Active audio filter (CB21770E)

This circuit was found in a 1977 documentation for radio amateurs. Integrated circuits are common operational amplifiers.

Picoammeter (CB6192E)
This circuit was found in a 1980s Intersil documentation. The integrated circuit used is not...
Triggered CMOS Astable 4001 or 4011 (CB10730E)
Although it is a common configuration today, these circuits were taken from an old publication. The...
Audio Oscillator 2 (CB12907E)
This circuit, from an old publication, can also use modern transistors. Note that the unit is...