Two-tone solar buzzer (CB20493E)

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

Precision Switch Oscillator (CB4171E)
This circuit makes use of a PLL 567 and the components must be calculated according to the desired...
Receiver for remote control via powergrid (CB9577E)
The transmitter can be that of CB9574E. This receiver uses a PLL to directly trigger a sensitive relay....
Negative Feedback Stage (CB6131E)
This circuit is from a 1967 US publication. The configuration can serve as a basis for designs...