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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.
With this circuit, a well known configuration, small speakers and even low-impedance headphones...
This circuit consists of an audio signal tracer using two 741 operational amplifiers. The output...
Using the LT128 and LT1037 from Linear Technology this circuit has a 400 MHz gain x bandwidth...