[AMRadio] Not AM, but a question about vintage

[CL in NC]

I am redoing a Galaxy V MK 2 that got on the cheap.  The manual says there is a CW filter that plugs in the back in an IN/OUT set of phono jacks.  I have been unable to find any info on this filter, the manual says it is the Galaxy F3 Selective Filter.  My old catalogs have the rig, and a line item for the filter, but nothing else.  Does anybody have a pic or schematic of this unit?  Taking a guess that it is  a tunable unit like the ones used in receivers similar to the HQ129X and others with a 'Phasing' control of one crystal and a coil/capacitor.

Charlie, W4MEC in NC