The AM Forum

I was told that a silver plated tank coil can have an increase of 10 to 15% effeciency as the Freq goes up.  I was told that on the low bands the difference is little.  I saw how my new J500 makes the same efficiency on the low vs high band and it has a silver plated coil.

Anyone every use this:

http://www.cool-amp.com/cool_amp.html

Its a do it yourself way to silver plate a tank coil.

C

Previous discussion on another board, the engineers conclude:  silver plating is good for cosmetics and corrosion resistance but makes no difference to RF below UHF because the layer is too thin to help surface effect.

That is interesting.  The guy I spoke with did tests on his rig and saw improvement.  Thanks for the comments!    I know that as far as improving the efficiency, the plate choke is the first place to go.  The modern computer designed plate choke that is sold by RF parts, has produced BIG gains on my rig on the higher bands.  I just wondered about the plating.

C

I think the reason we see great performance on the high bands on our Johnsons is simply because they DO use high quality overrated parts in the tank, silver plated or not!!  Good engineering... they included 10 meters so they made it work right!

I AM OF THE VERY SAME THOUGHT

I silver plate some of my PC boards and my copper tank circuits but for cosmetic purposes as I have heard that the plating is too thin to make a difference unless you use very heavy electroplating. I have a simple immersion formula that works great for a quick thin coat. It uses silver nitrate and sodium thiosulfate (photo hypo). A quick dip makes things sure look pretty.

Nitrate based immersion silvering bath:

15 gm silver nitrate
30 gm sodium tiosulphate (Sodium Thiosulfate)
10 gm ammonium chloride
1 lit water

Dissolve nitrate in 50 ml water,add chloride dissolved in 5o ml water,to this mixture add tiosulphate dissolved in 9oo ml water

It cost about $20 for a liter as the silver nitrate is expensive now.


Pat
N4LTA

I have used Cool-Amp and have found its effect to be cosmetic rather than improved efficiency.  I contacted silver plating companies and the thickness of silver they use was measured in micros of an inch.  At HF this is cosmetic.

My silver plating papers are not in front of me but if memory is correct then to gain efficiency one has to silver plate in fractions of thousands of an inch (not microns of an inch) up to a thousandth of an inch or so. The thickness for improved efficiency varies on the frequency in use.  

I know this is a vague answer but in most applications the effect of silver is cosmetic at HF.

Silver will help slow the oxidation of the copper.  As you know silver will also oxidize.  When I build a coil I give it a thin coat Caig Laboratories products such as DeoxIt or similar based products to slow the oxidation.

Chuck

Can any of the chemists in this group recommend an electrolyte solution for electroplating Silver onto copper that does not use cyanide or extreme acid ?

Chris

 

Not an electrolysis solution, but:
Clean copper to scoured shine. Polish with rouge. Clean and Dry thoroughly. Preheat piece in N2 atmosphere.
Dip in molten, 99 pure silver with all slag possible removed.
Dip again to achieve desired coating thickness.
Drain excess Ag into w4neq coin minting molds.
Spend coins for professionally crafted coil.  ;D

Computer designed plate choke that improves efficiency?

Can you give us a point to that?  (I didn't find anything quickly at RF Parts).

http://www.caswellplating.com/electroplating-anodizing/brush-plating-products/plug-n-plate-kits.html

Caswell seems to be one of the few vendors that caters to the home user.  I haven't used any of their products.

I have used the cyanide electroplating method. If you are not familar with chemisty, I'd not recommend it, but it works very well. It is the best way to plate a heavy coating on. You need to do it outside or under a hood.

You need silver chloride but you can make it yourself easily by desolving coin silver in nitric acid and precipitating out silver chloride by mixing table salt with the disolved silver. I used a 1 oz silver bar as the sacrificial electrode. It worked very well.


I still have most of a Kg jar of sodium cyanide left from my experiment years ago.  It's not easy to get rid of.

The Caswell suff is very expensive - you can have it done cheaper than buying the Caswell chemicals.


