the trigger is the part on the back where the amp can have a cable attached to it from a home theater processor, to send a signal, to turn the amp on remotely.
this version has a auto turn on feature. it is a simple electronic circuit that activates a relay, instead of the normal mechanical power switch that would be on a bryston...
This is probably what began the trend in brystons to have a soft touch switch power switch that is all ’electronics driving/controlling relays" as compared to the previous amp series...which were all mechanical switching of the 120VAC.
I finally looked at your images instead of the ones on the net, and I can see yours has no trigger section, whereas the other THX units I looked at with an image search, had triggers included. Yours looks like a 3BST with no trigger function. So the THX is essentially... just a paint job. Legitimate no doubt, but as far as alterations to the model underneath - just a paint job. ’Horsepower is adequate’, as Rolls Royce would say..
I have a policy of not clicking on stuff that people put in threads or in emails. Safety first. Wear internet condoms when you are out there poking around.....
Have to know the year, as well, or see it with the cover off. Looks more like a 3B NRB. Not a 3B ST. Depends on what is found inside. around 1994 as a build... right around the change to the ST model, and still made in Rexdale, not in the city of Peterborugh.
The switches on the back. They went to flat switches instead of toggles, around that time. That switch set tends to be one of the external indications of a ST vs an NRB. The NRB being silver metal toggles, the ST being black flat left-right switches.
The transformers on a 3B ST are flat and vertically mounted against the front panel, where with the earlier 3B NRB version, they are stacked on top of one another in the middle of the amp case proper. This should be visible through the top grille. If the transformers are against the front panel, then it is definitely a ST version. The transformer move is intimately linked to the circuit change from 3B NRB to 3B ST.
The whole thing appears to be saying you’ve got your hands on a 3B NRB, with a THX paint job added in.