Adding a derived ground to the heaters for the signal tubes is a must if you dont have one on the transformer. For the rectifier, it is not carrying signal so not to worry. But if you did that with an octal rectifier like the 5Y3 or 5AR4 etc, you would be grounding your B+ through a 100 ohm resistor, which is a No-No.
Did you use a choke across the 33uf caps? The Lightning has a hi gain front end. No choke & it could hum.
Any hum is going to be most pronounced when gain and master volume are turned all the way up. What if you dont turn the master all the way up & just the volume?
A picture would really help if you can post a link to it. Then we could look it over.
You can look over the TC-15 post and see how to wire a 15. In that build, I didn't have a choke to use! and it's pretty quiet.