Two-tone solar buzzer (CB20493E)

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

Short wave converter (CB9185E)
Found in Radio Electronics from the 90s, this circuit converts signals from the 9.5 to 9.8 MHz...
Synthesized Musical Bell (CB17378E)
This circuit was found in a 2000 documentation. The circuit generates a sequence of notes...
Powerful FM Transmitter (CB18668E)
This small transmitter with 2 transistors can reach several hundred meters using a 30 to 70 cm...