This circuit was obtained from a Radio Electronics from the 90's. The circuit limits the strength of an audio signal preventing saturation. Equivalent operational amplifiers can be tried.
This circuit, obtained from a 1965 magazine, can still be assembled using some modern equivalent...
This source was obtained from a book on transistors from the 60's. The circuit uses germanium...
This powerful inverter provides a high-quality sine wave signal. I found it in a Radio Electronics issue...