I ran usually my old TS440S-AT with 500Hz IF filters on USB mode for the Pactor lev 1 and 2, and for PSK31 very weak signals.
Some week ago I found in a Ham fair an FL100 CW filter for the IC746 at a bargain price, and in the last days it happened to me to have some time to devote to our hobby, and so I installed the 9 Mhz IF filter for 500Hz, FL100, on the IC746 for pactor 1 and 2 and psk31, as I am used to.
I followed the instruction on page 78 of the ICOM user manual.
After returning all the covers on, I went to page 60 of the instruction manual, to select the installed filter for the 9MHz-1 position.
I selected the FL100 . Then I went on page 42 for filter program mode setting as suggested on the page 60.
Note on the top of page 42, at the beginning of the chapter 5-11, 1st paragraph: " Optional filters ....omissis...
.. Filters can be independently selected for each operating mode."
And so I went to program mode setting and pushed the "filter" button for 2 seconds and then choosed to program the CW and the SSB-Narrow for 9M on 500Hz and 455k for 2.4 k ..... but - surprise - the FL100 was not available on SSB!
I suspiciously read carefully the manual and find nothing on selecting filters depending from mode choosen..... or relation between filter type and/or bandpass sensing... nothing. So I went to the usual "dirty trick way" to gamble with the filter program mode setting: I told the IC746 that the installed filter was an SSB Narrow 1.9kHz one, the FL223 type. All OK , hi hi ....
Then I went again on the procedure of page 42, and set the SSB-N filter mode for 9M "1.9 kHz" (hi!) and 455k at 2.4kHz.
It runs OK having now bandpass of 500Hz on SSB-N mode available for Pactor lev1 and lev 2, and PSK31. On the TS440SAT I had to correct for the IF filter frequency moving the IF bandpass slightly clockwise to fit it for the selected tone pair (1200-1400 Hz or 1400-1600 Hz) and the same had to be done on the IC746: selecting as usual USB I had to tune the outer larger one of the twin bandpass tuning about 90 degrees clockwise.
This proved to be quite a god setting for operation on USB Pactor level 1 and 2 using high tones.
I tested some lower tone pair compatible with the CW bandpass (but take care of the CW Pitch setting!!! it should be tuned fully clockwise or you'll get no audio out!) and tested with 400-600Hz, 500-700Hz and 600-800 Hz , but although the PtcII controller I use is very versatile on this respect, my ears are not, and so being used to "by ear search and pre-tuning" and then "spectra fine tuning" I endly went back to the usual 1500 Hz center frequency. I got 1500 Hz as I am also using pactor level3; before it I was using 1300 Hz center.
Here people using other controllers like KAM+ or alike have to adjust their bandpass tuning depending on the tones frequencies they use.
Actually I have not yet the FL52A 500Hz 455kHz filter; if I'll find it at bargain price I'll buy it and test it;
I saw by now that having 2.4 kHz bandpass on 455 kHz works.
I have to say that apart from this test and related trick to get the 500Hz bandpass for USB digital RX, I would not suggest asnecessary to buy and install such filters on the IC746 : with the PtcII controller you may work very well on pactor, psk31, rtty and other 500Hz bandpass modes on the IC746; (do not use the DSP and or NB, NR sometimes's good, some others no)
The same applies for the soundblaster software programs like Digipan or others, the normal bandpass is more than adequate, and you may taylor it using the twin bandpass tuning.
I recommend the narrow filters on TS440sat and alike: more,I suggest on them to replace also the 455kHz filters with other that have better performances (IN-RAD has some good ones) and the old good TS440S will copy nicely and happily very low level digital signals.
I hope this notes will be useful for some reader, I will appreciate any feedback on this matter.