Patent GB-711692-A (GB)
Title: Magnetic deflection means for cathode ray tubes
IPC: H03K4/26
Filed: 1950-02-15
Abstract: 711,692. Cathode-ray tubes. PHILCO CORPORATION. Feb. 15, 1950 [Feb. 15, 1949], No. 3881/50. Class 39(1) [Also in Groups XXXVI and XL(b)] A magnetic deflecting system for a cathode-ray tube comprises a closed magnetic core surrounding the tube neck and carrying two coils, to one of which is fed both the A.C. and D.C. components of the supply current and to the other of which is fed the A.C. component, the arrangement being such that the alternating fluxes are in opposition in the core but are additive across the tube neck, while the D.C. flux is substantially confined to the core. In one form, Fig. 2, the horizontal deflecting coils L1, L2, L3, and the vertical deflecting coils, L4, L5, L6 and L7 are wound on a rectangular core 12, the coils L1, L2, L3 on the main core body and the coils L4, L5, L6 and L7 are wound longitudinally on ears 22, 24 projecting axially from the core towards the electron gun. The core 12 and ears 22, 24 are laminated. High impedance coil L1 and low impedance coil L2 serve as a coupling transformer in the anode-cathode circuit of the sawtooth generator as well as deflection coils, and their resultant flux is made equal and opposite to the flux produced by low impedance coil L3. The core 12 has as small a cross-section as possible so as to reduce the distributed capacity and hence to avoid an increase in the flyback period. 'The ears 22, 24 serve to extend the horizontal deflecting field axially. The vertical deflection coils L4, L5, L6, L7 are also energized by sawtooth current from two separate generators connected in push-pull. The arrangement is such that the current flow in coils L4, L5 and L6, L7 is in opposite directions so that the D.C. components cancel. A single pair of coils could be used instead of the four coils L4, L5, L6, L7 but the arrangement would not compensate for the D.C. components of current. In a modification, Fig. 5, the horizontal deflection circuit has two high impedance windings L1, L8, the coils being connected in the anode circuit of the sawtooth generator 14, and the circuit also including diode 36 condenser 44 battery 39. The coils L1, L8 are interconnected by taps 40, 42. The generator 14 is cut off for each retrace period, and during this period oscillations are set up in the circuit due to the inductance and distributed capacity of coils L1, L8. After one half cycle of the oscillations, a new deflection cycle commences and the diode 36 becomes conductive to control the rate of decay of the oscillations. The decaying oscillation combines with the sawtooth current from the generator in such a manner as to give a linear sweep of the beam. The D.C. component of the diode current is equal and opposite to the D.C. component of the generator current so that the D.C. components. cancel in coil L8. The flow of diode current charges up the condenser 44 so as to increase the anode voltage of tube 14, and consequently causes an increased flow of current from tube 14 through coils L1, L8. The cathode 34 can be connected to winding L8 by a separate lead. In Fig. 6 the coil L8 is in two portions, the lower portion being connected to the negative side and the upper portion to the positive side of the condenser 44. In this way the condenser 44 can give a voltage "boost" to the generator as in Fig. 5. In another form. Fig. 7, the coils L1, L8 are connected in parallel, and the circuit has condensers 44, 48 and diode 36, and optionally a connection between taps 40, 42 which includes condenser 50. Condenser 48 ensures that the D.C. component is eliminated from coil L8. In another form, Fig. 9 (not shown) the rectangular core has three vertical legs around which coils L1, L2, L3 of Fig. 2 are respectively wound. In all embodiments one or more additional windings may be employed in the horizontal deflecting system so as to step up the voltage to a point where it may be rectified and used as the accelerating voltage for the cathode-ray tube during the flyback periods. U.S.A. Specifications 2,382,822 and 2,451,641 are referred to.