Last night I performed surgery on an RF-4900 to replace the pathetic
narrow ceramic filter. the LF-B4 has been replaced with dual LF-D6
configuration. the previous spec was 4K at 6db and 15 K at 40db !!!
BAD !!!
new spec is about 7k at 6db and 11K at 60db, incredibly sharp
selectivity. performance is FAR superior. project took only 15
minutes. I hope write an article soon with pics.