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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Liquid level sensor (CB23807E)
This sensor was published in Radio Electronics magazine in April 1962. The two-transistor circuit...
DC Motor Control 555 (CB24908E)
Another of the many similar configurations we have in this section. This one is from a Radio...
Solenoid Current Monitor 2 (CB5400E)
This circuit like the previous one is intended for 24V x 3W solenoids being connected from the...