First, a disclaimer: this post does not mean to make any comment about such now-rare fine beasts such as a Martin Mammoth, or the pre-WWII Conn or King "Jumbos" or any of that ilk. Second, it does not make any comment about such other now getting to be rare ordinary souzys such as "real" Reynolds and Holton, before the former went out of business and the latter was assimilated by the cyborg. This post is about those souzys that you can fairly easily get and fairly easily get replacement parts, whether new from the factory or from the crash parts bins and wall hangers of shops who have steady school and/or college work nation wide. Third, I am discussing the "conventional" configuration of bell front, and not the (original) raincatchers or helicon configuration.
Now, the post: but for the above mentioned special cases, there are only two brands of real souzys: pre-cyborg King and pre-Macmillian Conn. Everything since then is thin metalled trash. For the Conn, of course, the usual culprits are the 14K and the 20K, and if you have to be so inclined, the occasional fiberglass counterpart. As we all know, King made one standard model of souzy, with a fiberglass alternative as well.
Add to that the pre-war Conn Cavalier, which, along with the Pan American, are direct ancestors of the 14K, and are basically identical. And then for pre-WWII Conns, there is in addition the 38K Grand and its variants, as set out on the Conn Loyalist chart.
There. That about covers is. What I have noticed is that there are differences in the Conn necks. The one original neck I have seen, the one from the Cavalier I used to play and that another guy in Shrine band now plays, has a longer top part, so you only use one bit, as opposed to the current style necks that use two bits (and a shave, and a haircut, and I just couldn't resist!).
My opinion on number of valves: Three. Period. Why carry the extra weight when you don't have to? I know, 4-valves were and are made, and some people make a big deal about scavinging a second valve casing and the tubing to make a 4th valve, when it's not necessary. The Conns and Kings listed have great "false" pedal tones. Because of this, all you need to do is make the top loop of the 1st valve tubing into a movable slide with the left hand and pull about 1/2 inch or so for 12 G & D, a little more than an inch depending on where you need to set your 3rd valve slide for 23 to be in tune so you can play 13 C and low F, and pull as you will for the occasional 123 B nat and low E nat. The false pedals will take care of themselves nicely with open low Eb, 2 D, 1 Db, etc. as your lips and instrument can do or as you will. I had several pieces on the weekend picnic/concert that the trio went to the key of Eb and I was able to, outdoors, give a good resounding low Eb to end the piece. Normally, I wouldn't play this low outdoors, but it was a neighborhood party, and we sat up in a large side yard facing a brick house, so I had a good reflector to give that low Eb back to me, and I went for it. The guys loved it.
If you're not actually on a football field of an NCAA Division I school that you're trying to please both aurally and visually between 50,000 and 100,000 people per show, I also prefer the 24 inch bell to the 26. It is more centered in tone, and it is MUCH more maneuverable, especially through doorways, parade floats (yes, I sit on the trailer to play instead of march now. I'm still in good enough physical condition to march, but I'm also a lazy fart.), and the like.
For overall ease of playing and intonation, as well as, again, availability of repair parts, and in spite of the longer stroke, I am a fan of conventional valves over the 20K short stroke valves. I play upper brass as well, rarely. If I want a short stroke, I'll play trumpet or cornet. I expect to have a longer throw. Think about it: if it were that great of a deal, wouldn't the tuba makers have adopted it now that the patent has long run out? No, everybody else sticks (figuratively only, hopefully) with conventional stroke valves.
Next, go to a home center, get about 7 feet of clear 5/16 or 3/8 inch clear plastic tubing, depending on your rim wire, and using either an Exacto knife or the little jig Sam Gnagny describes, make yourself a bell protector. It not only protects against minor dings, but it also damps the overring that can happen on souzy bells, without affecting the tone. It actually will clear up the tone and give more core and projection from damping the unwanted, and usually inharmonic, bell ring.
Consider getting, at least as a backup or for really extreme temperatures, a Kelly lexan mouthpiece. I play a Kelly 18 outdoors, and it is the finest mouthpiece for outdoors I have ever played. I haven't tried the Kellyburg, as the rim is a little larger in diameter, and the 18's 32.5mm or 1.28 inch rim is as large as I can securely get centered tone. They don't break; they are insensitive to temperature extremes; they don't dent either themselves or your souzy when you drop them. Anybody who claims never to have dropped a souzy mouthpiece is just full of it, or hasn't played enough to matter. They're cheap, and they come in school colors. I have two: a blue one for myself and a burgundy one that matches both the university community concert band I play in as well as Shrine band. You may need to wrap a piece of lead golfer's tape around the throat to keep it from "cracking" at high volume, depending on how you play.
Finally, after having the privilege of the shoulder flange at times, I wonder why I ever endured the pain of the bugle digging into my shoulder otherwise. Have one made and soldered on. Your shoulder will thank you for it, and even if you do use a Wenger chair, it will provide a flat support for the top brace and make it more stable in the chair.
I know this post is just short of being a tirade instead of a mere post, but there you have it. I am unashamed and unabashed. I love playing a souzy.
