My Genesis G3020 Transceiver

 

Quiet and Simple Ventilation

After much searching I finally discovered a truly quiet fan. It’s a Sony product called Scythe S-Flex. There are several series of this fan but the one that had at least a prayer of fitting into my G3020 enclosure measures 80 X 80 x 25mm.

These fans are essentially silent. Incredible. Out in the open you almost have to put your ear next to the fan to hear it running. They have what Sony calls a Fluid Dynamic Bearing that makes it so quiet, as they explain in their literature. You can read all about it HERE. I purchased my SFF80B S-Flex Fan from newegg.com for less than $15 including shipping. It is rated to move air at the rate of 21.5 cubic feet per minute, and that is more than enough to cool the G3020, key down.

Here is an adapter bracket I sawed out of 1/16-inch aluminum. The irregular-looking clearance holes in the cross bar fit the holes I tapped for 4-40 screws in the top of the heat sink (I had to rat them out a bit after my drill slipped), while the holes in the upper left and lower right fit diagonal corners of the fan case. They also are tapped for 4-40 screws.

Installing The S-Flex Fan

Since the S-Flex fan was 5mm too tall to fit my enclosure, I had to saw off about 1/8-inch of the heat sink to accommodate its extra height plus the thickness of the adapter bracket. I pulled the solder pins on the bottom and sawed off that end, then drove the pins back in.

The adapter bracket obviously adds to the mass of the heat sink - that’s a GOOD THING - besides serving as a platform on which to mount the fan.

The top of the fan is flush with the inside of the top cover. The S-Flex fan requires a hole 3-1/8 inches in diameter.

Equally effective would be an attractive pattern of concentric circles of 1/4-inch holes that could easily be drilled with a hand or electric drill.

“Key Down” Test Results

All tests were run with the BIAS set to 4.2 Volts as suggested by Tasic Sinisa in an email several months ago. The original spec was 4.5 to 4.6 Volts. At 4.5 Volts the zero DRIVE power input was around 20 Watts. At 4.2 Volts it is around 10-11 Watts, a noticeable improvement. Still, heat buildup in my enclosure if tightly sealed, certainly would be ruinous.

Forced ventilation is required and the use of a suction fan at the top of the enclosure is the best way to accomplish it since heat naturally rises to begin with. Think of drawing the hot air out the top as assisting nature...

These tests were run in TUNE mode non-stop over a period of about twenty minutes. At each new power setting I let things stabilize for two minutes before measuring the temperature. Output power was set with the DRIVE control. Data was taken every 100 milliWatts to 1000 milliWatts output power, during which time the input power was more or less constant at 10-11 Watts. Input power increase thereafter is tabled in the following:

At 2 Watts output the input power was 12 Watts,

at 3 Watts out the input power was 13.5 Watts,

at 4 Watts out the input power was 15 Watts, and

at 5 Watts out the input power was 16 Watts.

Note that the total power lost inside the enclosure remained at about 10-11 Watts more or less regardless of output power. At no time did the temperature of the final amplifier transistor heat sink exceed 105°F.

These tests show conclusively that the rig thus ventilated could be run, key down, at any power it is capable of for an indefinite period of time with no problems due to temperature.

Instruments used in the above tests were the same as in those tests run in January 2010 and posted in Photos, namely, an Astro Whatmeter for input power, a OHR Model WM-2 QRP Wattmeter for output power, and a Cen-Tech Infrared Thermometer for temperature.



By nature, heat rises. The seven 5/16-inch holes seen in the side of the bottom cover in the above photo are, along with seven like holes in the opposite side of the cover, the “intakes” for ventilation air. The fan sucks air in through those holes, across the two heat dissipating transistors on the right side of the board, then up and out across the final amplifier heat sink, the warmest component in the enclosure, thus assisting nature in moving warm air upward.