Telephone amplifier (CB8630E)

This circuit uses a pickup coil to take the signal from a telephone line without contacts. The circuit is from a 90s Popular Electronics.

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Triangular Generator LM3900 (CB15629E)
To obtain triangular signals, we have the circuit in the figure that uses two amplifiers. One of...
Limiter with zener diode (CB7054E)
This circuit was found in an old Electronic Design. It makes use of sidacs and operational not very...
Audible Voltmeter (CB21395E)
This circuit was found in an American publication from 1969. Transistors are from the time and can be...