I am going to try to tighten up the spare Argosy/Corsair I 4 pole xtal filter from 2.4 kHz to as close to 500 Hz as possible. If someone out there could look at a Model 217 or 219 CW filter and let me know what the values of the shunt capacitors are it would give me a head start on my experiment. 73 & Tnx for the help. Tom WB1FPA