Pat
N4LTA

What advantage or disadvantage is there to (solder) tinning a coil vs. using silver or leaving it bare?

I did a thread here about a year ago on a process that is safe and only needs 3 or 4 amps to do a great job. Chemicals cost about $40. My Brother, a Jeweler turned me on to the company he deals with. There is a link in the thread. We silver plated  a bunch of copper straps. It looks nice but may help on higher HF bands

Seems like it would be cheaper, and much easier to wind your coils from silver wire to begin with.

Or, maybe better, and definately cheaper would be Sterling Silver Filled Wire.
Which is basically brass wire, coated with silver.

Not sure what Guage is needed, but 16 guage SSF is still less than $4 per foot.

The RF Parts plate choke (@$24.95) is also available from Ameritron for $20.00.

I plan to use one in my BTA 1R1 multiband conversion.

http://www.ameritron.com/Product.php?productid=10-15197

73 Jack KZ5A

When I was still gainfully employed, largely at taxpayers expense at a large defense company, I and a few others ran substantial tests on the silver plating issue; on our own time of course ::)

From 2 to 250MHz there was no measurable difference at small signal levels or the 150W from the distributed amp used. Surface area was the only parameter that mattered. The silver plating was real Mil Spec, not brushed on. At 222MHz  at high power there may be a small benefit and at UHF it appears to be universally accepted altho the 4CX250B cavity amp I built using copper pipe still puts out the same 250W on 440MHz FM at the same predicted efficiency as built around 1988-89

My bare copper flat plate 2M 3CX1000A7 amp has no problem at 1500W in the 25 years Ive been using it....no sign of any heat discolaration and the tuning doesnt drift during long key down testing.

The only choice in an amp is to size the conductor properly and surface area matters. This means that a 1/2" diameter flat strap is more efficient than say a #6 wire or 1/4" tubing at 10M at the higher power levels since copper conductivity takes a nose dive when overheated.

While many use well sized coils they then go to #14 or 12 as tap wiring to the switch, coax connector, tuning caps, anode, etc  and defeat the purpose. It may be OK in a very compact amp with say a 3CX800 or 8877 and minimum lengths but the typical 4X1 amp has individual leads spread out a foot or more and then they wonder why its a dog on 10M, even with a new tube.....and sings like a birdy to boot.

It also helps to have a tube thats still fully efficient at say 120-200MHz + for an amp that includes the higher HF bands. For you guys that believe the world ends at 7295KHz then most anything will work and this thread is moot.

Carl

Carl's comments confirm the research I've done over the years.  Thick, edgewound coils - common in the broadcast industry offer Q's that reach over 600 and are good for 20 amps without heating.  They are silver plated, perhaps not so much for  increasing Q, as to decrease the rate of corrosion and tarnish - which they do much better than bare copper.  With long-term corrosion prevention in mind, and a periodic need to move the adjustment clip (or roller) - is there any good alternative to Silver plating ?

Chris

Thanks for the information Carl.  I think I might try some simple upgrades to the wiring and report my findings.

C

One skin depth of copper and silver at 1 MHz is about 2.5 mils. Much much less at UHF. At UHF for cavity construction and unloaded Q its worthwhile and not very costly. At HF just beef up the gauge of Copper rod or strap, just not worth the effort and probably will not see its effect on Q. As a rule 4-5 skin depths would be nice and 10 mils of silver at 1 MHz is costly!

Ok. Got it.. I studied the two tanks and what I found is what carl was saying. The coil is large diameter copper but the wiring is solid 16awg wire running from the swtich all the way back to the loading cap switch.  no strap. That is likely why, alot of these radios fall off as you go up in Frequency. 

C

A note to silver users:

Oxidized silver turns white.  Pretty rare in reality.

The black tarnish you see is silver sulphide, mostly brought on from atmospheric sulfur.

73DG

So, avoiding abrasives which might scratch through the thin plating, what's the best way to clean all this nastiness off of silver plate?

