[Collins] F500B31 filter follow up

[Grant Youngman]

Yes, I'm still looking for one!  Maybe two.  If for no other reason than to compare filter loss and passband shape to establish some kind of baseline for what should be expected.

I opened up the dead one (the new one I received toady) and found that one of the magnetic wires that drives the resonant disks had broken loose.  Trying to align, straighten, and weld it back in place is far beyond my tools, patience and eyesight.  The little magnetostrictive needle is almost invisible.  I only found it because after it came loose, it found it's way to one of the bias magnets and was just hanging there … and discovered the hard way that it is EXTREMELY delicate.

But … unlike R-390A filters, there was no old support foam or goo or any sort of mess inside the case.  I found a clean filter assembly mounted using a couple of large rubber grommets.  Whatever the material, it was still soft and supple, and showed no signs of degradation.  

So presuming this filter is similar in construction to other B-series filters, I'd guess there shouldn't be an expectation of the innards turning to goo over time and causing issues, and that the filters should be reasonably reliable for some time to come. It may be that the welds will end up being a bigger problem down the road than the support material.  There is also no obvious reason that degradation in performance of these filters would naturally be expected with age.

Here is a photo of the filter:   http://home.roadrunner.com/~nq5t/500b31.JPG

Grant NQ5T