| 摘要 |
An improved telephone ringing circuit in which a ringing circuit is connected with a triac to allow an entry of ringing signals which are rectified by a full-wave rectifier connected in series with the triac. The D.C. voltage is being supplied to a sound producing device such as an oscillation circuit coupled with a speaker. The ringing circuit is also provided with a variable resistor for adjusting the D.C. voltage and a variable resistor in the oscillation circuit for adjusting the frequency of the A.C. output signals delivered by the oscillation circuit to the speaker.
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