Musical Riddle

Nine slides of brassy brilliance

Three valves and a trigger

Bell with a circumferance greater than a baritone

Compared to a trumpet, this is bigger

What instrument is this?

With all the slides and curves

What could it be?

It's very difficult to learn

The best shade of yellow

The gold tint of brass

Sounding so mellow

This instrument's sure to last

For you will never grow old

With an instrument like this

Always something new to learn

A musician's life is bliss

So can you guess?

Can you tell?

What is this instrument

With the big bell?