Practice code oscillator (CB21090E)

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

Adjustable Power Supply (CB15755E)
The circuit in the figure is from a source with the possibility to adjust the output voltage from...
Neon Lamps Sawtooth (CB13933E)
We found this circuit in an old magazine 73 of 1974. The circuit must be powered by a continuous voltage...
741 MW radio (CB10644E)
This circuit is from a 1987 American publication called Electronics Handbook. The circuit can be...