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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Variable Output Oscillator (CB16513E)
We found this circuit in a 1998 publication. The circuit has controls for both frequency and...
Auxiliary Telephone Bell (CB18817E)
This circuit for conventional lines was obtained in a 1996 documentation. The circuit uses common...
Capacitance Multiplier (CB16664E)
This is the conventional version of capacitance multiplier with operational amplifier that appears in...