I recently replaced the preamp tubes with Tungsols and the tone is a bit improved. But still have the Electroharmonix EL34s. When I turn up the volume I get something that sounds like tube rattle. Is there a better tube to replace the EL34s for this amp? If so, what tonal difference will I hear. Also what about speaker replacement. Is the Celestion 12" vintage 30 a good speaker... or can I do better?