I always buy my power tubes in sets of 4 matched tubes. That way, if you blow one at a gig, you can quickly swap in a replacement without rebiasing. And if you don't blow any, when the first two are spent, simply replace them with the remaining pair. Also, if possible, ask the supplier to give you the bias numbers as, assuming you like how they sound, you can then order similar new tubes, again without a need to rebias. Indeed, some tube suppliers pre-match their tubes this way and you simply order by number, e.g., MESA.
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