iiipopes wrote:Being counter-intuitive, has anyone "reversed" the first two rotors instead?
I thought I mentioned it under the "fads" thread that I've just finished with a tuba that did just that--it's an old Walter Sear string-linkage horn, where the valves rotate just opposite to convention. Because of a lot of damage to the original menchanism, I converted it to uniball.
Rather than move the stop blocks and change the direction of the rotors on ALL valves, I simply brazed "ears" onto the stop arm opposite the stop pin and attached the uniballs to these.
I can't tell any difference between this horn and another more conventionally-equipped horn.
With the experience related, I agree. Now it can be called "fad," and the subject moved over accordingly.
Thanks for posting your experience.
I think one aspect of all this with the rotors is the difference between flow theory and wave theory. The only reason we have any flow of air at all is because it is necessary to some degree with the anatomy of embouchure to get the buzz going and set up the compression/rarefaction cycle. Once that is set up, the actual movement of air is not what happens.
Even though I am not a good fisherman by any sense of the imagination, I have watched waves and wakes of boats. Have you noticed that even though the waves lap at stationary objects, that if you float something aways from shore, that what mostly happens as the waves hit is that the object merely bobs in place up and down without moving significantly laterally as the wave "passes" by.
Air, like water, and as all the engineer members of the forum can correct if I'm stating it wrong, although definitely oversimplified, is also a fluid, and so with the exception of compression properties, reacts very similar: the compressions and rarefactions progress through the horn, but except for the force applied by the breath just to get the buzz going, there is very little lateral movement of the air -- as the "smoke" tests show.
So, I would conclude, and not having any engineering training, just reading and observing others' experiments and experiences, and someone please articulate it better, that the critical element is not how the rotors turn, but just that they're not placed at the critical nodes where the turns or redirection by the rotors, or for that matter pistons, water keys, elbows in the tubing, etc., would interfere with the orderly progression of the compressions and rarefactions. This has been demonstrated for the water keys and to a certain extent a node's "tuneability" by Schilke's experiments.
Boy, what a long-winded way of saying, "FAD!"
Hey, Chuck(G) -- would you post a picture of your converted Sear? Thanks.
iiipopes wrote:Hey, Chuck(G) -- would you post a picture of your converted Sear? Thanks.
Well consider that the flow rate through a tuba is probably volumetrically almost glacially slow. It's hard to see any fluid dynamic reason for rotor direction to have any bearing on it.
The Sear's being gotten ready for lacquer (buffing and ragging time ) so the keywork and rotors are off, but when that's done, I'll post a photo.
Matthew Gilchrest wrote:.The only modifications that seem to have realistic benefits on rotary horns are the venting of the valves and the scooping of the ports if it is one of those goofy Cerveny's that has rotors smaller than the tubing it is activating.
I have never heard of this particular issue with Cervenys. Please enlighten me further. What models/years were affected by this? Also (forgive my ignorance), what is involved with this"scooping" and is it effective?
kegmcnabb wrote:I have never heard of this particular issue with Cervenys. Please enlighten me further. What models/years were affected by this? Also (forgive my ignorance), what is involved with this"scooping" and is it effective?
Here is a post by Jay Bertolet describing mods he made, including this one, when he was selling his modified Cerveny 601.
kegmcnabb wrote:I have never heard of this particular issue with Cervenys. Please enlighten me further. What models/years were affected by this? Also (forgive my ignorance), what is involved with this"scooping" and is it effective?
Here is a post by Jay Bertolet describing mods he made, including this one, when he was selling his modified Cerveny 601.
Apparently, Cerveny uses the same valves for their .835-bore tubas as they do for their .810-bore tubas, or something like that.
We haven't heard from Jay in a while but perhaps he still lurks and will add detail.
Rick "who misses Jay's input" Denney
They use(d?) the same slides and tubing but different sized rotors for .795ish and .830ish bored tubas. The rotors were undersized on .795 bore horns. I do not know if this is still the case. I owned a Cerveny piggy like that in the early 1990s and it was "old" then. I definitely do not want it back.
Anonymous wrote: it takes very little time (perhaps 1-1/2 - 3 hours for two rotors) to effect this change in the shop - and no more time at all for manufacturers to manufacture instruments this way.
Isn't that the truth...I know a little bit about rotor valve repair stuff, and the hardest part would be switching the linkage. All one would have to do, is take off the bumpers for the rotor, after the valve has been pulled out, put them on the other side, change the linkage, and Voahla! You reversed the linkage...
But that's my idea of how to change that...you'd probably have to do a few things with the valve itself, but other than that, it wouldn't be that hard...
I think I might end up as a grumpy old man when I get old...
) so the keywork and rotors are off, but when that's done, I'll post a photo.
