I have a modded 834p deluxe. I use GE 5751 black plate silver clip in the first position closest to the front. Of all the tubes I tried, this tube gave the best extension on both ends and the best bass by far, not really a choice. The middle and end tubes took a bit longer to find a match. I was told by EAR that these positions are the left and right output tubes, but one is NOT for the right and one for the left. 1/2 of one tube is for the left, and the other half of the same tube is for the right, ditto for the other tube. This allows for a sonic blending.
I tried many combinations and settled on Sylvania black plate 5751 for the back position, and a Mullard cv4004 for the middle. The sylvania brings the vocals a touch forward with a wonderful midrange, and the Mullard has very nice extension. I could go on trying different combos for years, but at some point you say that sounds great, stop listening to the tubes, and start listening to the records again. I just recently added 2 of Herbie's "sonic stabilizers" to the top of the EAR, and was quite blown away with the improvement, the next day I ordered 2 more for my Cary slp-98. Highly recommended.
I tried many combinations and settled on Sylvania black plate 5751 for the back position, and a Mullard cv4004 for the middle. The sylvania brings the vocals a touch forward with a wonderful midrange, and the Mullard has very nice extension. I could go on trying different combos for years, but at some point you say that sounds great, stop listening to the tubes, and start listening to the records again. I just recently added 2 of Herbie's "sonic stabilizers" to the top of the EAR, and was quite blown away with the improvement, the next day I ordered 2 more for my Cary slp-98. Highly recommended.