[R-390] Filter pins
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[email protected]
Thu, 5 Feb 2004 16:01:50 EST
Hi Dan, I believe the Collins-type 9-pin plug-in mechanical filter as used in
the Mackay tube receivers is the F455 J series, the same as is used in the
75A-4 receiver. Collins made a whole series of filters to plug in the 75A-4, the
F455 J 05 (500 Hz) the F455 J31 (3.1KHz) the F455 J 60 (6.0KHz) and some
in-between sizes. I think they made a F455 J08 and possibly a F455 J18 but not
exactly sure. I think it would be best to keep the socket ip lace on the chassis
and either look for F455 J series filters or make up your own plug-in
replacements. That way you can always swap filters later on if needed or wanted. It is
no problem to make up a 9-pin plug-in adapter for the R-390A series filter.
Both terminals on each end of the filter are floating so there is really no
"polarity" with them. I made up an adapter myself using a 9-pin plug and a short
piece of aluminum tubing that would slip over the lower end of the R-390A
filter to hold it in place. The bottom pins of the filter are directly wired to
the appropriate pins on the 9-pin plug. I ran the top 2 leads down through 2
short lengths of RG-174/U miniature coax and thru a hole in the side of the
aluminum tubing at the bottom to connect to the other 2 pins on the 9-pin socket.
The shields of the RG-174/U are soldered together at the ground pin on the top
of the filter. No impedance matching was needed and the plug-in filter adapter
works great. I used an 8KHz R-390A filter for wider selectivity of the 75A-4.
73 Todd Roberts WD4NGG.