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I have not done this, but tonight I decided to check something about my F that I have observed repeatedly but have also ignored because it made no mathematical sense to me.

I made my 5th slide circuit about 24" when the slide is pulled about an inch. All my other measurements worked out well, but this one did not. AI said it needed to be around 35.5" on an uncompensated f tuba. My math says one thing, it agrees with the measurements on other charts, and to lower any F, Eb, or CC tuba to play a low Bb, the total number of inches is the same.

HOWEVER… AI said that for a tuba in F, that much straight tubing through the valves will cause a LOT of resistance and cause massive response issues, just like with the low C. Something about impedance valleys.

For the other tubas, the Bb would be the same length, but for an F, it would need to have about ten inches more pipe than what mine has when pushed all the way in, almost exactly where I have been noting the slide wants to be, but that I have to tape it in place because it is just beyond the end of its pull. Dead on.

In the past, I have noted that on old rotary Fs with the classic crappy low C, on some of them with a long 4th slide, you could put it where it seemed to be designed to go and get this horrible, nasal, hole-in-the-horn tone. It was in tune, yes. It was *okay*, yes. But it sounded lousy and responded quite slowly (if at all) unless you wasted an inordinate amount of time learning to mangle your mouth to coax it out. Regarding my old Mirafone 180 F, I recall discussing back in the late 1990s on this board that the very long 4th slide allowed me to pull it out to more than a half step flat, and then suddenly it became "amorphous," and then with the pull of another 1/8" this clear, fat, in-tune C sang out. However, all other 4th notes above that had to be played 13. (Really only the bottom line G on that tuba.)

The AI I dumped on tonight claims that this longer 5th slide would net a low Bb in tune played 45, with 4 tuned to a C (which I can do since I have the 24 tuning fixed with 46). I do not know why this disagrees with the math so much, but it seems to work. So my measurement of a 5th side of between 24 and 26 inches, WHICH MATCHES EXACTLY HERR KURATH'S MEASUREMENTS (and shares this issue of a crappy low Bb), is wrong, and this weird 35.5" length is correct. And I came up with this same number independently, before I asked the AI bot. So I do not think the AI just hallucinated (as they are wont to do) and that this is correct.

BUT WHY?

A Bb is a Bb is a Bb, right? Shouldn't the length be the same on an F as on the other three instruments? The F is. The 4th valve C is. Why is the longer loop working for me on my F, and why did AI suggest that length to me without prompting?

Is this the end of life as we know it?

I want to revisit the old, sweet, rotary F tubas with the craptacular low range. Could all the disagreement about learning to play them be because some folks learned to pull 4th out really far, while the complainers did not? Was that all it was? I detest not understanding stuff…

Anyway, the upshot of this is that I am building a new 5th slide. I have the correct crook. I have enough outer tubing. I am short of the inner tubing unless I use brass, but it will be the *only* slide out of nine with brass legs. Silly, but that would indeed bug me. One solution is to install a spacer on the short side. (One runner comes up an inch shorter than the other.) I have enough for the long side's ferrule and the extended inner and outer tubes. I have the outer tube and ferrule for the other side. And as luck may have it, my first 5th slide layout used internal spacers to take up the gaps, and one of the legs was the length needed, and I reused the slide, so the internal sleeve is already installed, and the exact length needed. So I can do this as a trial thing without using a single part from the current slide assembly. If it sucks, I can easily switch them back.

Alternatively, I could build a longer slide using brass inner legs using the extra crook, and just use it without altering the outer legs until I know whether I want to do this.

I think I will do the latter. I am almost as lazy as Joe claims to be, so building a new, temporary slide using the existing outer tubes is an attractive idea.

I will give this a shot this week. Photos when it is done…


How things are right now: You can see that the numbers I came up with really do seem to be short. If you include the runners (and 2nd has a very long one underneath), 5th is not really twice the length of 6th as it should be. And double that would be just about what seems to work out with the tuner. So we shall see…

(apparent) SUCCESS!

The length I needed seems to be six added inches, so three per leg. I had to use brass inners as I had to cut one to 6" and the other one 3/8" longer, and the rod of NS I have is about an inch too short. Oh, well. Whatever. IT WORKED!

The entire low range was "Willson big", meaning good, but tight, a solid low C, but with a few pitch issues. Adding the 6th valve fixed just about everything, but that low Bb was still… weird. Sometimes it was there, and sometines is was on vacation.

