I’ve had this amp since 12/2018 (new) and am on my 3rd rectifier tube. Volume is always set at 8 to 9 (12 is max). I adjust down the guitar volume and sit approx 4 feet from the amp. I play the amp almost daily 60-90 minutes. Curious re whether frequency of tube replacement is normal; and whether my amp volume setting is contributing factor. Love the amp. Thank you in advance.