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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Relative impedance meter (CB7487E)
Found in a 1960 Sylvania manual, this circuit can be implemented with a modern equivalent...
Logarithmic Converter (CB19486E)
This configuration, already presented in other points of this section and website, is of a...
2 Meter Crystal Oscillator (CB4051E)
We found this precise crystal oscillator for the 144 MHz band, depending on the crystal used. The...