Is this a typo ? No mention of it on the Bogner website. Never heard of a factory equipped 6L6 Uber. The original, one off proto used 6550s, then they were El34 equipped until the Twin Jet came out w/KT88s. It seems everything but 6L6s was used in factory Ubers at one time or another.
I called and talked to Charlie at Bogner today....he said they do offer the Uberschall with 6L6's (it uses a different output transformer)....but they just don't market it. Musicians Friend seems to be the only one who markets the 6L6 version. You will also notice that the EL34 one is 120 watts where as the 6L6 is 100 watts.