The 1925 Gulbransen was designed to be tuned at A-440.  Since the pitch
has dropped that much, I would suggest that you "chip" the strings,
just as in raising the pitch of a newly strung piano.

First, I would inspect the soundboard for problems.  If it has any,
I would remove the strings and restring the unit.  It would be a good
investment, seeing that the piano action has little wear, a condition
that is seldom found in player pianos.

If restringing is not desirable, check to see that all plate bolts
are tight, especially around the bottom, and the flange.  Most old
Gulbransens have a 3/4 plate, so be sure to check to see if the
pinblock has pulled forward from the back beams.  If it has, drill
holes for lag bolts through the wrestplank into the beams, pour epoxy
into the crack, and pull it back into place.

Chip the piano.  Pull each right string in the right unison up close
to pitch, from the lower tenor all the way to note #88.  Then pull up
every other bi-unison (bass) close to pitch.  Do this as quickly as
possible.

Then pull each right string in the center unison up close to pitch,
from the lower tenor all the way to note #88, and then the single bass
strings.  Finally, pull the left unisons up, then the remainder of the
bass.

Before setting the temperament, find a good brass stock, and seat the
strings on the bridge with a hammer.  If the strings are high (they
probably will be, due to the soundboard loosing it's crown over the
years) you will hear a "zing" as the strings seat on the bridge.
Without doing this, the piano will be impossible to tune.

Never leave a piano at low pitch and tune it to itself.  If the
tension is too low, the piano will have no power or brilliance.  Piano
scales are designed to have a certain amount of tension, dictated by
the design of the plate and the diameter of the wire used.  In any
piano, the scale will perform the best when tuned to pitch.

If you find that you have false beats in the treble, this means that
the bridge pins have "bent" the strings in that area when it was at low
pitch, and have been pulled up into the speaking part of the scale when
the pitch was raised.  In this case they will have to be replaced.  If
the piano can't be tuned to pitch, it is unusable, and the situation
must be corrected.

Hope this helps

Andy Taylor
Tempola Music Rolls