Plant soil heater (CB7964E)

This circuit was found in a 90’s 303 Circuits. The components are from the period and the heating system depends on the resistive element.

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Old Push Pull Low Power Amplifier (CB12923E)
The critical components for this 1970s project are transformers. The original transistors are made...
In use telephone indicator (CB8657E)
Found in a 90s Popular Electronics, this circuit keeps an LED on when a phone is in use. Can be...
CMOS Frequency Meter Up to 12 MHz (CB13726E)
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