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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Filter analyzer (CB8227E)
Found in a 90s Popular Electronics, this circuit is interspersed between the filter and the...
RIAA Equalization Amplifier (CB4952E)
This circuit is from an 80's documentation. The integrated circuit is from the time and the...
Undervoltage indicator (CB9580E)
This circuit was found in a 80s American documentation. The zener diodes determine the points of...