Picture Tubes
|
|
By the time most of us who even remember cathode ray tubes (CRTs) were first introduced to them, the technology and manufacturing processes had been pretty much perfected - especially for the standard 525-line (or 625-line outside the U.S.) resolution type. The National Television System Committee (NTSC) published a standard for black and white (B&W) television in 1941 and then for color in 1953. This "Picture Tubes" article in a 1955 issue of Popular Electronics provides a look inside a CRT manufacturing plant at General Electric. If you want one of the best explanations I have ever seen on how a TV picture scan is implemented, check out this video by Displaced Gamers. If you don't understand raster scanning after watching it, you never will. You might be surprised to learn that there were not actually 525 lines of picture information, but that only about 480 to 487 lines of picture were included - the rest were for scan synchronization, retrace and blanking, and special signal information. In fact, the modern 480i digital standard evolved from that 480 lines of picture info. You'll also learn a little about how video game consoles repurposed the NTSC scan format to facilitate faster video updates. See also How the Cathode-Ray Tube Works, Picture Tubes, TV X-Rays, TV X-Rays Are Back. Picture Tubes
The first step in actual processing of a picture tube is screening, in which the phosphor picture screen is applied to the inside of the bulb's face. Note screens inside tubes at left. Hoses pour one mixture into bulb, other comes later.
On the screening conveyor, picture tubes move slowly along as the phosphor-silicate mixture settles inside of their face areas. At far end of belt, tubes will be tipped, and water will be run off.
Careful inspections follow the picture takes all the way during processing. Here as operator inspects phosphor screens on tubes after they have been removed from the screening conveyor belt.
Electron gun, which later will be sealed into neck of a picture tube, receives final inspection after assembly. At bottom are leads and glass tubulation of stem assembly. Above, in order, are grid No. 1, grid No. 2, and metal sections of anode structure. At top is focus electrode, the "getter," etc.
Processing "en route" takes place as completed tube is "aged" on a conveyor taking it to final test section. "Aging" is process whereby electrical characteristics are stabilized in tube.
"Merry-go-round" rotary aluminizer automatically coats interior of tube bulbs with film of aluminum four one-millionths of inch thick. In finished tube, this metallic layer on the back of the phosphor screen will reflect increased illumination for brighter pictures and better contrast. Machine handles 24 tubes. The "heart" of your television set is the incredibly complex C-R tube. Here is how it is made. Do you take your television receiver so much for granted that you never wonder about the complex circuitry and the vast amount of engineering "know-how" that is represented in your living room? One of the most fascinating components in your television receiver is the picture tube itself. While this is almost the only "internal" component that everyone gets to see, very few televiewers know how it is constructed or what is involved in the manufacture of such a tube. The photographs on this and the two succeeding pages show how such tubes are "built" at the General Electric Company plant in Buffalo. This factory now turns out thousands of picture tubes each day - including the 21-inch size. The mass production of picture tubes is no simple proposition, but the operation isn't as much a difficult effort as it is a delicate one. Every step of the operation must be carefully controlled. Every part that goes into a tube must be checked and inspected all the way through production. The finished tube must meet exacting standards before it is shipped to a set manufacturer or released for replacement applications.
After all of its processing, the picture tube bulb is now ready for installation of its electron gun. Step is performed on this rotary gun-sealing machine by welding process.
Almost completed, the picture tube is swung from automatic "tip off" machine after being pumped out to a vacuum and sealed at end of its neck. Later the base is added and the tube completed.
Final inspection of the picture tube consists of checking it for electrical stability, short circuits, brightness, and gas. Operator adjusts standard test pattern on a 21-inch picture tube.
In place in a home receiver chassis, the picture tube is checked before the completed unit is installed in a cabinet. Unit around neck of tube deflects electron beam to sweep the screen.
A "double-jointed" paintbrush, which bends after insertion through the bulb's slender neck, coats entire cone of nonaluminized bulb with an electrically-conductive paint as the bulb is rotated.
Into the bakeout oven's 350 degree C heat go the picture tube bulbs after screening and aluminizing or inside painting. Here heat removes the moisture and gas from these prepared tube bulbs. Basically, a picture tube is a conical glass bulb with a phosphor screen on the inside of the bulb face. Mounted in the neck of the bulb is an electron "gun" whose electron beam is directed at the screen to activate it and reproduce the transmitted image. The metal electron gun parts, including units about the size of a thimble, magnets not much larger than a pencil eraser, and tungsten wire finer than a human hair, are weighed, measured with fine-precision gauges, or inspected on a shadowgraph which projects their silhouettes, magnified 20 times, on a translucent screen. These various components eventually emerge as a television picture tube after going through the processes which are pictured in the photographs accompanying this article. During 1955, General Electric statisticians estimate that over 11,750,000 picture tubes will be manufactured, 5,600,000 of which will be earmarked for replacements in existing television receivers. The percentage of color TV picture tubes will still be relatively small, with the prediction, as of now, at about a quarter of a million tubes for the multi-hued television sets. The next time you step up to your TV set to turn on your favorite program, take a long, hard look at the "Cyclops" staring out at you. It is an eye-opener if you will only take the time to examine this electronic eye to your world of entertainment, education, and sheer fun. It can truly be classed as an "electronic miracle" of the first order.
Posted August 21, 2019 |
|
