I've had no luck trying to find a owner's manual... My question is on the back of the amp there is this slave \ direct INJN and the output ohm selector switch has an off position, also on the main board where the wire comes from the slave connection to the board the board says "mixer out"...
So the question is can I turn the output selection to off and use the slave connection to go into another amp or mixer without having to connect a cabinet?

I was even thinking possibly using it as a preamp before another tube amp just to see what it would do.

I added the send and return jack picture just show that the other is not an input or part of the sending return.

Couldn't figure out how to add pictures to my post so I gave the link to where I asked the same question in Marshall forum so if you wanted to see the pictures you can look there thanks in advance.

I posted this same thing in Marshall forum but I get no answers I couldn't figure out how to post pictures here