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Author Topic: Silver Pated Coils  (Read 5821 times)
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aa5wg
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« on: April 28, 2013, 08:10:59 PM »

Hi to all,

How thick is the silver plating (in microns) on the copper tubing coils in commercial amplifiers for AM Radio, FM Radio and Ham Radio?

Chuck
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W3RSW
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Rick & "Roosevelt"


« Reply #1 on: April 29, 2013, 01:25:33 PM »

Good question but taking the fact that Cu is just about as good a conductor as Ag and Ag2O at the frequencies we use, and the fact that a commercial manufacturer might plate the copper with just enough silver to be flashy, I'd guess that most manufacturer's thickness are pretty thin.

Don't rub 'em too hard.  Grin
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RICK  *W3RSW*
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« Reply #2 on: April 29, 2013, 02:24:54 PM »

To do any good, the plating would need to be substantial (heavy electroplating). Immersion silver plating is very, very thin but looks nice. It has little or no value as a skin effect conductor, especially at HF frequencies.


I use immersion silver to plate PC Board conductors because it makes soldering easy and is cheaper than buying liquid tin. A quart cost about $15 to make.


Pat
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W0BTU
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« Reply #3 on: April 29, 2013, 05:31:46 PM »

It has little or no value as a skin effect conductor, especially at HF frequencies.

This has been fairly well established over the years; silver plating does not really help much at HF when we plate bright shiny copper leads and coils with it. However, someone suggested (somewhere) recently that oxidized copper might cause a significant resistance at RF, since copper oxide is a semiconductor. So, what about the value of plating coils with silver (or maybe even tin) to reduce this "problem", if it actually exists?

I don't know the answer to this, but I do know that the copper between the 833C anodes and the pi-network is getting dark from oxidation. And eventually, it will turn completely black.
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73 Mike 
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K5UJ
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« Reply #4 on: April 29, 2013, 06:54:26 PM »

only case I can think of and it is not certain for HF, is you might want it on a roller inductor
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« Reply #5 on: April 30, 2013, 09:28:41 AM »

I have heard that tin plate reduces Q because of the high resistance. I have been told not to use tinned conductor for my LF coils because of reduced Q but again that was in the general lore and may not be proven. The same article indicated that copper stranded wire was better than solid wire and that it acted somewhat like litz wire. That to be seems a bit doubtful, but I can see no reason not to use copper stranded wire.

Pat
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W3RSW
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Rick & "Roosevelt"


« Reply #6 on: April 30, 2013, 09:30:00 AM »

Probably right. Wonder about solder coated boards; best to silver plate the traces or backplane at microwave freqs.

 But back to silver and copper:
 Where contact by another moving metal connector is required, especially when the contact is not sheltered such as a rotary inductor,  the siver is subject to wear in such an application on both the roller and the rollee, heh, heh.  So thick is good.

In a non outside contact copper application where the surface oxidizes over time, the conduction region will just be under the oxidized layer.  The skin effect will now be at lower effective radius in a coil and, of course, such will cause a lowering of inductance for that coil, all other things being equal.

In a non contact silver coated application over copper, then, the silver is just cosmetic but will prevent the oxidation of the underlying copper.  So take your pick. Black conductive silver oxide or green non-conductive cupric oxide with slightly less inductance over time in the case of a coil.

Both cases of non-contact applications can be shined up and preserved with high dielectric poly coatings or in the case of old brass telescopes a good lacquer finish.  Bond is important, because oxide creep is insidious.

I hope I've been adequately wordy. Grin
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RICK  *W3RSW*
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« Reply #7 on: April 30, 2013, 11:14:50 AM »

The last thing you want at microwave is silver as the sulphate tarnish becomes a dummy load. All the microwave stuff Ive done as part of my career over the decades is gold plated, even at 300 GHz.

Even on HF silver sulphate is a problem as many have found with coax connectors. I built a copper pipe 4CX250B cavity amp for 440 MHz about 25 years ago and the output hasnt changed. The tube has very low hours limited use in a contest and other than a smooth dry air patina the copper is fine.

Carl
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W3RSW
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Rick & "Roosevelt"


« Reply #8 on: April 30, 2013, 11:28:08 AM »

Wow, didn't realize that was so serious a problem. Industry still using gold in this application outside of NASA or mil. Same way? Does the sulphate oxidation come from the air in reasonably clean Environments ? SO3,4 stuff? Or just in cities, downstream of factories, coal fired plants, roadside? 

Sounds like you've had an interesting, experienced career so I'm all "ears" to learn.  Wonder at the price of gold these days if gold is still used the same.
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RICK  *W3RSW*
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