Found in documentation from the 1980s, this circuit uses an operational amplifier from that time. Transistors are also from the era, and general-purpose equivalents can now be used.
This peak indicator for stereo amplifiers uses a CA3130. The 80's circuit does not need a...
This circuit is from a 1967 US publication. The configuration can serve as a basis for designs...
Found in a Popular Electronics from the 90s, this circuit can act as a transmitter for an audio...