COLOUR TELEVISION DISPLAY TUBES

COLOUR TELEVISION DISPLAY TUBES Based on the gun configuration and the manner in which phosphors are arranged on the screen, three different types of colour picture tubes have been developed. These are:- 1. Delta-gun 2. Guns-in-line or Precision-in-line (P-I-L) 3. Trintron Colour Akshay Jilowa G.P.C.G. Jalandhar

Delta-gun colour picture tube (a) guns viewed from the base (b) electron beams, shadow mask and dot-triad phosphor screen (c) showing application of ‘Y’ and colour difference signals between the cathodes and control grids Akshay Jilowa G.P.C.G. Jalandhar

DELTA-GUN COLOR PICTURE TUBE This tube was developed by Radio Corporation on America (R.C.A). It employs three separate guns on for each phosphor. The guns are equally spaced at 120 degree interval with respect to each other and tilted inwards in relation to the axis of the tube. They form an equilateral triangular configuration.

Drawbacks of the Delta-gun Tube Convergence is difficult and involves considerable circuit complexity and service adjustments. In most delta-gun tubes, four static convergence magnets and a dynamic convergence assembly are employed. The focus cannot be sharp over the entire screen because the focus and convergence planes cannot remain coincident for the three beams which emanate from guns positioned at 120° with respect to each other around the tube axis. The electron transparency of the mask is very low since it intercepts over 80 percent of the beam currents. Akshay Jilowa G.P.C.G. Jalandhar

PRECISION-IN-LINE COLOR PICTURE TUBE This tube as the name suggests has three guns which are aligned precisely in a horizontal line. The gun and mask structure of the P.I.L tube together with yoke mounting. The inline gun configuration helps in simplifying conversions adjustments. The color phosphors are deposited on the screen in the form of vertical strips in triads which are repeated along the breadth of the tube. To obtain the same color, finest as in a delta gun tube the horizontal spacing between the strips of the same color in adjacent traids is made equal to that between the dots of the same color in the delta gun tube.

Akshay Jilowa G.P.C.G. Jalandhar Coma Effect Due to nonuniformity of the deflection field all the beams are not deflected by the same amount. As shown in Fig. the central beam (green) deflects by a smaller amount as compared to the other two beams. For a different nonuniformity of the deflection field, the effect could be just opposite producing too large a displacement of the central beam. Such a distortion is known as coma and results in misconvergence of the beams. Akshay Jilowa G.P.C.G. Jalandhar

Trintron (cathodes in-line) colour picture tube (a) gun structure(b) electron beams, vertical-striped three colour phosphor screen (c) constructional, focus and convergence details Akshay Jilowa G.P.C.G. Jalandhar