If B&S suffers from the Conn syndrome, where internal archives were destroyed deliberatedly at some point of time by a then new owner, then maybe the museum in Markneukirchen maybe has some notes.
I have two B&S instruments imported for the opening of a new brass store in Copenhagen during the spring of 1985. They have these numbers, where the X fills the space for a non-legible digit:
I don’t really know when B&S was founded or maybe rather reorganized from existing companies. I don’t think this happened right from the start of GDR in 1949. The first mentioning of Weltklang that I remember having heard would be shortly after 1970.
Your reading of the serial # very well may be right, only that this tuba was made well before 1985.
Yes, not compact at all. Like the fun 3 rotor sample discussed some months ago, this one has no inner-body Eb loop. The re-pitching from the basic F concept is all in the longer tuning slide environment. I see this one as a true B&S in the Weltklang disguise.
Has your instrument been around Rumania or Bulgaria?
As often told the GDR had an extensive holiday resort program for its workforce in an effort to keep down discontent. I have seen abandoned GDR workers’ camps in Bulgaria in 1993. GDR was, aside from space technology, the technological and quality product front rider within the Warsaw pact. They paid Rumania and Bulgaria partially with instruments for their orchestras and state bands. However GDR feared these countries trying to obtain $-convertible currency (DM, UK pounds, Danish kroner, and others) by re-exporting these high quality instruments, so they “downgraded” them by engraving them Weltklang rather than B&S.
Today we consider the S-links obsolete, but they were normal back in 1968. So my point still is that your tuba really is a B&S.
