Re: Problem with my strings
So: you tuned the strings, and found that within five minutes they were out of tune. You recently put a strap around the headstock behind the nut which you "delicately forced through" and perhaps the plastic "adjuster" is still sitting under the strings...? Maybe making it harder for the string tension adjust to uniformity the entire length of the string -- i.e., more string tension behind the nut than in the length of string between nut and bridge?
Should that be the case, as you pick, the strings vibrate and the motion of the strings in the nut slots allows the tension to equalize along the entire string length. The result may be that the portion of the strings that sound -- between nut and bridge -- may go sharper or flatter than their pitch when you initially tuned.
Old strings do hold pitch less well than newer strings, due to metal fatigue, flat spots worn over the frets, etc. But if the most recent change in your mandolin was the installation of the new strap, with the "adjuster" that had to be "forced" into place, I'd start with that. Take the strap off, and see if the problem persists.
Gibsn: '54 F5 3pt F2 A-N Custm K1 m'cello
Natl Triolian Dobro mando
Victoria b-back Merrill alumnm b-back
Stradolin Vega banjolin
Sobell'dola Washburn b-back'dola
Eastmn: 615'dola 805 m'cello
Flatiron 3K OM