During practice last night, my 6100 started having a problem, a few low pops, and then the power went to about half. I quickly stopped, and looked over the amp, I noticed it felt hot, I checked the tubes and 3 were glowing brighter than normal, one seemed less bright. I shut the rig down and changed the setting to low power (50 watt, from 100 watt), still in Pentode mode. I double-checked all the cable connections. I fired it back up, and it was still playing lower, but sounded fine otherwise, that only lasted about 2-3 minutes, as I was watching the amp, I looked at the tubes, through the vent hole, and the tube that was glowing lower, was now a nice bright blue glow. I immediately shut the amp down - the tubes are TAD premium select 24 hr burn in, EL34s, only about 6 months old. 1. Do you think this is just a bad tube? 2. Do you think any damage was caused to the amp, because of the bad tube?