| 摘要 |
A volume control for a telephone having a receiver, a manual key for generating a volume increment for each operation of the key; a volume increment counter connected to the manual key for counting volume increments; a controlled gain amplifier connected ahead of the receiver; and a gain control network connected between the controlled gain amplifier and the counter for controlling the gain of the amplifier in response to the number of volume increments counted in the volume increment counter. A unique feature of the volume control is that it maintains the selected gain level when the central office collects or refunds coins or makes an initial rate or coin present test.
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