The DIY599 PA500 amplifier created by Oliver DL4KA is a work of art. It is a feature-rich, efficient HF amplifier/tuner combination packed into a very small form factor.

Normally passively-cooled by it's CNC-machined aluminum body and heatsink, this 50 watt PEP amplifier is great for 3-season outdoor use (fall, winter and spring). However, on a hot summer day, with a little bit of sun and an aggressive operator who likes to call, the amplifier may reduce power quickly to prevent thermal overload.

The solution: strap a fan to the side of the amplifier to assist in removing the heat. But how to do so elegantly?

If you are rich, bid on an eBay auction for one of Oliver's limited-edition PA500 Expedition versions. These special builds have a higher-output PA and a fan mounted to the side.

For the rest of us, Ammed KN6STX offers a top-shelf solution: a CNC machined, anodized aluminum dual-80mm fan mounting frame (and hardware).

Here we see the finished installation where Mike VE7KPZ has chosen a pair of full-size Noctua NF-A8 ULN 3-pin fans to run silently and with minimal current draw to provide optimal cooling.

Running Noctua's supplied ultra-low-noise adapters for the already ultra-low-noise fans slows the fan speed even more and drops the current draw of each fan to just 22 mA at 13.3 volts dc. The two fans combined consume just 44 mA of current. Without the ULNA, each fan consumes 29 mA at 13.3 volts dc.

It is possible to power 12 volt dc fans directly from PA500 amplifiers v2.9 or later. The v2.9+ amplifier can fully control the speed of a single fan. For v2.8 amplifiers, one 5 volt dc fan can be powered. Please review the PA500 manual to confirm current limits for your amplifier's fan powering/controlling system. In Mike VE7KPZ's case with highly-efficient fans, the amperage draw is so low that there is no real need for fan control. Mike chooses to wire the fans directly to a nominal 12 volt dc power source. This also avoids any possible PWM switching interference. Direct powering is the only solution for PA500s <v2.8 but really can be used for all versions.

So far the solution is working very well for Mike VE7KPZ and the orange (and red) amplifier heat warning/gone-to-bypass lights have not been seen since installation. On a recent SOTA/POTA activation the amplifier stayed at ambient air temperature while operated in direct sunlight - this solution works perfectly.

For more information about the PA500 active cooling fan adapter plate, you can contact Ammed KN6STX via his QRZ email.

Ps: Mike first heard about Ammed's solution via