I just serviced a LK-800C and discovered 6-32 steel hardware in the RF path
on both sides of the plate blocking cap. One side was darkened overall and
the other was black where the threads entered the cap, it looked like rust
under magnification. This amp will do an easy 3500-4000W + with sufficient
drive.
Ive never noticed a problem with their 3-500Z amps.
Heath uses steel for everything but the power must be low enough to not
matter. However when I do 6M conversions they get brass. I smoked the steel
when I started doing SB-200 conversions in the mid 60's.
Nickel is a poor RF conductor, I wouldnt advise it at QRO or at VHF.
Here is a basic shart on RF conductivity, scroll to Page 39. Note how bad SS
is.
Carl
KM1H
.
----- Original Message -----
From: <TexasRF@aol.com>
To: <fqm@msn.com>; <amps@contesting.com>
Sent: Tuesday, November 23, 2010 6:33 AM
Subject: Re: [Amps] brass or BNP hardware
> 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@msn.com writes:
>
>
> --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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