Best tubes for Conrad-Johnson MV-50 or MV-52?

Svetlanas are very good . Also EH may make a nice EL34 . For the best tested and hand selected tubes try www.upscaleaudio.com.

I use Mullard EL34's for my CJ MV50. I bought them used on Ebay. I like them better than the Svetlana with Vandersteen 2CE Sigs. As far as 5751,I like the old RCA.

For 12 AX7's give NOS Tungsram's a try. Jon has some at The Tube Store. They really opened up my Quicksilver Mini Mites and were a big improvement over the Sovtek LPS tubes I was using (night and day). For EL34's I prefer JJ Tesla (early 90's if you can find them), or EH. Mullards are supposed to be great, but the price! Ouch! Unfortunately the current production Russian EL34's do not have reliability as a strong suit in my experiences. I've had several fail on me. If you buy from a reputable dealer like Jon and they do prematurely fail, you would likely be able to get a replacement. Mullards, on the other hand, have the reputation of lasting a long time. That is if you get a good set to start with. I'd be careful with the eBay sellers. It's a real mixed bag there and is certainly a calculated risk.

I like the way JJ Teslas sound on my CJ MV-55 better than the previous Svetlanas that I had.
cheers. Shahen