I did have some problems with 6550Cs this year and described the situation in some detail in a thread that seems to have been deleted. Basically, I bought a new amp and had a tube go out in 9 minutes, got another new amp from the manufacturer and had 2 tubes go out simultaneously within 200 hours, and had another another go out while on the bench for warrantee work.
I wasn't sure if I was just extremely unlucky or if there might have been some problems with the production of these tubes. Of course, the amp manufacture suggested that there was something wrong in my setup, but I am convinced there is not. It is entirely possible that a bad run could get out without detection.
I wasn't sure if I was just extremely unlucky or if there might have been some problems with the production of these tubes. Of course, the amp manufacture suggested that there was something wrong in my setup, but I am convinced there is not. It is entirely possible that a bad run could get out without detection.