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Can anyone please help me with this grand old Barth Musik Stuttgart 5/4 BBb.

It has removable grub screws in the back of each ornamental valve backplate - presumably for venting purposes[?] Ever seen this before? Also, it blows beautifully with a rich, full German sound and has great flexibility. What do people generally think of these instruments?

They're not vents.

Those are to tighten up for taking up the slack caused by loose/worn/poorly fitting rotors as the bearings get worn. It helps eliminate some of the slop and clanking.

I've never seen the Barth tuba model you're talking about, but it's an idea they copied from Miraphone.

Those look like Miraphone valves.

the elephant wrote:And yes, that is a take-up screw. It can help remove vertical play in the valve. It is not a permanent solution but can be very handy.

And, when overtightened, can lead to stuck valves.

Many many thanks. It was probably made for Barth [who became 'Radio Barth'] by Miraphone in those days. The valves look original. There are some archive photos of a brass manufacture line at Barth - probably early 20th century.

Yes, indeed, when fully tightened they actually stop the valve movement!

It sings so beautifully and is so nimble that it could well be a Miraphone. Unfortunately, I have to sell it. It looks terrible and really deserves a complete overhaul! Perhaps I'll try tubenet - but my tubas are all in UK. They will shortly be on ebay.

There at least WAS a Musikhaus (Music Store) Barth in Stuttgart, and like a number of other large music stores in earlier days, had
their store name stenciled on the brass instruments they sold. Giardinelli in New York sold their own flavor of Alexanders, there was
a large music store in Kansas City that had their own line (stencilled Conns), and Musikhaus Barth in Stuttgart sold Mirafones. Musikhaus
Christian Reisser of Ulm-Donau in Germany had their own line that was stencilled Rudolf Meinls, made by the grandfather of the current
Rudolf Meinl.
I have never heard the term, "grub screw," but what you have is a very effective way to removing excessive end-play in the rotor. Traditional
rotors have tended to have a cone shape inside the middle of the valve back cap. To adjust these, one must have a flat steel piece that is smaller
than the inner threaded portion. Mounted in a vise, the technician can put the cap on the special anvil, then carefully hit the ball in the middle
of the cap with a straight-down motion. This action will drive the cone inward enough to remove the end-play, and if done carefully-enough,
helps make for like-new rotor action. It is possible to drive the cone too far, in which case one would very, very lightly tap downward on the stop arm
to loosen the adjustment a little and restore enough clearance for the valve to work. Rudolf Meinl, Jr. taught me how to do this, and I have been adjusting
traditional rotors in this way for 25 years now. I wouldn't recommend trying this to anyone, as I shall not be responsible for the outcome unless I do it
myself!
The Mirafone way of doing this is to center-drill the cap in a lathe, thread it to 3mm x .5, and use an adjusting screw that is essentially 3mm x .5 all-thread
rod, with a screwdriver slot in the flat end, and filed to a point on the other end. For tuba rotors where the valve bottom cap internal cone has been trashed,
my solution has been to do as outlined above, making my own screws, and removing end-play from the rotors. I view this as more than just a temporary fix, and
it has worked for me on any number of instruments. Yamaha rotors have their own system, employing a moveable, pressed-in internal bushing, that will also
effectively remove end-play.

Very useful information Mr. Stofer.
Thank you!

Thank you so much Mr Stofer.