We found this circuit in an American documentation from the 80s. In it we have the way to control the amplifier gain by an input voltage.
Found in a 90’s 73 magazine for radio amateurs, this circuit provides a few milliamps of output...
The S-meter is signal strength meter, coupled to telecommunications receivers to indicate the...
This circuit of the 1970s uses Germanium transistors. Changes can be made to use silicon...