just a quick note, if you are using the green, and yellow with a green stripe, for the 5v rectifier fillament. then make sure you cut and heat shrink the end of the 6.3v green/yellow lead. once the rectifier is on, that extra lead will have your full DC voltage riding on it. so make sure it is not touching anything. there are some transformers that do have a center tapped 5v lead, but that is never a ground lead. it would be your HV lead. i have seen many hammond transformers like this. also do not make a artificial center tap for your rectifiers 5v, only for the 6.3v going to the rest of your tubes.