This circuit uses a crystal phone and can be built with more modern transistors like the BC548. The original circuit is from a 1979 publication and is powered with only two AA or AAA batteries.
To use the instrument for AC measurement, the tips are A and B. For CC use tips A or B for...
The interesting circuit shown in the figure, can have its gain digitally controlled and present two...
This simple MW radio was found in a 1975 publication, but it can be mounted with BC548...