Hi,

I recently re-found a homebrew receiver that I built back in the 80s and
am going to try to get it going again.

My question is regarding the Kokusai MF-455ZU-21H mechanical filter.
This was a popular filter in its day and I wonder how well they hold up
over time? I know some of these things had foam that
melts/disintegrates into mush. Any comments or observation on this
particular type would be appreciated.

Thanks,
Bill WX4A/KP4

On 27 Feb,
Bill M wrote:

My question is regarding the Kokusai MF-455ZU-21H mechanical filter.
This was a popular filter in its day and I wonder how well they hold up
over time? I know some of these things had foam that
melts/disintegrates into mush. Any comments or observation on this
particular type would be appreciated.

I had one in my KW2000A. It lost sensitivity and drive due to filter
degrading. I unsoldered the can and removed the goo that the foam had become,
much improving performance but it's still well below par. The transducers or
transformers at the ends of the filter are easily damaged and also likely to
fail. Somewhere on the internet are details for refurb. There was also an
article years ago on upgrading to a crystal filter but I can no longer find
it. I've now given up on that rig and gone to an SDR one.



--
G8AOE
Change lycos to yahoo to reply

wrote:
On 27 Feb,
Bill M wrote:

My question is regarding the Kokusai MF-455ZU-21H mechanical filter.
This was a popular filter in its day and I wonder how well they hold up
over time? I know some of these things had foam that
melts/disintegrates into mush. Any comments or observation on this
particular type would be appreciated.

I had one in my KW2000A. It lost sensitivity and drive due to filter
degrading. I unsoldered the can and removed the goo that the foam had become,
much improving performance but it's still well below par. The transducers or
transformers at the ends of the filter are easily damaged and also likely to
fail. Somewhere on the internet are details for refurb. There was also an
article years ago on upgrading to a crystal filter but I can no longer find
it. I've now given up on that rig and gone to an SDR one.



Thanks Brian. I was afraid of that. I never had the radio up to 100%
originally. It was a homebrew and I guess its like a new project
nowadays with all the pieces there to troubleshoot. Its not a
'necessary' rig but I'd sure like to get it in shape for old times
sake...if I can. It was a learning experience before - some things
don't change, do they?

Regards,
Bill

On Sun, 27 Feb 2011, Bill M wrote:

Hi,

I recently re-found a homebrew receiver that I built back in the 80s and am
going to try to get it going again.

My question is regarding the Kokusai MF-455ZU-21H mechanical filter. This was
a popular filter in its day and I wonder how well they hold up over time? I
know some of these things had foam that melts/disintegrates into mush. Any
comments or observation on this particular type would be appreciated.

I don't know which filters had the foam problem, all I remember hearing
about is "Japanese mechanical filters".

But they have been discussed before, I think here but maybe in the
boatanchors newsgroup. I can almost picture someone detailing how to
renovate them. I just tried "mechanical filter" foam and that gets
some relevant hits, but apparently aquariums use "mechanical filters" so
there must be some word that would limit it to radio. One post had a link
to a webpage, but the webpage is no longer there, so doing a more careful
search of the mewsgroup archives and then a websearch might help.

Michael VE2BVW