TromboneChat

I have a question for anybody who plays one of these instruments.

Can you please describe how you hold the horn to play effectively? I'm having a hard time holding the instrument so that the proper angle is maintained for the mouthpiece. As I hold the horn in front of me and play the valves, I find the instrument wants to slide around a bit and this changes the angle of the mouthpiece on my mouth making it difficult to maintain accurate playing. How do you stabilize the horn?

Take some pictures of how you're doing it and feel free to post them. Also, look at pictures of people playing these instruments from many different angles. What are the differences?

I typically cradle that type of instrument and play it almost sidways. When I did euph in grad school, I had an ergobrass for it. I think I may have actually left the plate on the euph but I retained the rod somehow. In either case, I definitely recommend the ergobrass for euphonium for sure. It isn't nearly as awkward as it is for trombone.

On my valve front baritone (I hardly play it any more) I tend to hold it with my right hand parallel to the long axis of the horn (horn is at a 45 degree angle to vertical) and use the left hand to support it; generally grabbing whatever piece of tubing is comfortable. I put my right thumb in the ring to help support and stabilize.

With my valve up Euph I hold it at a slight angle to vertical on my thighs. The mouthpiece fits OK that way. Some place it on a pillow on a chair. Others play it at a much more severe angle.

I think valve up horns are somewhat easier to hold than valve front, but there are some who really advocate valve front. I play a tuba with valve paddles in front (it's a rotary).

What Bruce said. ^^
I play my valve front baritone at about the the same angle. For me, that puts the bottom of the horn at my right hip bone, and my right elbow holds the horn against my body to steady it and to help the left hand support the horn's weight. Same horn position, standing or sitting.