Call Sound Amplifier (CB21273E)

Found in an older Radio Electronics, this circuit generates signals that can be used with regular analog telephones.

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Two Light Flashers (CB947E)
The circuits below were found in amarican publication of the year 1958. The transistors are...
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With this circuit it is possible to use a control voltage to select audio signals that pass...
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This PLL with operational amplifiers was found in 1969 documentation. The configuration can be...