The transistors of this circuit found in an English 1980s documentation may be the modern BC548 equivalents. The circuit is battery powered and the earphone must be crystal.
We find this circuit in a Popular Electronics of the 90s. The circuit is passive and the coils...
The configuration of this circuit was suggested by an old English publication that comes to...
In the circuit shown by figure 1, a10 mV AC signal applied to the input produces a 1 V signal in...