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October 23rd 03, 05:30 PM

On 22 Oct 2003 15:05:58 -0700, (Art Unwin KB9MZ)
wrote:

Richard Clark wrote in message . ..
On Wed, 22 Oct 2003 12:43:20 GMT, "Ronald Walters"
wrote:

I would ask the group for recommendations on cleaning the roller assembly and
inductor to ensure good conductivity after I am done.

Hi Ron,

One contact cleaner that I used that was better than most was
Cramolin. This is a monomolecular layer solution that you would use
very sparingly. However, as your tuner did not arrive brand-new (or
brand-used) with it, your problem may be more mundane.

The simplest way to defeat corrosion is with pressure.

Garbage
For continued use you must have a wipe or what is termed a
scrubbing action. Period. Even with silver or gold the lack
of scrubbing action will permit intermitent contact unless
the power is high enough to blow away the oxides.
Art
The spring
tension of the roller may have slackened up over the years.

73's
Richard Clark, KB7QHC

Hi Art,

You are out of your turf. Pressure is the way all contacts work to
break the insulating barrier formed by oxides. Your typical abuse of
language here with "wipe" is another example that demonstrates
pressure. The indiscriminate use of chemicals to treat a mechanical
problem is one that I have demonstrated as being wholly unnecessary:
none of your new gear, nor any old gear just acquired that works fine
came with this chemical bath treatment.

Long before anyone here was born, precision contacts were tapered
plugs that fit into tapered sockets. The sockets were bifurcated
(split in two halves) such that the plug created the closure between
them with a simple insert and twist to break the layer of oxide.
Note, there is no "wipe" as the twist translates the torque into
pressure (wiping has nowhere to deposit what is "wiped" away in the
tapered socket). No one needed sandpaper or a bottle of acid to erode
the surface and corrode other parts through the solvent's vapor (a
very insidious imposition). There is a very good reason why
electronics manufacturers avoid acid core solder (unless they use a
water wash down following board construction and faithfully use rosin
core solder for touch up work - with extreme care not to mix the two
solders).

For contacts that have little pressure, the voltage presented across
them can penetrate the barrier; however, there are applications where
those voltages are not sufficient, and when the contact pressure is
not enough either, you get into these problems. Mechanical TV tuners
back in the early days suffered this problem and a special grease
surfactant was used to insulate the contact face from corrosion while
the pressure was sufficient to displace it for electrical contact.

73's
Richard Clark, KB7QHC

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