CRT, probably making an adjustment. Immediately in front of the CRT is the two-plate color scanning device I described and hadn't seen for 55 years.

The long gear on the bench has to be a complementary signal generation device producing field-sequential picture as a test signal source which the setup at the rear reproduces. The signal generation device probably use a color wheel which would be entirely practical solution for a system with a small TV pick-up tube. (I have built sequential color TV systems with RGB color wheels myself and they work very well when there isn't too much motion. The first RCA cameras that went to the moon were of that type, too).