[Elecraft] How and How Often to Clean KPA-1500 Cooling Systems?

[Dave B]

Re:-

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> Subject: Re: [Elecraft] How and How Often to Clean KPA-1500 Cooling
> 	Systems?
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> 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.
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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


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