New strings tuning problem.

[goingdownslow]

I have just put a set of D'Addario short scale 45-100 strings on my Epiphone Elitist EB3 replacing the Elites 45-105 (no longer available) which I've had on for a very long time as I have not been able to find a reasonably priced set of 45-105s.
My problem is although open tuning and intonation is ok they are off (sharp) over the first few frets, most noticable when playing octaves.
I put the old strings back on and they are ok.
My head is like a ball of chalk. What gives?

Edited September 7, 2013 by goingdownslow

[iiipopes]

If it is the first few frets instead of the last few frets, then that is an indication of string core stretch. This usually means the nut slots are not deep enough and need dressing down a bit. If you are not comfortable with this, a good luthier can sort you out fairly quickly and inexpensively. If you do it yourself, get a proper nut file, and file back towards the tuners to maintain a good fingerboard edge "witness point" for the strings as the come across the nut.

[BigRedX]

Most likely a duff string. Take it back and get it changed for one that's right.

[iiipopes]

D'Addarios are notorious for core stretch. I have an Epiphone Alley Kat guitar. When I put Gibson flatwound strings on it or GHS Brite Flats strings on it, the fretting on the first few frets are fine. But when I put D'Addario XL115W's on it, 11-49, the round wound strings pull like anything and I have to use nut shims to bring the nut witness point forward so, especially on the E String, the F, F# and G don't pull sharp.

Edited September 5, 2013 by iiipopes

[goingdownslow]

Thanks for the replies.
The strings did look awkward coming over the nut giving a high action over the first few frets.
I have lowered the slots in the nut whilst also filing them to match the angle of the headstock which has cured the problem.
Getting .022" at 1st fret.