Variable oscillator for code practice (CB7317E)

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

Light Activated Switch (CB14457E)
This circuit is from 1968 documentation. We can assemble it with more modern components such as a...
Speaker protection (CB8193E)
Found in a 90s Silicon Chip documentation this circuit is intended to protect a speaker system in...
UV Sensor with UVTRON Tube (CB25942E)
The UVTRON tube is an ultraviolet radiation sensor. In this circuit from Radio Electronics from...