[R-390] Filters

[Bob Camp]

Hi

The coils on each end of the filter act as either a microphone or a speaker depending on which end you are looking at. The disks are the filter resonators. They are *very* precisely dimensioned to make things work. The wires between the disks are the coupling between the resonators. They also are *very* precisely dimensioned to make it all work. About the only thing that can be repaired are the windings on each end. If the disks or their coupling wires are damaged - there is no rational way to repair them. 

The goop / goo / stuff can act as mass loading on the resonators. With any mechanical resonator that can de-Q them or it can shift their frequency. Removing crud is good, damaging interconnect wires is bad…

Bob


On Feb 16, 2013, at 12:35 PM, quartz55 <quartz55 at hughes.net> wrote:

> Well, I don't think I've destroyed it yet.  The coils still measure around 52 ohms on the wires.  I got one of the coils out, it just pulled out with the wires, the tape tab just came out when I pulled on it.  There's a much better  repair link here, but if you look at my pictures, it adds a bit of info.  I wasn't sure where the magnet was.  The filter repair link is http://www.delphelectronics.co.uk/filter390a/ and you can see my pictures here http://s251.beta.photobucket.com/user/DogTi/library/R390A
> 
> I'm not sure what was wrong with this filter.  The tiny wire in the center of the bobbin is indeed small, I have a hard time seeing it.  All I've done at this point is clean things up.  There was a bit of detrius in between the metal coils and there is a bit more in there I need to get out.  I'm not messing with the center wires.  I'm not sure if the center wire goes through all the discs, I don't think so, I think I can see it on the top end it attaches to the 2nd disk from the end.  I can't see the center wire on the bottom end between the discs.  I'm thinking I'll have to use a tiny bit of silicone glue to hold the bobbins in place in the copper cylinder since they seem to be loose and the tape is doing nothing.  I see no reason to take the magnets off.  I've cleaned up all the spongy stuff and loose glue around the magnets.
> 
> I still measure infinity with my fluke from the bobbin wires to the discs.  I'm hoping just cleaning it up will do something for it.  We'll see.
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