This 80's circuit uses a germanium transistor like the AC121. The circuit has an output transformer of the type found on many transistor radios of the time.
The operational amplifier used in this application is uncommon today. This Raytheon circuit can be...
This receiver with two common JFETs was found in an old English documentation. The phone is...
This 1969 Philips documentation circuit makes it possible to control an engine through the sound...