Active audio filter (CB21770E)

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

0 to 30 V Regulator (CB15500E)
One of the problems with common 3-terminal regulators is that the internal reference, normally 1.25 V,...
Optocoupler Logical Transmission w (CB16928E)
This circuit found in French documentation, works with 15 V logic, but can be modified to TTL or 5...
Linear Ramp Generator (CB1485E)
We found this circuit in a 1972 documentation. The transistor, in fact, is a unijunction that can...