I have some experience with the JJ ecc99, 801s, 802s and ecc803s Myles. The stock Valvet P1 and Soulphonos come with JJ 803s or Full Music 12ax7s and JJ 801s and the Soulshine preamp comes with 802s and 99s. The JJs are cleaner than the Full Musics which to me didn't seem up to the task for phono use especially with SU ratios of 1:20. Head to head with matched and balanced TFK 803s and 801s, they in turn are noiser, less extended in the top end and the noise takes a bit away in lower midband definition by comparison. Still over all, I find them very good, probably my favorite new production tubes right now. Findings are similar with the 802s. I haven't compared the 99s with anything else. 12bh7s can be used but aren't exact substitutes. Jules at EMT likewise ships the PR66s with JJ 803s. Same impressions when compared to TFK 803s.
I have some experience with the JJ ecc99, 801s, 802s and ecc803s Myles. The stock Valvet P1 and Soulphonos come with JJ 803s or Full Music 12ax7s and JJ 801s and the Soulshine preamp comes with 802s and 99s. The JJs are cleaner than the Full Musics which to me didn't seem up to the task for phono use especially with SU ratios of 1:20. Head to head with matched and balanced TFK 803s and 801s, they in turn are noiser, less extended in the top end and the noise takes a bit away in lower midband definition by comparison. Still over all, I find them very good, probably my favorite new production tubes right now. Findings are similar with the 802s. I haven't compared the 99s with anything else. 12bh7s can be used but aren't exact substitutes. Jules at EMT likewise ships the PR66s with JJ 803s. Same impressions when compared to TFK 803s.
I have no direct experience with these tubes, but when I was re-tubing my Jolida a few weeks back I relied upon the advice of a local gent who's been working with tubed equipment for 40 years. He specifically told me to stay away from JJ tubes because of high failure rates and they can go out violently upon occassion. Apparently they don't take high plate voltages well. Take it for what its worth. I took his advice and re-tubed with Svetlana 6550C's and have been very happy with the decision.
I don't know about their signal tubes though, obviously high voltages should be such an issue.