Yep very nice.
Keratherm 86/82 thermal pads are very good (they are measurably better by a significant margin). I wouldn't use anything else except good old mica and goop assuming you already had that laying around.
Keratherm 86/82 thermal pads are very good (they are measurably better by a significant margin). I wouldn't use anything else except good old mica and goop assuming you already had that laying around.
I'm figuring out why I used the silicone to begin with. Mouser and Digikey don't have mica in the right size.
This isn't a problem worth $25 to fix at the moment. I'm not spending $25 at the grocery store to feed myself. I NEED money in a VERY urgent way for a number of things concerning my daughter and I just can't justify that. I'll roll back the bias or put the thing on a shelf.
you can always use TO3 mica
all you need is to punch hole and scissors to cut them around
tedious if you are mounting 40 outputs , but easy for 2 or 4
Back in 1990 I use to pay $30 for a single cd.
If you can afford it's worth it otherwise do what zen mod suggested.
Family comes first though.
One year we spent over $70,000 in therapy costs for my son. I'm still recovering from that. I just skip meals 😀.
Lately music has been my escape. I'm extremely thankful to be able to listen as well as I do and this amp is a big part of that. I appreciate the help and advice and all the contributors to this thread because I poured over it relentlessly as parts were showing up for this amp. The story with my daughter is crazy and complicated and I need to get a lot done in two states and I'm short on resources and, quite frankly, scared on so many fronts it's not funny. If anyone wants to know the story or pitch in to help an extremely promising young girl out, hit me up.
I'm throwing in the towel. I looked up the specs on the pads I'm assuming .27C-sq-in/watt is decent resistance. I'd assumed the hottest point on the case would have been fairly close to the junction temp. The math to figure this out is way over my head and I just don't have the patience for it lately.
Hi Kosst, I just had an idea looking at your picture. Those silicone pads are considerably thicker than mica, and more compressible. So the way you've got your transistors screwed in may be tilting them.
Two things you could try:
(1) Take the washers off the cap-head screws so you're not applying a tilting force. Just clamp down on the tab of the MOSFET with the screw itself.
(2) Switch to mica. It won't compress, so even the tilted washer will still clamp the MOSFET down flat. (You can get mica pads from Arrow for 50cent each. https://www.arrow.com/en/products/56-02-101g/aavid-thermalloy)
Don't give up!
Two things you could try:
(1) Take the washers off the cap-head screws so you're not applying a tilting force. Just clamp down on the tab of the MOSFET with the screw itself.
(2) Switch to mica. It won't compress, so even the tilted washer will still clamp the MOSFET down flat. (You can get mica pads from Arrow for 50cent each. https://www.arrow.com/en/products/56-02-101g/aavid-thermalloy)
Don't give up!
The pads are ceramic/silicone deals from Laird with a thermal resistance of .27, give or take for clamping force. They're .005" thick, not all that much thicker than the .0028 I'm seeing for most of the mica pads out there. I'm beginning to feel a bit skeptical about the measurements I'm taking.
It's not just the thickness but also the thermal resistance of the material.
I can't comment on what you have because there is quite a bit of variation in that regard. The generic silicone pads I have are absolutely crap compared with either keratherm or mica.
Like you said your measurements could be off too.
If you put your thumb on the mosfet how hot does it feel?
I can't comment on what you have because there is quite a bit of variation in that regard. The generic silicone pads I have are absolutely crap compared with either keratherm or mica.
Like you said your measurements could be off too.
If you put your thumb on the mosfet how hot does it feel?
This is all >10 years old :
http://www.diyaudio.com/forums/pass-labs/37262-mica-goop-2.html#post1032023
https://linearaudio.net/sites/linearaudio.net/files/v3 euvl.pdf
(See table 1 of the Linear Audio article.)
Patrick
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http://www.diyaudio.com/forums/pass-labs/37262-mica-goop-2.html#post1032023
https://linearaudio.net/sites/linearaudio.net/files/v3 euvl.pdf
(See table 1 of the Linear Audio article.)
Patrick
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It feels pretty freaking hot with 1.1 amp buzzing through it. I can lay my hands on 60C for as long as like. I know this because I've run the sinks up that high on this thing. I've had the thing idling for over an hour and I just stuck my fingers inside it. I can lay my finger right on the side of a MOSFET for about 10 seconds before it's too much. I'm going to guess that's about 64C, give or take, and that's about what it's measuring if I'm not looking for a hot spot. The sink immediately behind it is at 55C. If I hunt real good with the IR thermometer pretty close up I can find a 74C spot. I can't feel it because there's a thermister right there.
I glossed the article EUVL posted. Based on what I saw after pulling the pads the other night, there does appear to be uneven distribution of force, and the spec sheet for those pads makes it clear that their usefulness drops off sharply without some rather staggering kinds of pressure. I took 2 picoDumbs up on his offer for the mica so we'll give those a try.
Has anyone ever used peltiers to actively pull heat off a transistor around here?
I glossed the article EUVL posted. Based on what I saw after pulling the pads the other night, there does appear to be uneven distribution of force, and the spec sheet for those pads makes it clear that their usefulness drops off sharply without some rather staggering kinds of pressure. I took 2 picoDumbs up on his offer for the mica so we'll give those a try.
Has anyone ever used peltiers to actively pull heat off a transistor around here?
try using a water cooling kit from a pc, it's better and does not need big heat sinks.