Low battery indicator 555 (CB9551E)

This circuit can operate with different voltages, depending on the zener used. We found it in a 90s American documentation.

Transistor Replacement Box (CB21670E)
The idea of this circuit from a 1960 publication is simple: we can switch the transistor being...
LM3914 Audio Level Meter (CB25459E)
Using a small speaker as a microphone, this 10-LED circuit was found in the March 1992 issue of...
2 W Amplifier LM380 (CB13758E)
We found this circuit in a 1977 documentation. The National Semiconductor's LM380 is no longer...