This type of answering machine was common at the time this circuit was published. Using two tape recorders, it was published in the June 1986 issue of Radio Electronics magazine.
This is the traditional configuration of an inverter amplifier with operational. The operational...
In the figure we show how to implement a voltage-controlled oscillator. The circuit is from Texas...
Found in a 1967 American publication, this circuit with feedback for two transistors has a gain of...