Crystal variable oscillator (CB9506E)

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

150 Hz to 1.5 kHz Wien Bridge Oscillator (CB25907E)
This circuit was found in the December 1995 issue of Electronics Now magazine. The circuit...
Telesimulator (CB4294E)
The basic idea of this 1989 circuit is to trigger a relay for a while when a call signal occurs on...
100 Hz high pass filter (CB6935E)
Found in Radio Electronics from the 90s, this circuit uses a 741 and can be changed to other...