Hi 2nd tenor, thanks for the reply and of course you're right: it's a BBb tuba. Thanks for the correction! The instrument maker I contacted in Germany would make a new valve for about $ 140 which seems to be quite reasonable but he needs a valve to measure the dimensions or the exact measures ...

Hi, I have a besson compensating Bb tuba from about 1920 here (serial number 111130) and the second valve is missing. The valve specialist I asked about rebuilding the missing valve told me that he would have to take the tuba apart completely to measure the valve casing which makes it too expensive ...