I think it really depends on where your overdrive is coming from. If you need a power amp tube to clip sooner then that's one thing, but it will take some serious volume before that is going to occur. If you rely on
power amp distortion and that is your need then look for a tube that is more suited for that.
Most folks get their distortion from the
preamp gain stages, usually 12ax7 type tubes. There are tons of choices and I have been trying to research the differences myself. Good information can be found at
www.thetubestore.com and if you do a web search for vacuum tubes you can dig up other sites and discussion boards.
An interesting new tube that is supposed to sound great is the new Sovtek 12AX7EH. There is also an Electro-Harmonic brand of the same type number, but ElectroHarmonic tubes are made by Sovtek anyway so it's just marketing I believe. JJ/Tesla 12AX7S tubes also reviewed well. Power tube wise, Svetlana EL34s and JJ EL34L types reviewed well also, as did Electro Harmonic. I think the holy grail of power tubes is Mullard NOS tubes but expect to fork over around $400 for a matched Quartet and they will likely by used anyway.
If you switch out power tubes, you're gonna need a bias job done by someone who knows what the heck they are doing. Don't over look that or your amp may wind up as a pile of ashes.
