Hi

I'd suggest the Kiwa filters regardless, but especially if you have
the older version. I have the newer version, which uses filters
labelled as LF-H2S and LF-H6S. You can open up the case to check
whether these are present in yours. I believe older versions contained
Murata CFW455H and CFW455I filters, and these had inferior ultimate
rejection and shape factors. My receiver was purchased new in early
2002, and the manual still showed the Muratas on the schematic, but
the receiver came stock with the LF-H series filters, which are pretty
good. The only real problem is that AM wide is too wide for SWLing.
The stock narrow is good, however.

Passport's White Paper gives the following measurements for the
earlier (pre 11/93)and revised versions:

Early:
(shape factor, -6dB/-60dB)

Wide AM: 7.6/17.9 KHz {1:2.4}
Narrow AM: 6.9/17.2 KHz {1:2.5}
Ulta Narrow AM/SSB 2.6:3.7 KHz {1:1.4}

Revised:

Wide AM: 9.1/15.3 KHz {1:1.7}
Narrow AM: 4.5/7.7 KHz {1:1.7}
Ulta Narrow AM/SSB: 2.6/4.3KHz {1:1.4}

Passport measures the newer filters as having an ultimate rejection of
70dB+, whereas I believe Radio Netherlands review tested the older
version as having U.R. of around 50dB, which is poor.

The SB filter is the same in both, so this was probably a sample to
sample variation, but you should be able to tell if you have an
improved version or not by switching between the AM wide and narrow
positions. If the difference is marked, you probably have a newer
version. The AM wide sounds nice on a clear signal, whereas the AM
narrow sounds a bit muffled. (Hint: get the Kiwa audio mod as this
helps big time).

If you have the older version, the two bandwidths sound virtually the
same, or so I'm told. If you have the newer version, I'd definitely
recommend replacing the AM wide filter as it lets in too much splatter
and annoying hets. The Kiwa narrow is also better than the stock
narrow, but the difference is small.

Hope this helps

Andy