Water activated alarm (CB7993E)

This rain, flood or leak sensor was found in a 90s Popular Electronics. All the components used are common today. The transistor can be the BC548.

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Up to 10 MHz Oscillator using Transistors (CB9416E)
This circuit, from a 1973 documentation, can be made with BC549 transistors. The frequency depends on...
12 V x 50 mA Regulator CB8803E (CB8797E)
Found in a Philips documentation from the 90s, this circuit uses transistors from that time....
Log Voltmeter (CB903E)
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