Introduced in 1924, the Radiola 104 "loudspeaker" was one of the first AC operated devises offered by RCA. Not only a powerful electromagnetic speaker but an amplifier and power supply is also contained in the cabinet.

The tubes used in the electronics are: 2 - UX-216B rectifiers, UX-874 voltage regulator, UV-876 ballast (or line regulator) and UX-210 power amplifier.

The "RPA" (as referred to by RCA) also supplied A & B voltages needed to operate the Radiola 28 receiver.