As was mentioned, a powder inside the envelope is a classic sign of a loss of vacuum. Although a leak at a tube pin is most common, In recent years I've seen a leak in the glass seam that runs from the top to the bottom of the tube. Normally these tubes are eliminated in the quality control process but some slip through. This can happen when a defective tube is pushed hard.
Maybe I've been lucky but this has only happened to me once in decades of tube amp use. Rest assured that this isn't normal, tubes can have a very long service life. Here are some guidelines for when to change tubes: Tubes | TalkBass.com.
Maybe I've been lucky but this has only happened to me once in decades of tube amp use. Rest assured that this isn't normal, tubes can have a very long service life. Here are some guidelines for when to change tubes: Tubes | TalkBass.com.
