I purchased some NOS 1953 Sylvania 6Y6G in their original Leprechaun green boxes. They look mint and they tested fine. I had cleaned the pins with DeOxit and wiped them off. I placed them in the unit and turned on both sides. The left side amp would only light the 6Y6G's and the 12AU7 input. The other tubes (6X4; OA3, OC2) would not light.

I popped the 6X4WA into the tester and it would not light. What would cause this sudden tube death? I put the OC2 back in and it lit. I have to check the OA3 tomorrow.  

I replaced the 6X4, OA3 and OC2 and the unit works fine. I am so agitated by this experience that I cannot clear my head to evaluate the 6Y6 versus 6V6 sound.

From bad to worse. With the new Sylvania 6X4 rectifiers in place I turned on both sides. A light show ensued in the right side 6X4 rectifier and the whole unit went down. I guess it blew a fuse. I took the 6X4 out, tested it and it is shorted. I never had this trouble with the 6V6 tubes.  

I noticed that the right 6X4 tube was rocking in the socket. That might be what caused it to short out. I put a new 6X4 in there and bent the pins outward slightly so they would all make contact. I changed the fuse and put in my Tung Sol reissue 6V6's, new 6X4's and all is well.  There did not seem to be anything wrong with the 6Y6's I tried.

After reflecting further on the whole episode, I am convinced that the 6Y6 tubes were very frisky. One of them was either arcing slightly or just presenting the rectifier with more current than it could handle. As a result of this I am stocking up on regular 6x4 variants and also am securing an adapter to use the 6CA4/EZ81 rectifier in place of the 6X4. This was O.K'd. by Steve and I am anxious to try the new rectifier.