Review: PAE-Kx31 heat sink for the KX3 from WA4PSC

The KX3 is amazing QRP radio, probably the best in it’s class. One of the more remarkable features is it’s built in PSK/RTTY mode. Recently, the fact that when running 5-10 watts for prolonged transmit times causes the KX3 to heat up to a point where the temperature monitor will force you to scale back your power. While this is very annoying, it’s necessary  in order to protect the KX3.

In the KX3 online discussions, a number of aftermarket heat sinks have been developed for the KX3. After reviewing the various designs, I took the plunge and placed a pre-order for the PAE-Kx31 from Pro Audio Engineering. More than just a chunk of aluminum on the back of the Kx3, this promised to have several features that I wanted:

  • Fins for better passive heat transfer
  • No sharp edges to snack in a backpack, clothing, or myself
  • Anodized instead of powder coated
  • The ability to continue to use my SideKX end plates and SideKX LEXAN cover

I got word last week that the item had shipped and it arrived Friday (April 18th). Excited as I was, I couldn’t perform the installation until Sunday. Here is the step by step with pictures along the way.

IMG_0040The package contents included the heat sink, four replacement screws to accommodate the additional thickness of the heat sink base plate, an installation guide, and a small package of thermal grease.

IMG_0041 The heat sink in more detail.

IMG_0045The small packet which contained the four screws and the thermal grease packet.

IMG_0046The heat sink measures just a bit over seven inches long.

IMG_0047The heat sink is about one and a half inches high.

IMG_0048The heat sink is about five-eighths of an inch thick. Note there is a notch on this end of the heat ink base plate. This is to accommodate the lip of the SideKX LEXAN cover.


IMG_0043The instruction guide is well detailed.

IMG_0053The one provided screw that is longer must go in the hold closest to the DC power supply.

IMG_0054You can see the size difference, accommodating the thickness of the base plate.

IMG_0055Removing the factory heat sink plate, you can see the original screws in the front row and the provided replacements behind them. Sadly, this means my brass ID plate from Arkay Engravers will have to find a new location.

IMG_0056With the original plate removed, the new heat sink is ready to go on. There are instructions for three different installations. I performed the first, which is a simple replacement of the original plate with the new heat sink. I did not use the thermal paste.

IMG_0058You may have to open your case and re-seat the locking nuts that the middle two screws attach to.

IMG_0057You can see these two screw holes next to the battery pack. When I removed the original screws, the nuts fell out of place and I had to fish them out. I attached these two screws first, and then attached the two on the end last.

IMG_0059Here the nuts are in place with the heat sink attached.

IMG_0060Behold, the heat sink is attached!

IMG_0061You will notice, the anodized black is an excellent match to the black of the KX3. It’s an excellent detail that was attended to.

IMG_0062Sitting on the legs, the heat sink doesn’t add any perceptible bulk to the KX3. The rounded radial fins help reduce that impression.

IMG_0064Also important, the SideKX LEXAN cover fits perfectly. That little notch on one end of the plate was thoughtfully included.

All in all, I think this is a very fine product. Howard Hoyt (WA4PSC) paid a lot of attention to the details of this aftermarket heat sink and I think it was worth every penny!

Coming soon, I’ll do a key-down time vs temperature chart comparing operation with the new heat sink versus with the stock plate.

Posted in KX3
One comment on “Review: PAE-Kx31 heat sink for the KX3 from WA4PSC
  1. Mike Klein says:

    Nice review. Good pics. Thanks for the work! mike ac2ex

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