This is from my own personal way-back machine (OK, I really just searching the
TT list archives for my old posting in 2001).Might be valid to the person
looking for the 208 audio filter.http://www.vectronics.com/ for one source of a
variant, but MFJ CWF filter is about the same if found used.This was a common
op-amp audio filter, same basically as audio filter in older TT rigs inside
OMNI C etc.
My personal Triton IV has an MFJ CWF board inside it for CW filtering,
installed by previous owner. I advise setting it such that it can be switched
in and out of the audio chain, as is possible with the 208 filter.
There are now other very good audio filters - the new CALF filter, Switched
Capacitor filters (NESCAF) and the Idiom Press SCAF-1 (Idiom Press' new owners
say that is back and available supposedly this month) as examples.
FWIWBrienVE3VAW
---------------This is the info I sent on the subject of the Triton IV filter.
Some of you now or in the future (archived) might find it of use.
You have a good chance of achieving filtering this way:
In the QST review of the Triton IV analog rig version ( I believe) Doug Demaw
published the FULL
schematic of the filter - which actually has 4 widths (and not just the
one the TT filter made available by their front panel switch). So if you
build the
filter and house it in a box (like the 2 width filter used by the Argonaut
509) you have a nice 4 width filter exactly as the Triton IV had (but which
did
not use all available widths). This is really simple to build, in my
opinion, since it is just an LM747 dual opamp and some caps etc. Easy to
build with prototype board (copper strips and holes), or dead bug or
Manhattan style construction.
See QST of July 1979, page 46.
You could also buy the Vectronics CW filter, which is exactly the same
filter and schematic from what I can see ( I looked yesterday and the
whole assembly and parts manual for it is online at their site in Adobe
.pdf form). While they have it set up as an external audio filter to be
used at the headphones there is no reason one could not insert it into the
audio chain inside the Triton where it works before the audio amp stage.
This is the same design as TT - it was common at the time in various
forms and I think possibly also was in QRP Classics, an old ARRL compendium.
Now, if you want even MORE fun and performance, if you look at the QST for
Sept 1981, page 17, there is an article describing how to hook in a
external TenTec Model 217 500 HZ filter into the I.F. chain, giving the rig
some good
narrow CW I.F. filtering. Very nice, taking the thing overall pretty much
into TT OMNI C territory (if I can go so far as to say that..) since one
would then have a switchable I.F. cw crystal
filter in or out, as well as a multiple width CW audio filter if you build
and use
the QST opamp-rc design from the review's spec, or use the Vectronic
filter.
The Vectronic filter is I think pretty much what the old MFJ CW-1, CW-2
etc. external filters are/were and which are found at hamfests and other
venues of used ham gear.
Hope this helps you out.
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