Found in 1967 Raytheon documentation, this circuit uses a company coupler consisting of a lamp and an LDR. The transistor is according to the load current.
This circuit of a 1978 American publication monitors a telephone line by triggering a relay. The...
This interesting FET-tester circuit was obtained from an old American documentation. The bipolar...
This old VHF TV booster that also serves FM was found in Radio Electronics magazine from April...