Found in an American publication of 1968, this circuit makes use of a pilot light of the time. It can be replaced with LED with appropriate series resistor. Transistors may be modern equivalents.
Using JFETs, this circuit from a 90’s American documentation can generate signals of 0.15 Hz. The...
Found in a 1970 EEE, this circuit generates signals that depend on the C1 capacitor. Transistors are...
This watt meter was found in an old telecommunications documentation. The circuit is interspersed...