I would like to share some initial impressions of a few heptodes.
There is something about the Amperex E91H, a special quality that I really like. Although the treble is very slightly rolled off (more "tuby"), it has a great musicality and balance and even between heptodes it sounds that bit cleaner and has a better focus ("spooky"). 1/7 sounds fine, At the moment, I haven't decided which strapping is the best. Mainly I am still making up my mind between 1/7 and 2/7. 1/7 and 2/7 sound louder than unstrapped, which is a small problem. Besides, 2/7 sounds opener than unstrapped, a bit more forward and brighter. 1/7 is in between.
After some more listening, my tendency goes to 2/7 (again ;) ) as this removes (most of) the treble roll off and makes the tube more engaging.
The Siemens EH90 would be brighter, sounding a bit more engaging if you wish, with a focus quite close but not exactly there. The EK90 (saucer getter) would be following them in terms of focus, not exactly as open sounding but with a very similar signature to the EK90. To me, so far the EH90 sounds better than the EK90, almost a brighter version of the Amperex but not quite.
First impressions of the Russian 6A2P are that their focus compares with the Siemens EK90, their treble is quite nice because it is extended but round as well.
The comparison was done with the 1/7-strap for all and all tubes perform on a really good level. I am going to look at them some time later again after more burn in. The Amperex was burned in most (~ 18 h), others were about 10 - 12 h.
Edited twice: Corrected Siemens type in the 6A2P impression and Amperex differences between 1/7, 2/7 and unstrapped.
Edited by Acapella11 - 6/30/13 at 4:45pm