[Boatanchors] 75A3 Modification

[Tom NØJMY - AAR7FV]

Greetings.  Some time back I traded for a really good looking and playing
75A3.  I will be offering it up for sale shortly , but I have a question
before I do.  It has a 6SN7 with the plates wired together, stuck in the
NBFM socket.  Without going into a lot of detail, it appears to be inserted
in the circuit between the last if trans and the plate of the detector.  Is
this a home-brew mod to add a product detector?   The only product detector
mod I could find on the web used a 12AU7 and a 6AU6, and had a control for
front panel tuning.

Thanks in advance,
Tom