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.

2-Transistor Amplifier (CB22508S)
This 1950's circuit used one of the first commercial transistors and had two stages for audio...
Audio compressor (CB22154E)
Using integrated circuits from the time, we found this audio compressor in an English publication from...
Micro Radio (CB18167E)
This is an experimental crystal radio that uses no power source. The antenna must be very long (at...