Crystal variable oscillator (CB9506E)

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

Amplifier Speaker (CB26145E)
This circuit can be used as an amplifier for musical instruments or even with your cell phone. The...
Digitally controlled attenuator (CB9029E)
This circuit, which can act as a shield, was found in a 1970s American documentation. The...
Timer CA3140 and 555 (CB14932E)
This timer produces a continuous sound at the end of the timer set in potentiometer RV1. The...