Haven't had a chance to read through this entire thread yet but wanted to start documenting some of my experience with tubes in hopes that others may more easily decide which is right for them.
Source: PC / Laptop / Android - Spotify 320kbps - some 24bit FLAC
DAC: Ifi Nano iDSD (smooth, musical, non fatiguing)
AMP: Project Sunrise III
Headphones: Hifiman He-4 These are detailed headphones that are sensitive to alteration of the higher frequencies (tend to get fatiguing with the wrong stack)
Reference Music: Muddy waters - The Folk Singer, Various Chesky reference samples, Lamb of God - Wrath, Alt-J, Some Dubstep / etc, MTV Unplugged albums (nirvana), Roger Waters live, Marlinsky Orchestral recordings (mixed)
Review Format: Tube (price if I know) - Rating (enjoyment) - Short Description
Shuguang 12au7 - 5/10 - Relatively flat sounding - not overly musical or enjoyable. Sound is overall a bit thin / weak and fatiguing
J/J 12au7 - 5/10 Very aggressive sound - extremely fatiguing - I did not enjoy this tube Tried it three times and took it out almost immediately.
Groove Tube 12au7- 6/10 Punchy and detailed, very refined sound with loads of separation. Vocals sounded a little artificial and the sound was fatiguing over long periods. Bass was present but not as powerful as I'd like.
International Service Master ($15) 12au7 7/10 - I bought this tube on a recommendation. It was the fourth tube I tried with the amp and I liked it best of the bunch. It was very clear and clean...but still fatiguing. It has a special liquid/sparkly character but Something about the mid-highs just wasn't quite right. Couldn't manage to listen to it at length.
RCA (tried a few)
"Clear Top" 12au7 ($9) - 8/10 - Clean and clear - exceptionally well balanced. Feels like a good reference. Not especially "fun" or special, but a solid performer. This tube almost had a "high definition" sound to me and was incredible with some of the classical performances - Not overly aggressive - just smooth enough for extended listening but not the best tube for vocals. Really high quality, especially considering the price.
"Black Plate" 12au7 ($7) - 7.5/10 Syrupy and smooth tube. Left it in the amp to warm up for a few hours and the bass became a little muddy and soft in the low end. I had a few so I tried another to the same effect. Really just a little too uncontrolled in the low end and consequently thin up top with very full / busy music (Rock/Metal esp) - This is my favorite for minimalist vocal / acoustic recordings as it is the most relaxed and least sibilant tube I've tested. It's definitely "dark" though and the coloration doesn't always work when surfing a broad assortment of music.
12AV7 unknown RCA ($2 from a swap fest) - 8.5/10 online I've read that these tubes are generally noisy and generally not very musical so I knew it was a risk. To me this is the warmest tube of the bunch. Vocals are especially emphasized and sound rich soft - just a hint of graininess though. It isn't the most detailed, but the character it imparts is very nice and midcentric. This was the best tube by far for "Lamb of God" and other such heavy metal. Bass is very tight and controlled. Really enjoyed this tube though I am sure it is technically not the top performer.
These were my impressions, I'll try to add some more detail later.
Edited by RobxMcCarthy - 6/20/14 at 5:23am