Tung-Sol 6550 - Current Issue

Just curious has anyone had any issues with these tubes? I replaced my Sovtex 6550 (as they were a little long in the tooth) with the Tung-Sol back in September and since then I've had two of the Tung-Sol die on me (seems like I get three or four months and then one of them dies). I have a Jolida 502A and I had the amp checked out in December and replaced the resistors and capacitors by Deja Vu Audio so don't really think it's the amp. I like the sound of the Tung-Sol but their reliabilty seems to be not so great, especially with their 6550s. The Deja Vu guys have been good about replacing the tubes, but nevertheless I'm wondering if it the amp or the tubes? I live close enough to Annapolis (50 miles) that I could take the amp to Jolida have them check it out, but if it's the tubes then I might be better going back to the Sovtex. Of course I'm wondering if the tube sockets might be going bad?

Thoughts anyone?
Hello, CUH -
Not sure this will illuminate anything for you...perhaps more by way of commiseration. I have a JoLida 502B. It came with stock Sovtek 6550s that ran without problem for almost 6 years. They seemed bullet proof. I went to JJ/Tesla KT88s and had reliability issues similar (I think) to the failure frequency you encountered with the TungSols. I am now using Penta Lab (Shuguang solid plate) KT88s. So far, so good. My B is now almost 7 years old. Haven't replaced any of the circuit components to date but have been thinking lately about a rehab.
I bought a quad that have been going strong for around 200 hours. I bought them in March from a reputable dealer. He told me he burns them in and tests them carefully. He said he returns all that are below par, and actually got a call from the rep. asking why his returns were so high. It seems they have some quality issues.

I'll keep you posted on mine but so far they are a fantastic tube in my VSi-55.
I currently have quads installed in Mac MA2275, Audio Research CA50 and a pair in my ASL MG SI 15 DT (single ended)all integrated amps. The CA50 is tough on tubes but these have been in for about 6 months with no issues. The MA2275 has been up and running with them for about 3 months and the Pair in the ASL MG SI 15 DT have been in for Just over a year also without problems. See the attached link below for Jim McShane's take in AA.