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.
National Semiconductor suggests the figure circuit for stabilizing the peak value of an...
This stage for JFETs was found in a 1965 US publication, but is valid for modern components. |...
This circuit was obtained in a Popular Electronics of the 90s. The circuit can be assembled with...