My technique is returning, and (I suppose) that's encouraging me to examine the instrument itself more.
I also suddenly find myself with a superior combo amp (which simply means that the amplifier and speaker cabinet are all-in-one).
This amp offers MUCH better electronic interpretation of "articulation" than with any of my other amps...
ie. It "hears" (much better than my old amps) what my right hand fingers are doing to begin sound events.
This factor got me to thinking about "set up".
I started looking at the string heights.
...not "ridiculous", but much higher than I remember having set them back when I was a working "bassist".
@Rick Denney no vowel after "bass", so - likely - no argument from you, regarding this word.
I remembered that a friend asked me (after I wasn't playing much anymore) if he could "set it up" for me...so that HAS to be what happened to the string heights.
This bass sports a flawless (arrow straight) neck (which has NEVER wavered) whereby I can get away with remarkably low string heights (AS LONG AS I don't beat the crap out of the strings, and let the amplification system do the work.
BACK TO PREVIOUS BLATHER:
SINCE this combo amp does such as great job with ARTICULATION, I do not NEED to "hit" hard to get a good "front" on sound events...medium-light touch: the amp says "I HEARD THAT!"
Now that I've lowered all strings (guess what) my SPEED instantly improved.
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RELATED TO "SETTING UP" A TUBA
Over the years, I've had quite a few people tell me that they want (pistons) stronger springs or (rotors) stronger spring tension, so they can play faster.
1/ Assuming reasonable finger strength, the valves will be actuated (depressed) as fast as the finger can actuate it.
2/ If the "RETURN" speed of a valve can consistently "outrun" the speed of a player's fingers, those springs are plenty strong enough.
3/ Valves should be CLEAN and FREE OF LIME DEPOSITS, which maximizes (any type of) valve speed with any particular strength of spring.
4/ OILING all the valves (before AND after each playing session) discourages the buildup of filth and hard lime deposits on valves and casings.
5/RATHER THAN $5/oz. "valve oil", I'm able to afford to (generously) adhere to 4/ via the purchase of "Ultrapure Parafin Lamp Oil" - $.1X/oz. (Amazon, by the gallon - whichever is cheapest...along with those cheap red plastic Harbor Freight funnels, and (pulling the nipples from empty valve oil bottles and popping them back in place, after refilling them) I then have quite a few years of value oil, and (using it quite generously) I use up a gallon prior to it become putrid (aka "smelly" - as with old gasoline).
summary:
a. Avoid over-tensioning valve springs (or springs which are intrinsically stronger than needed).
b. Oil before and after each playing session, and to the point of (what may seem to be) absurd generosity with the oil.
c. Buy oil for a few cents per oz., rather than several dollars per oz...in order to easily afford b.
d. Valves may need to be professionally cleaned. A "bath" (with soap or detergent, seemingly popular among tubaists) does nothing at all, as far as removing lime deposits (and most players lack the attention to detail to remove all of the filth lurking in the tubing "knuckles" leading directly into the valve casings.

