Speed control circuit for a 12v computer fan

I have a 90mm, 12vdc, 200ma computer fan that I need to control the speed in an application unrelated to the computer. Power supply is 12v, 400ma. Does anyone have a circuit schematic that I could use to accomplish this. I tried the attached circuit with a 555 timer but I'm not getting any speed control with that circuit; just full speed. I believe these fans typically don't work well at voltages below 50%. I tried increasing the capacitance of C1 to bring the frequency down (on recommendation of circuit designer), but without any luck. I am an amateur here so I could use some help. Thanks!

Adjusting R1 should alter the speed. (according to the article.)

pwm

I would double check that everything is wired correctly. If the 555 is not working you would have your symptom.

compare it with these which have little difference:

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or with this which has much more differences:

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