Practice code oscillator (CB21090E)

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

Germanium Transistor Voltage Regulator (CB987E)
This circuit, found in an old magazine of the year 1968, uses a Power germanium transistor. This...
Oven control (CB7962E)
This sequential circuit with an optical coupler was found in a Popular Electronics from the 90s to...
Fuzz effect (CB17975E)
This guitar effect circuit was found in a 2002 documentation. The circuit can be powered by a 9 V...