Found in a 90s Radio Electrconics, this circuit is an operational one with a power stage using two transistors. The output current can reach several amps.
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...