Bad resistor, cap, diode, transistor, new doesn't mean every part is tested Johan. Some may be marginal and not caught. That's why Joe specs only those that have been shown to be reliably good parts, but even then some can slip by. Another thing to drive a guy crazy, and another thing that makes each amp different, a difference in tolerance can make them different, don't know if it's audible in all cases, but I'm bettin in some it is...