I have a Bugera 333xl head with 4 Bugera EL34 powertubes in it. I am thinking of buying a set like these: http://www.thomann.de/gb/tad_jj_el34_roehre_quartett.htm.

I plan on replacing the whole lot just so I can improve my tone a little bit (because ive heard the Bugera tubes suck). My question is: Do I need to rebias if I were to replace my stock Bugera tubes with that set?
Main Rig
Korg Pitchblack > Digitech Bad Monkey
Peavey 6505+ 112 w/ 2x12 (Celestion Vintage 30 and WGS Veteran 30)
[Effects Loop] Boss GE-7 > Boss CE-5 > TC Electronic Flashback
Yes, tubes are generally sold as matched sets but still need the bias set.
Unless you get tubes with the same voltage rating as your old tubes, you should rebias.
Hi, I'm Peter