Thinking back to the days when every drug store had a tube tester in it, it would have been nice to have foreseen needing one in the future and picking up one as they were pulled from the stores.......
Can using a bad tube hurt an amplifier?
If you're using a tube for a while, and everything's fine, and then voltage changes over time gradually, and then it damages an amplifier? are amps Built with controls to prevent that from happening?
How can you trust using a tube if it potentially could harm an amplifier?
Assuming You're using the correct tube in the slot provided.