Practice code oscillator (CB21090E)

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

High Input Voltage Regulator (CB13050E)
The 78XX series voltage regulator integrated circuits do not support an input voltage greater than...
Multimeter Circuit (CB23623E)
This is the complete circuit of a multimeter using a 50 uA instrument with a 2k coil. The circuit...
1kHz Double T Oscillator (CB10957E)
This circuit came out in a Popular Electronics from December 1995. It is a double T configuration that...