This traditional configuration was found in a 1984 publication and does not innovate anything we already know. A simple audio oscillator can be obtained from the circuit in the figure. In this circuit we use a potentiometer to control the frequency (P1) and a selector switch to change capacitors and, therefore, the selection of bands. At the output there is a second potentiometer that controls the signal strength applied to the external circuit. Note that the resistance of this potentiometer and, therefore, of the load, is limited to a minimum of the order of 100 ohms.
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