[R-390] Mechanical filter postmortem

[John Kolb]

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