Another report on tube rolling with this thing. When reading this, note that I’m totally new to tubes and tube amps so have no reference points... Amperex 6DJ8/ECC88 ‘A-frame’ with orange ‘PQ’ label, Heerlen 1972 Amperex JAN 6922 with orange ‘globe’ label, NY 1967 Electro-Harmonix 6922 (stock tube), Russia 2017 Telefunken ECC88, Berlin 1972 Short version: Telefunken or Amperex A-frame (depending on taste) > EH > Amperex 6922. The A-frame is smoother through the mids, particularly the upper mids, and is slightly more extended in the treble than the stock EH. Bass is stronger but more rounded at the edges. The EH seemed to me the lightest of all in the bass and has a slight peak in the mid-treble. The JAN Amperex lacks the A-frame’s smooth mids as well as its (and the EH’s) treble extension. It seems to have more amplitude in the bass, but doesn’t seem as coherent across the range as either of those others. The Telefunken is more extended and precise than the A-frame and EH at both ends, but not as smooth as the A-frame in the midrange; it comes across as more ‘analytical’, but is great at bringing out microdetail. Although the label was worn on this one it otherwise looked like it might not have been used, and did seem a trifle smoother after c. 24 hours of burn-in (the other tubes were more obviously used and I didn’t give them any burn time). The rest of my chain is Mimby and HD6XX. The entirety would be viewed as being on the warm side (Marv’s first impressions of the MCTH as neutral were of a pre-production version; well-known warmfolks – you know who you are – later declared the production version slightly warm). I’ve decided that while I’m not one of the warmfolk, neither am I obsessively 'neutral'. I go between preferring the Telefunken and the A-frame, appreciating the former’s technicalities and extension but the latter’s smooth presentation. I suspect I’ll be switching between them depending on mood & genre. Others’ preferences will depend on chain and tastes. In the same chain, those who prefer more warmth would likely pick the A-frame every time, those who lean more neutral, the Telefunken. Personally I'd wish for a combination of the A-frame's smooth midrange and the Telefunken's highs & lows, but I like both well enough that I'd rather spend the hunting-time listening and the money on more music. I should say that I didn’t find the EH hugely different from the other two in either respect, so I’m not saying anybody should roll tubes; I really only did it because I hadn’t before and thought it’d be fun to see if I could hear differences (and as usual was amazed that I could). Also – I have a second A-frame, purchased as a pair with the one described above, the two having date codes within 6 weeks of each other, supposedly testing within 3%, and having a similar history (Tektronix stock). @msommers heard this second one before I did and found the highs to be noticeably truncated vs the EH. When I subsequently compared the pair, the characteristics were otherwise the same – but #2 was indeed rolled off in the treble cf. #1. #2 looks like it’s had more use, and I know it’s no news to the experienced that there are variations between used tubes of identical manufacture. Indeed it was noted in the tube rolling thread that there’s little correlation between a tube’s test results and its sound.