[MrFixr55]

Arran, I agree with requiring caution in "modding" a chassis, but I have not been anywhere as happy with the sound from an AM transmitter as I am with direct in audio. Yes, RCA, Zenith, Philco and others made "phono oscillators. My 41-255 had a sticker advertising Phono and TV sound (some Pre-War TVs had only line level audio to save money) "The wireless way"

Adding an external input jack could be considered "period" if using period parts, as this may ha e been a common mod made by a TV shop, especially if the set was sold with an external phono attachment. RCA manufactured and sold a jack and switch panel complete with a wiring harness with instructions for modding the circuit. Some Zenith wiring diagrams (for example the official Zenith documents for the 6-S-27 / 6-S-52) contained a schematic for adding a phono / radio switch. A clean mod can be made by using an external metal box or panel and switch, with wiring passing through a convenient hole in the chassis. Existing screws and / or screw holes can be used for mounting. Under chassis plugs can be used to add or remove the device. Ahis can be acceptable on all but the most expensive or historically important sets.