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This has been bugging me for years now and I have not been able to figure it out. So, I have decided to consult tubenet ... the one true source of all important information.

I have a rotary-valved tuba. I have also (as pretty much all of us have) played on various tubas made by various companies/people. One thing that strikes me is how, on some tubas, one does not have to depress the keys as much as one must on other horns. Even within the same brand of horns, there are discrepancies between models.

I brought this up with my professor during a private lesson and we got to measuring various aspects of our valve sections. I play on a Miraphone 186, he plays on a 188 (his horn is also much older than mine). Overall, the measurements were almost identical. The distance from the brace to the rotors, the distance from the brace to the end of the keys ... everything except for how far we had to depress our valves. His horn required much less movement (about 1/4" if I remember correctly) than mine did. We spent about 30 minutes on this and could not figure it out. I have pretty much ruled out the bore of the horn making much of a difference because both the Norwegian Star (a horn with the same bore size as mine) and the newer St. Petersburg tubas (horns with a larger bore than mine) both have a much shorter action than my horn does ... and the older St. Petes are about equivalent to my studio teacher's horn as far as the action is concerned (still much better than mine).

So, my question is this: What is it that determines how far one must depress a rotary valve on any particular horn? Furthermore, is there anything that can be done to reduce the action? If so, are there any drawbacks to doing this?

It's a matter of simple mechanical advantage. I can see two places that matter:

1. The distance on the rotor stop arm from the shaft to the pivot on the linkage.
2. The distance between the main key pivot (with the spring) and the pivot on the lever that connects with the stop arm.

Often, you'll find that where a conversion has been made between S-arm to uniball, the key dip is less because the distance (2) becomes greater than it was with the S-arms.

Chuck(G) wrote:It's a matter of simple mechanical advantage. I can see two places that matter:

1. The distance on the rotor stop arm from the shaft to the pivot on the linkage.
2. The distance between the main key pivot (with the spring) and the pivot on the lever that connects with the stop arm.

Often, you'll find that where a conversion has been made between S-arm to uniball, the key dip is less because the distance (2) becomes greater than it was with the S-arms.

Hey, Chuck! The distance from where the finger is placed on the paddle to the center of the pivot rod can make quite a difference, too!

To the original poster.... when you shorten the stroke anywhere in the linkage, you change the force that is required to make the linkage work. It's a simple matter of mechanical advantage... more stroke = less force. less stroke = more force. You can change anything you wish... EXCEPT for the actual rotation of the rotor..... which should be 90 degrees.

TubaTinker wrote:Hey, Chuck! The distance from where the finger is placed on the paddle to the center of the pivot rod can make quite a difference, too!

No quarrel there, Dan. I thought that the original post had discounted this possibility in the referenced situation.

When I've done an S-link to uniball conversion, I've had a couple of people comment that the valves seemed to act faster.

So then, in theory, if I were to straighten the bend that goes between the main key pivot and the pivot on the lever that connects with the stop arm, I could decrease the amount of movement required?

josh_kaprun wrote:So then, in theory, if I were to straighten the bend that goes between the main key pivot and the pivot on the lever that connects with the stop arm, I could decrease the amount of movement required?

Yup, but you'd probably discover that the arm would start hitting the tubing below after a point--then you'd need to raise the key mechanism to make some room.

However--be aware that you don't get this for free--it will require more force on your keys for the reduced stroke. Archimedes and all that stuff, dontcha know...

bloke wrote:An interesting point here is that regarding this issue rotary linkage CAN be adjusted, whereas pistons - for all practical purposes - cannot.

Didn't one of the Ferree's newsletters a couple of years ago have a patent application that presented a linkage that would allow piston valves to operate just like rotary valves?

http://www.ferreestools.com/June2004FerreePress.pdf

(corrected for the right URL)

Aprill, Mayl, Junel, Julyl...

Chuck(G) wrote:It's a matter of simple mechanical advantage. I can see two places that matter:

1. The distance on the rotor stop arm from the shaft to the pivot on the linkage.
2. The distance between the main key pivot (with the spring) and the pivot on the lever that connects with the stop arm.

Often, you'll find that where a conversion has been made between S-arm to uniball, the key dip is less because the distance (2) becomes greater than it was with the S-arms.

