This weekend, I was messing around with trying to get one of these beasts to run off of 12 volts DC so it would be a reliable receiver for a translator application. Thinking this would be an easy task; I rounded up some stuff from my junk box to convert 12 volts in to the required 5-volt and 10.5 volts the Sony is happy with. For my first attempt, I used some garden-variety regulators chips that you can buy at any Radio Shack. With good heat sinks, they can usually handle about one ampere. I built my prototype, using the aluminum cover of a small handy box as the heat sink. When I substituted it for the Sony’s internal power supply, it worked fine, for about three, maybe four minutes. The radio then let out a very disgusting ripping noise, and went silent. Upon investigation, the 5 volt regulator was WAY too hot to touch, and was no longer functional. Out of curiosity, I put an ammeter in series with the Sony power supply and noted that the 5-volt supply delivered a whopping 1.25 amps. No wonder there is no battery powered version of these radios. Four D cell would last just a few minutes.
The 10.5 supply is no problem. It runs cool and should be quite reliable. The 5-volt supply is another question. My current version uses two 1.5 amp regulators in parallel, mounted on a piece of scrap heat sink from a dead PC. It is about 2" square and has the appropriate fins. Although it seems to work OK, it still gets very hot to the touch. The only way I feel comfortable with it is to use a fan. I can do that, but it seems like just one more thing to go wrong. To do this right with no moving parts, I can see that I need a very big heat sink and a high current regulator.
I suppose this shouldn't come as a surprise, but in my wildest dreams, I never thought the power requirements would be this high. Now I know why it runs so hot.
Freebird mentioned he has done this already. What did you use for a 5-volt regulator? A LM 123 looks like a decent choice, since it can do 3 amps at five volts. I suspect it still needs a big heat sink