[Hammarlund] Cleaning SP-600 coil fingers, lube question?

[Barry Hauser]

Phil wrote

> Today I am continuing on the alignment of the SP-600.  I've run into 
> some frequency instability on the highest band, especially at the top 
> end.  This isn't gradual shifts but "jumps" in frequency.  I've "double
checked 
> and cleaned" the tuning capacitor sliding contacts to no avail.
> 
> I 'think' it may be due to the fingers on the coils and am cleaning 
> them with deoxit and a paper towel, hoping that will cure it.  Many of 
> the contact fingers are oxidized black and it's taking some vigorous 
> scrubbing with the towel to clean them (I' not using any abrasive as I
don't 
> want to take off any more "silver" than is already gone).

By "fingers" I assume  you mean the posts on the ceramic turret modules. 
In addition to oxidation, these may be scored on the sides due to the
stationary "pincer" contacts on the bottom of the RF strip being set at
too extreme an angle.  This exposes the sharp edges rather than the broad
flats of the stationary contacts to the posts which can sometimes upset
things a bit. A full-blown "tweak" is to remove the RF strip (remembering
to turn the bandchange knob to halfway between detents) and reset the
stationary contacts so that the two "pincers" are flush with the sides of
an appropriately sized drill bit or allen key as a gauge to sub for the
posts.

Also, if the posts are badly grooved, you can turn them 90 degrees to
expose a fresh surface.  But after that, you'll have to replace or
re-machine them in 50 years, so make a note of it ;-)  (OK, so maybe you
can go to 45 degrees in 50 years.)  You may have to heat up the solder
connection allow rotation.  In moderate cases, you can try burnishing the
grooves to smoothen them out a bit using the shank of a screwdriver or
similar to at least get rid of the sharp flash.

In addition to a bad component, another possibility may be a deteriorated
solder joint or loose component on one or more of the ceramic modules --
or a module that is not held snug enough in the turret and is shifting as
it moves into contact position under the RF strip.(Or anything the
slightest bit loose on a high band module.)

If this is actually occurring on all the high bands -- but just more
aggravated on the top one, the small cam operated switch at the back of
the turret housing may be involved.  (Switches in double conversion.)

I have spent hours cleaning the black off silver contacts.  Somebody once
told me it doesn't make any difference as silver oxide conducts as well
as silver itself -- but that hasn't been my experience.  Perseverence
with DeOxit usually does the trick.  Of course the silver could be worn
through to the base metal.  If so, this can be cured by making minute
adjustments to the tracking of the contact(s) so that it touches silver
again.  I've even done this with wafer switches.

I would NOT recommend using the contact grease.  Most of that stuff is
intended to preserve solid connections from the weather.  I have a
TV-7D/U tube tester that had a lot of something similar on the wafers of
its rotary shorts/test switch.  It migrated around and caused false
shorts readings. It was a pain to clean it out. That's unlikely with the
SP-600 turret, but I'd be concerned about the stuff slinging off the
turret pins or "spitting" out when it gets to the RF strip's contacts and
landing where it could cause problems.  If there's some splatter on the
inside of the turret housing or bottom cover, no problem.  I suppose that
leaves the bottom of the RF strip -- the ceramics and exposed circuitry. 
If the ceramics were to get contaminated with the stuff ... ? 

Just my 2 cents. Hope some of this helps.

Barry



> 
> Question.  Is it ok to VERY lightly lube these critters?  I have a 
> tube of
> "Ox-gard" used to enhance electrical connections, antenna assembly 
> etc.  Is
> it usable for this or NOT RECOMMENDED?
> 
> 73 de Phil  KO6BB
> 

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