I've only demoed these with HE-500s which I know are not ideal with the amp; however, I hope this will be useful information regardless.
Tubes tried so far:
Hytron JHS 6AK5: tl;dr: “tubey,” incredible soundstage depth, rolled off highs
RCA Black Plate 6AK5: tl;dr: Textured, clear, detailed, excellent impact on kick/snare/piano, depth/breadth of soundstage, slightly muddy on very complex classical passages
Tung Sol 6AK5: tl;dr: Accuracy with a noticeable hint of warmth.
GE JAN JLRV 6AK5: tl;dr: very flat, sometimes to the point of being unengaging. best for classical.
Alo’s Russian Tubes: tl;dr: 4/5, a bit veiled but warm, very good for vintage recordings/ vinyl rips.
Hytron JHS 6AK5
I hated these at first but they grew on me. They’re on the warmer end of the tubes I’ve tried without sacrificing too much accuracy. They might be the fastest of the bunch. The busy passages in Chopin’s Sonata No. 3 are really well articulated. The bass impact on John Lee Hooker’s “No Shoes” was particularly engaging. Fun, yes. Crisp, probably not. Jesus christ, as I was writing I put on Agoraphobia by Deerhunter and it sounded shockingly good. Really excellent instrument separation and three dimensional presentation. Soundstage isn’t the widest but that is by no means a huge issue. These might be my favorite with my go-to first test track, Roygbiv by Boards of Canada. Bass is strong and tight but the treble is a bit rolled off, I think. Orbison’s vocals are also unbelievably syrupy and smooth. The female vocal harmonies over top of Blue Bayou are really warm and soft. These are my favorite tubes with Brian Jonestown Massacre’s “This is Why You Love Me.” The vocals aren’t too raspy, the three guitars are very evident as distinct entities, and the jangle isn’t too abrasive. Bass guitar sounds magnificent with these, better articulated than any of the other tubes.
RCA Black Plate 6AK5
These are probably my favorite of the bunch. They’re pretty remarkable at pinpointing aspects of recordings I hadn’t noticed before.I’ve literally been listening to Blue Bayou by Roy Oribson for years and this is the first I’ve noticed that there’s a harpsichord. I also never really noticed before how ******* annoying Anton Newcombe’s voice is. They can get a little congested with very complex classical passages but aside from that they can’t do much wrong with me. Impact on piano keys, kicks and snares is the best of the bunch. They presented the boominess of the kick on Slint’s “Breadcrumb Trail” really well. The soundstage is also the widest I’ve come across so far. Vocal presentation very forward and pleasant. Of course, forward vocal presentation on recordings with vocals that are already egotistically advanced will sound a bit uncomfortable. Slightly recessed vocal recordings like “Wish I Was Skinny” by the Boo Radleys come into their own with these tubes. The highs are detailed but not abrasive at all. It’s a fabulous tube for warm songs, I’m really enjoying John Lee Hooker’s “No Shoes” right now. I’d say these tubes are more “textured.” Old jazz recordings are particularly smooth with astonishing soundstage depth and spacial reproduction.
Tung Sol 6AK5
These tubes are really punchy and warm without sacrificing the high end. They have a wide soundstage with not as much depth as the Hytrons, for example. The articulation on Chopin’s third sonata is the best of the bunch. I’d say these are likely a tie with the RCA’s as my favorite. The busy passages remain both musical and legible. These edge toward accurate bass, with less weight. I’d call these somewhat airy.
GE JAN JLRV 6AK5
I found these to be too bright and abrasive for any phones but the Hifimans. That said, they do pretty marvelously with the micro details to make your FLAC feel “extra lossless.” I wish I had my turntable here, I think these would complement vinyl pretty well. These handle the more congested passages of Chopin’s Third Sonata in B minor much better than the RCA’s; however, they sacrifice some of the low end impact of the RCA’s. Nonetheless, these are probably the better choice for classical; they are especially good with strings.
While the guitar portions of the rock songs I listened to (Agoraphobia- Deerhunter, Glass Museum- Tortoise, Hillbilly Motobike- Stereolab, This Is Why You Love Me- Brian Jonestown Massacre) were especially detailed and fun, vocal presentation falls flat. They do, however, give the music a sense of space. I could hear the room in which Anton’s vocals were recorded. The same goes for jazz, linear presentation at the expense of some of the dynamic characteristics. Dry tubes have their uses. I much prefer these tubes in the Little Dot.
Alo’s Russian Tubes
Pretty, pretty, pretty good is the short answer, I guess. They’re relatively engaging with any electric guitar-type music, good depth of field , but they were noticeably veiled with a lot of things I put in front of them. The treble extension made for some abrasive highs on jangly tracks. These are reasonably good for electronic music, I think. Bass response is a little better than okay. I think where they really shine is on vintage recordings. They lend something to stuff that was recorded on tape probably because they’re warmer. Vinyl rips of the Velvet Underground and Roy Orbison were very pleasant.