| 摘要 |
PURPOSE:To make always correct channel selection possible without generation of malfunctions, by fixing the AGC voltage to a predetermined voltage to lower the gain of the hihgh-frequency amplifying circuit, for sweep of the tuning voltage. CONSTITUTION:When the keyboard switch is depressed, the start signal to start sweep of the tuning voltage is gnerated; and when this signal is applied to NAND gate 15, FF30 is set and output Q becomes H-level. Transistors 17 and 18 are conductive, and their collectors become approximately 0V and 12V respectively. The AGC voltage of the VHF tuner supplied to terminal 27 is fixed to a low value forcedly, and reversely, the AGC voltage of the UHF tuner supplied to terminal 28 is fixed to a high value. As a result, the gain of the high-frequency amplifying circuit is lowered. |
