There is no simple answer to this :
Tube amps generally fall into the following
OTC = output transformer coupled
OTL = output transformerless
OCL = output capacitorless
I guess strictly speaking you could have any number of amps ( solid state and vacuum state ) fall into these categories. The problem is not every OTC amp sounds the same because there are several design elements which go into the amplifier itself and the various transformers impose a sound of...