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I had to use a pair of resistors for one of the 10K connections. I got within about 0.5K of precision with them. This circuit works great! Now I am going to reverse-engineer a schematic, figure out all of what "makes it tick", and create a fact sheet for the project records. :-)
Worked perfectly the first time! Put a scope on it, and the frequency range is ~467Hz to ~16.57 KHZ. Good, loud amplitude, and steady, even signal tone.
How to Make a 555 Timer Chip Circuit