The AN/URA-17 and AN/URA-17A AFSK converters were changed from 2550 Hz center frequency to 2000 Hz center frequency in the 1960s.

I believe the AN/URA-17B already had the change to 2000 Hz center

I know that the AN/URA-17C and AN/URA-17D were 2000 Hz

There was an earlier Field Change that may have been cancelled - it switched the filters from 2550 to 2000 and called the new unit AN/URA-53. I have never seen a URA-53.

Changes to the URT-17 manual to cover 2000Hz change, AN/URA-17A, AN/URA-17B, and AN/URA-53

 I have the following manuals on line

AN/URA-17

AN/URA-17C

AN/URA-17D

Note - URA-17E, -17F, and -17G are completely different units