On 6/18/2012 4:42 AM, David Robertson wrote: ( ... a long message I won't include here where he improved amplifier cooling by tightening heatsink/right panel screws and used heatsink compound.)
I operate my KPA500 with the fan speed set to #1 continuously which delays the increase in the increase in fan speed once the amplifier starts putting out power. My amplifier did not exceed 58 deg C after 10 minutes at 500 watts carrier output into a dummy load and it stabilized at about 60 degrees in a 25 degree C room. My right panel to heatsink screws (the ones under the handle) were all tight and that explains why my experience was better than was Dave's originally before he tightened his heatsink screws and added heatsink compound. I then added heatsink compound to the mating surface between my heatsink and the right side panel. There was no difference in cooling performance at all. I just wanted to know .. and now I do .. and so do you. The KPA500 fan is as quiet as any muffin fan ought to be but it was still annoying to me. That is not an amplifier fault .. it is just that I have good hearing and I prefer a *very quiet shack. For those who may be like me in that regard here is how I reduced the normal fan noise of my amplifier. In my amplifier much of the fan noise was actually coming from the sheet metal of the amplifier structure which was being excited by the vibration of the fan which is rigidly attached to the amplifier structure so that fan vibration was communicated to the structure which then resonated and amplified the fan noise. When I removed the fan and held it loosely in my hand while it was running I could feel the light high frequency 'buzz' produced by the rotating magnetic field of the fan and also, crucially, the lower frequency throb caused by a slight weight imbalance in the rotor. I used a small piece of sticky pad (normally used to mount components to a chassis, etc) and placed this very small weight at various points on the rotor blades until, by trial and error, found the 'sweet' spot which resulted in greatly reduced throb. That reduced fan noise considerably. Then, to reduce transmission of fan vibration to the amplifier structure even further, I mounted the fan loosely to the back of the amplifier using soft quarter-inch cushions between the fan and the amplifier. I used light wire to do the actual attachment instead of the long screws that are standard. The overall effect is considerably less fan noise and I am very happy about that. The fan mounting is fragile and not to be recommended if the amplifier is to be moved very much but in my installation it is just fine. By the way, I carefully compared cooling performance before and after the fan mounting modification and found no difference at all. I also noticed during my testing that the direction of airflow makes no difference. Don K7FJ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
