This circuit was found in a 1966 General Electric documentation. It makes use of direct contact water sensors and therefore requires an isolation or low voltage relay drive transformer.
In the figure we have the circuit of a multi-range ammeter using a 50 uA full-scale instrument. The...
We found this circuit in a Radio Electronics magazine from December 1969. The circuit uses a...
This blocking oscillator was found in a publication from the 50's. The coils determine the...