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Re: [TowerTalk] Silver Solder

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Silver Solder
From: Jim Lux <jimlux@earthlink.net>
Date: Fri, 07 Aug 2015 09:51:28 -0700
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On 8/7/15 9:24 AM, mike stokes wrote:
Hello

I need to improve my radials and lightning protection.  What Silver Solder
is best for the job and where is a good place to purchase it ?


I'm not sure silver solder (called silver brazing these days) would be appropriate for lightning protection. It's certainly not what the code requires for grounding (approved clamps or exothermic welds), although I think it's a reasonably workable solution.

For RF purposes (e.g. your ground radials), though, silver brazing isn't a bad idea. It's rugged, it's easy (assuming you have the right equipment).

I doubt that the specific alloy makes a lot of difference. What you're really looking for is that the melting point is higher than that of tin/lead, and that it's mechanically more rugged. I've used a variety of "hard solders" from the local hardware store. Typically, they are around half silver (price varies with silver content). Pretty much anything will work with copper/brass (if you're brazing steel, you need to be a bit more careful in material selection). A typical alloy is something like Silvaloy 355 which is about half silver, 1/5th copper, and the rest zinc and tin. No cadmium. At least that's what I found out in the garage that still has a label on it.. I'm not a pro welder, with ovens to keep my rods dry, records of material certs, etc.. Others on this list ARE much more knowledgeable and may have some recommendations on the best alloys.

As with all "melt metal to stick metal together" things, the right flux and the right heat source is probably more important than the actual metal you're melting.

I use the solid white paste flux, and I've used both a oxy-mapp rig (one of the ones with the two "propane torch" sized bottles) and a oxy-acetylene rig (with a fine tip on the torch). Either works. The bigger rig (with big bottles, either oxy mapp or oxy acetylene) is nicer because you don't worry about running out of gas. If you could borrow or rent the rig, life is easy.

Silver solder alloys melt around 1000F (compare tin-lead at <400F), but lower than bronze brazing rod (typically >1500F). Note that 1000F is "red heat"

I'd say that in a few hours, if you've got experience soldering (especially if you've done plumbing) you can crank out perfectly serviceable electrically and mechanically brazed joints. They may not be pretty, they may not be something you'd trust your life to for mechanical reasons, but they'll work fine.

I find brazing, in general, MUCH easier than doing good plumbing fittings with soft solder and a propane torch, and MUCH easier than real fusion welding.

With real welding, you have to worry a lot about the metal you're welding, and getting the temperature right, and getting just the right penetration (whether gas or arc), and it's a lot hotter. With soft solder and plumbing, there's a real art to getting the right flux, and the right temperature on the whole joint (not too cold, not too hot) so that you get a nice even solder layer with no pinholes and no globs. And with plumbing there's always the whole "wet pipe" and "don't light the wall on fire" thing.

A small oxy-gas torch has a nice small hot flame that's easily adjustable and not too bright, and there's a big temperature range over which a good joint can be made (iron and steel melt at >2500F, copper melts at 2000F, the brazing filler melts 1000F less, so lots of room between), and the overall lower temperature means you don't need as much eye protection, so you can *see* what's going on.

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