Mica and Goop

[EUVL]

Kapton has a thermal conductivity of 0.37W/m/K.
You can compare that with the values in Post #51.

Patrick

 

[powerbecker]

Patrik:
"Kapton has a thermal conductivity of 0.37W/m/K."

I found here

http://www2.dupont.com/Kapton/en_US/index.html

only 0.12W/m/K

Heinz!

 

[EUVL]

There are Kapton & there are Kapton.
Kapton MT, which is a thermally conductive variant, has 0.37W/m/K.

http://www.dupont.com/kapton/products/H-38497-1.html

In any case 30x worse than Kerafol. But of course one can compensate by using 30 times thinner foils, in this case it would be 3 microns ! Just need to make sure heatsink and transistor are also better than 0.1 microns flat, and do not deform under temperature. Minor details, shall we say.....

: )


Patrick

 

[meanman1964]

By Thel-Audio they use the kapton isulators for their projects,that's whij I think you can use them.Or am I wrong?

 

[EUVL]

There are people (amateurs as well as professionals) who use mica, silpad, kapton, aluminium oxide, ........ As long as you know how to calculate, and you are happy that the lifetime of the transistor is not compromised, you can use what you want; just like some people use large heatsinks, some use forced convection, some water cooling ..... The choice is all yours.

The world is a wonderful place because of all these varieties. I merely tried to draw your attention to another. The only recommendation I would make is to understand the physics behind (no rocket science), and then choose the solution for yourself, be it large heatsinks, exotic insulations, ......

And if I am not wrong, Thel's power amps are class AB. So he doesn't have too much dissipation to worry about.


Patrick

 

[john_ellis]

Hi all
I've just installed boron-nitride washers on my latest 100 Watter - and so far the transistors (TO-3) run pretty cool.

Previously I've used mica and grease, and silicon never seemed to be quite as good. Mica+grease is typically rated at 0.4 C/W, silicone washers are supposed to be the same but seem to be not quite so good (but I have not actually measured them).

Stated performance of the boron nitride loaded silicones are 0.2 C/W. I'd say that they are performing better than the mica; but as Nelson P said, they can split and only seem to work once.

But they also cost half the price of the transistor!

cheers
John

 

[Stocker]

Minor details, shall we say.....
Patrick

haha, minor! 1 micron small, minor! Funny!

There are people (amateurs as well as professionals) who use mica, silpad, kapton, aluminium oxide, ........ As long as you know how to calculate, and you are happy that the lifetime of the transistor is not compromised, you can use what you want; just like some people use large heatsinks, some use forced convection, some water cooling ..... The choice is all yours.
Patrick

Well said.

If we could all agree that the other fellow's solutions were (maybe almost) as good as our own and at least good enough, there would be much shorter and less interesting threads.

 

[meanman1964]

I'am planning to build the Aleph30,so what should I use for isulator?

 

[EUVL]

This might be a good starting point for you :

http://sound.westhost.com/heatsinks.htm


Patrick

 

[EUVL]

http://www.diyaudio.com/forums/showthread.php?postid=1032023#post1032023

For those living on the Continent, Keratherm is now available from www.conrad.de.

E.g. Part no. 189058-29 Keratherm 86/82 190x190x0.25mm
Thermal conductivity 6.5W/mK


Patrick


Disclaimer : I have absolutely no business dealing nor financial interest with the company who produces the stuff !!

 

[nonoise]

Another good grease Laird (use to be Thermagon) T-grease 880
3.1W/mK

Another interesting material is graphite T-gon 800

Also a often overlooked parameter is the optimal pressure on the thermal interface

 

[awpagan]

How does this compare
http://www.techbuy.com.au/p/32574/COOLING_THERMAL_COMPOUNDS/Arctic_Silver/AS-CMQ-22G.asp

I have it on a class A amp at present.
The ceramique version is non conductive.

allan
ps the output devices havn't blown up yet

 

[anatech]

Hi All,
Well, all I can say is that mica and thermal compound are consistent performers. The other types are normally used to increase manufacturing efficiency. I am not a fan of alternative insulators. They have "gottchas" it seems. I have seen many fail in service.

Last point. Watch out for conductive grease! Graphite and other electrically conductive compounds should be avoided. Why tempt fate?

-Chris

 

[awpagan]

Good point Chris.
I do use mica and the goop together

Any kind of goop just by itself, i couldn't trust, or trust myself to correctly apply it.

allan

 

[anatech]

Hi Allan,
The best device I have found so far to apply thermal compound is a #2 artists brush, flat about 1/2" wide. Go to the nearest art supply store. I've worn out two so far and cracked one.

-Chris

 

[Nelson Pass]

Around here we call it Beauty Cream

I just dip my fingers in the jar and smear it on. I personally
don't find the pre-applied micas to have a generous enough
amount, although it's true that I have to leave my output stages
horizontal for a few days or it drips.

 

[anatech]

Hi Nelson,

I just dip my fingers in the jar and smear it on.

LOL!
I won't let my guys do that. You know grease travels and makes a mess. Also, I don't want the stuff contaminated (8 oz jar). The artists brush naturally leans towards a thin coat that just beads around the insulator when it's torqued down. Just right.

So Nelson, what do you use to get it out from under your finger nails?

-Chris

 

[GRollins]

Gojo

Grey

 

[anatech]

Hi Grey,

Gojo

-Chris

 

[GRollins]

Every so often I do a search on my own name just to see if I missed a question directed at me. This is one such time. I'm a bit late answering, but better late than never.
Gojo is a creamy waterless hand cleaner that will remove virtually anything from your hands. No, it's not harsh. In fact, I believe it has lanolin in it. It's readily available here in the US, but perhaps not elsewhere in the world.

Grey