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Author Topic: Brass Taps for Copper Link Coil - Galvanic Hardware  (Read 11758 times)
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aa5wg
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« on: November 11, 2011, 11:21:33 PM »

Hi to Everyone:

I am getting ready to build some brass taps for my home brew link/tank coil.  The taps are made of two parts that pinch/hold the copper tube.  

Do you think the following hardware will work, that is, not corrode vs the Galvanic differences of materials.
(1) tap is 360 brass
(2) flat washer is brass
(3) lock washer is bronze
(4) screw is 316 stainless steel

Galvanic chart states values of these materials as follows: http://www.dataweek.co.za/News.ASPx?pklNewsID=14930&pklIssueID=422&pklIssueTypeID=5&LIU=15

Brass/Bronzes = .40
High Brass/bronze = .45
Stainless steel from the 18% chromium type, i.e. 316 stainless = .50

Chuck
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KA2DZT
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« Reply #1 on: November 11, 2011, 11:49:43 PM »

I think you'll be OK with the hardware you're using.  I think most builders don't get things that close as far as the galvanic differences.

Stainless and aluminum don't mix too well but are used together on antennas with success.

Fred
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aa5wg
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« Reply #2 on: November 12, 2011, 06:37:43 AM »

Fred:
These taps are taking a bit of time to make.  There is a lot of talent on this site
and I wanted double check the hardware.

Thank you.
Chuck
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KA2DZT
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« Reply #3 on: November 12, 2011, 10:32:32 AM »

Chuck,

Another thing I just thought of is that brass ground clamps are used on copper pipe all the time.  Doesn't seem to have any problems or they wouldn't use brass.  Copper and aluminum are joint together, but there you need to use a compound called Penetrox.

Fred
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KL7OF
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« Reply #4 on: November 12, 2011, 11:19:12 AM »

It will work just fine..Don't overthink this one.....Good Luck.
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aa5wg
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« Reply #5 on: November 12, 2011, 12:44:06 PM »

Fred, KL7OF and all:
I will give this hardware a try.  Thanks for the help.
Chuck
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k4kyv
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Don
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« Reply #6 on: November 12, 2011, 01:13:02 PM »

Two metals that don't work well together are copper and zinc.  This includes zinc-plated or galvanised towers and ground rods.  Brass clamps make a satisfactory intermediary between those two metals, allowing copper wire to be attached to zinc-coated metals.

Besides dissimilar metals, it takes two other substances to produce galvanic action: water and some form of salt or minerals.  Chances are, the coil and taps will be kept in a dry place, although humidity and air pollution can be a cause when the unit is left outside, such as the case of a remote antenna tuner located outdoors even in a protected but unheated enclosure.

I'm not sure what material commercial coil clips like the ones produced by EF Johnsons are made of, whether brass or some alloy closer to pure copper.  They seem more springy than pure soft copper and appear to be nickel plated. I wish I could find some of that stock metal to homebrew some more of those clips.  I did homebrew some years ago for my 160m tuner at the base of the tower; they work fine as long as they are left undisturbed, but the soft copper doesn't have the holding power of the springy stuff, and they don't work as well when moving taps around to initially set. Commercially made clips are getting harder and harder to find.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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aa5wg
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« Reply #7 on: November 12, 2011, 03:21:52 PM »

Don and all:

Some of the historical commercial coil clips are hard to find.  However, I did see some expensive coil clips that were solid brass with stainless steel screws. They were very nice clips.

I have some clips that are springy and seem alright for small wire.  There was one ham, on the net, who built his link coupler and the taps he used were over heating with 500 watts.  Don't recall what mode or band he was working.  He had to make a change in his clip design.

It is a lot of work to build these and I don't want a heat issue.  A copper clip is to hard for me to machine.  The stuff is too gummy.
Don, sounds like your new feed line is going to work real good.

Chuck

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W0BTU
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« Reply #8 on: November 12, 2011, 04:54:58 PM »

Besides dissimilar metals, it takes two other substances to produce galvanic action: water and some form of salt or minerals.

Precisely. That's why, if we use a grease like DeoxIT or silicone dielectric compound between copper/aluminum or copper/zinc junctions, those connections can remain reliable for years, even outdoors. The grease keeps the water out and helps prevent corrosion.

