This circuit is from a Radio Electronics from March 1970. The crystal depends on the frequency at which the signal is to be captured and the resonant circuit determines the tuned band.
A circuit in which the light turns on smoothly and goes out quickly, but which can be adjusted more...
This circuit has been found in an old documentation and therefore uses a lamp as an indicator. In a...
This circuit was found in a Popular Electronics from the 90's. The transistors are general-purpose types...