This relieves stress on the tubes, and allows the tubes to stay with in a 'fixed bias range' longer. Usually in the case of a fixed bias amp, the norm is to have a lower out put power. As with adjustable bias, a time will come when the tube(s) are not biased correctly and sound listless. 'Instead of having a pot to bias each channel, the bias is referenced, through resitors to a ground point. However, a member on this forum in the archives said something differently about the EL-34's in the Sophia: According to Sophia's customer email support, I would need to send my amp back to the factory in order to get it rebiased for new tubes. I am not quite sure what that means, as I am new to the tube world, but I am getting confused as to whether or not I can simply swap out the factory supplied EL-34's with any other EL-34's. I've heard many times now that the Sophia EL-34 is a 'fixed bias' amp. Specifically, I read a thread from 2006 where people discussed the possibility of swapping out different EL-34 tubes in the Sophia EL-34 integrated amp, which I own. Hey guys, this is my first post here, and I stumbled upon this forum by getting a link to the forum archives through google.

Where to ground bias guitar amp