Chris

Re-quoted for Truth.  There's a LOT of ill-advised advice going around to the effect of "don't worry about that black on the silver, silver oxide conducts electricity as well as silver".  Unfortunately as TFO pointed out, that's NOT silver oxide, and it does NOT conduct electricity well!

Tarn-x makes easy and fast work of removing tarnish (silver sulfide).  And you can tell - the chemical reaction results in a sulphur smell.

So Tarn-X does not harm the silver?
The Silver Sulphide is the result of harm already done?

Unfortunately the silver oxide myth predominates on many forums as well as so called "expert" web pages where its never going to get changed.

Carl

I've used Cool-Amp on the windings of a 200 kva buck-boost mechanical voltage regulator that had chain-driven contacts sliding along the copper windings - like a variac.  It did lessen heating with lower IR drop at the point of contact, but was so thin that it was a regular maintenance item to replenish.  Easy to apply though.

Chris

Cool Amp definitely helps on contact resistance, we use it all the time for that. But not for RF losses. Look up skin effect and see that you would need a great thickness of silver to carry RF current at HF. At VHF and UHF it begins to play (as Carl mentioned). Copper alone is very conductive, at first. But over time it oxidizes and RF conductivity decreases at the surface. So the RF current must penetrate deeper, according to skin effect theory. If there isn't enough material there, and it is very oxidized then heating and RF loss is apparent. Q goes down in resonators and inductors. Adding a silver skin, via plating, that is of appropriate thickness (typically recommend 3-5 skin depths to carry 99% of the current) and you now have a conductive layer over base copper (or other metal). Silver sulfides are less conductive, and form in the atmosphere over time. So the trade off is having something with better long-term stable conductivity (of lower mhos) versus something with high conductivity at first that degrades over time. I design high power cavity amplifiers for work, and this is a huge consideration. If there are tuning contacts, that must wipe the walls and work with hundreds of amperes of RF, then copper alone is not suitable except in a prototype. Right now I am operating an aluminum cavity (for weight and cost) at 250 kW average power at 200 MHz, that has a thin electroplate of copper (for adhesion) followed by 0.0006" thick pure silver plate. It took several companies and $11,000 of testing expense under electron microscope just to qualify a source to make this, that didn't have voids, and other problems. I have a great plater now who is NASA qualified and do first class work, for a higher cost than the local outfits.

A. Fowler published an interesting piece, 'RF Performance of Electroplated Finishes" in Proceedings of IREE in Australia in 1970. In it, he expounds on the idea that most commercial electroplaters don't do what RF engineers want, and use various alloys and additives such as phosphorus for de-oxidizing agents. He specifically is talking about copper tubing coils for transmitters in this report. He reports a range of conductivity of a plated piece from 0.13 to 95% of the conductivity of pure electrical copper, which is reference at 100%. So following Fowler's advice, you'd be making a mistake to silver plate a coil without specifically knowing the composition of the plating bath and even testing for conductivity. He does talk about tin plate (worse resistivity) and using a coating such as lacquer on top of bare copper to protect it.

Devices like roller inductors need to have silver or gold plating, just for low contact resistance for the wiper, similar to cavity circuits for the same reason. Materials such as Rhodium top layer have been applied in some cases, but care must be taken to protect it from fracturing. My advice to hams is to use copper and cover it with a spray finish for protection, unless you must have wiping contact, which then can use Cool Amp or silver plating. If you are running kW's above 2 meters, then you should consider further electroplating of the appropriate thickness to satisfy the skin depths required for current. Skin depth may be different for each material, so its not as simple as a single value for everything.

Thanks for the information. I enjoyed the read and learned alot John. 

The kings Tank coil is copper and was coated in a varnish.  That varnish was cracked and falling off.  I used steel wool to remove the coating and then used tarnx to polish the coil.  That was 5 years ago now. 

I wonder if the author was suggesting it was a good thing to clear coat the copper coil or a bad thing? 

C

I read the Fowler paper on electroplating last year and it is fascinating.  It shows how making (wrong) assumptions about plating processes can give you a finish that is worse than no plating at all.