This inductance bridge uses an external audio signal. The circuit is from a Radio Electronics from January 1966. The instrument can be a common multimeter in the lowest current range.
This circuit uses discharge tubes as active elements. The circuit is from a 1960s Signalite...
The circuit shown in the figure trips when a slight swing causes the pendulum to touch the ring...
This circuit is from the Linear Applications Handbook of the National Semiconductor of 1994. The...