"Pete KE9OA" ) writes:
Those filters were pretty awful................I don't remember the name of
the company name, but it started with the letter K.
They were used in the NRD-515 and in the Yaesu FRDX-400. They were filled
with some sort of foam substance that turns to a sticky jelly after many
years, causing the insertion loss of the filter to degrade. Peter Bertini
had an article in Popular Communications a few years ago on how to repair
them. I did just that for a friend's FRDX-400. You have to dismantle the
filter and clean out all of the goo with alcohol..........I used a product
called Flux-Off.

Of course, one pays quite a bit for Collins mechanical filters, and
that's always been the case. Those Japanese mechanical filters were
significantly cheaper, at least back then. Reading the old magazines,
I've sometimes wondered if at least some times people were calling
ceramic filters the wrong thing.

Your description of the insides reminds me that some guy wrote about
a homebrew receiver in the early sixties, I think it was in CQ, and
he made his own mechanical filter. No, I don't have it handy and
can't specify the issue, but every so often I come across the article,
and wonder how practical it was to do. It seems like we'd have
read more about doing it if it was something easily doable.

Michael