[Collins] 75S-3 "BFO TEST" jack

[Bob and Sue Jefferis]

Greetings,

I just acquired a 75S-3A that has the "BFO TEST" jack in the chassis. The jack hole was punched, the jack label is there, and original, the jack itself, and the mounting screws are perfect matches to the HFO and VFO chassis jacks. Even though this jack is disconnected, there are red Glyptal [sic?] artifacts on the center post. So, I am currently believing that this jack was installed at original build time.

I discovered that a previous owner made some very curious modifications to the product detector and BFO. I think the BFO TEST jack may have been disconnected during these mods. I have 2nd and 3rd edition manuals, but this jack is not shown in them, both the photos and the schematics. Does anyone have a first edition manual or hands-on experience that would tell me how the jack was originally connected? I would like to put it back to "stock" configuration while I undo the product detector mods etc. Thanks for any help here.

Bob, KF6BC