| 摘要 |
1,082,429. Colour television. HAZELTINE CORPORATION. May 10, 1966 [June 2, 1965], No. 20580/66. Heading H4F. A " colour killer " circuit 19 in the chrominance channel of a compatible colour television receiver is arranged to respond to the variation in D.C. level at a point 15 in the anode circuit of the chrominance amplifier 13 which is brought about as a result of the action of the automatic colour control (ACC) system 10. Thus, during monochrome reception point 15 is at a comparatively low potential, since the ACC system produces no bias for the grid of amplifier 13, whereas during colour reception point 15 becomes progressively more positive in response to increasing amplitude of chrominance signal as the ACC system applies a negative bias to the amplifier grid. Circuit 19 applies a cut-off bias from source B 2 via saturation control 24 to the grids of demodulator stages 17, 18 and includes a neon tube 23 which is non-conductive during monochrome reception when point 15 is at a low potential. However, when a colour signal is received and point 15 increases in potential, at a useful level of colour signal as determined by the adjustment of potentiometer 22, neon tube 23 conducts and the potential applied to the modulator stages is increased to render them opera tive. Neon tube 23 may be used to furnish a visible signal that a colour signal is being received. In a second embodiment, Fig. 2 (not shown), a second neon tube (30) is included in the connection from point 15 so as to reduce the D.C. potential applied to potentiometer (22<SP>1</SP>) without reduction in the D.C. variation. The circuit involves a modification of the bias circuit of the demodulator stages. Since the second neon tube is continuously conductive when the receiver is operative it may function as an on-off indicator. |
