Or you can buy a transformer with dual 110/240 primary and 1.5V and 7.5V AC outputs at enough current for even "big" battery valve sets (like Hallicrafters S72). Readily available.
Also you need a regulator! Even the contemporary unregulated ones used a choke to improve the smoothing, as the capacitors get infeasibly big and peak current in rectifiers gets high and generates RF! The resistance of choke and voltage was chosen to account for drop in selenium rectifiers and give 1.35V. A parallel load to use it on 125mA nominal sets instead of 250mA. Such PSUs designed for the number/type of valves. They would over run the remaining valves if one failed. This is why from 1938, (Octal Sylvania 1.4V tubes) in USA, and 1939 in UK that any sets for mains used series filaments and higher voltage supply, the dropper provided more smoothing and regulation.
German sets used Y base metal can tubes optimised for 1.25V so that an NiCd (DEAC) could act as parallel regulator. Even up to 1959 and Dx96 tubes that could be serial, the German models used this scheme.
So a simple solution is 5V phone PSU, resistor and a 10,000mAH NiMH D cell as regulator. Select resistor for what ever current the radio takes to drop 5V to 1.35V. This will be less than 1/10th C. Don't leave it plugged in too long if battery is charged. (i.e. a box with USB socket like on any gadget, RF filter, wire wound resistor and NiMH cell is your battery eliminator. For a 125mA set a 3,500mAH C cell will do)
Note that recommended supply is 1.35V, +/- 5% by valve makers. They are nominal 1.4V tubes and the battery is 1.62V fresh to 0.9V at end point. They are not 1.5V filaments.
A 10% increase from 1.35V will more that HALF life of filament.