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-   -   LM4780 insulators? (https://www.diyaudio.com/forums/chip-amps/91558-lm4780-insulators.html)

BrianDonegan 5th December 2006 11:55 AM

Cheaper, but not as good.

CarlosT 5th December 2006 12:20 PM

I'm sorry...not as good how? Both are kapton...right? Both are about the same size, thickness, etc.? Berquist has the je ne sais quoi of kaptoniness? :D

Expand...or retract...

BrianDonegan 5th December 2006 01:25 PM

Actually, I was thinking about the standard Wakefield pads, not the Kapton. However, the Bergquist pads do have better specs: higher thermal conductivity ( 1.3 vs 1.2) and lower thermal resistance* (0.24 vs 0.40).

http://www.wakefield.com/pdf/accessories.pdf

http://www.bergquistcompany.com/obje...PK10_0305E.pdf

Expanded ;)

* Note that the Wakefield datasheet does not list at which pressure this number is achieved, so we must assume it is at the recommended pressure of 350lb/in2. Bergquist achieves it's number at 200lb/in2. This would seem to indicate that less mounting pressure is required with the Bergquist pad.

CarlosT 5th December 2006 03:44 PM

Interesting...I'll have to look at that again. Short of a Kapton Shootout, it's hard to kow who's tweaking the numbers to make their stuff look good.

Related question...if you have a nekkid LM4780, besides the obvious kapton/sillyputty/mica pads, is there such a thing as a little bushing that goes inside the mounting tab hole to keep the screw threads from making contact?

chipco3434 5th December 2006 03:56 PM

Mouser has stuff...

http://www.mouser.com/catalog/628/1610.PDF

BrianDonegan 5th December 2006 04:56 PM

Quote:

Kapton Shootout
Yeah. If I had paid attention and realized you were talking about the Kapton stuff in the first place, I would not have even brought it up. I think either pad would do a fine job.

Quote:

there such a thing as a little bushing that goes inside the mounting tab hole to keep the screw threads from making contact?
You could use a shoulder washer as mentioned, but I have never used one with the 4780. I didn't think the metal was exposed to the hole, though. I should look again. I thik I just used 6-32 cap screws with washers.

head_spaz 13th December 2006 05:40 AM

Kapton Film - good deal on e-bay
 
Thanks for everyone's input.

This is what I ended up with.

Polymide Kapton MT Film 2 mil thick insulator
(Dupont 200MT). - Dirt cheap on e-bay


Item number: 180028543577
5.5"W x 72"L (that's six feet long !)
Buy it now price is : US $8.99
US Postal Service First Class Mail is : US $2.25
Shows Qty = 13 in stock.

For you bulk buyers, the same vendor has:
Item number: 180028544664
5.5"W x 144"L (that's 12 feet long)
Buy it now price is : US $16.49
US Postal Service First Class Mail is : US $3.00
Shows Qty = 8 in stock.

An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.


P.S. I'm not affiliated with this vendor, just thought I'd pass
the info to you'se guys. Is this a bargain or what??? :D

CarlosT 13th December 2006 11:54 AM

Interesting...that's significantly thinner than the Wakefield stuff so it should transfer heat nicely. I've heard that it's tough to cut. Let us know...

In the same vein of thought...has anyone considered making their own heatsink adhesive? The two-part epoxy stuff is awful expensive and comes in Lilliputian quantities with dubious shelf lives.

I was thinking about taking some regular silicone sealant and mixing in metal powder for conductivity.

BrianDonegan 13th December 2006 01:35 PM

Adding metal powder will make it electricly conductive as well, so be cautious of shorts.

CarlosT 13th December 2006 03:37 PM

So are there any thermally conductive silicone adhesives available to mere mortals...like at the Home Depot or something? Are we relegated to boutique adhesives at $35 per 1/2 ounce?


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