Thermostatic control with mercury sensor (CB21388E)

This former temperature sensor with a mercury sensor was found in a General Electric documentation from 1967. The SCR must match the load.

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Tunable notch filter (CB7404E)
We found this circuit in an English publication from the 1980s. The circuit uses current...
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The circuit shown in the figure can be useful in cases where a common telephone extension is used....
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We found this circuit in an American documentation from 1977. The circuit must not be powered by a...