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 Post subject: Potting Tar
PostPosted: Jan Sun 23, 2011 7:48 pm 
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Location: Waukegan, IL
What ype of tar does one use to pot components? In this insatance, when the enclosure is mounted, the electonics will be upside down, and there are a couple of heavy choke coils in there. So, I figured ta will be the best way to hold them in. And I want it to be easy to remove in the future. I did save the old tar, but can't find the can i put it in. long gone I bet.

Can you use some type of roof cement?

Tony

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 Post subject:
PostPosted: Jan Sun 23, 2011 8:00 pm 
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Location: Pocasset, Cape Cod, MA
Roofing tar would probably work, the stuff that's melted in kettles and mopped on hot. But even that will flow a little at summertime temperatures (and I don't know where you'd get it anyway).

I would omit the potting. The parts will run cooler, and hot tar is somewhat dangerous, both for the obvious reasons (fire and burns) but also because it contains a lot of nasty chemicals that you really don't want to breathe.


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 Post subject:
PostPosted: Jan Sun 23, 2011 8:05 pm 
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Google search words: "Asphalt Potting compound"

http://www.solarcompounds.com/products/epec.asp

Look to the bottom of the page.

Chas

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 Post subject:
PostPosted: Jan Sun 23, 2011 8:10 pm 
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I would use wax, Maybe 80% paraffin and 20% beeswax.

http://www.caryaudio.com/articles/Potting.html

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 Post subject:
PostPosted: Jan Mon 24, 2011 3:17 am 
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In this application thee components need to be secured because the components are suspended upside down once the enclosure is mounted in the chassis. So, either wax or tar. no epoxy because I want to get in there next time it needs repair.

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 Post subject:
PostPosted: Jan Mon 24, 2011 12:44 pm 
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Location: Pocasset, Cape Cod, MA
A bowed length of steel strip would hold the cores in.


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 Post subject:
PostPosted: Jan Mon 24, 2011 2:10 pm 
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Location: Sandwich, IL, USA
Yes Brian, but what exactly is that "special high temp wax material" that Cary has discovered???? There are machineable waxes and waxes used in lost wax casting that are harder and better at holding their shape at elevated temperatures than paraffin and bees wax.
Denny Graham
Sandwich, IL


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 Post subject:
PostPosted: Jan Mon 24, 2011 7:45 pm 
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Location: Santa Rosa, CA
How about a few dabs of hot glue?

Machineable wax is very expensive.

I wouldn't use tar. It may be fine for roofs, but who knows what additives may be in there that might degrade electronic components.

The best choice is solvent-cured silicone gel. That's what's used in commercial electronic modules. It's expensive and hard to find in small qty. Don't use bathtub or aquarium caulking.

Rich


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 Post subject:
PostPosted: Jan Mon 24, 2011 11:32 pm 
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Location: Nashville TN
There is roofing caulk that might work or even jb weld or gorrilla glue?Just a dab might do it..Roofing caulk you have to get at a roofing supply store ,cant buy it at Loews or Home Depot..Sprman 8)

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 Post subject:
PostPosted: Jan Wed 26, 2011 5:35 am 
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Location: Louisville, Ky.
I have occasionally used the black asphalt-like compound salvaged from scrap neon sign transformers. You can peel the sides off of the transformer with a hammer and chisel and pry out the asphalt, or just heat the can with a torch or on a hotplate until the compound softens enough to remove the coils & core. Best to do this outside since it may get a bit smelly. Or you could likely buy a small amount from a roofer that installs or repairs hot asphalt roofs.

Mike


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 Post subject:
PostPosted: Jan Wed 26, 2011 7:44 am 
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Location: Burbank, CA and Thailand
I would avoid caulks, glues, etc. And remember that silicon products can corrode wiring and electrical parts.

The good stuff is encapsulation compound, which is similar to epoxy. There is a plunger that combines and dispenses the resin and hardener from separate reservoirs, and it sets in a few hours.

I use Loctite E-60NC. Here's one link, but it's available from many sellers. http://www.ellsworth.com/display/produc ... =935&Tab=V

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 Post subject:
PostPosted: Jan Thu 27, 2011 7:43 am 
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Location: Waukegan, IL
we should only suggest items which can be reversible. Wax and tar are easy to remopve in the future. Just heat. I doubt any modern adhesive will be revesible. A small amount of sillicone can be peeled away or even heated and scraped, but I'm sure a large glop of silicone will not be easy.

Remember, we should use things that can be reversed, for future repairs, and sometimes, the oiginal ways are what will work again.

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 Post subject:
PostPosted: Feb Wed 02, 2011 5:35 pm 
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Location: E. Stroudsburg, PA
Hi Guys...my first post here. I found your forum while looking for info on an old Philco VTVM and since I am the owner of a couple of Hallicrafters Ham receivers and a Johnson transmitter, I spent a couple of hours looking through the forums.

I've some experience with potting material, having rebuilt the CDI ignitions on several Kawasaki H series motorcycles. First off, DO NOT heat the housings to remove the old potting compound inside your home or garage!!!! It will take several days for the smell to dissipate, and the odor of hot potting compound makes a ticked off skunk smell like a bunch of flowers. Don't even do it on the back deck if the sliding glass door is open. Took 4 of the longest days of my life to get the stench out of my house and though not intentional, it got my ex-girlfiend (correct spelling) to finally gather her stuff and move out.

There are replacement 2 part "potting" compounds that are available at electronics stores, but they are very expensive and are nothing more than 2 part epoxy. I found that cheap latex caulk works well to hold the rebuilt circuit in the metal can. It won't work for a true restoration if someone is going to go looking that far, but it's a functional replacement. Just give it several days to dry completely before powering up the circuit.

Jeff


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 Post subject:
PostPosted: Feb Fri 04, 2011 2:30 pm 
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Location: St. Louis, MO, USA
Awhile back, I did something similar to what Trainman suggested. I melted parafin into an AK-40 power supply in place of the tar and then applied a thin coat of black RTV on top of it to retain the black tar look. This should make future servicing easy.

- Dennis


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