Practice code oscillator (CB21090E)

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

VCO (CB21488E)
This circuit was found in a 1967 Raytheon manual. The transistors are from the time. Equivalent modern...
Signal Injector 555 (CB10568E)
This circuit was published in a 1979 magazine, but it can still be easily assembled as the...
Pulse Generator (CB13238E)
The circuit presented generates short pulses. This configuration was found in a publication from...