[DMcMahon]

Double checked that C2, R4, R6 &, R2 are definitely not fitted/ are missing and am sure these would have been for the DC polarising supply for an old condenser microphone.

The mic transformer is mounted on an insulated board (Paxolin type) and the board is riveted to the metal chassis side panel, so looks like it could have been original build, maybe there was an option then for Condenser mic or other.

There are 2 pairs of wires coming out of the transformer, one wire of one pair goes to the metal body of the transformer case and from there a black wire connects to earth, the other wire of that pair goes to the normally earthy side (but not earthed in this case) of the mic jack socket.

The first wire of the second pair goes to one of the 3 wires on the mic jack socket and the second wires goes to one of the 3 wires on the radio jack socket.

Bit confused why these mono jack sockets have 3 wires as well as an earth connection, the symbol in the schematic for these jack sockets does not help my confusion..

Later in the day will plug in a mono jack plug and buzz out (continuity/resistance check)
the jack plug to the jack socket 3 wires then all should become clear. I will not buzz out the microphone jack connections as I have read forum posts that say microphone transformers can be damaged by resistance checks.