The two posts belong in different forums, but - if both are to be posted together, thematically - that's impossible.
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[1] repairing a Jupiter marching baritone:
It's shiny and only had a few small dents (which I removed in a couple of minutes - mostly with magnets, but one - under the mouthpipe bell brace - with a rod-and-ball..."courtesy" dent removal...
The main problem was the #3 piston. I suspect (but do not know) that - since they went to stainless steel pistons (a decade or so ago) they also decided to tighten up the specs. Almost no one other than children (children: ages 11 to 21) play these things, so quite a few pistons are dropped on the floor or concrete, which defines (with tighter specs) more pistons which will not go up-and-down.
This one arrived with a #3 that hung - part-way down. The other pistons worked in the #3 casing, and this piston behaved poorly in the other casings, so: PISTON.
I began examining the piston and - even with my 65-year-old eyes and no dime-store reading glasses - I could see a little c. 3/16"-long crooked horizontal draggy place showing up about 1/4" from the top of the piston...
...so NO "pulling out the Wisconsin expandable brass casing 'lap' ", no "lapping" the valve...
I just sat in my chair, listened to the guy ranting on the radio, grabbed a little piece of used 250 grit cloth-backed sandpaper, and sanded out the bump (horizontal sanding). After I decided that I had sanded it enough to remove it, I went back and sanded (same 250 grit) the direction of the piston stroke, and then finished it with more vertical sanding with 1000 grit (until the appearance of the surface matched that of the rest of the piston. (again: I still wasn't focusing the best that I could; my glasses were "over there".)
With no oil (cheater, yes?...because the OTHER pistons were going up-and-down with no oil - children do not oil valves), I put the piston back into the casing, and it now works as well as the other two...
...no standing, no buffing, no rotary electric tools, no doing way more than was required, no using more technology than was required, and no "following some outlined procedure simply for the sake of following it, when the goal is to repair the thing - and not to follow some procedure".
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[2] OK...This one should be much shorter (though - per usual - I'll probably type too much...due to being an actual "typist").
My new-to-me Miraphone 98 (a "kaiser orchester b-tuba") is proving itself to live up to what people say about this family of instruments:
that there's a limit to how much energy can be "stuffed" into them, and inserting any more energy than "that much" (simply) defines LESS sound, WAY LESS resonance, and an ugly (unmarketable - ie. "We enjoyed having you" but we're NEVER calling you EVER again) sound.
The thing is this: When this (and probably most other instruments of this type) reach their resonance limit, they are already putting such strong sonic vibrations "out there" that the audibility is QUITE enough. I don't know if anyone has ever messed around with a tuba and a decibel meter, but "high range" tuba (in a very resonant place) will quickly "peg out" a decibel meter, whereas very low frequency pitches won't activate a meter all that much (regardless of the size/shape of the place where the tuba is blowing near one of those meters).
I don't pretend to be a physicist...I'm describing in musician terms, and not-at-all physical/scientific.
This differs from many of the 5/4 and 6/4 (often 3/4-inch bore) piston tubas of various shapes and sizes, whereby many of those instruments will "accept" much more energy and do "something" (usually: not much louder - decibel-wise, but more "burn" - whether good or not-good) with that additional energy.
...so I'm learning where the limit is, with this "kaiser orchester b-tuba, which - being a hybrid, with a wider bell than most - also serves well as a "wind-band" tuba. It's not difficult to figure out where the limit is; all that's required is listening. It's also slightly easier to hear oneself (with this particular model) as it's only c. 40+" tall (vs. some that are 45+" tall), as the upper bow is very tall as well, which allows the bell to not extend up so very far.
Anyway..."blowing into" this thing has its effective limits, so - in that respect - this is another example of "less is more".
