"Michael Black" wrote in message
...

Well there were other manufacturers who made mechanical filters in
the sixties. You'd see them in the Lafayette catalog, and mentioned
in reviews (though I've always wondered if some of those reviews got
it wrong, and they weren't mechanical filters). But they were never
commmon. They were cheaper than Collins filters, but I have no idea how
absolutely cheap they were for the time. I don't recall coming across
real specs in the old magazines, either. I also recall in recent years
that it was those other filters that used foam rubber inside, and by
now much of that has deteriorated.

Michael VE2BVW


I had that happen with the filters in my NRD-515 JRC receiver.
Fortunately, it wasn't too difficult to open the filters up, which
allowed me to dissolve the old foam rubber
blanket that cushioned the mechanical filter elements. The
foam had to decayed to a chewing gum consistency and the
filter losses skyrocked. These were late 70s or early 80s
vintage IIRC. Regarding the patent issues, I don't recall
the particulars.

Pete k1zjh

Uncle Peter wrote:


I had that happen with the filters in my NRD-515 JRC receiver.
Fortunately, it wasn't too difficult to open the filters up, which
allowed me to dissolve the old foam rubber
blanket that cushioned the mechanical filter elements. The
foam had to decayed to a chewing gum consistency and the
filter losses skyrocked. These were late 70s or early 80s
vintage IIRC. Regarding the patent issues, I don't recall
the particulars.

Pete k1zjh

Does the name Kokusai ring a bell? I used one in a hoimebrew set in the
mid-70s and it was a really good filter. But alas, I recall hearing
later that this was one of the brands that had the foam problem.

-Bill

"Bill" wrote in message
...
Uncle Peter wrote:


I had that happen with the filters in my NRD-515 JRC receiver.
Fortunately, it wasn't too difficult to open the filters up, which
allowed me to dissolve the old foam rubber
blanket that cushioned the mechanical filter elements. The
foam had to decayed to a chewing gum consistency and the
filter losses skyrocked. These were late 70s or early 80s
vintage IIRC. Regarding the patent issues, I don't recall
the particulars.

Pete k1zjh

Does the name Kokusai ring a bell? I used one in a hoimebrew set in the
mid-70s and it was a really good filter. But alas, I recall hearing
later that this was one of the brands that had the foam problem.

-Bill

I'm hearing more ringing than might be attributed to my
tinnitus affliction.....

Hi,

The "DX Engineering" rf speech clipper models
made for both the Collins 32S-3 and for the KWM-2
used a Kokusai mechanical filter following
the clipper stage. You'd remove a tube
from the IF strip of the Collins transmitter,
plug the DX Engineering device into the tube socket,
and plug the tube into the DX engineering device:
and Bingo, you have a speech clipper available.
There was a toggle switch included for in/out control.
Your effective clipping level was determined by the transmitter's
original audio gain control.

They sounded pretty good on the air,
compared to many "processors" of the time.

The British KW company used a Kokusai filter
(model MF-455-10AZ) in their KW2000 SSB transceiver,
which was pretty highly regarded.

A Kokusai filter assembly (including two matching transformers)
cost around $20 in the Lafayette catalog.
A Collins filter cost about twice that in the early 1960's.

I saw a Popular Electronics article, about adding a mechanical
filter by replacing an existing IF transformer in a receiver.
In the article, he used a resistive load in the plate circuit
of the previous stage, and capacitor-coupled
to and from the two Lafayette matching transformers.
I guess he didn't trust the transformer voltage rating.

I recall a Japanese web site had pictures showing
the disassembly and cleaning of a Kokusai filter.
I believe he used acetone to clean off the gunk
that had once been the foam plastic shock absorber
surrounding the mechanical filter disks.

73,
Ed Knobloch



Does the name Kokusai ring a bell? I used one in a hoimebrew set in the
mid-70s and it was a really good filter. But alas, I recall hearing
later that this was one of the brands that had the foam problem.

-Bill