Eb tuba sounds like C
S4 - Minor
When I import an Eb tuba, the tones I write sound like a C tuba. It is the same as on the piano. A D is a D. But normaly it would sound a sixth lower as notated right?
Score needed. Maybe you need to toggle concert pist?
It's not clear what you mean by "import". Are you trying to import/convert from a pdf? If so, then the convertor seems to have not recognised the instrument properly.
Note that it is only really in brass band context that an Eb tuba part is written in treble clef transposing down a 6th. In other contexts (orchestra, concert band etc.) there is no differentiation between differently sized tubas and the generic tuba part is usually written in bass clef at concert pitch.
If you are entering the notes yourself as a treble clef transposing part, make sure that you are using the correct instrument and have the concert pitch button unselected.
For more help, please attach the score (.mscz file) and the original source (e.g. pdf file) you are working from.