Main tuning slide

[roweenie]

Invariably (with one exception that I've seen), main tuning slides on front action piston tubas* have two different bores on each of the legs.

Is there something about this specific location that makes it necessary to increase the bore?

What would be the pluses or minuses of having a MTS with the same bore on both legs?

*edited for clarification

[bort]

I've always thought it was less about being "necessary" than it is about being "convenient." That is, after all of that cylindrical tubing through the valves, you've got to start getting conical pretty quickly after that. Why NOT use 2 different bores in the MTS? Don't some trombones do that as well, smaller bore in the top tube of the slide, larger in the bottom?

Is the one exception the Hirsbrunner HB2P (with the MTS in the leadpipe loop)? Just guessing, but it seems like a change in bore before the valve set would be pretty weird.

[iiipopes]

Invariably (with one exception that I've seen)....

My 186 is the same on both legs. King tubas and souzys are the same on both legs. Most tubas that have a main tuning slide in the leadpipe before the valve block are the same on both legs.

[roweenie]

Invariably (with one exception that I've seen)....

My 186 is the same on both legs. King tubas and souzys are the same on both legs. Most tubas that have a main tuning slide in the leadpipe before the valve block are the same on both legs.

If the King you're referring to is the 2340/1, I beg to disagree (I can't speak to the sousaphone).

(I should amend my original question to apply to front action piston tubas only, sorry for the miscommunication.)

[roweenie]

Ok, so here's my situation -

The valveset I intend to use has a bore of 20mm/.787 exiting the 4th valve, but the small side of the tuning slide I've got is 19.5mm/.767.

I could use a MTS with 20mm bore, but then that gives me a mismatch on the large side, where the dogleg is 20.5mm/.807 bore, and the larger MTS would be 21mm/.826 on the large side.

Follow so far?

Now, what I could do is use a crook that is 20.5 on both sides, provided that a single bore MTS wouldn't screw things up sonically.

[roweenie]

Sorry, piston

[roweenie]

Actually, 20mm seems pretty standard these days on the 4th valve. The other 3 valves are 19mm.

[roweenie]

I guess I'm old school. It used to be you never saw a piston set Larger than 750 to prevent the valve stroke from getting too long

I'm definitely old school, too

The older Bauerfeind (and Böehm & Meinl too) valvesets were 19mm/.748 bore through all 4 valves, but at some point they seem to have transitioned into this larger 4th valve scenario.

[Dan Schultz]

Ideally... the entire tubing length should be conical. But then... you couldn't have adjustable slides, could you?

Courtroise messed with the concept of have NO tuning slides. that idea wasn't so hot during a time when the industry couldn't even settle on a standard for pitch.

[windshieldbug]

Courtroise messed with the concept of have NO tuning slides. that idea wasn't so hot during a time when the industry couldn't even settle on a standard for pitch.

That was Couturier, and each horn came with 3 slightly longer main tuning slides to keep the cylindrical length to a minimum... but on most horns the valve slides were fixed so that they could continue to increase in diameter THROUGH the valves...

[roweenie]

I've got to think that there's a specific reason (other than just being an opportunity to expand the bore) that these horns have a dual bore MTS. I mean, that tiny amount of expansion (roughly .040) could easily be incorporated into one of the several other branches, couldn't it?

After all, it must take a lot more trouble to make a crook with an expanding bore, where a crook with all the same bore would be much easier and convenient...?

BTW, the only piston tuba (not sousaphone) that I've ever seen without a dual bore MTS was a small bore (.656) Conn (not sure of the model, maybe the 14J?)

[roweenie]

It would be so cool if those folks that did all the R & D "back in the day" were to have written down the reasons why they settled on what they did.

It would be even cooler to go back in time and pick their brains.....

I'm assuming the only way to truly know the answer to my question is, in the words of York-aholic, is to "tack it together and see how it plays" Personally, I'm simply too lazy to reinvent the wheel....

I think what I'll do is use an MTS that is 20mm/21mm, and then cut the dogleg further up the taper, at a point that will be equal to 21mm, or expand it slightly to accommodate 21mm at the present end....

Short of that, if any of the gurus out there have a method where a 19.5 mm tube can be affixed to a 20 mm knuckle, I'd be greatly appreciative to find out what it is

???

[iiipopes]

If the King you're referring to is the 2340/1, I beg to disagree (I can't speak to the sousaphone).

Point taken. I'm older than that. At least the older souzys does have a "down and back" main tuning slide before the valve block.