1. Check the Embouchure: Ensure that your embouchure is relaxed and properly formed, with even pressure from the corners of your mouth. A tight or uneven embouchure can affect intonation, particularly in higher registers.
2. Adjust the Reed: Try using a different reed. A reed that is too soft or too hard can affect intonation. A medium-strength reed is generally recommended as a good starting point.
3. Check the Octave Key: Make sure the octave key is closing completely and accurately. If it doesn't seal properly, it can cause intonation problems in the second octave.
4. Check the Palm Keys: The palm keys (C#, Bb, and F) should be adjusted so that they open evenly with light pressure. If any of these keys are not properly aligned, it can affect the intonation of nearby notes.
5. Adjust the Neck: The neck angle and position can affect intonation. Consult a qualified saxophone technician to make sure the neck is properly adjusted.
6. Consult a Technician: If the intonation problem persists despite the above suggestions, it's best to take the saxophone to a qualified repair technician. They can assess and identify any underlying issues with the instrument's mechanism that might be causing the intonation problems.
Remember that older instruments might have some quirks or challenges due to age and usage, and it's important to handle them with care and expertise to ensure optimal performance.