A well designed output stage SHOULD be hot to the touch. The temperature component of protection in Elecraft output stages seems to kick in when the internal temperature approaches 70 deg C. You can see this, for example, by watching temperature in the KPA500 and listening to fan speed. The function of the heat sink is to act as a conductor between the semiconductor junctions and the surrounding environment, and increased mass acts as a sort of buffer.

73, Jim K9YC

On 8/5/2017 2:53 PM, Jan wrote:
""I've been doing a lot of FT-8 using my KX3 and my KXPA100 at 20 watts,
and have noticed that the KX3 is heating up quite a bit and is almost
hot to the touch""

Why should the KX3 be heating up, when the AMP is running only 20W ?
Is the KX3 "drive" not backed-down at this level ?? HELP

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