Posted by Jay Bertolet on August 25, 1999 at 12:35:50:
In Reply to: Re: Adding a fifth valve posted by JRTapes on August 25, 1999 at 11:50:27:
I think the reason is simple logistics. Most rotary valve tubas don't have enough straight pipe between the end of the valve stack and what comes next (either the main tuning slide or the curve into a side pull main tuning slide) to fit a valve into. All rotary tubas I've ever seen have the fifth valve right before the first, in the straight stretch of leadpipe just prior to entry into the valve stack. It helps to look at the same model of tuba with 4 and 5 rotary valves to picture what I'm talking about. In 4 valve models, there is usually a straight piece of leadpipe right before the first valve. I think you don't see any 5th valves after the stack, in the manner of piston valve tubas, because the expansion of the pipe is too large after the main tuning slide. The reason you can do this with a piston instrument is because the leadpipe is so much shorter than on a rotary. On a piston instrument, by the time you get out of the main tuning slide you're not as far into the overall pipe as on a rotary so less overall expansion has occurred. Even so, there are piston valve tubas that expand so wildly through the main tuning slide and afterwards that it is hard to find a valve big enough. It is also a cause for much debate as to whether or not a larger bore 5th valve is more desirable because you're going to be using it primarily in the low range where you might put a higher priority on less resistance. Obviously, the typical piston valve construction model is going to yield a comparitively larger bore 5th valve because it is always going to be later in the overall tube than on a rotary.
Basically, 5th valves added to 4 valve tubas are a very desirable upgrade in my opinion. What's not to love about having that many more fingering options for intonation concerns? Also, a 5th valve obviates the need to use false tones to play chromatically down to the fundamental of a given instrument. There have been many discussions of the merits of 5th valves on this BBS and they can be found in the Archives section.