Gary -

    Per your request here's my experience on replacing the 8KHz first IF filter in my R4C with the FT/International replacement GUF1:

    Physical Installation: This is a much smaller physical package than the original Piezo filter. It seemed to me that the easiest way to install this was to locate the filter in approximately the same place on the chassis, and drill 4 new holes for the two mounting screws and two I/O leads. I made a cardboard template of the holes required and marked them with permanent marker, then drilled 'em out. The one lead from the transformer needed to be lengthened, and it was installed within an hour.

    Operational Differences: In Wayne's words the filter "transforms the receiver". Now, what I lack from Wayne's experience is a ton of time behind this receiver so I'd have a better feel of the change........so I can't give a very good A vs. B comparison. You might want to anticipate some tests to conduct BEFORE you replace the filter so you have something objective to compare it to. Let me at least tell you about some of the things I noticed after surgery.....

    When you turn the receiver back on....it still sounds the same. Not much difference there....however what I started to get a real appreciation for was its' selectivity near to loud stations. This is something that plays real havoc with my Yaesu FT757Gx...if I am within 20 KHz of a very loud station I can still hear him creating intermod and splatter or clicks. Not so with the Drake....I think that this was pretty good prefilter change, but now I am astounded in how well it handles loud QRM.

    Just a quick test....I found a 40dB over S9 SSB signal on 75M I could not hear him 3KHz later on the high end of his signal, and he disappeared after 2KHz on the low end of his signal. (I have the stock 2.4KHz filter installed). I found a 30dB over S9 signal on CW, and he was completely gone within 500Hz using the 500Hz filter.

    In a way, using this receiver is really strange now, since when you're on a particular frequency....that's it. You're not going to hear the rest of the band along with it. You have to FIND stations now.

    Let me know how it goes if you decide to go for it.