Burning question about two VAC amps and dead tubes

I borrowed a friend's PA 80/80 and like it so much I bought a PA 100/100. While borrowing the 80, I noticed the tube on the far left overheating. I took it in and replaced all 8 tubes, the unit had never been retubed. It was plugged directly into the wall. When I picked it up I did not reinstall it in the system as the 100 had arrived. Everything was fine for a week aster i iinserted the 100. I then noticed a hum in the left channel coming from the speaker. The hum got louder. Tonight while idling, the far left tube went black, the other three overheated. The bias lights were all green. I turned it off immediately. The first set of tubes were original vac tubes in the 80. The tube that died tonight and took the other three with it were gold lion reissues with RCA clear top 12au7. I have another quad of gold lions and Mullards but am afraid to use them until I get some advice......power issue, demonic possession? I'm open to suggestion. It seems like more than a coincidence that the far left tube would fail on more than one amp.