Freezing sensor (CB21288E)

This circuit was found in a Popular Electronics from the 90's. The components are common. The potentiometer adjusts the circuit's trigger point.

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Touch or leak alarm (CB22092E)
This circuit was found in old documentation. The SCR can be any of the 106 family. Note the sensor...
Staircase generator (CB21847E)
This circuit was found in Ferranti's 1974 transistor manual. The transistors are from the period and...
Transistor relaxation oscillator (CB12680E)
Short duration pulses can be obtained with the relaxation oscillator that uses common transistors and is...