Have fun experimenting and gathering info. I have never played an Ambassador trumpet, but hope to find one someday. The wraps are more comfortable on my cornets vs trumpets. Thanks for your take on your discomfort. Although I have been playing since the Stone Age, I am not really accomplished. I use a 7c most of the time, sometimes a 7, 3C or Jet Tone Merian C. I use the original equipment mp on the Roth, which is great, and have used a 5c that came with the Olds and recently , a 10 1/2 C I got from somewhere that perfroms well. The type of MP you use is particularily determinative of the sound from a cornet. There are many threads here and on TH about this.
I am sure there are sources of modern formats for the Arban's. I have mine still from the late 50's.
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Dave Rafferty
07 Barrington Trumpet, 1972 Reynolds Medalist
55 Besson 8-10 trumpet
55 Roth by Reynolds Cornet
73 Olds Ambassador Cornet
30's Czech small bore Trumpet
Getzen 80 cornet, 33 American Standard cornet
66 Olds Ambassador Trumpet
www.kalamazooconcertband.org