I sometimes connect ground radials made from zinc-plated steel electric fence wire to copper using a big wire nut filled with grease (outdoors). Done properly, it's almost as good as silver-soldering, and far easier.
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73 Mike 
www.w0btu.com
Bill, KD0HG
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« Reply #9 on: November 13, 2011, 01:09:26 PM »

Old buzzard coil brass tap clips are still being made. Kintronic Labs sells them.
Made for both tubing and flat strap inductors. Actually, the whole Kintronic catalog is pure QRO droolness. We ocassionally do business with them.

http://www.kintronic.com/products/productInfo.aspx/InductorClips/

Bill
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k4kyv
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Don
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« Reply #10 on: November 13, 2011, 01:30:12 PM »

But how do you find out exactly what products they stock?  All I see is a photo of a few clips made for tubular inductors, but no active links to specific lines of products.

I'm sure they would be priced the same as what you would expect to pay for ones made of solid gold, but I still might be interested in purchasing a few of the smaller size made for edge-wound flat strap inductors, if they sell in reasonably small quantities.

Quote
Inductor Clips
Manually positioned taps are available for all sizes of Kintronic manufactured high Q, RF inductors. 
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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This message was typed using the DVORAK keyboard layout.
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K5IIA
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« Reply #11 on: November 13, 2011, 01:31:13 PM »

Awesome link bill!
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73, Brandon K5iia
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« Reply #12 on: November 13, 2011, 01:35:59 PM »

Hey Don a friend of mine is a machinist. And deals with slot of brass. If you want any clips made of brass send me an email. His shop is at his house and smallstuff like that he enjoys doing. he does awesOme work.

My email is bspn33 at gmail
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Be kind, for everyone you meet is fighting a hard battle.

73, Brandon K5iia
k4kyv
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Don
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« Reply #13 on: November 13, 2011, 02:50:17 PM »

Thanks Brandon.  I may take you up on your offer.

I could make my own if I could get some stock metal without having to buy a large quantity just to get a few small pieces.  I'm not sure if the commercial clips are made of brass, or some kind of hard-drawn copper or copper alloy.  Whatever it is, it is springy, not limp like soft-drawn copper. I'd like to get hold of some of the same stuff EF Johnson used, although it doesn't necessarily have to be nickel plated.

I hate to solder directly to those nice edge-wound coils, especially if there is any likelihood I'll be moving the taps around in the future.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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This message was typed using the DVORAK keyboard layout.
http://www.mwbrooks.com/dvorak
K5UJ
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« Reply #14 on: November 13, 2011, 08:04:09 PM »

The problem with anything made today and sold brand new that is QRO AM broadcast grade stuff is that it costs a small fortune.  I priced Kintronic turns counters around 12 months ago--I think I called them up and talked to a guy there and they wanted enough to drive me back to searching fest flea markets for old Groth (like searching for the Holy Grail).  Lo and behold at the indy fest a guy had the pair of brass turns counters and panel out of a T368 for sale for $20.   

But clips.  This has nothing to do with coils but when I was throwing my latest L network for 160 m. together I wanted a fast easy way of adding and removing fixed value caps.  I did  not want to fool with a switch and since the tuner was gg to have no cover the better to reach in and fiddle with things, I figured straps with clips to a common connection point would be okay.  I wound up buying 25 silver plated copper knife switch clips from Surplus Sales for $10.  I soldered them on to narrow copper straps and use them in places where I want to make and break connections.  So far they work okay but they are too wide and fat to be used as coil taps.  The copper under the silver plate is very stiff springy alloy.   I broke a few getting the hang of working with them.

I uploaded a couple of photos of them in the L network tuner between a Johnson inductor and Cardwell cap.   The fixed caps are these Russian doorknobs, 470 pF 16 KV.  They seem to be okay for 300 w. on 160. 

rob


* Ltuner_upgrade7.jpg (1265.38 KB, 3648x2736 - viewed 851 times.)

* Ltuner_upgrade6.jpg (1147.31 KB, 3648x2736 - viewed 861 times.)
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"Not taking crap or giving it is a pretty good lifestyle."--Frank
KA2DZT
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« Reply #15 on: November 13, 2011, 08:12:53 PM »

Wondering if the contacts from ordinary AC outlets could be made to work on edge wound coils.

Anyone ever try this??

Fred
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aa5wg
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« Reply #16 on: November 14, 2011, 10:26:20 PM »

Kintronic Labs sells the edge wound taps.

I don't see them on their web page but a year or so ago they said they had them.

http://www.kintronic.com/

Chuck
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