how to convert 120v to 48v

hello,
im brand new to this end of electronics, and have recently modified a vintage tube preamp. i am now trying to create 48v+ phantom power, the preamp has 3 transformers in it, the main power supply starts at 220 i believe and goes to 100 i believe. how do i find out how much juice the other transformers are putting out or, how do i convert the 120v into 48v? i thank you in advance

Use a multimeter to measure the transformer voltage.

You can convert 120V into 48V+ (DC?) with a transformer, a bridge rectifier and a filter cap.