We found this circuit in a 1964 Electronic Design. The triac and SCR can be replaced with modern equivalents according to the load. The circuit is for 160V network.
This simple polarity indicator for continuous voltages can operate with voltages from 3 to 15 V...
This circuit with RIAA equalization is from 1985 US documentation. The circuit has a flat response...
This circuit, suggested by an Electronics World of 1969, keeps a blinking LED for a while when a...