Hello Warren,I would have a new set of tubes on hand .You can compare the
sound quality between the old and new to give you an idea how worn your tubes
are.Also to get an idea what is changing as the tubes age.I ve noticed in guitar
amps that the sound gets duller,less vibrant as they age .Kind of like a set of
guitar strings getting old and flat sounding.You can also keep a set of old tubes
to remind you how much better your amp is sounding with the new,or newer
tubes.Ive noticed some of the worn tubes seem to lose some volume as well.
sound quality between the old and new to give you an idea how worn your tubes
are.Also to get an idea what is changing as the tubes age.I ve noticed in guitar
amps that the sound gets duller,less vibrant as they age .Kind of like a set of
guitar strings getting old and flat sounding.You can also keep a set of old tubes
to remind you how much better your amp is sounding with the new,or newer
tubes.Ive noticed some of the worn tubes seem to lose some volume as well.