In an earlier post I talked about installing a large 70s-spec Model T output transformer in a 90s reissue model. Because the 90s reissue uses an OT that has a separate secondary winding to create a balanced XLR lineout (it’s the Tonemaster/The Twin OT), I lost that functionality with the switch to the new OT. To get it back, I installed a small 1:1 transformer on a 30/1 voltage divider coming off of the 16-ohm tap of the OT. The secondary of the small transformer runs to the +/- pins of the XLR output, with pin 1 grounded to the amp’s chassis. This puts out 1.45V on the output, just about exactly what the previous arrangement did (+3 dBV, or 1.425V).
This mod can be done to any amp with enough space for the transformer and line out jack. It’s superior to lineout setups that use preamp signal because it includes the tone-shaping done by the power stage and output transformer, so that whatever you record from the lineout only needs to have a cabinet impulse added to it to sound fairly natural.