On second look, the "AAGC" position on the far left knob probably inserts a compressor into the "Master" channel... maybe.
Looks like a sweet beast.
Oh it compresses alright......
What I do know about it was that it was used at NBC in the 40's with 2 mics going in and a compressed mono output for broadcast.
Well, the first thing that you should do is (obviously) replace every component inside with modern replacements to make sure you are getting everything that you can out of it......
It sounds amazing..... I've been toying with it for a few days now hoping the artist/producer will let me use it in a song.
The man who owns it restored it very well. And it only works well with a pad on the input AND output leaving me to guess NBC used this as an all in one mic pre/compressor back in the day.....