Charger protection relay (CB26312E)

This circuit was obtained from an Elektor magazine from the 90s. The circuit is to protect batteries while charging.

DC Motor Control (CB12292E)
This circuit is from 1977 documentation, but can be assembled with BC548 for Q1, Q2 and Q4, BC558...
FET caracteristic curve plotter (CB20730E)
Found in American documentation from the 90s, this circuit uses components that are still common...
Piezoelectric Mike Preamplifier (CB786E)
This high impedance input amplifier is suitable for the use with piezoelectric sources such as...