Not sure how you determined that. The 0-252 wires are your mains - the power from the wall outlet. Depending on where you are you use the 0 and the 120 or the 220 or the 240v to wire to the mains. That leaves you with the 16-0-16, which makes about 20vDC. And the 8-0-8 which makes about 11vDC.This transformer can handle two 6L6GC and two 12AX7 without any problem ( I think ).
Your tubes all require 6.3vAC for the heaters. You could use DC for that, but The voltages are wrong as they come out. You'd need to use some resistors or something to drop that 8v down a couple. And then there is the thorny problem of no high voltage for the tubes. If your 252 had been a secondary we could have used it, but it is not. You have no high voltage winding.