The 5751 is such a great stager that I can't help but say try the RCA late 50s vintage triple mica blackplates white letters or if you can the Sylvania triple mica blackplate is very detailed and tops in terms of demand. The GE tends to have a slighly overwhelming bass response which may have obscured the low level details and dynamics.
The other suggestions I would venture is the EH6CA7 fat bottle for outputs. As a rule I used JJ E34L exclusively until I heard this incredibly dynamic Russian tube. I am not convinced it will respond to every amp however so caveat emptor. I am in a wait and see position, on the Gold Lion reissue KT-77s but the KT-88s are all what they promised and then some.
If you can swing it try some 7316s in the 12AU7 position. They were made by Amperex Heerlen Holland and typically OEM labeled for early 60s computing and testing devices by Beckman and Hewlitt Packard etc. Make sure it has an acid etch with Ct, a number, (1-5 are early and desirable) then the Heerlen right triangle, with __two other numbers on a line below. These tubes can be outright halographic. Yes they are expensive but supposedly very long lived. There are always a couple of pairs on e-pray every week. I rarely had trouble if the seller gives you the etching info.
The other suggestions I would venture is the EH6CA7 fat bottle for outputs. As a rule I used JJ E34L exclusively until I heard this incredibly dynamic Russian tube. I am not convinced it will respond to every amp however so caveat emptor. I am in a wait and see position, on the Gold Lion reissue KT-77s but the KT-88s are all what they promised and then some.
If you can swing it try some 7316s in the 12AU7 position. They were made by Amperex Heerlen Holland and typically OEM labeled for early 60s computing and testing devices by Beckman and Hewlitt Packard etc. Make sure it has an acid etch with Ct, a number, (1-5 are early and desirable) then the Heerlen right triangle, with __two other numbers on a line below. These tubes can be outright halographic. Yes they are expensive but supposedly very long lived. There are always a couple of pairs on e-pray every week. I rarely had trouble if the seller gives you the etching info.