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.
This circuit is from 1993 documentation. The table provides the values of R3 and R4 according to...
This circuit is from 1982 documentation and has some interesting uses, despite its extreme...
This crystal oscillator generates a 20 MHz signal. Equivalent transistors such as BF494 and 2N2222...