Practice code oscillator (CB21090E)

Found in Popular Electronics from the 90's, this circuit consists of an audio oscillator for Morse code practice.

Remote Volume Control (1) (CB12469E)
The intensity of an audio signal can be controlled by a remote potentiometer on a DC circuit,...
Car Alarm (CB3835E)
This alarm circuit is from a 1987 publication, however the components used are still modern. The...
TTL Function Generator (CB18884E)
This voltage-controlled function generator circuit was found in ancient European documentation. The circuit...