This circuit indicates when the voltage of a 12 V battery is low. With changes, for example, the zener, the circuit can be used to monitor other voltages.
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...