To be honest, I'm not really sure... I bought the amp about a month ago, and I've only used it for weekly practices (2-3 hours) at moderate volume. I've asked the previous owner, waiting on a response.
Most excellent, cheers for that man, I'll definitely keep this in mind. Had a management change at work this week and the new guys are taking over this sunday, have two other jobs lined up so I'll see how I go