I've got a Yamaha 413s 12 string.
It's a great guitar plays and sounds like a dream.
I need to change the strings as they're old.
I've ordered some d,addario EJ 39 phosphor medium .12-.59's.
Are these strings likely to warp my neck/bridge?
Would you recommend only tuning to D?
Does anybody here have experience with medium strings on a 12 string?
Any warping?
Is the tone a lot better?
Also looking at the bridge area it's very slightly raised as if it's being pulled. Is this normal or a warning sign to tune down?
Don from D'Addario here - EJ38 is our best-selling 12-string gauge. Sometimes manufacturers will recommend what gauge for a particular guitar and even ship that guitar with the brand and gauge installed. If you're moving gauges from .010 to a .012 - you have to be careful that the nut and saddle are cut to support the larger gauges. You're also smart for questioning the tension - our EJ38 set carries 250 lbs of tension, where as the EJ39 set has an increase of over 27% - with 319 lbs of tension.
Don Dawson
Marketing Specialist
D'Addario / Planet Waves
Looks like I might have to return them when they get here and go for the 38's then.
I don't want to risk damaging the guitar.

Thanks for the reply
Might be a safer call - plus a little easier on the fingers

Good luck with it!
Don Dawson
Marketing Specialist
D'Addario / Planet Waves