[Amps] brass or BNP hardware

Tue Nov 23 03:33:24 PST 2010

Virtually any metal can be silver plated, even aluminum. Depending on the  
material, there may be one or more layers of other material applied before 
the  silver. Aluminum for example requires a layer of nickel then copper and 
finally  silver. A local plating company can discuss all this with you.

I have had stainless steel screws silver plated for use inside a 1296MHz  
plate cavity. The cost was reasonable as I recall. There is a potential 
problem  of mixing up screws when disassembling for repairs. No danger of this 
when  copper screws are used as the appearance is distinctively different.

73,
Gerald K5GW

The big bolts used in telco copper buss bars years ago were solid copper;  
not sure about these days.

In a message dated 11/23/2010 12:36:56 A.M. Central Standard Time,  
fqm at msn.com writes:

--Forwarded Message Attachment--
From:  jim.thom at telus.net
To: amps at contesting.com
Date: Mon, 22 Nov 2010  05:23:14 -0800
Subject: [Amps] brass or BNP hardware

Date: Fri, 19  Nov 2010 13:36:22 -0700
From: "John Lyles"  <jtml at losalamos.com>
Subject: [Amps] brass or BNP  hardware

In RF power amplifiers, HF to VHF range, I have used brass  or nonmagnetic 
stainless steel hardware for years, after having been "Burned"  by steel 
screws - pun intended. Several times in my career
I have seen  bolts turned black and tarnished from RF heating this way. If 
RF current can  flow in the steel, then it can make eddy currrent losses and 
heat up. However,  if it is not carrying current, not a problem. 
The reason I try to stick  with brass or SS is that later on, someone is 
working on the product, cannot  remember why this special screw is only in 
this hole and that. So by making it  all one type, when inside the RF 
compartment, you 
make service, repair and  spare parts inventory simpler. These simple 
policies are carried on in my mind  when starting new amplifiers. 
73
John 
K5PRO

##  In  Bings infamous RF software, one of the features is the skin depth  
calculator.  It also has a table that list every kind of metal you can  
think of.    The worst of the bunch was SS.  Per his
list,  rusted bailing wire would be better than SS.  He didn't say whether 
it  was magnetic, or non magnetic SS.... or if  304 SS or  the cheaper  
variety..which I think is  18 type. 

SS  appears to  work fine, if used to clamp cu straps together, etc, where 
the main RF current  patch is not though the actual SS threads. IE: cu strap 
wrapped around a  tubing tank coil, brought back on itself, then
machine screwed, which  pinchs the cu strap tightly, onto the tank coil.    
Where I   got into trbl was  when  double nutting SS  machine  screws  and 
placing strap between the two nuts.  Then the RF path  is  now through the 
SS threads
and stuff heats up..fast. [ I did this  on a ceramic vac cap]   

The SS that's  locally  available in common sizes like  4-40, 6-32, 8-32, 
10-32   1/4-20   etc...  will just barely stick to a magnet...and I  mean 
barely...and that's  with a big magnet.  If a small magnet is  used, they won't 
stick at all. 
N6BT  once had a pix on his old F-12  website, where he tried using solid 8 
ga SSS wire  for a 40m helical hair  pin.    The exact dead  center of the 
coil  had  turned  jet black..over  a +/- 1 " portion. 
F-12 typ uses   SS  10-24  hardware at feed point of their ants/yagis'.     
They also double nut them... with the balun lugs between the 2 x  nuts.   

##  I noticed on one of these sites that  supplies ant materials  for high 
power AM  SW  broadcast and  commercial users.... recommended   sizes  of   
hardware   for the  feed points  of various SW  ants...
including curtain array's... rhombics, V beams, LP yagi's   etc.    It went 
from 1/4-20   and  1/4-28   up to real big stuff like  3/4"..and 1".   It 
was a  table of power VS  bolt size.   Interesting enough... ALL the  bolts
used  consisted of  phosphor bronze.   None of it  was SS / brass / or 
nickel  plated brass.....or anything else.  I'm  sure  Mosley  used  phosphor 
bronze  screws  for  the  feed-points  of their yagis. 

##  so what's  the  story on Phosphor bronze?   Is it really the preferred  
material to use for RF  ??     I have yet to try to see if  I can silver 
plate any of this stuff.    Back in the 70's/  80's  and early 90's.. telco's
used copper bolts into tapped copper  buss bars on a regular basis. 
[1/4"-20   + 5/16"]   But  I  don't think they were solid copper.  I think they 
were copper  plated material, but don't know what the base material
was.   I  didn't want to scrape any cu off... exposing the base metal, if 
they were  plated... as the CU bolts  were scarce to start with, and we 
needed all  of em. 

##  Brass is plentiful at the local stores.    I  was surprised that they 
even stocked   huge  5/8"  hex  headed   brass bolts, in various lengths.   I 
have never  seen nickel plated brass... and never heard of it
till now.     Phosphor bronze on the other hand, is readily available   
from a  variety of sources, in just abt any size.    I have never had any  
problems  with silver plating CU.     Dunno if it's even  possible  to silver 
plate  say 
phosphor bronze, SS, or  brass/nickel  plated brass.     I don't like the 
way   SS  interacts  with Aluminum  tubing or Aluminum   plate.   The AL 
always ends up grossly  discoloured.

later....... Jim   VE7RF  

+++  Silver plated stainless steel screws and bolts do exist. We use them 
in  
high-vacuum systems, the silver plating acting as a thread lubricant.  
Most vacuum systems are stainless chambers, tubing and flanges, with  
stainless 
hardware used as fasteners. The screws tend to be a little  expensive, 
probably because of the limited market for them. In a pinch I  have our 
plating shop silver plate ordinary 304 stainless screws. It  works. 

Mike K6MDS

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