Beating the heat

Francis J. Drake Jr., KL7IPV

This article describes an external modification I made to my Icom IC-706 MkII. It may also apply to any radio where the heat buildup is a problem.

I have been a member of the HF Pack Group for quite a while but never put my radio into a backpack out of concern for the amount of heat it generated. This little radio generated a LOT of heat! I called Icom and asked what would happen if the radio was placed in a closed environment like a backpack. They told me nothing would happen; the heat was not enough to affect the operation of the radio since it had a fan that automatically came on to cool the inside. Even with that assurance, I did not put it to use in a backpack. Instead, I used aluminum material to convert the radio to travel and also act as a heat sink on the sides of the radio. It evidently wasn’t enough. Heat killed my radio. I sent it to the factory and the technician told me one of the internal resistors was hot enough to burn him. I paid my money and wondered what to do to keep it from frying again.

The first thing I did was replace the radio with my third in the series of IC-706 radios, the “G” model. Now if the MkII dies, I will still be on the air. The next thing I did was figure a way to protect the radio from the internal heat it generates. It has a fan and it runs a lot but it isn’t adequate. I needed to do more. I measured the surfaces available on the outside of the radio and wondered if it would be possible to place heat sinks on it to draw the heat from the radio even if the fan failed. I perused the number of catalogues I get and found just the item I needed at All Electronics Corp (www.allelectronics.com). They had used heat sinks for sale that were just the right size to put six of them on the top of the radio and draw that heat off. Figure 1 is a photograph of the individual heat sink I used.

The heat sinks were from computer usage and had a lip that needed to be filed off to mount them flat on the radio. I also needed to figure a way to mount them that would allow me to get the screws that hold the top cover to the radio. My Dremel tool came in handy for that little task. I placed the heat sinks on the radio cover and cut and ground each one where needed to allow access the screws. The heat sinks covered the top of the radio perfectly.

Next, I had to bolt the heat sinks to the radio cover so the heat transfer would be sufficient to do the job. I needed to take several things into consideration when I drilled the mounting screw holes. The cover sits about one-quarter inch above the board in the radio. There are spring fingers that ground the cover to the internal boards as well. The heat sinks will also sit above the internal divider that separates the final board from the front end. That space was too small to allow for bolting the heat sink to the cover unless I moved the bolts off center a little.  I drilled the holes as close to center as I could and still miss all the stuff I needed to miss. After I bolted the heat sinks to the cover, I ground off the extra threads of the bolts and smoothed them out, so when this goes into a backpack, the threads won’t tear the insides of the backpack.

The final mounting looked good but not good enough. It needed to be painted. Knowing the amount of heat that could be generated by this radio, I bought some flat black barbecue spray paint to paint the heat sinks. I thoroughly cleaned the heat sinks with acetone before applying the paint. The final outcome looks nice.

While the radio is on, I feel almost no heat from the cover of the radio. I have had the radio on for hours and the fan still has not come on. When I finally take it out in a backpack I will feel much more comfortable knowing the heat won’t stay in the radio where it has proven to be a killer, whether or not the fan comes on.  HF Pack Group, here I come; finally. And I will be cool, too.