[R-390] Filter repair

[Bob Camp]

Hi

Yup, the proper term for a coined block of metal with glass to metal seals in it is a header. End cover = header.

Bob

On Mar 9, 2013, at 9:19 PM, Norman Ryan <nnryann at yahoo.com> wrote:

> Hi, All,
> 
> I suspect Bob is referring to soldering the bobbin wires to the end cover terminals.  This link might be helpful for better understanding the challenge of soldering hair-fine magnet wire:
> 
> http://www.microjoining.com/articles/FlashSoldering_Extending_Applications.pdf
> 
> (If clicking the link doesn't work, copy and paste to your browser.)
> 
> This mechanical filter repair thread is of great interest to me.  Sometime down the line I want to try my hand at mechanical filter restoration and hope eventually to have results worth sharing with the group.
> 
> Carry on and good luck!
> Norman
> 
> 
> --- On Sat, 3/9/13, Bob Camp <ham at kb8tq.com> wrote:
> 
>> From: Bob Camp <ham at kb8tq.com>
>> Subject: Re: [R-390] Filter repair
>> To: "r-390 at mailman.qth.net Group" <r-390 at mailman.qth.net>
>> Date: Saturday, March 9, 2013, 4:07 PM
>> Hi
>> 
>> There is a problem when soldering small diameter copper wire
>> known as "neck down". It's an issue once you go past about
>> number 36 wire. If you cross section the solder joint you
>> can see it fairly well. The diameter of the wire is smaller
>> inside the solder than it is normally. The reason is fairly
>> simple - some of the copper dissolves in the solder. 
>> 
>> Here's where the problem comes in - the dissolved area
>> extends *above* the surface of the solder. The diameter of
>> the wire shrinks before it hits the joint. The why gets into
>> how flux and solder do their thing.  The net result is
>> that the wire is both weaker and less stiff right at the
>> joint. Motion in the wire (think vibration) will break the
>> wire at the joint. 
>> 
>> The solution is fairly simple - dot the joint with something
>> that will stiffen things up. Epoxy works, so do various
>> other fairly rigid plastics. You don't need very much at
>> all, anything that runs up a dozen or so wire diameters is
>> more than enough. 
>> 
>> The other solution is to not use copper wire, go to
>> something like steel. Not much of an answer in this case. 
>> 
>> Bob
>> 
>> On Mar 9, 2013, at 2:21 PM, quartz55 <quartz55 at hughes.net>
>> wrote:
>> 
>>> I've got the lost magneto wire welded back in the 4K
>> filter, but as I say, it's a #34, not 40, and the bobbins
>> installed and glued.  But what the heck.  Anyhow,
>> I'm pretty tired of it today, I've need to cut some more
>> foam PE from the hardline. I find it's easier just to take
>> the soldering iron to fasten together the pieces of PE, RTV
>> doens't stick, but then I'm using 5 minute epoxy to attach
>> the PE to the filter bodies and the bobbins in the copper
>> cups.  I've got all the dimensions for all this stuff
>> and I'll list it later.  But here's where it stands
>> now.  I notice the bobbin wires seem to have lost some
>> of their covering, so I'm going to mask them and spray them
>> with some enamel so they don't short out when I install
>> everything.  It's just a matter if getting it back
>> together now and see if it even works.  I'm sure
>> soldering those #40 wires on the end caps is going to be
>> challenging.
>>> 
>>> I haven't been looking foreword to winding any of those
>> bobbins, but hopefully between all the old filters I have
>> and the broken ones, they can be re-used.  They don't
>> seem to be different at least between the 455 models.
>>> 
>>> http://i251.photobucket.com/albums/gg287/DogTi/R390A/filterassembly_zps90ed7d6f.jpg
>>> 
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