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Anyone ever try a tuning slide stick on a comp or non comp euphonium? Could you possibly move it with your left thumb wile still operating 4th side valve? After the adjustment period, I really like the one on my yfb621.

LTTP

There was a simple spring and thumb ring upon the third of a king 2280 euph. Kind of like just a large size of what’s common to trumpet.Works okay a bit of spring noise. But would not work the same on a main slide because of wider width of bow and not close to something the brace maybe.

I had added Master tuner paddle on my besson, after market part a bit cheesy, the levers and arms were not efficient, just okay. My repair guy hated the part.
Not this one but something like it

https://shop.mtp-music.de/article-detai ... -SII1.aspx

At that price, you might try or look to something custom.