[R-390] Filtersq

[Bob Camp]

Hi

What you need is a but weld rather than a tab weld. Often these are done with headed wire to increase the weld area. Back in the era the filters were in production, California Fine Wire (CFW) was one of the places you got the stuff from. They have long since moved into other lines of business. The wire isn't quite taken to a nail head, but it's bulked up quite a bit at the end. 

It's the sort of weld that you probably get right after the 10th or 20th try at the settings and a half dozen trials on many of them. Generally you only get one "shot" at the right location. The alloy on the filter disks may be marginally weldable, which would narrow down the useful setting range. 

Bob
 
On Feb 17, 2013, at 1:57 AM, Lizeth Norman <normanlizeth at gmail.com> wrote:

> Hi all!
> Have been following this thread with great interest.
> What about battery places? Most of them here (Central FL) have welding
> machines that attach tabs to batteries. The weld footprint of the
> welding machine is actually pretty small.
> Too big probably, but might be worth a try.
> 73 de Norm n3ykf
> 
> On Sat, Feb 16, 2013 at 4:58 PM, Bob Camp <ham at kb8tq.com> wrote:
>> Hi
>> 
>> There's not much to see in the picture. We are either talking about a wire that attaches to 1) the coil bobbin (which is visible), or 2) the center of the end disk (which is not visible at all), or 3) the edge of the disk (which is not obvious). It's slightly possible we could be talking about the ground strap (which is not the wire in the earlier picture).
>> 
>> The coupling wires are resistance welded between the disks. The actuator wire was either resistance welded or silver soldered onto the center of the end disk. If it's silver solder, any change in the amount of solder will change the mass of the disk and it's resonant frequency. To a lesser extend re-weldig could have the same problem. Of course the whole description of the center wire as an actuator may be a bit off in the case of the filter you have. It is the terminology used in the article on rebuilding filters.
>> 
>> How does the "broken" end of the filter compare to the "correct" end of the same filter?
>> 
>> What ever the attachment method of the wire, it needs to have good acoustic properties at 455 KHz. That rules out most plastics, and many ceramics. Hard solder or welding are the obvious choices.
>> 
>> Bob
>> 
>> On Feb 16, 2013, at 4:02 PM, "quartz55" <quartz55 at hughes.net> wrote:
>> 
>>> Here is a pic of the top end with the copper cylinder that holds the coil bobbins.  It looks like it's soldered to the end disk.  This too may be problematical.  Not sure if I can unsolder this thing from the disk to attach the wire, and then how to attach the wire?  MIG or TIG?
>>> http://i251.photobucket.com/albums/gg287/DogTi/R390A/filtercoppercyl_zpscf59576c.jpg
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