Estimating heatsink thermal resistance

[firestorm]

I'm constantly collecting parts for varous projects that I'm interested in. As you might have guessed, I'm interested in music and its reproduction. I like to try my hand at building a decent amplifier, something that'll perform above and beyond a Marantz PM17 I'm using.

I salvaged a couple of large heatsinks amongst other things from a ups, about the size of a small fridge, the single width type that fits below kitchen work/counter tops. It was designed to used with fan cooling and probably could dissipate hundreds of watts easily. There are 27 power transistors mounted on it !

I'd like your opinions on whether they're capable of dissipating about 150W heat with a temperature rise of no more than 40 degrees in free air. I'd like to avoid using a fan.




Full size ones here
http://yfrog.com/b9p1140959j
http://yfrog.com/jtp1140960j
http://yfrog.com/79p1140954j
http://yfrog.com/74p1140955j
http://yfrog.com/jtp1140956j
http://yfrog.com/79p1140957j




Thanks
fs

[firestorm]

It must be the some what dry title, does it help if I chose to use something like "Super size me heatsink for Class A Monster Amp"?

[ostripper]

Originally Posted by firestorm

It must be the some what dry title, does it help if I chose to use something like "Super size me heatsink for Class A Monster Amp"?

Yeah , perceived value is acknowledged even in the choice of thread title.

Those units look about as big as 2 of the 8 heatsinks on my genesis chassis. I am using no fan with a 225w amp on just those 2 and never even get close to 40c under normal conditions (25c ambient). I have no AC , and ambient is close to 37c (97F) today , but the heatsinks are only just at 40C.

OS

[firestorm]

Hi OS,
thanks for the input, I was feeling a little left out ;-)

I need to work on americanizing the title I use

I'm considering building the DC Moskido, Aikido tube front end with class A pp mosfet power section. I've got two of these sinks, so I should be ok, theres around 150W x 2 to get rid of, depending on what bias current I choose.

Cheers
fs

[ostripper]

Originally Posted by firestorm

Hi OS,
thanks for the input, I was feeling a little left out ;-)

I need to work on americanizing the title I use

I'm considering building the DC Moskido, Aikido tube front end with class A pp mosfet power section. I've got two of these sinks, so I should be ok, theres around 150W x 2 to get rid of, depending on what bias current I choose.

Cheers
fs

My heatsinks were originally for a class A amp. The one I fixed got HOT (50c+), so think your sinks could dissipate 400w + but you would (could) get over 40c with a class A setup ( I use class AB ). It looks like you have what is known as "OVERKILL". Which is VERY nice .. BTW
OS

[firestorm]

Great, now the small matter of which amp to build now !
I'm considering :
1) Moskido (Aikido tube driver, pp class a mosfet power section)
2) JLH 96 (BJT pp class a)
3) ??

The JLH is a simpler implementation due to just the single bipolar psu. The Moskido needs a HV psu for the tube driver, although it is possible to use low voltage tubes and 24v B+.

I might just start a new thread, as the title is just too boring :=)

Thanks for your help OS