I use to know the answer to this. The heads were modded for the preamp out. The power section of the amps was not used. Someone will post info and some pics im sure, but once you see how it was setup itll all make sense. Before I sold my twin head a year or so ago, i almost had a friend of mine mod it so i could run it like Jerry did. As much as that would of been cool, it just made more sense to get the SMS CTP. I didnt want to modify a late 60's Twin.
Basically the SMS is a Twin Reverb preamp section in a rack form and you connect it to a power amp. The way Jerry used his Twins was the same concept, he only used the preamp section of the Twin. Makes more sense to just buy the SMS imho. But hey thats just like... my opinion... man...
Blues Jr Mods, Tubes and kits.
"Bound to cover just a lil more ground"