This circuit is from 1999 documentation. However, it can still be easily assembled, as all components used are common. The sensors can have their quantity increased, being connected in parallel.
This 1950's circuit used one of the first commercial transistors and had two stages for audio...
Using integrated circuits from the time, we found this audio compressor in an English publication from...
This is an experimental crystal radio that uses no power source. The antenna must be very long (at...