OK i'm a novice at this game, i use an atomic reactor and the sound went crackley a few weeks back but i tolerated it, now the sound is muddy as hell and the tone is gone, the amp is over a year old and i use it every day and often loud so my guess is the tubes have gone. It uses jj EL84's they look simple to replace just yank them out and put new once in, is this correct or do they have to be biased (i'm still not sure about this process) ? :fingersx: