I wonder what is your analysis of failure mode on that unit, an open primary winding ?
If the primary is open, have you vewwy carefully, surgically peeled back the thin fishpaper covering and used a magnifier, hi-intensity light, surgical tweezers and ohmmeter to see if you lucked out, with the break being externally-accessible and can be micro-repaired on the re connection to its main lead wires.
It looks like in the referencing in the RCA service info, that the one sub that is suggested is having to be mechanically remounted AND the real point is that it is a conventional transformer with a single winding and no hum bucking tap.
They just want you to then compensate by heavier DC filtering.
The only other source that I see is the site I give below, to then see if they still have those in stock. Both units given have tapped primary windings for the RCA’s hum bucking aspect.
The first ones impedance match will be giving a skosh more treble response, while the second one will be giving a skosk bit more bass .
If you go for the usual sourcing of a Hammond you would be paying QUITE a bit ‘mo munny, and STILL no hum bucking tap like the units below are offering .
1012-072 OUTPUT THOROTEST TA20T SP (1.7K z0 TO 3.2 VC, W/HUM TAP, 3-5 WATTS, FIG 3, NEW.. 1 2 3/8 1 3/8 1 1/2 $7.50
4565-116 OUTPUT THORDRSN T-24S89 SP (3K Z W/3% & 6% HUM TAPS) TO 4 V.C., 3-5 WATTS, FIG 3,N 1 2 3/8 1 3/8 1 1/4 $8.75
73's de Edd