I have recently purchased a Mandola with the aim of learning the instrument, but am having some trouble setting up and am wondering if anyone on here can provide some assistance.

I am fairly sure it is a Tenor Mandola, the fretboard measures just under 28cm in length.

However, I have put a set of GHS 'Tenor Mandola' strings on it (gauge 12-24-34-48) and when I tune it to CGDA the intonation- especially on the C string- is terrible, over 1/2 note out on the 12th fret.

The intonation is fine on the A string and OK on the D and G, so I don't think moving the bridge is the answer. I can't see damage to the neck, so the only thing I can think of is that I'm using the wrong gauge strings, but I want to make sure before wasting £10 on another set.

I have no previous experience with this instrument so apologies in advance if my problem is glaring obvious to those in the know.

Thanks in advance...