Metronome using operational (CB22060E)

We found this circuit in an English publication. The transistor can be BC549, and the power supply can be between 5 and 9 V.

Amplifier for light beam (CB26241E)
This circuit for link or alarm was found in the Encyclopedia of Electronic Circuits Volume 5 of...
Siren for motorcycle (CB6491E)
This circuit is from a Popular Electronics of the 90's. Any power MOSFET can be used. The circuit...
Circuit for milliammeter (CB22310E)
This circuit extends the scale of a milliammeter. We found it in a documentation from the 60's. The...