This circuit was obtained in an Electronics Now from the 90s. The circuit uses operational amplifiers from the time and the indicator is of the Sonalert type with internal oscillator.
We found this circuit in an American publication from the 1970s. The MC1555 is the version of the...
This circuit for FET was obtained from a 1977 Radio Handbook. The input impedance is 150 ohm. The...
This is the receiver circuit for the CB13978B, found in the same 1977 Elettronica Prática...