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