[Boatanchors] RCA AR-88 problems

Richard Knoppow 1oldlens1 at ix.netcom.com
Tue Jun 4 17:37:14 EDT 2013


----- Original Message ----- 
From: "David Stinson" <arc5 at ix.netcom.com>
To: "Boat Anchors List" <boatanchors at mailman.qth.net>
Sent: Tuesday, June 04, 2013 1:35 PM
Subject: Re: [Boatanchors] RCA AR-88 problems


>I know this is a pain, but...
> This is just the sort of "mystery" problem caused by Hi-Z 
> grounds.
> H-Z ground points are forming because of the formation of 
> thin films of resistive oxides between screws, washers and 
> chassis.
> Also, molecular metal migration away from the pressure 
> points is an issue.
>
> Fixed lots of problems just by applying this principle:
> Go through the set from one end to the other.
> Find every grounding point- every chassis screw- every 
> place
> that looks like it should provide ground to anything.
> Give the screws a little "tweek" to tighten them.
> An eighth-turn or less usually "does the trick."
> Give the rivets a "tap."  Check the solder on solder lugs.
> It's time well-invested.
>
> 73 DE Dave AB5S
>
     I am going to do that beginning with the trimmer caps. 
The chassis was very dirty when I got it. Part of this may 
have been from outdoor storage and part from stuff 
evaporating from the bathtub capacitors under the chassis. 
When I got the set the bottom plate was covered with 
congealed oil and wax and the upper part of the chassis 
appeared to waxy grime on it which was extremely difficult 
to remove. For the most part the underside of the RF 
compartment looks pretty clean but there may be bad grounds 
in several places.
     When I replaced the bathtub caps I grounded the new 
caps through the terminal strips but put star washers under 
the mounting terminals to insure they would ground well. I 
can't believe this was a problem with the set was new.
     The RF tracking is also off slightly on two of the top 
bands but not the other.  Something very odd here.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com 



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