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This variable frequency oscillator was found in an old American documentation. Transistors allow more modern equivalents and coil data are found next to the diagram for several frequency bands.
Using the 741 operational amplifier this circuit was found in the August 1993 Electronics Now...
We found this circuit in a 1967 documentation. The circuit can be designed based on current...
Found in Popular Electronics, this configuration can be powered by voltages from 6 to 12 V....