----- Original Message -----
From: "Dr. David Kirkby" <david.kirkby@onetel.net>
To: <amps@contesting.com>
Sent: Monday, October 04, 2010 8:08 AM
Subject: Re: [Amps] Skin depth: silver plating of tank circuit coil feasible
with chemical plating kits?
> On 10/ 4/10 12:42 PM, LB3HC wrote:
>> I am working on some loss estimates for the tank circuit of my GS35B
>> amp. design and I am considering if silver plating of the tank circuit
>> coil is feasible or not. I intend to use copper tubing intended for
>> camping gas installations in the tank coil(s), as it is readily
>> available. According to VE1ALQ's tool, the 3 times skin depth for RF
>> current on 10 meters wavelength is 36 Microns. Silver plating kits
>> that are available on the market** typically states a plating
>> thickness of 70 micro inches, which is only 1,7 microns. This is 1/20
>> of what is necessary to have silver down to the 3 x skin depth, if my
>> calculations are correct.
>>
>> What are your experiences with silver coated contra non coated tank
>> coils?
>>
>> Polishing the copper tubing will reduce the RF skin current resistance
>> according to some sources. Is this true, and in case it is, what are
>> the mechanisms that makes polished copper conduct better (RF) than non
>> polished copper?
>>
>> **
>> http://www.cool-amp.com/product%20info/COOL-AMP%20One-page%20Info%20Sheet%20&%20inserts%20%28FINAL%2004.30.09%29.pdf
>>
>> 73
>> LB3HC
>
> I don't know the depth, but I know I had a 2 m anode line silver plated
> for a
> dual 4CX250B amplifier. Careful measurements before and after plating
> showed no
> statistically significant difference. The line was brass, which is a
> poorer
> conductor than copper, so the difference between brass+silver should have
> been
> better than between copper+silver. But it was a waste of time - other than
> it
> looked nicer!
>
> A friend got the plating done free, and I know it was deeper than normally
> done,
> though I can't recall the depth.
>
> You really are wasting your time at 10 m if you think you will improve
> efficiency. Anybody that tells you that it made a difference at that
> frequency
> is kidding themselves.
>
> If anything, gold plating would be more useful, as it would stop
> oxidation. In
> which case, you need only a very thin coat - forget about skin depth. 99%
> of the
> current will be in the copper, not in the gold, but the gold will stop
> oxidization.
>
> Oxidization might be one of the advantages of cleaning the copper, but I
> don't
> really think it will make much difference until you reach a few GHz.
>
> I was once told silver oxide is a conductor and copper oxide is not, so
> that's
> an advantages in using silver. I've never looked in the professional
> literature
> to see if that is true - it may be a lot of rubbish.
>
> dave
Agree, silver plating is strictly for show up to some unknown frequency.
Ive been running a 2M flat plate line 3CX1000A7 for over 25 years and its
still running the same 1500W with the same tube. Use is limited to contests
and interesting band openings.
A 4CX250B cavity for 440 ran 250W out when I built it 30 years ago for FM
use in contests, it doesnt have many hours on it. I checked it an hour ago
and its still the same. Construction is from copper water pipe.
The biggest problem I see in amps is poor RF connections causing crystalized
solder joints and increased RF resistance with the copper or silver coil and
connecting wiring getting the blame. If youre going to run real power then
silver solder as well as bolt together anything that can be bolted. Dont run
#14 or 16 wire to the bandswitch, especially 20M and above. At a minimum use
silver bearing solder for all RF connections.
Carl
KM1H
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