man,, there is something we are missing here!
now that you have the transformer out, and i assume all the leads can be taped off
so we can do some more testing?
if so, lets power up the field (blue wires) removed from the rectifier x and xx
put 24vdc to the two wires
start the engine and bring it up to speed,
check each phase on the output again, a-b, b-c and c-1 and note the output voltages
lets make sure we are getting relatively even voltage on each of the 3 phases
lets see what we get from that.
if you get somewhere around say 170 volts or more, can you apply a load to that? like a brush motor circular saw? you guys use 220 single phase in england iirc?
the idea being i would expect the phase to hold a relatively steady output with somewhat of a load.
maybe an electric heater or something?
i have a load bank here that i can provide a load for about anything from 12 volts to 240volts, but you are there and i am here, so that doesn't help.
something else came to mind a bit earlier
you mentioned in the OP that the unit was recently acquired and had been sitting for 10 years? and the selenium rectifiers released the magic smoke (toxic as it is).
there is a real possibility that someone was monkeying with the internal connections trying to make the thing work sometime back before it was put to rest (over 10 years ago).
it might be something a stupid as some wiring connections that have been moved around and not connected correctly. this might explain why the selenium rectifier burnt up, when the problem originally was it probably just needed the slip rings cleaned up.
so, do the above test if you can
and if you are fairly confident the transformer is good, then i would suggest going to the schematic fig2 and go through every single connection to make sure everything is connected correctly.
i also read in the manual that a provision to shut down the field could be accomplished with the addition of a 15amp switch to short the field. this i find quite strange, as a shorted field would through a lot of heat on the rectifier and transformer i would think. however the manual states this as a possibility, so you need to check to see if there is a switch in the panel somewhere? it is unlikely there is one, because how are you able to get 24 volts to the field if there is a blown switch? but then again, maybe under load the 24volts isn't really 24 getting to the field coils?
can you take pictures and post of the transformer, from front and back, i would like to have a look at them.
i assume that the unit failed before it was put into storage, and left to sit for 10 years, what we don't know is who or what happened after it failed, and what was done to try to get it going again... that is always a big red flag in my book.
a lot of guys won't touch electronic equipment that has had other hands messing around in the insides, not unless they specialize in that particular piece of equipment and have the exact schematics and other resources.
i recall a Zenith TV repairman years ago, he was about to retire and wanted me to take over the business... he told me "never ever, work on anything you don't have a schematic for, and never ever ever work on something someone has made a mess of"
now i don't know if that means it will be a real pain to fix, or something that in his experience can't be fixed?
a generator however is a rather simple piece of equipment and we have a schematic
so we are missing something,
so lets tape off all the loose wires, remove the field wires from the rectifier, power up the field, start the engine and see what voltage comes off each phase of the armature, note the readings, and then lets apply some load and see if the voltage drops like a rock or remains somewhere in the same area.
lets do that first
then lets take some pictures of the transformers and post them,
then lets reinstall the transformers and check each and every wire, to make sure it is connected according to the schematic.
and finally
are you absolutely certain the rectifier bridge is good? i know you installed it to replace the selenium rectifier, but we sure don't want a bad replacement part to drive us crazy chasing other directions assuming it is good. i don't trust any part these days! and i don't much care who makes the part, it seems failure rates are much higher than they used to be.
this is turning out to be a fun project
bob g