> Disagee on all counts. Unless you heat to the point of
distorting the
> grain structure (AND you must also let it cool slowly)
there will be
> little or no effect. As far as splatter and rosin, all it
takes is a
> competent solderer and mineral spirits.
It has nothing to do with grain struture. It isn't a temper
issue. It has to do with expanding the metal in a pressure
fit area and then letting it cool, and depending on a solder
joint to hold something that constantly shakes, bends, and
flexes. Solder is not very good at standing that type of
stress. If the connection between a contact button and
contact support bar was problematic and solder was a valid
cure, manufacturers would already use it. To my knowledge,
no one does. They mostly just stake, and I've never seen a
loose contact problem yet.
By the way, the #1 defect in new relays is rosen spatter on
contacts. Just the tiniest dot of rosen can come back to
haunt a manufacturer. We had to have Relay Service Company
(they make the relays in RCS-8V and in many amplifiers)
totally change how they soldered leads on relays because of
reliabilty problems caused by spatter, even though they were
working well away from contacts! Those relays had solvent
baths and still had problems.
> <i>Actually woven braid is the worse possible thing to
use. The best
> would be
> something like thin wide copper foil, and a close second
would be flat
> parallel strands that are NOT twisted. The worse case
situation would be
> a
> loose-woven conductor. The reason is skin effect.</i>
>
> I suspect that very few of us will worry about that at HF
as amp
> manufacturers have used braid for decades with no
problems.
RF engineers and manufacturers avoid using braiding in areas
with high RF current. Tightly packed braid of good design
shield-type lays has about 4 times the RF resistance of an
equal outside size smooth conductor.
The result is you have to greatly oversize a braid to handle
the same current as a smooth-surface conductor. As a matter
of fact, the only reason coaxial cable manufacturers get
away with using braid is the large surface area of the
shield dwarfs the center conductor area, and yet the braid
is still a significant portion of loss! That's why low-loss
coaxial cables, for a given size, have smooth aluminum or
copper against the center instead of woven materials. For
really low loss, they even use a smooth center conductor.
Braid from RG-8 coax, when "unpacked" and made loose, has
about the same 30MHz current capacity as a #14 tinned copper
solid wire. It also has much higher series impedance for a
given length because of the weave and skin effect. The
shield from RG174 is about equal to a #20 or #22 wire in
conductivity at 30MHz.
The RF weak point in most relays having wire connections is
the woven or braided lead to the relay movable contact bar.
That's why the RCS-8V did away entirely with that lead and
the relay will handle about eight times the power of the
very same relay with stranded wire leads. It wasn't contact
heating, it was wire lead heating. Thin copper or brass foil
is many times better than a braided lead.
The same things that make braiding undesirable for lightning
grounds apply to RF leads.
73 Tom
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