This shield circuit is from a 1968s Motorola documentation. The relay is according to the supply voltage. R1 can be reduced to lower trigger voltages.
This circuit is from the 1983 Intersil Databook. In it we have the use of the ICL7135 as an AD...
This MW radio circuit with varicap tuning was found in an English documentation from 1989. The...
This circuit was found in an American publication from the 70s, but it can be assembled with more...