Variable oscillator for code practice (CB7317E)

This circuit is from Popular Electronics from the 90s. The integrated circuit is not very common nowadays.

Divider by N with the 4017 (2) (CB12131E)
With this circuit it is possible to divide the frequency of a rectangular signal by values between 2...
Precision Hysteresis Alarm (CB26242E)
This circuit was obtained from the Encyclopedia of Electronic Circuits volume 5 of 1995. The...
High Voltage Regulator (CB19513E)
This circuit can supply output voltages from 50 to 250 V from an input voltage of 300 V. The...