Moderators: Dave Moll, Andrew Davie, Steve Anderson
FlyMario wrote:I always look at these CRT demonstrations and can't understand why TV CRTs can be easily converted to an X, Y Scope without having to build some big deflection coil to put on the neck. TV already has deflection coils. What is the difference between the two Deflection coils? It seems that tv pretty much works the same way. It scans across and up and down.... x and y.
FlyMario wrote:But I have an XY scope and the neck on the tube is extremely long. Always wondered why the tube is so long.
Dave Moll wrote:And, of course, with the larger screen size used in televisions, the CRTs needed to have shorter necks to avoid a set that extends several feet into the room - which is why some early sets had the tube mounted vertically to accomodate the length of the CRT, with a 45º mirror above. Just think of the shape of the average 'scope scaled up to a display 20"+.
Klaas Robers wrote:That is strange........
In almost all cases a burn-in hole in the screen is at the center. When the deflection fails, the spot returns to the center of the screen (electrons running straight). And especially in a corner of the screen....... Then there was still a static horizontal and vertical deflection.
Very strange.
Steve Anderson wrote:In 'normal' TVs the deflection is AC coupled, generally via some form of transformer or other, so a collapse of either, or both deflections can result in a burn either horizontally (vertical failure), vertically, unlikely as the EHT is usually derived from the horizontal deflection, or some other bizarre reason. (CRT cathode-grid short, internal to the CRT, it doesn't matter anymore, it's toast! ).
Whatever, it shows that when experimenting with CRTs of any type you must have a way to cut-off the beam when need be. Either manually (careful!) or automatic.
Steve A.
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