[R-390] Mechanical filter postmortem

[Jerry Kincade]

Since we fearlessly get into molecules on this list, I'll throw this one in:
Many types of foam = many different chemicals in their makeup. Stick some in
a small sealed container with several types of metal for a while, especially
under heat, and no telling what chemical migration will or won't attack the
metals inside. Maybe there's more to this than just grabbing some handy foam
and putting it in. OTOH, if it's blown to start with, what the heck....
:-)
73, Jerry W5KP

----- Original Message -----
From: "Jordan" <jordana@nucleus.com>
To: "John Kolb" <jlkolb@cts.com>
Cc: "Barry Hauser" <barry@hausernet.com>; <r-390@mailman.qth.net>
Sent: Monday, April 08, 2002 2:14 PM
Subject: Re: [R-390] Mechanical filter postmortem


> Yes the foam sheet I have used is a form of closed cell foam....I don't
know how
> well it would hold up if you were resoldering the filter case, the Yaesu
filters
> are not soldered near as much a the Collins filters are, but then the foam
was
> used when they were both originally soldered, so....?    73 de Jordan...
>
> John Kolb wrote:
>
> > On Mon, 8 Apr 2002, Barry Hauser wrote:
> >
> > > You wrote
> > > > I have repaired several Mechanical filters in Yaesu gear, but they
open a
> > > > lot easier than the Collins filters do... In the Yaesu filters, it
is
> > > > usually migration and decay of the 'foam' padding that causes an
increase
> > > > in loss through the filters... Yes I have had to resolder a couple
of the
> > > > pick-up coil leads also.. 73 de Jordan...
> > > >
> > >
> > > Did you replace the foam stuffing?  If so, with what?  Is it
necessary?
> > >
> >
> > When I repaired a couple  of Kokusai filters, I used loose cotton
> > from the filler in a medicine bottle. Someone recently (Barry?)
> > reported using a sheet of closed cell foam, which sounds like
> > a better idea to me.
> >
> > Comments on Buzz's postmortum - GREAT!
> >
> > That wire he pictures "sticking up in the middle" that's
> > the magnetostrictive element - if that breaks off, writeoff
> > the filter.
> >
> > Judging from my experience with the Kokusai filters, yes
> > the polyfoam in the Collins filter could get on the disk
> > elements and cause them to become more lossy. If the filter
> > bias permanent magnets became weaker, that could also be
> > the cause of a weak filter.
> >
> > I've repaired a small number of Collins filters with open
> > coils - if the wire breaks at the terminals, it's an easy
> > repair - once found a  filter with a terminal that had never
> > been soldered. With care, a wire broken halfway between
> > the filter coil and the  terminal can be spliced. If the wire
> > breaks at the coil on the outside of the winding a little
> > can be unwound and extension soldered on.
> > If at the end of the body but coming from the coil pi winding
> > from the other end of the coil, It can be losened from the
> > glue blob and extended. If the broken lead is from the inside
> > of the coil - the part next to the core, the coil is toast.
> > I have, however, done a coil transplant from another filter.
> >
> > After spending lots of time holding a 250 watt iron trying
> > to unsolder the case on D/E case or the small V case filters,
> > I gave up and just cut off the filter end with a mototool
> > with cutoff wheel. Save the end piece and glue  it back
> > on with hotmelt glue.
> >
> > > Just a sec... YO!  BACK THAT TRUCK FULL 'O FILTERS IN RIGHT HEEEUH!
THAT'S
> > > RIGHT, A LITTLE MORE, COME BACK .. COME BACK ... WHOOOAAAA!  UNLOAD
'EM
> > > BOYS!.
> > >
> > Actually I do have a box of bad filters waiting for the time
> > I can get back to trying to repair more of them - have never
> > been willing to sell them as I've afraid I might end up buying
> > one of them back at the swap meet labeled good  :) All the open
> > coil ones have been worked on, sucessfully or not. Remaining
> > 40 or so have more serious problems. No R390 filters
> > among them however.
> >
> > Commercial plug- e-mail me if you want a copy of my list
> > of filters for sale.
> >
> > John
>
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