Tubes are pretty variable in their internal construction from one to the next. Sometimes all that this will mean is that one tube reveals more of the heater filament to the eye than does another. If one tube shows a noticably different color than the rest (usually either much whiter or bluer), or its intensity goes up or down periodically as it is being run, then you need to check it out. But this is one reason why I might hesitate to buy an auto-bias amp - you don't have an easy way of checking whether a tube is operating in its optimum range, or how far out it might be from the other tubes. Even 'pre-tested' tubes can arrive out-of-spec.
Tubes that Glow Different
DOes it mean anything when tubes on my amp sometimes glow less bright than other tubes that are of the same "batch"? I have some 6SN7s where one of them isn't glowing as brightly. Sometimes, my output tubes also differ in how they glow... the longer I leave the amp on, the more the same their glow becomes...what's up with that?
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- 5 posts total