Two-tone solar buzzer (CB20493E)

This circuit was found in a 1991 publication. The transistor can be a general-purpose type.

Amplifier Protection (CB24882E)
This circuit is used to protect an amplifier from excessive power output that would cause problems for...
Assisted Ignition 2 (CB4349E)
This circuit was found in a French magazine Toute LÉlectronique from 1978. Transistors are not...
Photocell powered frequency standard (CB20521E)
This circuit was found in documentation from the 50's. The circuit uses transistors of the time...