Patent GB-785588-A (GB)
Title: A cathode-ray tube with deflection control
IPC: H01J31/04
Filed: 1953-02-04
Abstract: 785,588. Cathode ray tubes. KRAWINKEL, G. H. Feb. 4, 1953 [Feb. 5, 1952 ; March 31, 1952], No. 8363/55. Divided out of 785,587. Class 39(1). A cathode ray tube has means for deflecting the beam by an input signal and target means for producing in an output circuit a current whose magnitude depends on the magnitude of the beam deflection, the target means comprising a secondary emissive target and a secondary emission collector, the target comprising means to absorb or block the emitted secondaries so that the number of secondaries reaching the collector increases or decreases with increasing distance from a line of the target which line extends transversely to the direction in which the beam's deflection is proportional to the input signal. In one form, Fig. 1, the beam is deflected by the input voltage applied to plates P1, P2 and then passes between plates E1, E<SP>1</SP>1 which have voltage gradients from top to bottom but in opposite senses so that the beam is deflected at right angles to the original deflection by an amount proportional thereto. Plates E1, E<SP>1</SP>1 are solely of resistance material, or of such material coated on a carrier by evaporation, chemical deposition or mechanically, and are connected across D.C. current sources, Fig. 2 (not shown), resistances being' included in the circuits to determine the point of zero deflection which preferably but not necessarily corresponds to the position of the beam when undeflected by plates P1, P2. The beam is then given a further deflection in the same direction as and proportional to the origin. al one (between plates P1, P2) by plates E2, E12 constructed similarly to plates E1, E<SP>1</SP>1. There may be more than two pairs of plates E1, E<SP>1</SP>1, E2, E12 to further amplify the original deflection. The deflected beam impinges on target S which comprises secondary emitting strips V, Fig. 4, connected to bar V1 and resistance strips W connected to bars W1, W2. D.C. source M is connected between W1 and W2 and its positive pole is connected to V1 so that secondaries are blocked at the lower ends of V but pass to an approximately linearly increasing extent to a maximum at the top ends ; the effective secondary emission consequently depends on the point of impingement of the primary beam. Electrode S1 may be a collector or a further secondary emitter associated with collector S2. The device may be used as a voltage amplifier or, since the secondary electron current characteristic has a lower bend, as a rectifier or modulator. The working point can be shifted along the characteristic by applying an additional fixed bias between E2, E<SP>1</SP>2 or P1, P2. Modulation is achieved by applying a modulating voltage between E1, E<SP>1</SP>1, or E2, E<SP>1</SP>2 or to an intensity modulating electrode in the gun. To prevent deflection of the primary beam by the transverse fields of target S, both V and W are of resistance material but are oppositely poled, Fig. 7 (not shown). Thus there is maximum secondary emission at the field free region at the centre and decreasing emission towards the ends due to the positive strips collecting secondaries from the negative strips and the negative strips blocking emission from the positive strips. The support plate for the strips may be of a semi-conductive glass to prevent accumulation of charges between the strips. In another form, Fig. 8 (not shown) the two sets of electrodes are connected at one end only to separate oppositely poled potentiometers ; the device may be used as an amplifier, modulator or demodulator. Deviations of the beam from the working point can be corrected by (a) cathode resistances traversed by the output current or (b) making the target voltages dependent on the secondary emission current, for example by shifting the field free zone in Fig. 8 (not shown).