Wooaahhh! Evil tube

[slayercannibalsuffohead]

My XXX started to loose bottom end today, thought it was just my ears, then a hum started to appear, then it got louder and PEEWF! Did a fuse.
Decided to take the fuse from my 6505+ (which I checked was exactly the same), switched it on and the same damn hum appeared again with the loss of the bottom end also. Checked the back of the amp and the 1st EL-34 was glowing like satan, (completely bright orange), while the other 3 were fine. I thought it was going to melt!
So my assumption is that shes fucked, so I thought Id ask if I need a complete quartet overhaul, a duo overhaul, or knowing the number on the box, can I replace just the one? My hunch is at least a duo is on the board. Any help appreciated.

 

[GuitarHack]

Ideally you should replace all 4 with a matched set. A matched set should last longer since all tubes are doing the same amount of work. Picking up a random tube and putting it in may not be any worse than what came stock with the amp though. My 6505 came with an extremely poorly matched set. In that situation 1 or 2 of the tubes do more work than the others and consequently they don't last as long as the others. Maybe that was what happened in your case.