I've owned tube amps since the mid 60s, and I will never stand for even a moment of any crackling sound. Others may tolerate that sort of thing, or think up silly explanations based on nonsense to explain it (flakes falling on the cathode? really?), but tubes should sound fresh and noiseless or they will not be used in any of my hifi or guitar amps. I've had preamp tubes (new or vintage NOS) last far longer than predicted by so called "experts" and have had others basically explode immediately...ya never know, but the damn things are generally trouble free for their life span, and any noise gets 'em tossed.
must you play music to break in tubes
I have some GE 12ax7 longplate tubes that make some loud crackling noises. The Seller claimed that this is common with nos tubes and that it will go away after they are broken in, but it is too alarming to hear and sounds risky to the speakers. Might leaving the amp powered up for a while, but with no signal passing, break them in adequately? Kind of hate wasting the power tubes lifetimes, but I don't have any old tubes to use in that amp.