I have a 3gp1 crt and wired it for the pilot tv but all I got was a dim green square and no pic. Is it possible that being this tube has the cathode wired in with the heater it won't work with the type of tv it is circuit wise even though I have a separate 6.3 transformer wired in the set already for crt protection. Just a green square, anyone know why this is ?

Try a test pattern with horizontal gray scale bars, NOT the usual vertical ones.
Capacitance of the heater to ground won't bother that.