[R-390] Filter pins

[Dan Merz]

Hi,  Pete, John, and Todd and thanks for the helpful comments.  I wonder where I can get a
male 9 pin plug.  I have a vector tube extender but it's a shame to ruin that and it's not
really constructed  to make it's use easy for my application.  I suppose I could make a
socket into a plug by putting pins into it that would extend into the chassis socket.
Seems like somewhere there would be some 9 pin plugs???  I do like the idea of keeping the
original socket on the radio chassis,  Dan.

ToddRoberts2001@aol.com wrote:

> 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.
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