A) There is a horrible ringing from my tubes when I hold a power chord out. My power tubes ring like crazy (sounds like a broken lightbulb being shaken) whether they're hot or not. B) I want to change them because of this and because... C) My distortion channel is really saggy/ spongy. I suspect poer tubes will tighten it up. D) My preamp tubes are fine, newish, and minimally microphonic. Should I change the tubes? If so can I just order a matched pair of EL34s? I don't really want to rebias, so how can I ensure that I order the right grade of tubes?