European EBC90/EBC91 triodes
While these tubes do not strictly conform to the "British - Holland - German sound continuum", I have still tried to organize them in terms of their "warmness" to make this review easier for me to write and for the reader to follow. Obviously, with this many tubes (6 total?), it is beyond my limited capabilities to provide much more than a few cursory comments regarding differences in tonality. Even so, I hope it is enough to help others decide which they might be interested in procuring.
To begin, I have to say that all of these tridoes have seemingly unbounded crystal-clear highs, with a tight, low and punchy bass. Moreover, they are all excellent tubes, differing primarily in warmth and fowardness. Sonically I believe these triodes are equal rivals to pentodes and yes, even heptodes, and I encourage everyone to try at least one. :)
First , the warmest and most mellow are the Tungsram EBC91. These are cozy and comfortable with excellent highs. I might call this a very safe tube.
Second, we have a tie. The Mullard EBC91 and the Philips Miniwatt CV452/EBC90 (6AT6). These tubes have a similar warmth to the Tungsram, but are just a bit brighter. Even though the Mullards were manufactured in the Blackburn factory and the Philips in the Heerlen factory, these two tubes sound identical to me, and in fact, appear to have identical construction. At the least, the EBC91 should have more gain, but since the LD 1+ is configured to derive no gain from driver tubes, it is hard for me to discern small differences in output level. Either way, if you like the warm, classic Mullard sound, either of these is a keeper. Excellent tubes.
Third, the Telefunken EBC91. These are less warm than the Mullard, but brightness and trebel detail is about the same. I did not find them as foward and bright as the Telefunken EK90 and EH900S. So if the Mullard sound is just a little too warm for you, these just might fit the bill. These too are excellent tubes.
Fourth, the Lorenz EBC91. These are noticably less warm than the Mullards, but still, as AFB notes, while they are quite forward, the vocals have this sultriness about them, which is hard to describe. That and the crystal-clear highs and strong bass, make these quite special in my opinion. Again, excellent tubes, but they require some time to fully appreciate them.
Fifth, the Amperex EBC91 (AKA RCA 6AV6). Yes indeed! Amperex put their BugleBoy name on these black plate RCAs! These are similarly forward like the Lorenz, but the vocals are smoother and more neutral. That and the crystal-clear highs and strong bass make these a standout for those who eschew the classic Mullard warmth. Since they lack the upper-bass / lower-midrange warmth of the Mullards and the sultriness of the Lorenz, these might seem to have less bass presence. However, the bass goes just as deep and has just as much punch. So on the "Euro-Tubiness Continuum", I judge these RCAs as the most "German" of the "European" tubes I have heard to date! lol
Hope this is helpful to somebody... And now I am ready for a break! :)