Since we're on the subject, let's talk about changing your tubes. . .
Preamp tubes have a much longer life than power tubes. You are not likely to have to replace them unless one or more tubes fail. Preamp tubes can have a life span of at least two to three years and usually much longer. If it’s been a few years or you regularly change your power tubes and feel like the amp has become lifeless, it may be time to freshen up your preamp tubes.
If you play regularly, power tubes should be changed every 6 months to a year. If you don’t play frequently, they can last longer. NOTE: While power tubes can simply and suddenly fail, they generally degrade over time. So while your tubes may be working, they will not sound the same as they get older. People often go years with the same power tubes and never replace them claiming, “Well, they still work fine.” You can be assured that the amp, however, does not sound the same as it does with new, functioning tubes. DON’T WAIT UNTIL YOU HEAR A DIFFERENCE. FOLLOW A REGIMENTED TUBE CHANGING SCHEDULE TO AVOID HEARING A DIFFERENCE.
When it is time to change power tubes, bias should always be checked. It is easiest to have a qualified tech retube and rebias your amp.