One of my first jobs was at a electronics tube,and some other supplies such as tv antennas,picture tubes,etc. dealer.In my grade schools years,I tested tubes for service techs,and the public.They had about 5 testers,and some were better than servicemen had.While working there,I tested literally in the thousands,maybe tens of thousands of tubes.I've found the opposite of what they state to be the case.Yes,an amp that is not properly designed,or rapid cycling of the power switch can cause problems.But as a general rule,the failure rate back then was highly in favor of the tube failing more often than the amp causing the problem.An old out of spec amp is a different story.I still find tube failure to be more common than an amp problem,decades later.Here is the link to their statement.>>[http://www.emissionlabs.com/html/articles/white-spark.htm]
