pls help. what is this on heatsink???

Hi.

I have one amplifier, SCS 2350A mosfet, which I want to use for subwoofers is studio. But it has loud fan. I would like to reduce fan speed, to make it quieter.

Amplifier is rated 2x350W/4ohm. I do not plan to drive it hard, my subwoofers are 200w peak. And I really work at low to moderate sound levels.

There seems to be already some speed control there, mounted on the heatsink. But what is that? Please see picture http://84.255.203.119/scs2350A.JPG. This thing has label on it, and it says "77-24 F140 88/J". It seems to be product of company called Elmwood. It is paralleled with 300E/10W resistor. DC resistance measured over both is 70ohm. I tried to heat the heatsink, but no change in DC resistance, so it is not NTC, i guess.

Fan is rated 110V, but gets 240V on one rail, and some 160V on another. Is that thing regulating the other voltage, depending on temperature, while 240V on other side remains constant? It is connected directly to mains switch. It runs somewhat like this... Mains -> parallel "300E"+"thing" -> fan -> ground.

How would I reduce fan speed further?

Heatsink is quite large. Maybe I could just disconnect the fan?

thnx

quick google search elmwood electronics makes sensors
elmwood is a division of honeywell.

Honeywell's Elmwood brand offers thermal and humidity sensors

Click to expand...

So location makes sense if that is what it is. I would imagine it is the thermal sensor for turning the fan on and off :?

..it's a thermo-switch..

Thank you both for quick reply. I checked Honeywell, and found similar product. It is standard thermostat, switching at 140F temperature (60C). It actually clicks, after being heated, you can hear it. 330E resistor reduces voltage to fan. At overheating thermostat closes resistor, and thus makes fan to run faster.

I will increase resistor value, and thus lower speed at low temps. At high temp, it will go full speed.

I just need 10W resistor. I may try and put light bulb instead of resistor. Lets see...

thnx