[Don_S]

I love the smell of melted rubber in the morning.   

[srb]

I love the smell of melted rubber in the morning.

That's why I mentioned that it probably wasn't a good idea for Class A amps!  The melting point of neoprene seems to be around 250 degrees F.
 
Of course, if your heatsink temperature is 200 degrees + F, you have a thermal situation with your amplifier that should be addressed.  Still, silicone rubber would be a better choice, as it usually has a high temperature limit of 500 degrees + F.  Silicone rubber tubing, slit on one side, would eliminate any worries.
 
http://www.amazon.com/Silicone-Rubber-Tubing-Thickness-Length/dp/B000FP0IV6/ref=sr_1_1?ie=UTF8&s=industrial&qid=1269296584&sr=1-1
 
Steve

[jules]

If you put those rubber strips on each heatsink fin, you'll significantly reduce the effectiveness of the heatsink.

I agree with Nagys on this one. The tip of a fin is critical for radiant heat loss. The base part of fins in a sink can only radiate into the fins beside them while the tips of the fins radiate into free space. Air is not needed for radiation of heat. The inner section of the heat sink fins rely on air and convection. Both are important.

jules 

[gerald porzio]

"Ringing bad but greatly reducing the effeciency of the sinks is fine."

It has not been established that this ringing is audible thru the spkrs. This is a dubious cure for a nonexistant issue.

[satfrat]

No problem.  I try to be helpful when I can.  There are 3 posts by an AC member in this thread that say "You are ignoring this user.  Show me the post."  I didn't click on the links, as I am 99.9% sure they would be non-constructive.
 
Steve

Yeah,,, me too Steve. Works pretty damn good, doesn't it?   
 
Cheers,
Robin

[srb]

The tip of a fin is critical for radiant heat loss. The base part of fins in a sink can only radiate into the fins beside them while the tips of the fins radiate into free space. Air is not needed for radiation of heat.

The tip of a fin is NOT critical for radiant heat loss.  Amplifier designers and manufacturers select heatsinks based on square inches of fin area as well as mass.  The surface area of the edge of the fin is minute.  If the edge of the fin was so critical, heatsink fins would only be 1/4" deep.
 
Steve

[jules]

I respectfully disagree.

The depth is there for convective heat loss but as I said above, the tip is vital for radiation. Heat radiated from the inner fins, for the most part will hit a fin opposite [same temperature thus no significance] hence radiation only happens towards the tips.

jules

[NagysAudio]

This discussion can be easily solved by BobM. Put the rubbers on each fin and measure the temp of the transistors. Then do it without the rubbers. I'm willing to bet there will be quite a difference. Maybe you should just put the rubbers on every other fin?

What amp is it? Where are the heatsinks located? You can try putting a metal cone under the heatsink. But usually, it's much more important if you drain the vibrations from one point in the amplifier, usually the middle, near the power transformers.

Try this... Use 2 rubber feet in the front and a metal cone in the middle, a little closer to the back from the center. That should make a much bigger improvement than rubber on heatsinks.

[jules]

Steve,

for the most part I think we're on the same track and the term "radiate" is probably the matter of difference. I quite agree that convective heat loss is the most important issue here though the radiant loss at the tip of a fin is going to be more significant than it  might appear to be. Of course it's also true that the back of a heat sink radiates into the amp case [most of the time] and while that's not ideal, it can be compensated for by the convective heat loss outside the case.

There's a factor that might not have been considered. If you use a strip material like the one shown earlier in this thread and it's maybe 1/4" wide, it will reduce the gap at the open end of the fins down to near nothing [or it might not even fit]. This would only allow air to enter the fins from the bottom and would undoubtedly reduce convective cooling massively.
jules

ps wrote this while you were posting Nagys

[sts9fan]

You could also just put a little sticky rubber foot on each one.

[BobM]

My amp (McCormack DNA 500) runs exceptionally cool. It wouldn't even melt a Hershey's kiss if I left it on top of the heatsink. I also would only use a small piece on each fin, say 1/2" to 1". Just enough to reduce ringing. I would also propose to vary the location from fin to fin to (theoretically) change the resonant frequency of each fin so there is little uniformity from one to the other.  (~~~~~)

Will this make a difference? Damned if I know, but I doubt if it will hurt in my case, and I like these kind of experiments that don't cost much and promote a theoretical engineering discussion. A lot of stuff comes out that otherwise may not be thought of. Then the actual physical experiment takes place and I make a subjective opinion on the sound (better, worse or no change) where everyone bashes me for not following their science. 

Should this be done to an amp that runs hot? Absolutely not. At best I would suggest putting a small dab of silicon caulk on each fin in that case. I did that with my old amp and it worked wonderfully. The fins don't ring, but it is not an easy experiment to reverse and see what the true effect (positive, negative or neitral) was. That's why I'm looking for a reversable solution this time. The silicon caulk is removable after it hardens but it also could leave a stain. Your call on that one.

Steve, I went to my local Ace last night and couldn't find the product. I may hit a different store tonight. I need about 8' of this to cover the 40 fins per side. My fins measure 1/8" wide at the end using my calipers. How stiff or flexible is the material? I want it to fit snugly, so I'm guessing the 1/16" wide gap is probably better than the 1/8" wide gap, but it depends on the stiffness of the material.

Thanks for the interesting discussion guys.

[rollo]

 Bob WAY to much time on your hands. If you tap the heatsink does it ring through the speakers ?
 Nagy suggestion of the rubber and cone placement yields VG results.


charles

[BobM]

That would provide support for the bottom chassis, but does nothing for the cover (where some Isodamp or something similar could be used on the inside or a weight of some sort put on top) or the heatsinks (where I am looking for a solution to test out).

My amp does have 5 feet on the bottom, in the pattern described. My old amp actually had a spike in the center position - the new one has a footer, which makes more consistent sense to me than the spike (aka mixing metaphors so to speak).

[satfrat]

Bob, is it possible for you to just fit the heatsink with a heat resistant O-Ring? O-Rings are used on tubes as vibration fighters, why not heat sinks? 
 
Cheers,
Robin

[BobM]

I'd need 80 of them. Not cost effective.

[gerald porzio]

All this analysis & angst, w/o a hint of audibility thru the spkrs. This seems like the classic case of having nothing to do & all day long to do it.

[BobM]

Gerald, if you don't have anything positive to contribute then please go haunt someone else's thread.

[satfrat]

Gerald, if you don't have anything positive to contribute then please go haunt someone else's thread.

Here you go Bob, this works just fine for me regarding continuing nonconstructive posts. It's a wellknown given by most that you won't be missing a thing in this case. 
 
Cheers,
Robin
 

[BobM]

Well it's good to know that you haven't blocked me yet Robin 

[satfrat]

Well it's good to know that you haven't blocked me yet Robin 

Just 1 person to date and it ain't you Bobby-boy.