The R-Core power trannie looks similar to the PT-877 which was on sale from Tube Depot a few months ago, which has 6.3VAC @ 3A and 260VAC @ 200 mA
secondaries, and 100VAC primary. (these were intended for use in Japan, where 100VAC is a normal line voltage)
They tested it with 120VAC on the primary, and got 7.56VAC and 312 VAC, loaded at the rated currents.
I bought four of them (they were cheap) and used a tapped autotransformer to test one at 100VAC,
and loaded the 260VAC winding with a 40W, 230V light bulb (about 180 mA at 260VAC), and the 6.3 VAC winding with a 6AS7 filament(2.5A)
the transformer just barely got warm, even after several hours' continuous operation.
I figured, use it on 120VAC with 8BQ5s and 8CG7s (or 8SN7), in a modified Clementine or Budgie SE design. The filament voltage might be a tad(about 5%) low,
but it is still within operating specs for these "series filament" tubes... 8SN7s do exist, though they are not really "common", I have a few "Zenith" branded ones.
Lower gain then the original 12AX7 / ECC83s, but then, that's what preamps or line stages are for
/ed B