The very first Yamaha comp. E-flat featured a 17" bell...
Whether it was that, other factors, or all factors, it was way better than any of the subsequent Yamaha comp. E-flats (with apologies to those this statement - lacking "perhaps" or "in my opinion" - triggers).
Very few of the YEB-631’s were sold (assuming that is the model you bought and flipped). Yamaha couldn’t give them away. They were (comparatively) very heavy and had some unusual pitch tendencies. It was a parts bin horn that was put together in a hurry. We had several of the prototypes around here for a while (the local orchestra guy regularly used a custom built, non-compensating Yamaha Eb on the job and was often their sounding board when Yamaha was in GR). On the final version, it got to the point where the opinion was (quietly) “it will do for now…”