Phone Call Amplifier (CB21271E)

This circuit was found in an old Electronics Now. The transistors are general- purpose and the circuit is powered by an external source.

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Digital Voltmeter (CB18102E)
We present a circuit formed by six voltage comparators. Each comparator will analyze the voltage...
Time base (CB8933E)
This circuit can generate time base signals from 5 to 1500 Hz. We find it in a documentation about old neon...
Undervoltage Switch with the CA3140 (CB12144E)
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...