Not anymore.

Pics later, after I have soldered it together and cleaned it up.

Initial impressions (using an OG Ultimate and a 1960s-era C0nn Helleberg): Worth redoing this using the parts I want to use. Heck, yeah!

I watched a video of one of the DC guys playing a 4 valve Eb helicon; for a joke he pulled the 4th slide way out, hung a beer stein on it and proceeded to play perfectly in tune. I'd consider that validation of your idea.

I asked Gemini three times and it gave me three different answers each time, and gave me some nonsense trying to justify them, so I would take blind AI recommendations with a grain of salt. I am sure you are vetting and testing before actually putting anything into practice.

Keep in mind these are just language models and spit out random information they find elsewhere on the internet. Some of the erroneous numbers were being pulled from articles discussing how to calculate compensating tubing lengths, for example.

Yeah, know. I put its feet to the flames and repeatedly corrected its wrong info, had it recalculate the numbers, and never told it that I had come up with the same conclusion. I find it disturbing that when it gets so many things patently wrong, it nailed this. I don't understand it. The math used for its justifications worked out, but it did not seem to be using formulae that applied to what I was trying to do.

Bizarre.

And it really kisses your a$$ while doing it.

Anyway, the work is done. The tuba is better. I am happy.

Now I have to go change out the cat litter.

Then a shower.

Because… dirty cat litter…

I use AI probably more than most people... I find it works best when used like Wade... as a tool to help me focus my own thinking though an adversarial discussion rather than as an Oracle to give me an answer.

Just responding to the TITLE of this thread...
We've all seen what the tubas look like in Dylan King's reels (a lot like those pictures where there's one more smokestack on the top than there is on the bottom), and - just yesterday - AI told me that Calvin Coolidge is one of the visages on Mount Rushmore.

Yeah, right now it is garbage for a lot of the things I might ever need it for --- laughably so in the case of Finale or music engraving practices.

However, it is really great for math and science, until it isn't.

I still cannot figure out how it got to the same, exact answer as me, using the nonsensical method it described. The actual math says that what I built is correct. It is not. But what I used my ear and chops to adjust it to, while *incorrect* worked out great, AND the AI agent produced the same result using what seemed to my non-math brain as junk.

That is really, really weird…

I'm pretty lazy, and - were I to fab up a 5th and 6th valve for an F instrument - I would just build a first and second valve for a c instrument, stick them on, test, and then (based on results) either view myself as a genius or as an imbecile.

When I put my "6th valve only" valve on my Holton B flat tuba, I tried to make it twice as long as the one for my F tuba. Fortunately, it kept being a little bit too long, so I didn't ever have to start over.

I tend to find that circuit lengths apparently involve more science than just mathematical sciences alone, but those sciences evade me.

I did that. It was WAY off for this tuba. It needed to be a 35.5-ish" loop rather than the 24.5-ish" loop the math (and my CC tubas) would indicate.

Again, this was the case for me with my Mirafone 180's 4th slide: it had to be *much* longer, and then it was more or less great.

Not so with my Yamaha 621 F, though. 5th was about 23" and I had to pull it about .75" to get a solid BBb and in-tune low register… well, as in tune as you can get with that design, at least…

I'm sure it was exactly the right length to begin with, you just haven't had enough lessons with Arnold Jacobs.
S-L-O-W A-I-R


Wade knows I'm jerking his chain...
So y'all don't need to stick up for him.

I will put my usual lack of two cents in that the first real tuba I owned, a MW 182 F, what I noted was that the low C actually wanted to center considerably sharper than C, and that I thought a whole lot of extra tubing might make it more playable. However I sold it and it is now in Pittsburg from what I've been told.

Mary Ann wrote: Fri Oct 23, 2026 5:30 pm I will put my usual lack of two cents in that the first real tuba I owned, a MW 182 F, what I noted was that the low C actually wanted to center considerably sharper than C, and that I thought a whole lot of extra tubing might make it more playable. However I sold it and it is now in Pittsburgh, from what I've been told.

I've had one of those here. You definitely made a good choice in what you did. Those instruments are good for harvesting valve sections from them (but they need to be offered at a low enough price to justify it).
Yes I've seen (in writing, such as an internet post) a few people rave over them. When I see that, I don't argue with them, (Why would I? ...particularly if they're really happy with theirs) I just continue to scroll.