Crystal variable oscillator (CB9506E)

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

Overcurrent oscillator (CB9627E)
The frequency of this circuit depends on the crystal. The transistor supports a modern equivalent. We...
High-gain composite amplifier (CB8069E)
Indicated in Maxim's documentation from the 90's, this circuit has a gain of 40 dB and an output...
Timer with 741 (CB12281E)
The time obtained in this circuit, from a 1978 publication, depends on R3 and C. R3 can have...