Hello Amp Fans:
I have been following these discussions, and thought I might wade in
finally, as a manufacturer of both silver and gold plated conductors.
Silver plated conductors, whether used as wiring components, or as coils,
contacts, etc., are rated for continuous use to about 200 degrees centigrade
for military interconnect applications. Only above this temperature will
the silver start some oxidative process, and at room temperature, there is
no possibility for oxide formation. Because of its very low contact
resistance, it makes an ideal choice for interconnect systems, which is why
it is basically the standard for military interconnect on most fighter
airframes. With over 500,000 connections on a typical small tactical
fighter, you don't want even a fraction of one percent failing, no matter
how redundant the systems are.
While it is straight forward mathematics to calculate the depth of
penetration of RF current, at any given frequency, it suffices to say that
at HF, there is no penetration, and hence the currents flow within the
center of the conductor, rather than at the surface, or skin effect
currents, at the intended frequency of operation for HF amplifiers.
As stated here previously, silver oxide is a good conductor, and copper
oxide is not. Long term stable connections, whether by soldering, or
mechanical bonding methods are facilitated by silver plating. The need for
active fluxes is eliminated, and the interconnection stability and long term
reliability are further increased.
The discoloration of silver is in most instances found to be due to
sulfurization of a clean silver surface. Silver is a tremendous getter for
sulfur ions, found in air. The silver surface collects the sulfur, and
forms silver sulfide surface compounds over time. Sulfur is not a desirable
element to have around, as it can form other brittle intermetallic
compounds, which can drastically reduce the long term stability of
interconnect, and as such, the military wants sulfur avoided in all cases.
Thin coatings of silver are indeed found on wiring systems. The military
has adopted 40 millionths of an inch, or about 1 micron, as a standard for
aircraft use. Thicker platings, about double this thickness, are used in
space applications, where use in oxygen rich atmospheres, lead to corrosion
considerations. Silver plated copper conductors, if only the least bit
porous, in the presence of oxygen and water, will very rapidly corrode, with
the copper being the sacrificial element, once Faraday's Law sets in, and
cuprous oxide starts to form. This is the famous "Red Plague", which can
result in total circuit failure, and rather quickly.
Silver plated tank coils, represent an improvement in long term
interconnection stability, whether bonded by any acceptable method. The
silver plating avoids discoloration of the copper substrate, which will
discolor and blacken fairly quickly, if used as an unplated tank coil,
depending on both the temperature, and atmosphere of operation.
Gold provides much of the same protection, but at a much higher cost, both
due to processing considerations, as well as the intrinsic cost of the gold
metal. Certain applications need to avoid the presence of silver, for
specific metallurgical reasons, and here gold is also specified.
Silver is certainly a good choice for amplifier tank circuits, for long term
stability. Gold is technically not necessary in an amplifier at HF, but
will offer the avoidance of discoloration due to the presence of sulfur in
the environment.
73 and Happy Dxing,
Mike Schatzberg
WB2AJI
----- Original Message -----
From: "Will Matney" <craxd@engineer.com>
To: <amps@contesting.com>
Sent: Friday, June 17, 2005 1:30 PM
Subject: Re: [Amps] RE : copper or silver in tank circuit?
Bill,
That's all I could think it would be used for, where the skin effect
increases with frequency. I'll about bet that military stuff wasn't plated
very thick either, maybe 1-2 mils at the most. The only other place in
electronics is electrical contacts. Gold is just too expensive to be used as
a very thick plating. When I did some gunsmithing years back, I checked on
the price of some small gold anodes for plating small parts. Needless to
say, over the cost, I didn't invest in it. For HF work, I cant see any
benefit really, especially if the coils they're using are still the same
size. My opinion is, the gold coils are there as an extra money maker and
sales gimmik in these last Alphas.
Best,
Will
----- Original Message -----
From: "Bill Fuqua" <wlfuqu00@uky.edu>
To: hermans <on4kj@skynet.be>, "'Steve Thompson'" <g8gsq@ic24.net>,
amps@contesting.com
Subject: Re: [Amps] RE : copper or silver in tank circuit?
Date: Fri, 17 Jun 2005 10:35:18 -0400
>
> Gold has low conductance, but gold plating is usually very thin. Since it
> has low conductivity it has greater skin depth and since gold plating is
> usually around a micron thick most of the current flows thru the material
> under it. However, it does provide for a good deal of protection for that
> underlying material from corrosion. I have junked a lot of military
> microwave stuff in my younger days that was used in aircraft. The cavities
> were gold plated inside and out.
>
> 73
> Bill wa4lav
>
>
> At 11:14 PM 6/16/2005 +0100, hermans wrote:
> > hoy All,
> >
> > Silver plated wire, we only used it in applications where very high Q
> > was necessary. It helped stability in oscillator coils, since silver
> > oxide has the same resistance as silver. So it is also OK for contacts,
> > when Current passing through is not very low. ( less then few tenths of
> > micro Amps).
> > Gold .....is used for the same raisons, its good looking, but
> > expensive.....
> > Silver plating can easily be done with silver cyanide, but be aware it
> > is a very very dangerous procedure when done at home without good
> > knowledge and precaution. SO DON’T DO IT AT HOME.
> >
> > Jos on4kj
> >
> > -----Message d'origine-----
> > De : amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] De
> > la part de Steve Thompson
> > Envoyé : jeudi 16 juin 2005 17:23
> > À : amps@contesting.com
> > Objet : Re: [Amps] copper or silver in tank circuit?
> >
> > Larry Carman wrote:
> > > I was told by a pro amp builder to leave out the silver and use copper
> > only
> > > in the tank circuit. Reason: because it helps prevent parasitic on the
> > > higher frequencies. I'm speaking of HF amps working to 30 MHz. Any
> > Merits to
> > > this???
> >
> > Not to mince words, it sounds nonsense to me. If that's the
> > difference between a amp that's stable and unstable, them
> > there's something much more fundamental needs fixing.
> >
> > I recall an article in RF Design (but not in fine detail)
> > where the writer argued that oxidised copper wasn't as much
> > of a problem as people sometimes think, as the current will
> > tend to head for lower resistance paths, driving it deeper
> > into the wire/tube/stripline.
> >
> > Will mentioned tin plating - I've seen harmonic filters
> > (VHF, 200Wish) burn up pcbs and unsolder chip capacitors
> > from the heat when enamelled wire was replaced with tinned
> > to save on preparation time. Where the loaded Q is low, it
> > will probably matter less.
> >
> > Steve
> > _______________________________________________
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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> > _______________________________________________
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>
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