You can get the temps down on the outside with a fan, but to get the internal temps down to a decent level, you really need to run it on 12v. My 7100 was nice and cool outside with a fan, but inside, there was still components that were painful to touch.
I did both with both my R7000 and R9000.
I started with a fan but was not totally happy so I ended up getting the proper connector to plug into the shorting connector that were already plugged into the rear of both radios.
The only issue I ran into was with the R9000, it seems part of the metering circuit is taken before the internal supplies voltage regulator stage.
I think it was just the center tune function if my memory is correct.
It was not a problem really as my external source is very well regulated but the meter does not indicate center tune correctly if my external cells start to drop below the regulators drop out voltage. It does not drop out but of course can no longer maintain a voltage output unless I use some form of buck and boost power supply.
I don't care to use a buck and boost supply though as those are kind of like inverters where they are not 100% efficient and use some of your battery power. I can run at least three days as it is with many of my receivers powered on, a cell charger keeping the cell charged up so I can use it for my internet connection to a single laptop.
I strongly advise using an external supply with these old receivers.
Heat is a killer of electronics and with the age if these old Icom's now, an external supply just makes sense.
You can still run a fan to help lower self generated heat from some of the chips if desired but the radio may not warm up to normal temps so you may see some slight frequency error. Nothing a TXCO would not help compensate for though.
I always aligned my old Icom's using the internal supply set to the correct output voltage and then I'd set my external supply to equal the internals output at the same test point.
