I use a three valve tuba, but have been playing around with 3d printing an 'extension' to replace the main tuning slide with another valve that could direct the air flow through a longer pipe, just like in 4-valve tubas, but cheaper and lighter (so easier to march with). Does anyone know if any products like this exist, as I haven't yet got it working?
That's a neat idea. But there are some technical problems you'll meet when you perform with it.
You know already that many trombones have a trigger that adds an extra loop of tube, dropping the pitch of position 1 by a perfect fourth.
The side-effect of adding that loop of tube is that each slide position also has to be lengthened slightly to be in tune.
If you add an extra loop of tube to your tuba, for the sake of argument, let's say the extra loop lengthens the instrument by 10%, the open notes will be in tune but the notes that involve your other three valves will be slightly too sharp. They need to be 10% longer too.
Valved low brass instruments often use a compensating system where each piston valve has extra ports in it, allowing the instrument to play in tune whether fourth valve is pressed or not.
You'll be able to use your add-on provided each valve's tuning slide can be adjusted to be in tune with the lengthened instrument.
Also, your fourth valve will be on the main tuning slide, which will make it harder to hold the instrument and operate the fourth valve at the same time.
That’s wild! Cool idea, if you could get the tolerances close enough with your printing for it to blow right it’d be like a Coolwinds or P-Trumpet valve added on 😄
If all goes well, it’d act like a non compensating four valve horn. I’m gonna go out on a limb and say the large majority of four valve tubas don’t compensate, so that’s def par for the course.
Check out the “plug-in” (added onto the tuning slide) 5th valves that were made for Yamaha YEP321 Euphoniums for a while, if you could find a big rotor kickin around, you could maybe use that levered design to have something more permanent put together!