The length of the stop arm is probably the bigger one. Because the two pivots are close together, a small change has a big effect, and the measurements have to be fairly precise.

The distance from the S-link pivot (even if it's straight) to the long spring shaft and the length of the paddle from the spring shaft are important, but require a bigger absolute difference to make the same percentage difference.

My vote goes to the stop arm. The difference is harder to see, and with the migration from S-links to uniball linkages, more likely to have changed.

To play with the arithmetic, let's say the normal travel is an inch on the newer horn, and 3/4" on the older horn. That's a 33% increase from old to new. That could happen by making the stop arm 33% longer. If the stop arm is only 1/2" long, that increase would add only .16", possibly small enough not to notice without actual measurement.

Straightening linkages will have no effect. The only thing you can do is move pivots, but there's usually not enough material to move the pivot such that the paddle travel is less. Depending on the shape of the stop arm, you might be able to move the linkage pivot in towards the rotor shaft a bit, but I suspect it would be easier to find old stop arms and modify them for the uniball mount.

Rick "who has an old Miraphone on hand but not a new one" Denney

Rick Denney wrote:Straightening linkages will have no effect. The only thing you can do is move pivots, but there's usually not enough material to move the pivot such that the paddle travel is less.

What I interpreted the question to mean was that he proposed taking the sideways "alignment bends" out of the keyarm. This would certainly move the pivot. Of course, it'd make the lateral lineup of the keyarms to the stoparms harder to achieve, but that's his problem, not mine.

I had a string-action Cerveny-Sear BBb and later a Piggy CC with the same string action. On both tubas the mechanisms were set up to have rather short action, which resulted in a very sluggish feel. It's not just the fact that shorter stroke requires more force to work the springs; it's also the fact that short stroke makes the rotors feel more massive, and those suckers were too heavy already. On both horns I made plastic bushings to increase the diameter of the part that the string wraps around. The result was a longer stroke, but a lighter feel. For me that was a big improvement because I am accustomed to lightweight piston valves.
Try this experiment: place your hand on a table top and tap the surface by moving one finger up and down as rapidly as you can. Count how many taps you can make in 10 seconds, or how many seconds it takes to tap 25 times. Then repeat the test with a longer or shorter stroke. I get the same numbers whether my stroke is half an inch or one-and-a-half inches.

That Rampone-Cazzani I had with the 0.900" bore and solid rotors needed such strong springs that it made my fingers ache after awhile.

Rick Denney wrote:.... My vote goes to the stop arm....

It's true that a shorter stop arm will have the most dramatic inpact on the distance the finger paddle travels. However... here's the spot that is probably the most critical in the function of the rotor. The shorter the stop arm, the more force that is placed on the pivot pin and the upper rotor bearing. These two points are already where most of the wear on the linkage system is concentrated. Moving the pivot toward the center of the rotor will compound the wear. Once the upper bearing wears a bit, the rotor will rub the inside of the rotor housing.... THEN, you've REALLY got problems. It seems to me that the manufacturers have already pretty well optimized this area.

Maybe someone could manufacture some Christian Lindberg type rotors like are used by Conn on the 88HCL trombone. For a tuba, they would be quite large but the range of motion of the rotor would be reduced quite a bit from the normal 90 degrees.

TubaTinker wrote:It's true that a shorter stop arm will have the most dramatic inpact on the distance the finger paddle travels. However... here's the spot that is probably the most critical in the function of the rotor. The shorter the stop arm, the more force that is placed on the pivot pin and the upper rotor bearing.

I agree. But without having examples in front of me, I can imagine that the effective length of the stop arm with the split clevis-style attachment of an S-linkage is shorter than a stop arm that is long enough to provide clearance for a ball link. In my conversions of instruments with S-links, I have put the ball link out front (with respect to the instrument in playing position) of the rotor shaft to provide clearance, rather than adjacent to the part of the stop arm that fits over the rotor shaft. I don't know if they are different, but I can see why they would be and that would also explain the difference noted by the original poster.

I wouldn't think that using the same effective length was was traditionally used would have too damaging an effect on wear.

Again, I'm speculating...I only have the older style stop arm in my possession. You probably have examples of each that you could measure.

Rick "who prefers a positive feel to short action" Denney