Re:- ------------------------------------------------------------------------ > Subject: Re: [Elecraft] How and How Often to Clean KPA-1500 Cooling > Systems? > Message-ID: > > <byapr07mb6214cdc56a6c16894c5a71889e...@byapr07mb6214.namprd07.prod.outlook.com> > > Content-Type: text/plain; charset="Windows-1252" > > As you know, I run my amp in a single amp, SO2R configuration. During a > heavy 2BSIQ session on RTTY, temps reach 90 deg C. Fans go to 5 > occasionally. Not a problem. Don?t worry. ------------------------------------------------------------------------
90'C is too hot for the heatsink. One wonders what the actual device junction temperatures (the critical value) might be for that, but that can't be measured directly. You need knowledge of the actual power being dissipated, and the various thermal resistances between junction and heat sink, where you can measure temperature. Plus the difference between what the heatsink sensor records, vs the temperature at the device, varies as well. Solid-state power devices (DC and RF) do not like heat, the hotter they are, the less likely they are to last a long and trouble free life. Plus, all the thermal cycling (heat/cool) can stress soldered joints to them that will eventually fracture and cause a fault. Yes, keeping a stable (even hot) temperature will reduce thermal cycling stress, but the overall MTBF of the devices will still be very much shorter at elevated temperatures than if they were kept cooler. Plus, RF device production life-cycles are notoriously short as the development pace is fast, especially with LDMOS devices. Also, often the new "better" devices, are different enough to /not/ be drop in replacements. Electrically or physically. As for cleaning. As often as needed, every site/shack is different. If you see dust accumulating on the outside, it's inside too! Many commercial amps have air inlet filters. But they need to be kept clean, as a clogged filter is just as bad for cooling, as an inadequate heatsink/fan combination and no filters. Regards. Dave G8KBV -- Created on and sent from a Unix like PC running and using free and open source software: ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
