Class A heat - "pull my finger" is 50 not 60

lgreen · 9th October 2009, 05:53 AM

I have seen a LOT of posts (or is it in the NP articles) that say for a heat sink, if you are able to hold your finger on it for a second or 2 or 3 and then pull off due to high heat/ pain, its probably about 60 degrees C, which is as hot as you want to get a heat sink given saftey considerations and the operating temp of the semiconductor, which is going to be a few degrees hotter.

Ok. Makes sense.

Today I measured a Class A amp's heat sinks. I believe that this 'finger' test gives you a heat sink at about 50C, not 60C. So good news, the devices are operating a lot cooler than I thought.

I don't think I am wussy but who knows. I used a thermocouple on a DMM and gave it time to settle in. Damn things get fric***in hot!!

Brian Kingsbury · 9th October 2009, 06:45 AM

After being a line cook for several years, I'm fairly certain that there's no universal "finger test" that will correlate to an actual temperature. I've seen guys take things out of a 350F oven barehanded and not blink twice and other people who can't even pick up something that barely feels luke warm to me.

I propose a less subjective test: try to cook an egg over easy on your heatsink!

lgreen · 9th October 2009, 06:50 AM

Yeah I was surprised to measure this; I thought it was so hot that it would be about 65-70C but turned out to be in the 50's.

Nothing like learning by doing. Hell's Kitchen?

Brian Kingsbury · 9th October 2009, 07:06 AM

Maybe we should be testing our heatsinks with a steak? 60C is 140F.. which is a perfect medium rare.

I gotta stop, I'm making myself hungry here..

wwenze · 17th October 2009, 12:13 AM

Reminder: Half the conductivity = twice the temperature required to get you to "pull my finger"

9th October 2009, 05:53 AM	#1
lgreen diyAudio Member Join Date: May 2003 Location: San Diego, USA	Class A heat - "pull my finger" is 50 not 60 I have seen a LOT of posts (or is it in the NP articles) that say for a heat sink, if you are able to hold your finger on it for a second or 2 or 3 and then pull off due to high heat/ pain, its probably about 60 degrees C, which is as hot as you want to get a heat sink given saftey considerations and the operating temp of the semiconductor, which is going to be a few degrees hotter. Ok. Makes sense. Today I measured a Class A amp's heat sinks. I believe that this 'finger' test gives you a heat sink at about 50C, not 60C. So good news, the devices are operating a lot cooler than I thought. I don't think I am wussy but who knows. I used a thermocouple on a DMM and gave it time to settle in. Damn things get fric***in hot!! __________________ My DIY audio projects- PartTimeProjects.com.

9th October 2009, 06:50 AM	#3
lgreen diyAudio Member Join Date: May 2003 Location: San Diego, USA	hot or not? Yeah I was surprised to measure this; I thought it was so hot that it would be about 65-70C but turned out to be in the 50's. Nothing like learning by doing. Hell's Kitchen? __________________ My DIY audio projects- PartTimeProjects.com.

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9th October 2009, 06:45 AM	#2
Brian Kingsbury diyAudio Member Join Date: Aug 2009 Location: San Diego, CA	After being a line cook for several years, I'm fairly certain that there's no universal "finger test" that will correlate to an actual temperature. I've seen guys take things out of a 350F oven barehanded and not blink twice and other people who can't even pick up something that barely feels luke warm to me. I propose a less subjective test: try to cook an egg over easy on your heatsink!

9th October 2009, 07:06 AM	#4
Brian Kingsbury diyAudio Member Join Date: Aug 2009 Location: San Diego, CA	Maybe we should be testing our heatsinks with a steak? 60C is 140F.. which is a perfect medium rare. I gotta stop, I'm making myself hungry here..

17th October 2009, 12:13 AM	#5
wwenze diyAudio Member Join Date: Mar 2008	Reminder: Half the conductivity = twice the temperature required to get you to "pull my finger"

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