| 摘要 |
A four-transistor bridge amplifier is adapted for use as a bidirectional speech amplifier between a telephone line and an electronic telephone subscriber's instrument. The amplifier is powered from the line and includes two-transistor sections, one or other of which functions dependent on line polarity. The output of the amplifier to the subscriber instrument is taken across a resistor connected between the transistors such that the output always has the same relative polarity whatever the line polarity.
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