Hi all

I received my FL-33 9.01MHz IF filter yesterday and quickly installed
it into my R71, following all the instructions in Don Moman's
excellent R71 Performance Manual. The thing is, I can't hear any
difference with it installed. I was wondering if anyone knows a way to
check if it's actually working or not.

I replaced the stock 455KHz 3rd IF 6KHz ceramic filter with an LFH4S
from Kiwa a few months ago. This has a -6dB bandwidth of 6KHz, a shape
factor of about 1:1.7 and an ultimate rejection of 70-75 dB. The FL-33
also has a -6dB bandwidth of 6KHz and a shape factor of about 1:2. It
has an ultimate rejection of about 90dB. Because the Kiwa is slightly
tighter, I didn't expect to hear much difference on any but the most
powerful signals, but while switching between the on and off positions
on the filter switch on the main board, I could detect no difference
at all. Even removing and re-inserting the FL-33 produced no
detectable difference to my ears, or to the reading on the S meter.

I had imagined that the filter would make a difference in ultimate
rejection. To test this, I tuned in the strongest AM signal on Medium
Wave, tuned about 5 or 6KHz away until I could only hear a bit of
splatter, and then flicked the filter switch between on and off.
Again, no difference between the Kiwa alone, and the Kiwa preceded by
the FL-33.

I used short wires between the snipped ends of resistors R58 and R52,
as recommended in the performance manual, and this had the result I
expected, namely causing a 2KHz offset in the narrow AM mode, but I'm
wondering if I should be able to hear a difference with the FL-33 in
AM wide.

Any help or suggestions would be most appreciated.

Thanks

Andy