Hi Friends! I need to change all the tubes in my 400 + I have read many post about this, I think the power tubes going to put this: (Winged C) Winged "C" (SED) 6L6GC If someone recommends something better I would appreciate it forever. Respect to the preamp. I have many doubts. Leave that has original tubes (I've read that the valves do not need to be changed before long) Or change a better tube. But I do not know what can be better in the preamp. Thank you for your contributions.