tube suggestions for cj MV50?

I've been using a cj MV50 power amp for a number of years. Up until now, I've used mainly Sovetek EL34s and with them I've had very few failures. I would like to try other manufacturers' tubes, but am not sure where to start. A quad of Svetlanas sounded better, but didn't last more than a 3-4 months of moderate use. Maybe one of the tubes burned out prematurely, I don't know. If you have used one of these amps, I'd appreciate any suggestions as to what works and what doesn't. Thank-you!

I have had a MV-50 for a number of years. I also had reliability problems with Svetlana.
I bought some used Mullard EL34's abaout 1 1/2 years ago and never looked back. They have way more bass than the Svetlana in my system. You can pay alot for NOS Mullards, but I bought used (a pair here, a pair there)for maybe $125-$150 for a quad.
Good luck.
Anything is an upgrade from Sovtek. I am surprised that Svetlanas burned out so soon. My current set get used about 10 hours a week and is 3 years old. They still test over 85%. The Svetlanas were designed to copy Mullard. If you liked the sound but want a little better quality, spend the dough on NOS Mullards!
Did all of the Svetlanas fail or just one? Get them tested?
I have had Siemens, Sovteks, Tesla JJs and Svetlanas in my MV-50. The Svets are my favorites with there nice sweet mid-range. The Teslas are good as well. Not as nice in the mids as the Svetlanas. A little better bass. My experience with Svets mirror Enzo in reliability. Currently have nearly 2 years on a quad set with no problems. If money is no problem, NOS Mullards are clearly the way to go but the Svetlanas are the next best thing.
My C-J was the MV-55, but close enough. I much preferred the Svet's sonically over the Sovteks, and had no reliability problems with either. The Teslas sounded better than the Sovteks, though not as good as the Svet's, but I did have repeated reliability problems with them, although their higher-rated "E34L" version seemed a bit better in that regard. I have not tried the EI's, but believe C-J only rates the Russian tubes as being acceptable for this circuit from a capacities standpoint. I would give the Svet's another chance before switching - there was no area of sonic performance that I thought either of the other tubes bettered them in, and I think they generally make a very durable tube.