May 2, 2020 at 9:42 am #14089
The 1960 RCA tube manual lists the load resistance for a 6F6 as 7000 ohms.
So a 7000 ohm primary and a secondary of 4 or 8 ohms , whichever the speaker impedance is.
Your radio is also here – http://www.nostalgiaair.org/pagesbymodel/215/M0029215.pdf
Hope this helps.