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对于具有预选功能的黑白电视机,只要增加一个开关和一个预选器后,便可增加预选台数。其改制电路如图所示。图中虚线框内是新增加的预选器,当开关K闭合时,新增预选器上的预选电压将叠加在原预选电压上形成新的预选电压VD,供给后续电路。实践证明,使用增加的预选器可以调出两个以上的台来(例如同时按下频段相同的两个预选开关,调其中一个电位
For the black-and-white TV with pre-selected functions, the number of pre-selected stations can be increased by adding one switch and one pre-selector. The restructuring circuit as shown. When the switch K is closed, the preselected voltage on the newly added preselector will be superimposed on the original preselected voltage to form a new preselected voltage VD for supply to the subsequent circuit. Practice has proved that the use of additional preselector can be deployed more than two Taiwan (for example, press the same preselection of the same frequency switch, adjust one of the potential