In the meantime, here are some pics of all the heptodes I've been testing in the last weeks (including boxes when relevant):
The Telefunken 5915/EH900S made by Sylvania in the US of A in 1977, aka Tele/vanias 5915, with the Bundeswehr West German military "eagle". Probably my second best tubes at this point.
The Telefunken boxes -they look nice and genuine don't they?- with part of the military tags.
The "real" Telefunken EH900S, actually made by Telefunken in Ulm, Germany, in 1975, and with gold pins -not that it matters.
The -atypical- Telefunken boxes the tubes came in, just for reference.
The Philips E91H, made and labeled for IBM in Heerlen, Holland, D-getter, 1960. Probably my third best tubes at this point.
The Haltron, made by Siemens, CV453 (one tube labeled CV453, other 6BE6/CV453), aka Haltmens EK90 or Haltmens CV453, made sometime, somwhere. Note the dark getter flash, thick ribs on the plate and the holes next to the the fold on the plate (also number on the base); these look exactly like genuine Siemens EH90, so the probability of a Siemens origin is very high. Not that it matters anyway; these are my best tubes yet -and that's unburnt-in!
The colorful Haltron boxes the tubes came, with CV453 labels and neither 6BE6 nor EK90.
The other -yeah, I wasn't going to run the risk of a dead tube ordering, like, the last pair of Siemens EK90 in the world lol- Haltron, made by Siemens, 6BE6, aka Haltmens EK90 v2 or Haltmens 6BE6, made, yet again, sometime somewhere... Note how different these are from the other pair of Haltmens with different labels (both tubes are labeled 6BE6 and nothing else), thin ribs on the plate, more "clear" appearance and getter flash, and still the holes next to the plate fold (and still a number at the base); Siemens origin again seems like a given here. Apart from the holes close to the plate fold, these are virtually identical to the genuine Siemens EK90 seen on pics in this thread. I have yet to even test these, but I'd at least like to know which of my two pairs is the more recent production, for reference.
The boxes the second pair of Haltmens came in, very different from the other boxes; don't these look "older"?
And finally, the Telefunken EK90, made by Telefunken in Ulm in 1973. Untested.
Typical Telefunken boxes these came in; smaller than my other Tele boxes though.
Just for feedback on heptodes up to here, and different strapping techniques:
- Tele/vanias 5915: unstrapped = excellent (natural and good ambiance, great soundstage, a bit tube-y compared to 1-7), 1-7 strapped = excellent (awesome soundstage and detail, feeling of "being there", a bit thinner than unstrapped)
- Telefunken EH900S: unstrapped = very good, best setting (a bit forward, pretty detailed, interesting house sound), 1-7 strapped = pretty good (too forward "in your face", a bit bright and fatiguing)
- Philips IBM E91H: unstrapped = excellent, best setting (natural and cozy signature, detailed, good soundstage), 1-7 strapped = very good (same as unstrapped but brighter and more fatiguing, less natural and a bit thin), 2-7 strapped = pretty good (less thin than 1-7, less focus than unstrapped, much I like is lost on that setting, worst out of the three)
- Haltmens CV453 (Siemens EK90): unstrapped = glorious, best and only good setting (natural and realistic soundstage and detail, great focus and sense being there, outrageously engaging), 2-7 strapped = pretty good (almost all of what I like unstrapped disappears, more blurry, much less focus, not as natural, and also brighter and fatiguing)
I'm trying to like the 2-7 setting -I really am- but I can't... I keep trying, it gives different results for each tubes, and it makes somewhat sense to "neutralize" grid 3 by cathode strapping, but it always turns out to sound worse than the two other setting -or just the basic unstrapped setting- so I think I'll stop burning up my tubes sockets with that mod, at least until a few people encourage me to try again.
1-7 strap, though losing in favor for some tube type like the 6BE6, still sound great on some 6BY6 tubes imo; the strapped 5915 are very very good!