Most modern altos will fit in a ProTec case. But ProTecs aren't just for modern horns, either.
I have three ProTec cases - they can hold a '25 TrueTone, a '32 Cigar Cutter, a Big B Aristocrat, a MKVI, and a Ref 54 (horns I have now). These horns have all three styles of bell pads - split, left side, and right side.
And, most altos have similarly sized bells. True, some have larger bells than others (like a CB Big Bell or a TH&C) so that would be a factor, but your Yamaha is not dissimilar to other modern altos. DAVE
I have three ProTec cases - they can hold a '25 TrueTone, a '32 Cigar Cutter, a Big B Aristocrat, a MKVI, and a Ref 54 (horns I have now). These horns have all three styles of bell pads - split, left side, and right side.
And, most altos have similarly sized bells. True, some have larger bells than others (like a CB Big Bell or a TH&C) so that would be a factor, but your Yamaha is not dissimilar to other modern altos. DAVE