Door buzzer or alarm (CB20492E)

This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose NPN.

RIAA preamplifier (CB8250E)
This circuit was obtained in an Electronics World of 1968. The operational amplifiers ones are...
AC Load Crowbar Circuit (CB5881E)
This circuit trips by shorting the load to quickly blow the fuse when the voltage exceeds a...
Divider by 4 320 000 (CB12304E)
This circuit, obtained from ancient English documentation, produces a pulse every 24 hours when a 50...