[MrFixr55]

Hi Morzh,

Attached is the section of the 1933 RCA "Red Book" that covers this radio.

RCA R73 fr 1933 Red Book.pdf Size: 3.13 MB  Downloads: 302

Below is a link to a website that discusses restoration of the rather similar RCA R7A "Suprette" 
RCA Radiola R-7 Superette Restoration (mcclellans.com)

Very interesting volume control on this set. This set uses the 55 Duo Diode / triode as a detector / AFC / 1st AF Amp, as opposed to the R7A. One would think that the volume control would be in the usual place, but no, volume is controlled by varying bias on all AVC controlled stages. This set has no phono provision (at least not on the schematic) but putting in a switch, volume control and jack (external panel) ould not be hard. This will allow playing an MP3 through the unit which should sound better than over the air.

Hope this helps.