Problem with my Mark V? (Volume cut out in Mark IV Pentode)

[BigAl]

So today I decided to put my Mark V combo through its paces (using my 4x12 Recto cab only). I noticed something rather odd though in the Mark IV mode on my amp, and this issue only occurred when in the pentode mode. With the loop bypassed, I cranked the master to about 1:30-2:00, and whenever I hit a hard chord the volume would instantly dip, and the sound would break up. I tried this in the other channels and got no such dip in volume. I also tried this in triode in the Mark IV mode, Mark IIC+ mode in both triode and pentode, and Extreme in triode and pentode, but there was no dip. Is this a normal occurrence? It only seemed to happen when the loop was bypassed and I was really pushing the power section.


Edit: At one point, the amp switched to channel 2 by itself when this was happening earlier.


What say you?


(It's not an issue with my cables or anything of the sort - I made sure to rule that out first.)

 

[BigAl]

Nobody?

Just an update though, I won't be pushing my amp that hard again any time soon, except to see of this still happens.