Negative ion detector (CB21001E)

This tube circuit was found in the magazine 73 for radio amateurs in an issue from the 1980s. Note the transformer used to power the circuit.

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Residential Alarm (CB17228E)
This simple alarm circuit was found in a 1998 documentation. When the sensors are activated, the...
Microphone balanced amplifier (CB9388E)
This circuit was found in an old American documentation. The integrated circuit used is uncommon...
Increasing the voltage of a fixed regulator (CB8476E)
Found in a 90s Electronic Design, this suggestion to have a higher voltage in a fixed regulator...