This variable frequency circuit was found in a Popular Electronics from the 90s. The circuit outputs to a small speaker and can be powered by voltages as low as 3 V.
September 2017 - Digi International's SX 868 RF modules for low-power 868 MHz CE / RED operation...
Indicated as an amplifier block for various applications, this circuit was obtained in a 1966...
This circuit is from Motorola's Linear Interface ICs of 1993. The circuit can be powered by...