[1000mp] PTT with outboard filters

[Thomas Beltran]

I use either a Timewave 599zx, or an NIR-12 outboard filter with my Mark V.  On CW, both filters have a feature, where a PTT line can be hooked up, turning off the filter, so that one can hear the unfiltered sidetone.  I also use an SB-220.  I thought the proper way to get the PTT switching on the outboard filters, was to use the TX GND plug, which I also use for my SB-220.  This doesn't seem to work.  Is anyone else using a similar filter?  If so, how does one obtain the PTT switching?  Tom W6EIJ