I can confirm what John K5PRO says - I worked at Gates Radio in the early
1960's in the AM broadcast section . If a piece of steel hardware got put in
about anywhere in the RF areas of the 50 and 100KW HF transmitters it would
be turned black before the TX got out of final test . All hardware at that
time was supposed to be nickel plated brass.
73 hank K7HP
----- Original Message -----
From: "Mike Saculla" <fqm@msn.com>
To: "amps@contesting" <amps@contesting.com>
Sent: Monday, November 22, 2010 11:35 PM
Subject: [Amps] brass or BNP hardware
>
> --Forwarded Message Attachment--
> From: jim.thom@telus.net
> To: amps@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@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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