| 摘要 |
895,176. Tuning indicators; pulse circuits. BLAUPUNKT-WERKE G.m.b.H. Oct. 31, 1958 [Nov. 2, 1957], No. 34935/58. Classes 40(5) and 40(6). A television receiver in which the picture tube is used to provide also visual tuning indication, is characterized in that there is connected to the grid of an amplifier valve 9 connected to the picture tube a series arrangement of a diode 11 and a control potential source 12, and that in parallel with this arrangement there is fed the sum of two signals derived from the line timebase, the first being derived from across a booster diode 3, Fig. 4, and the other from a tuned circuit 6. 7 Fig. 3. The waveform of Fig. 4 results from the charging of capacitor 4. Valve 1, Fig. 1, is the line timebase O/P valve and the two derived waveforms, Figs. 3, 4 are combined to produce a waveform as shown in Fig. 5 which is applied to the control grid of valve 9. This control grid is clamped by diode 11 to negative control potential 12 derived from the I.F. amplifier, the operating conditions of the valve being such when the receiver is correctly tuned, this negative potential holds valve 9 cut off. When the receiver is incorrectly tuned, the bias on valve 9 is reduced, and a negative going puise, Fig. 6 (not shown) is produced at the anode and is fed to a control electrode of the picture tube to produce a black bar, the width of which depends on the degree of mis-tuning. When tuning is completed, valve 9 can be used as an image sharpening amplifier by switching a proportion of the vidio signal to the grid. |
