GB1218068A - Convergence system for a color picture tube - Google Patents

Abstract

1,218,068. Cathode-ray tube circuits. SONY CORP. 20 Aug., 1968 [24 Aug., 1967], No. 39753/68. Heading H4T: [Also in Division H1] In a colour television display tube of the type wherein three co-planar electron beams pass through a common lens system and then through convergence deflection plates which converge the beams on a colour grid or a shadow mask, spherical aberration is corrected in the plane of the beams by a dynamic convergence voltage applied to the convergence deflection plates and in the other plane by a suitable non- linear magnetic field in the respective scanning deflection system. Preferably the beams lie in a horizontal plane and the dynamic convergence voltage is derived from the horizontal scanning waveform. In this case the vertical scanning magnetic field should be barrel-shaped (Fig. 4, not shown) and this may be provided by the coil system shown in Fig. 3 wherein the vertical deflecting coils 35a and 35b are connected in series with coils 37a and 37b which are oppositely wound on the core 36; the horizontal deflecting coils 40 are also illustrated. The distortion of the magnetic field depends on the angular extent of the four coil portions and of the gaps between them. If the beams lie in a vertical plane the horizontal scanning magnetic field should be pin-cushion shaped (Fig. 7, not shown) produced by oppositely wound horizontal deflecting coils (Fig. 6, not shown). Fig. 5 shows a circuit for generating a convergence voltage; the static convergence component is derived through diode 30 from a transformer 23 fed from the line fly-back transformer 21, and the parabolic dynamic component is derived across capacitor 28 which is in series with inductor 27. A variable impedance 25 allows the convergence to be adjusted, and the E.H.T. voltage is derived from a rectifier 34.