I have an old Sunpak 3600 thyristor flash unit which I was warned not to connect to my D90 which was fair enough. The other day though I received a set of Yonguo RF-603N to use as a wireless remote shutter release. As these are also flash triggers I'm wondering if I could these to trigger my old Sunpak or am I still facing the same voltage problem? (I have read the thread on the forum regarding flash connectivity but I don't have a volt meter) Any help gratefully received.