Watsup people! new to the forum and line 6.just picked up a used (but never really used) spider valve 112 mkii. the guy who sold it to me barely ever used it and never changed the tubes since he bought it in 2015. seems to work fine for now but first question... Should i change the tubes now before i really start playing with this amp? is there a way to tell if the tubes are still good? also just want to make sure these are the correct tubes for this amp. https://www.long-mcquade.com/46848/Guitars/Parts/Sovtek/Pair_Of_Matched_5881WXT_Tubes.htm and https://www.long-mcquade.com/13150/Guitars/Parts/Sovtek/12AX7_-_9_Pin_Preamp_Tube.htm and lastly do i need to bias my amp when i change the tubes? Thanks guys!