This circuit is from a 1969 RE Experimenters Handbook. The circuit is powered by the voltage of the circuit being tested. Integrated circuits are 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...