[ct-user] PTT interface problems

[n4zr@contesting.com (Pete Smith)]

I am trying to use the classic CT/TR/NA interfaces (with a 2N2222) to both
key CW and switch PTT on my Mark V from an LPT port.  The CW keying works
fine but the interface won't switch the PTT.  Any ideas on how to beat the
problem?  It appears that the interface may not be pulling the PTT line low
enough -- haven't I read something somewhere about a passive "pull-down"
circuit that could be used (mirror image of the "pull-up" resistor
notion?).  If so, I can't find it now (and I have looked). 

Any help much appreciated.

73, Pete N4ZR