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Old 04-13-2018, 08:23 PM
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Jeffhs Jeffhs is offline
<----Zenith C845
Join Date: Feb 2003
Location: Fairport Harbor, Ohio (near Lake Erie)
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Originally Posted by Telecolor 3007 View Post
Me curios: what made early color sets so unrelaible? (black and white ones could work for years with no problem).
In color television's early days, the technology was brand new and had a lot of bugs that had to be worked out, as with all new technologies; yes, even flat screen HDTVs when they first appeared on the American TV market. The first flat screens were also very expensive and had bugs, not the least of which was a phenomenon called "image burn-in" in which an image could and all too often would permanently burn itself onto the screen; this ususally occurred if a stationary image was left on the screen for an extended period of time. It was for this reason owners of plasma flat screens, now obsolete, were warned not to view stationary pictures or images, such as network or TV station logos, for any length of time, otherwise the image would burn itself into the screen, ruining said screen. Such damage would not be covered by the manufacturer's warranty.

Color television sets are also much more complicated than b&w sets, which meant the early ones, especially, had more to go wrong with them. Another problem with early color sets was that the set could not be moved from one location to another, even in the same room, without the CRT becoming magnetized; this meant having to "degauss" the tube every time the set was moved any distance, using a degaussing coil. Black and white (monochrome) television CRTs did not require degaussing, since they had no shadow mask to become magnetized. B&W tubes did, however, have a device called an "ion trap", a magnet which fit around the neck of the CRT. As its name implies, the ion trap traps negative ions and prevents them from burning the CRT screen, which of course would ruin the tube immediately. The ion trap must be adjusted for maximum brightness, usually only after the CRT is replaced.

Later color sets (and all sets up to the end of the NTSC era) had automatic degaussing systems, with the coil mounted permanently to the bell of the CRT; the coil was activated by a thermistor. These auto-degausser systems degaussed the tube every time the TV was turned on. This auto-degaussing system made it possible to move a color set from one room to another (or anywhere, for that matter), without having to worry about the CRT's shadow mask becoming magnetized. A magnetized shadow mask would cause purity distortion and other problems that would degrade the picture. This would not harm the CRT or the television itself, but it would cause ugly color blotches on the screen, most noticeable on b&w programs, although these blotches will also be seen on a solid color raster (usually red) which is normally used for purity adjustments.
Jeff, WB8NHV

Collecting, restoring and enjoying vintage Zenith radios since 2002

Zenith. Gone, but not forgotten.

Last edited by Jeffhs; 04-13-2018 at 08:32 PM.
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