| 摘要 |
A television tuner comprises a tuning circuit including a voltage controlled variable capacitance diode. The tuning circuit is housed within a shield casing. The shield casing is provided with a terminal for electrical connection to the variable capacitance diode and the terminal is supplied with a tuning voltage from a channel selecting apparatus. A Zener diode is connected between the tuning voltage terminal and the shield casing, whereby the upper limit of the tuning voltage being applied to the variable capacitance diode is restricted. A predetermined voltage determinable dependent on the Zener diode is selected such that the tuning frequency established by the tuning circuit when the predetermined voltage is applied to the variable capacitance diode may be a predetermined upper limit frequency of a desired receiving frequency band. The lower limit of the tuning voltage is also restricted so as not to become lower than a predetermined voltage. Accordingly, the tuning frequency is prevented from being changed toward a higher or lower frequency deviating from the corresponding variation range of the desired receiving frequency band.
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