Crystal variable oscillator (CB9506E)

Found in Radio Electronics from the 90s, this circuit can vary the frequency in small values around the crystal frequency.

Intercom LM386 (CB11567E)
This circuit is quite simple to assemble, having been found in a traditional American publication. The...
Oscillator with Frequency Doubler (CB18885E)
This rectangular oscillator produces signals of two frequencies, one double the other. The circuit is...
Quartz PNP Oscillator (CB18933E)
This oscillator can generate signals up to about 10 MHz, depending on the crystal used. The...