This harmonic oscillator controlled by crystal was found in an American documentation of the 90's. The circuit uses transistors of the time. Current equivalents can be used.
This circuit was found in a 1987 edition of the United States' Hands-On Electronics magazine. The...
This amplifier circuit is from a 1952 documentation. The frequency of the amplifier signal depends on...
Found in Popular Electronics from the 1980s, this circuit can use more modern transistors such as...