[Arran]

Before you drop the voltage to the primary too much remember that these sets use #26 tubes, which have 1.5 volt filaments, at 1.2 amps each, so a drop in voltage at the primary could cause a commensurate drop on the 1.5 volt secondary. I would test it on a variac before making anything permanent, 115 sounds like it may be a safe primary voltage as it is within original specs, 110 may be too low. Does the primary tap allow one to operate the set on 125 volts or just 117-120 volts?
Regards
Arran