Kinda has me baffled. For equipment background, I have two Mesa PH210's and two PH212 cabs. Been using a Mesa Prodigy since mid summer. I mainly gig with my two 210 cabs, all's been fine, casino work, amp is on for 4-5 hours usually. The 212 cabs mainly stay at home and rarely only come out only a couple times a year. A week ago decided to bring just one 212 and the mentioned Prodigy. First couple of hours the rig sounded fine. After hour 3 the attack started sounding squishy and by hour 4 it was hitting distortion pretty easy. I didn't hear any of these noises two weeks prior with the Prodigy and both 210 cabs. So I figured the power tubes being original and over six years old are probably done, but I still didn't touch them yet. Yesterday hit a thrown together jam with some new players. I brought the Prodigy and only one of my PH210 cabs. We were playing loudy and for 3 hours...and I didn't get any squish or distortion, so that tells me the amp and its tubes are fine. Ok, so seems the drivers in that PH212 are doing whatever I was hearing. But never heard that before and why did it take 3 hours before doing it? Casino work is not loud at all-they keep low stage volumes, the amp volume is only at 9'o-clock and the bass knob setting is actually cut from center. I suppose I need to take the grill off and check for any rubbing.