Heat Sink Question

cstmar01

I've noticed that on certain amps that the heat sinks will turn a purple color after usage. Normally will be the class A amps seeing I know they run hotter and thus could lead to the discoloration if I'm on the right path.

For example. http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1304391341&/Pass-Labs-X-350-


however other models of the same type don't do this.
http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1302901706&/Pass-Labs-X350-

I would figure its due to the usage of the amp. So would one be wiser to pursue something without the purple as it seems that it would have been used more compared to the others. Or ask for lower pricing as they have been used more?

Also would it ever be worth swaping them out for new ones? So say would it help resale value?

Just was wondering what some peoples impressions are on this.

steveinaz

Probably just the way different anodizing methods work, and how they are affected by heat. I now this is somewhat unrelated---but you'll notice older blued Ruger revolvers look "plum" in color, probably for the same reasons. The plum ones are highly sought after in the gun world.

disneyjoe7

I don't think an amp gets that hot to change a metal color, like an engine exhaust or gun being fired.

heiney9

disneyjoe7 wrote: »

I don't think an amp gets that hot to change a metal color, like an engine exhaust or gun being fired.

Actually it does become discolored because of heat. It's anodized aluminium in most cases. My Aleph, I can't put my hands on the sinks for more than 10 seconds without quite a bit of discomfort.

Chris, it's nothing to worry about as it doesn't indicate anything is wrong. It's mostly due to age and the variations Steve mentions.

I've seen this on some Adcoms (slight) and it can be more pronounced on some of the earlier Pass Labs Aleph's that used the cube for a chassis. Those were machined from a solid block of alum. and sometimes the fins become discolored.

The conventional chassis used on the later Aleph 30 and 60 are the same as the current First Watt chassis and this is not an issue.

H9

disneyjoe7

Come on no way is that amp have purple heat sinks because it got hot. It was made that way. I could see the heat sink change cooler right by the transistor, but not the whole thing.

heiney9

Anodized alum can change color with heat, it does......look at the photo. Ask any amp designer that runs a full class A output.........they'll tell you the same thing. It doesn't happen everytime, but I would guess it's based on variation in materials.

Look at older Krells or Levinsons or Nakamichis, anything run with the semi-conductors heavily or completely in class A you'll see discoloration? Believe me they didn't come that way.

H9

heiney9

Get a piece of anozided alum...............heat up to 160*F for several years, be sure to cycle off and on several hundred to thousand times and see what happens.........it will most likely turn different shades of eggplant in color.

H9

FTGV

As mentioned its the heat cycling and variations in the anodizing.I've seen them turn purlpe , green and blue-ish.

disneyjoe7

But everywhere on the heat sink would be the same color?

I'm confused I was an electronic tech which fixed amps, and if I seen a heat sink like that and I would think the transistor heated it to do that. I would think the transistor would be ashed up done, maybe everything would be gone also.

Before I got a meter in my hands to checked stuff....

heiney9

disneyjoe7 wrote: »

But everywhere on the heat sink would be the same color?

I'm confused I was an electronic tech which fixed amps, and if I seen a heat sink like that and I would think the transistor heated it to do that. I would think the transistor would be ashed up done, maybe everything would be gone also.

Before I got a meter in my hands to checked stuff....

You can run Mosfets very hot without failure or ashing.

H9

steveinaz

I can't keep my hand on the top of my HCA but for about 10 seconds after she's warmed up--that sucka gets HOT.

heiney9

Mosfets have around 300* F chip tempurature ratings. Most manufacturers run them at a fraction of that temp. But you can see if they are run at approx 25% of the max chip temp rating and you have 6-8-10 or more on a heat sink the temps get right up there.

H9

heiney9

I'll use the Aleph 30 as an example since I have those numbers handy.

6 mosfet output devices per side with on chip temp between 75-125 w/max 180*F for each mosfet. Anything over about 180*F thermal cut off happens. Again that's for each chip not all them combined. Even with very large, heavy, ventilated heatsinks that's a lot of heat. Hence the reason one can see discoloring over time.

disneyjoe7

Anyone got pictures of a heat sink that changed colors around the output part?

heiney9

What else would attribute the discoloration to disneySteve? Why is it that the ones I've seen in photos are always class A or heavily biased class A amps? Forte and Threshold are others that one can see discoloration on sometimes.

H9

disneyjoe7

cstmar01 wrote: »

For example. http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1304391341&/Pass-Labs-X-350-

Ok so how did this amp do that? So the heat sink is the same color everywhere? I don't believe it, it was built that way.

heiney9

Steve, they don't build them that way!

I guess we will have to agree to disagree.

cstmar01

Thanks for the information.

My biggest concern was that it was run harder and thus, possibly might have a problem sooner down the road vs ones without the discoloration.

And they do not come in purple. You will notice the heat sinks also will change on Krells, BAT, and other amps that are class A or have a bias into class A etc.

I just remember an ad for a BAT VK-500 were the guy was commanding a higher price because his was not discolored and thus "a better model" because it was used less. Didn't know if that was really true, and thought he was way too high for the price.

steveinaz

Who knows what actually causes it, but some anodizing does go "purple" nonetheless. It's not that uncommon, bottom line. I believe heat plays a major role, but I'm sure that depends on the method of anodizing as well. Some anodizing completely disappears in the prescence of sunlight over time. I have a black anodized address thingy on the front of my house, it has been silver for 5 of the 6 years it's hung there---the anodizing is GONE.

WilliamM2

disneyjoe7 wrote: »

Ok so how did this amp do that? So the heat sink is the same color everywhere? I don't believe it, it was built that way.

I've had black anodized parts on my motorcycles turn that color. Parts that don't heat up all, nice and even too, just like those heat sinks. I always figured it was just a poor quality anodizing job, that didn't age well. I've also had red parts turn orange or pink, no heat at all, just age.

FTGV

disneyjoe7 wrote: »

Ok so how did this amp do that? So the heat sink is the same color everywhere? I don't believe it, it was built that way.

A properly designed heat sink will have heat distributed fairly evenly across it's surface area o thus colour change should be evenly distributed.The culprit is the quality of the anodizing with some being more affected by heat than others.I have seen some vintage Brystons (of the same era) with completely different hues.