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I've been pondering various alternative valve configurations for both Frankenhorn jobs I have planned (alto euphonium and G bari bugle-based cimbasso). It's a fun game of "are there better ways to configure the additional valves after the first 3 so that you get additional mileage and less slide pulling, while also only using configurations that are possible to extract from using donor valvesets from dirt cheap bell-front baritones and the like". I highly recommend it to anyone looking for something profoundly useless yet mentally stimulating to do.

Anyway, one of the simplest thoughts I had early on is that if you started with a standard 3-valve compensating piston set, you could add a 4th valve that lowers the pitch by a perfect 5th instead of the usual 4th, and have a fully chromatic instrument. The real question in my mind was: would the 4th valve notes be anywhere near in tune? I tested it today by trying it on my single valve Conn 72H bass trombone, whose F attachment can be pulled to essentially Eb (just a tiny bit off the bumpers). Test results: the 5 notes in the Eb valve (Eb2 to B1) are either exactly on an open slide position or very close, and easily lippable if you don't move the slide to the exact right place. This translates very well to a compensating 3-valve set, whose valve combinations will be generally close to as in tune as a correctly-placed trombone slide. Logically, then, putting a quint valve after the 3 compensating valves (in a larger bore, presumably) will result in a fully chromatic instrument with minimal lipping or slide pulling required.

There's lots of compensating 3-valve tubas and euphs out there for dirt cheap or already in peoples' possession. If you loved how one of those played but wanted to make it fully chromatic, I think this would be the way to do it.

I've thought about this too. A compensating set would allow you to set up the fourth valve for the low notes and use the 3v set for all notes that a 4th valve aren't required for.

BUT, a 4 valve compensating set would fix all your issues and not require any more thought. Compensated Ebs and BBbs are very unpopular in the states. One can be had for $500-$1000 if one is patient.

Of course, this isn't meant to replace a 4v compensating setup at all. Just a way to make the most of a 3v comp set you might be starting with.

The added loops on the first and second pistons of a three valve compensating system add tubing to the 1-3 and 1-2-3 combinations, but only enough so as to be better in tune with the open bugle length for which they are designed.
A five step fourth valve would certainly offer the next pitch down, but the combination 5-2 wouldn’t make for a very nice next half step, and I’m thinking that 5-1 would err just as much on the other side of the pitch. What am I missing?
Below those, I could guess that some mixing and matching might result in serendipity (or a couple of things sort of close to serendipity), but I would probably rather play-test then do the root calculations, because I’ve found that the proof is more in the playing than in the mathematics.
(I’ve spent a few minutes here and there wondering about a cheater extension for 3-valve compensating system, and really never came up with anything that seemed practical… but if someone else does or has, congratulations!)
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To a related topic, I think I might possibly be completely re-tubing an Elkhart 72H playing slide next Wednesday night.

bloke wrote: ↑Wed Aug 31, 2022 11:03 pm A five step fourth valve would certainly offer the next pitch down, but the combination 5-2 wouldn’t make for a very nice next half step, and I’m thinking that 5-1 would err just as much on the other side of the pitch. What am I missing?

5-2 would be a useless fingering. On my 72H with the valve pulled to Eb (equivalent to this hypothetical quint valve), Eb is in 1st, D is just barely above 3rd (easily lippable), Db is a low 4th, C is a bit above 6th, and B is at 7th. With the 3-valve compensating block (which I realize is not PERFECTLY in tune, but you wouldn't know it on my 3v compensating baritone horn), this matches up to 4 for Eb, 14 for D, 124 (or 34) for Db, 134 for C, and 1234 for B. You would only have to lip the D, Db, and C just a tiny bit (or have a trigger on the 1st valve slide, which would also be useful for the sharp 6th partial) to get them exactly right. 14 and 234 would be pointless fingerings, unless you wanted microtones.

All play-tested, not using math!

Finetales wrote: ↑Wed Aug 31, 2022 8:03 pm… profoundly useless yet mentally stimulating to do…

This describes all the work I've done to my horns in a nutshell.

Even Blaikley in the late 19th century abandoned the plan to have a 4th valve on a 3-valve comp to bring 1+2+3 B nat and low E nat into tune due to logistical difficulties, the rarity of those notes in standard literature, and the ability to lip down because, frankly, the notes were so stuffy they tended to play "flat" anyway.

Year ago, I tried to devise a plan to have a 4th valve to get the near-pedal notes below low E nat that just aren't there on a 3-valve B&H/Besson comp. It was an exercise in futility, due to the nodes and antinodes being in the wrong places through the valve block that simply damped any resonance or ability to make the notes speak.

Go the other way: everyone knows about the "dent" that makes low C on an F tuba actually speak promptly and in tune, due to the alteration of the behavior of the horn with where the nodes and antinodes are on a typical F tuba. The same thing happened to me on my Besson BBb 3-valve comp: it had a dent in the primary knuckle between the 1st and 2nd valves. This altered the response so that 5th partials were not flat and 7th partials were almost playable with simple fingerings. I had an overachieving tech that tried to take the dent out, and the 5th partials went flat. I took a ball peen hammer and gradually re-introduced the dent to get it back into tune.

Play a 3-valve comp for what it is: a near-perfect instrument (near meaning you may have stuffiness on 1+3 C and low F, but a small price to pay to have everything else in almost perfect tune) for what it is, with a range that encompasses 99 44/100 % of both concert band and brass band traditional literature, and use a Wick 1 mouthpice with as much air support as you can give it to bring out all of its room-filling, band-supporting, broad-but-still-with-core superlative tone and intonation it has to offer.

I understand:
so skip the half step valve, and other ones are close enough to make do.

bloke wrote: ↑Thu Sep 01, 2022 7:05 am I understand:
so skip the half step valve, and other ones are close enough to make do.

Exactly. The D and C are close enough that it may be that the only note you would really need the trigger for is Db (if at all). You just have a couple of useless fingerings to skip, but more of the ones you have left are in tune than what you have on a 4v non-compensating instrument (which also has a useless fingering in 14).

Realistically, I think the only time this would be useful is if someone had a 3v compensating instrument they REALLY wanted to add the missing notes to, or if you were gathering donor parts for a Frankenhorn and had a 3v compensating block lying around.

It might be interesting to collect all of the different ways you could make a parts horn fully chromatic and how much work each method would be based on the different valve sets you have at your disposal. 3-valve piston sets, 4-valve piston sets, 3v compensating sets, 2 piston valves (from a G bugle), a lone piston and rotor (again from a G bugle), 3-valve rotor sets, 4-valve rotor sets, a single trombone/bass trombone rotor or fancier valve, and any combination of the above.