Sorry for resurrecting an old thread. But for those who still own this amp this is what I've found in terms of the tubes that I've tried in the Audiotailor Jade, the original version. I listen to the Jade fed by a Little Dot DAC_01 using FLAC files through an optical tolink from the computer. A couple of years ago I had also swapped out the Infinicap 0.22uF-630v upgrade with some AmpOhm, polyester in oil/aluminum foil, FE-XAL-AL. I had to install the 0.33uF-630v version because the company ceased operation and the 0.33uF were all that was left in stock from one of the retailers. I'm very sad for the loss of that brand because these capacitors are a wonderfully transparent capacitor through which I can't sense any coloration. The Infinicaps seemed to me to be lacking that transparency.
I listen with Sennheiser HD650's and the type of music ranges from acoustic, electronic, industrial and classic rock. There's a variety of tracks of good and poor recordings I use for some critical listening. Nine In Nails, Mat Kearney, Diana Krall, Pretenders, Three Dog Night, Arcade Fire etc.
Reissued Mullard 12AX7 2-mica, grey plate, halo getter (B-)
Bass and mid-range are not as defined as they could be. A little shallow there. The treble is not as controlled as the Raytheon (windmill). The treble does have graining which likely contributes to the lack of definition, or clouding, of the bass and mid-range definition. Probably a B- tube but a decent/average tube.
Reissued Genalex 12AX7 Gold Lion 2-mica, grey plate, small halo geter (B)
An improvement over the Mullard 12AX7. More definition in the bass and mid-range which is probably helped by a slightly cleaner treble presentation. Nice reproduction in the upper mid-range, improves on vocal translation. So there is more control in the treble than the Mullard. But am still hearing a bit of a lack of control and am unfortunately hearing a bit of slurring contributing to less precision and definition in the treble. There is decent channel and instrument separation I think due mainly to the improvement in the mid-range performance. A B tube.
Sylvania JAN-5751 2-mica, grey plate, halo getter (B+)
A more controlled, refined, treble presentation than the 12AX7's above. The details of an acoustic guitar comes through well. The mid-range is improved a bit more but for some reason the lower mid-range and bass feel just a wee bit recessed, not a prominent issue though. This isn't a big issue because the treble is much more smooth/controlled and which helps to improve imaging. A decently defined bass presentation none-the-less. More balanced than the 12AX7's but some may not like the recess in the upper treble I'm sensing. I can't distinguish where the frequency is dipping exactly because the very highest frequencies are being retrieved well enough. It doesn't hurt imaging but the retrieval of treble detail might not be as prominent as some would like. Not quite an A tube but a very good B+ tube.
Raytheon JAN-5751 2-mica, black plate, windmill getter (A-)
This tube improves upon the Sylvania grey plates. The same treble smoothness but with a more prominent treble extension. I really like the lower treble presentation. For some reason the presentation on some tracks there's a bit of a lack in depth. Weird because this tube does better with the frequencies where the Sylvania grey plates are lacking. It might be the mid-range. The mid-range is just shy of the clean definition of the Sylvania grey plates. Good channel separation though. Everything else is quite good. Very good with the treble smoothness and extension. The lower bass is well defined... there's just something missing in the lower mid-range. In general, an improvement over the Sylvania 2-mica grey plates. An A- tube.
Sylvania 5751 (consumer version not the ruggedized) 3-mica, grey plate, halo getter (A)
Definitely more refined in the treble than the Raytheon. These have a very sweet treble. The mid-range and bass are wonderfully detailed but with just, and only just, a hint of looseness. What always hits me about these is the smoothness and control in the treble. It might be a little too smooth for some but they're still very good at retrieving detail. Hence the sweetness/just-right sense coming from the treble. Still... this may not be for everyone. For this reason the impact in the treble might appear lacking. And for this reason I'd say they're not quite as balanced as the black plate version of this tube. If there's anything fatiguing about this tube is that the musical detailing will relax you. But with something like Nine Inch Nails I find these expose details that one might not hear otherwise. But again, the treble smoothness might not match the heavy or industrial rock genre, but I like it. These lack a bit of the edge of the black plate version but are an A tube because of the detail retrieval. I bought these in a guitar shop and were supposedly made for a specific guitar amp. This isn't the usual place I buy tubes.
Sylvania JHS-5751 3-mica, black plate, square getter (A+)
This is the best of the 5751 tubes I have. The treble is clean, the bass is tight and well defined, and a very good mid-range presentation. There's good detailing/imaging/instrument separation. This results in a very smooth/sweet/balanced tube. There's also just the right amount of authority in the presentation. It's impossible to get perfection but so far this is my A+ 5751 tube. If I were to be nit-picky I'd say it could do with a bit more instrument detailing and retrieval. What I mean by that is the impact of the presentation might distract the the detailing. But even then that's hard to argue over with this particular tube.
Forgot to mention that I use the RCA 6AS7G power tube. Wouldn't mind trying a Tung-Sol 5998 or the mythical round bottom, brown base Chatham's... but alas...
Added May 1, 2012:
RCA 5751 3-mica, black plate, square getter (A-)
Very similar in construction to the Sylvania black plates. I'd say these would be on par with the Raytheon's I tried, but on par for different reasons. The RCA's are a very good tube. There's smoothness in the lower treble range with just a hint of high treble smearing. This isn't a sibilance or a grainyness, just a hint of treble sloppiness/smearing. Because of this the RCA's don't quite resolve as well in the treble as the 3-mica Sylvanias, nor the Raytheon, but are still just oh so close. A really great mid range for clarity in the instruments. However, the bass articulation is lacking just a bit of definition. Bass isn't quite as resolved. It's not detrimental, but it can't quite match the Raytheon or 3-mica Sylvanias. However, the overall presentation is more similar to those 3-mica Sylvanias in that the tube does sound balanced even with the slight shortcomings. But even still, I'd rate these on par with the Raytheon, but forvery different strengths than the Raytheons. The RCA's don't have the treble clarity of the Raytheon, but are still very competent in the treble. That hint of smearing in the treble means it's not quite as resolving in the treble as the other A tubes. This doesn't mean that they don't have good extension into the treble... they do. Because strings and guitars sound very good with this tube none-the-less. I think I would rate these as an A-, the same as the Raytheon. But like I said, the strengths and weaknesses of the Raytheon versus the RCA are different. The RCA seems more balanced and smooth whereas the Raytheon are a bit more impactful and treble extended.
