[Amps] Fan sounds like F-15

[Vic K2VCO]

   I've been using my new 4CX1000A amplifier for a few days. It works great.
   But  there is one problem that I need to solve: the fan -- it's a flat
   centrifugal type -- here's a construction photo from my website:
   [1]<http://www.qsl.net/k2vco/4CX1000A/Underside.jpg>
   which provides somewhat more air than is needed. But it also provides more
   noise  than  is  needed,  somewhat  like  an F-15 pilot kicking on his
   afterburner. OK, a little exaggeration. But not much.
   I would like to implement a thermostatic control system. I envision a sensor
   stuck in the chimney above the tube that would operate a relay to switch the
   fan from low to high speed.
   Has  anyone  done  this?  What  kind of sensor should I look for? What
   temperature should it switch at? The fan is an AC motor with a capacitor
   across half of the field -- is it safe to reduce speed by putting a resistor
   in series with the motor?
   I know a simple solution would be to remote the fan, but it would mean
   building a new amplifier! And good noise-cancelling phones cost $300.
--
Vic, K2VCO
Fresno CA
[2]http://www.qsl.net/k2vco/

References

   1. http://www.qsl.net/k2vco/4CX1000A/Underside.jpg
   2. http://www.qsl.net/k2vco/