Kapton and Copper Spreaders

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Kapton and Copper Spreaders

Postby Tom WA3KLR » Sun Nov 13, 2005 11:03 pm

Frank,

I read the QEX article on your amplifier. I really like the idea of the integral heatsink spreader/shunt capacitor. That will give you the best shunt capacitor - lowest ESR and series inductance possible. I can't imagine any better.

So where do I get the 0.003" Kapton material?

And where do I get the copper spreader material 1/8 to 1/4 inch thick?
Did you have them machined or are they standard stock?
Tom WA3KLR AMI #77
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Postby frank carcia » Mon Nov 14, 2005 12:27 pm

Tom,
Check ebay for kapton. I have a small stash but I know guys who have bought it. Copper I bought a slab of it and not cheap. Check scrap yards.
My next rig will have larger spreaders to eliminate the need for door knobs. Let me know if you can't find kapton. I can give you some. fc
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Postby Tom WA3KLR » Mon Nov 14, 2005 1:20 pm

Frank,

I just thought to try McMaster-Carr and MSC. I can get a 3 foot bar 3" wide X 1/4" thick from McMaster for $51.14 . It's silver-plated on one side too, cheaper than the non-silverplated. Same thing from MSC is 6 foot and $102.

As far as Kapton sheet, McMaster-Carr has 5 mil 12" X 12" sheet for $19.50 . No other specs on the exact Kapton material used.

I didn't see anything comparable at MSC. McMaster has a 2 mil sheet also.

I have never made a personal order from McMaster-Carr, but looks like I will be soon.

I calculated from your 3 mil spreader in the article that I would get all the shunt capacitance I need for my 160 meter design from a 3 x 5 spreader. With 5 mils, it will be bigger, but that is o.k. considering the capacitance/spreader size will need to be less on 75 and 40 meters.
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Postby frank carcia » Mon Nov 14, 2005 1:42 pm

Tom,
Remember there will be a number of holes with nylon inserts to reduce area. Check McMaster for the nylon inserts. Mine came from them.
Their SS hardware is also cheap. I have a friend into battle bots and he tells me every time he places an order. Addictive place though.

Copper prices way up during the summer I bought 1000 feet of 12-2
for $114 I'm ready for a second spool and new price is $211.
Man a house eats up wire when you have 40 breakers to play with.
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Postby frank carcia » Mon Nov 14, 2005 1:46 pm

Remember to lap each sheet of copper and the heat sink. Those little voide really kill the expected C. Wet sanding works best. I would use the 5 mil. 2 is just too easy to crush through. You have to be very careful with 3 mil. fc
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Postby WA2WVL » Sat Dec 24, 2005 10:04 pm

I am using 5 mil Kapton and I measure 60PF/ square inch

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Postby frank carcia » Sun Dec 25, 2005 9:19 pm

That sounds about right I think I was close to 100 pf for 3 mil.
Then you have to subtract all the hardware area and add drain- source C.
I used 3 by 4 inches on a side then added 2000 pf per side. I did it in 500 pf steps. The more I added the more power I could run. Then RDS on started making a dent into efficiency.
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