Hank74 wrote:I've heard though the 4th valve is needed on baritones if you want to play notes between the middle Bb and F on the bass clef scale.
It's true in the very low range, below E below the bass clef (lowest 2nd partial with 3 valves) and above Bb (highest 1st partial.) I've seen this kind of "tenor tuba" playing - a baritone player backing up a couple of big steyrische accordions, for a performance dance group that I think may have been roughly Bavarian. He was using a silver plated oval euphonium, presumably Chinese and with 4 valves.
For a while I had a really odd German bell front baritone with 4 top valves, with a real big bore and some potential for "tenor tuba" applications if it had played better, maybe it was designed for this (though I doubt it.) That thing had little or no "false tone" potential, so the 4th valve was essential, though honestly, it was hell trying to work through those combinations - it's hard to get 5 adjacent tones that are really in tune down there, with the 4th valve.
That said, I think the folks who would really know this stuff don't frequently visit this site.