| 摘要 |
1321146 EHT supplies GTE SYLVANIA Inc 19 April 1971 [9 March 1970] 23543/71 Heading H2F [Also in Division H4] A voltage related to the high-voltage employed in a television receiver is derived from the horizontal output stage 25 (Fig. 1) via a network 33 and utilized, when it exceeds a threshold level set by diode 41, to shift the frequency of the horizontal oscillator 21 to outside the range of synchronization so that the resulting distortion of the displayed picture provides a warning to the viewer that the high-voltage has increased to a level at which X-ray radiation may emanate from the receiver. The network 33 includes a voltage dependent resistor VDR 35 the logarithmic characteristic of which results in emphasized voltage variations appearing at the junction of VDR 35 and resistor 33 and when such voltage variations exceed the threshold level of diode 41 the control effect on the horizontal oscillator 21 is arranged to be such that synchronism cannot be restored by the viewer by adjustment of the horizontal "hold" control 22. During normal operation synchronization is effected by AFC network 19 which compares the received synch. signals with signals derived from output stage 25. |
