Sluggish fifth valve.

[Tubaguy56]

check the linkage action, I know on an old rotor horn of mine the linkages would move around if not tightened enough, and would sometimes play perfectly and other times stick horribly

[Mark]

If Miraphone rotors "dry out", they will exhibit the behavior you describe. The easiest way to stop this from happening is to play your tuba daily and make sure you put the fifth valve to good use.

This is an great excuse to work on your low register!

[Dan Schultz]

The fifth valve on my 1291 is very inconsistent. .... After playing with it for a while (moving it a bit) it eventually frees up. ....

Rotors often will 'freeze up' simply from non-use. You are likely to be having problems with small calcuim/lime deposits from condensation inside the rotor. Too much heavy oil inside the rotor casing can also cause rotors to be sluggish.

[iiipopes]

Roger and others recommend putting a couple of drops of Al Cass down the leadpipe to keep everything lubricated. My body chemistry likes Roche-Thomas plain valve oil better. Others use Hetmans, Paxman or another "purpose designed" rotor oil. Singer sewing machine oil is also cheap, @$2.00 for a 4 ounce bottle at Wallyworld, and you can use it on the bearings under the cap and base of the rotor shaft as well.

At least rinsing your mouth, if you can't brush, every time before you play, is of course highly recommended to prevent accumulation down the leadpipe and into the rotor casing.

[iiipopes]

Quantum also has a Hot Sauce grease. Hmm. I wonder how that would be on your 1st slide?!

http://www.cabelas.com/cabelas/en/templ ... hasJS=true

[iiipopes]

Most generally, on a 6-valve F tuba, the 5th valve is a long whole step just as on a 5-valve CC tuba. The 6th valve can have a number of configurations, but a long half step to aid intonation of some of the lower notes is most common.